machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"
I made a video of this first run, but I am experiencing great frustration uploading it, due to our totally pathetic Internet speeds here in Australia. I will include it later in this post, but the resolution is way down. I will upload a higher res version next weekend.
Stuart Tankard’s superb gas fired vertical boiler, was also getting its first run powering a steam engine.
We did not connect the condenser until later.
OK, so here is the video. Again, apologies for the low res quality.
I was very excited to see my triple running reasonably well on air recently. But it was tight, and required a decent gutful of air pressure to turn it over. But it did go!
Then it seized.
The cause was the intermediate cylinder valve rod seizing in its guide. Probably a bit tight,and not getting any oil.
So I have loosened the gland, installed a displacement oiler, and made and installed a flywheel. I also finished the pipework around the condenser.
Displacement oiler top left, brass flywheel, and pipework. The condenser on a marine engine would have been cooled with seawater, pumped with a separate pump, but I have used the 2 pumps on either side of the Edwards air pump. In future I might install another pump. The book “Marine Steam Engines and Turbines” has been been very useful.
I just like all of the brass and copper and components in this picture.
The flywheel is too big for the scale, but my model does not have the weight and momentum of a propeller shaft and propeller, so a sizeable flywheel seemed appropriate. Later I will add some gear teeth on the flywheel and a cranking handle on a removeable pinion, which some medium size engines had to assist with cranking to a starting position.
So, tomorrow I will hook my triple up to Stuart Tankard’s vertical boiler, and see what happens. I am sure that steam leaks will be revealed. Hopefully there will be a video worth posting!
This is a short video of the first run of the Bolton9 Model Triple Expansion Steam Engine, which I have been building on and off over the past 3 years.
The video is a bit shakey, because it is taken on my hand held phone while I am using he other hand to operate the controls. I really did not expect the engine to work!
It runs a bit roughly, and is still quite tight, but settles down in the final few seconds.
It is not running very smoothly, because it is on air rather than steam, and because it is probably only powered on the high pressure cylinder, and maybe a bit on the intermediate, and not at all on the low pressure cylinder.
The next day it would not run. Very frustrating. I suspect that one of the eccentrics slipped on the crankshaft, and threw the timing out. Not the easily accessible low or high pressure valve, but the intermediate one, which needs another teardown to get to it.
But Hey! It will work. I can see the light at the end of the tunnel.
One of my readers has requested a description of the triple engine timing procedure, so that will appear on this blog soon. Unless you have a particular need for the timing info I suggest that you give that post a miss.
I bought cylinder cocks from Reeves UK, and the picture shows them fitted. In case I eventually install a mechanism to open all of the cocks simultaneously, they are in straight line, which necessitated making extension peices for the high pressure cylinder cocks.
The handles required bending to clear the pipework.
The cocks look a bit strange to me. Too big, and the handles are wrong. I am thinking about making a set from scratch. But that can wait.
Drain pipes from the cocks will be installed at some stage. Still deciding where to run them. And whether to join them into a common trunk.
The engine turns over by hand, but it is still a bit stiff. There was a tight spot which took many hours to locate. It turned out to be a valve rod thread which was about 0.5mm too long, touching the inside of the high pressure valve chest. Fixed in a jiffy.
I hooked up the engine to a small compressor at 30psi, but general stiffness prevented the engine from rotating. So I gave it an hour being rotated in the lathe at 200 rpm. It is noticeably more free, and getting very close to working. The valve timing is approximately correct (checked by my expert friends Thomas L, and Rudi V), but will need fine tuning at some stage.
The Bolton 9 engine is assembled, almost completely. The valves are approximately correctly timed. I can turn it over by hand, just. There are a few tight spots.
So today I mounted the entire engine in a lathe, oiled all bearings and slides, and tentatively ran it for a few minutes. The lathe was set at 60rpm, in back gear.
All seemed OK, so I ran it for about 30 minutes. Then increased the rpm to 90 for another 30 minutes. After that the tight spots still exist, but much less pronounced.
I kept a check on bearing temperatures with a laser thermometer, and none were running more than a degree or two different from any others.
The test did show that a low pressure cylinder drag link is touching the condenser, and will need some relief. Also the high pressure cylinder eccentrics need to be repositioned a little on the crankshaft. But nothing major. And it was very nice to see everything moving in quite an impressive manner.
I will upload a video when the upload speeds are reasonable.
Well, almost another whole year has elapsed, and still the triple is not finished. Come December, and that will be 3 years that this project has occupied my thoughts and workbench. With a few other projects in between.
Last week I assembled the components, in preparation for the Geelong Show. GSMEE is a bit light on for new models, and it was suggested that the triple might fill some shelf space, despite being unfinished.
So I bolted it together. All 429 fasteners! And stood back and admired it. It really is quite impressive, complex, and interesting. So I took some pics.
This is the condenser side, and the Edwards pump
The other side is a bit lessy fussy, showing the steam inlet valve, the Stephenson’s links, weigh shaft and controls.
And the top, showing some of those 429 fasteners,
The high pressure valve chest cover. I will fill those holes where bolts cannot go.
And the low pressure end, and links for the pump.
And a close up of the steam valve and weigh shaft.
Not quite ready to run it yet.
It needs side covers for the cylinder block, drain cocks for the cylinders, and general freeing up. It is still very tight.
Not to mention painting. I expect that I will paint this one. No idea of colours yet.
Thinking about the options for a base for the triple expansion marine steam engine..
I looked at every photo I could find on the net, and thinking about whether I want to be historically accurate, or just really solid, or a bit interesting with an historical flavour.
At this stage, the decision is not set in concrete, but I am going with the last option. Photos later in this post.
But first, I have pulled all of the major components apart, and I am spending time doing a few of those jobs which I had been avoiding because they are difficult and imprecise, and if they go badly it will be a major disaster at this stage. Like drilling the oil holes and wells for the big ends.
Nothing precise about this. The con rods and big end shells and bearings have been painstakingly machined, and I do not want to think about remaking them if I stuff up. And drilling into curved surfaces, with a 1.5mm drill bit…
That thread is 3mm dia. The hole above the nut is the oil way, 1.5mm dia. Very tricky and too anxiety provoking to be thinking about a video. Amazingly, it all went well! I now have 2 oil holes for each of the 3 big ends. I will need to fill the well with oil with a medical syringe and fine needle, but.
The crankshaft, turned from stainless steel a year or two ago, and the conrods. The big ends now with lubrication points.
And here are the major engine components, after partial disassembly.
At top left is the condensor, then the cylinder block in 2 parts, then the steam supply valve. The square section tube is going to become the base. And so on. You get the picture. I will count the bits at some stage.
Then I cut and drilled the square section aluminium tube for the base.
The cast base of the triple, with main bearing studs and column studs in place. All sitting on the square section alu. Have not decided whether to bolt it together, or just Loctite it.
Those holes in the square section were drilled and chamfered on the CNC mill.
I am close to disassembling the Bolton 9, before gradually reassembling it in preparation for running it on air then steam. Most of the components have now been made. Most recently I completed the pipework associated with the Edwards air pump and the twin water pumps.
This is the combined air and water pumps, and new pipework. Most joins are silver soldered, but a couple are Loctited. Loctite should be adequate. These components will not get super hot.
This valve is one of the few components on this engine which I have not personally made. This one came from the effects of the late Harry Close, who was a valued member of our Model Engineering Club.
The pipework adds to the overall interest , yes? It will look good when polished.
And the “tails” for the valve rods, which are attached to their respective steam chests. The BA7 bolts are a bit oversized for the job. The intermediate cylinder tail screws into place. I am not sure why it is different from the other two.
So now I am making a list of tasks which need to be completed when the engine is taken apart, hopefully for the last time before it is run. The list is not complete, and so far it runs to 3 pages. Mostly like fixing parts which interfere with each other, and freeing up tight bearings.
I got this far in assembling the model triple expansion steam engine, then lost courage and put it aside (again). You can see the high pressure steam chest labelled “top”, the steam valve and handle, the drag links and levers for the reversing mechanism for the high pressure cylinder, and the worm and gear and control wheel for the reversing mechanism. The reversing levers will need pinning with taper pins when the correct positions are finalised. The short rod in the middle of the pic is temporary. I need to make those properly. The drag links clash with the condenser cover. That was predicted in Bertinat’s notes. The cover will need some material removed. Slowly progressing, but taking frequent breathers.
The high pressure mechanisms are the most exposed, and easiest to access, and they were very tricky, and not yet compeletely installed. I dread to consider what the intermediate pressure ones will be like, buried in the middle of the engine. Then there is the valve timing. Help!
Making the new valve rods, as predicted, took me an entire day. They required a high degree of precision, and being in stainless steel, not an easy material to machine, and quite thin and delicate, multiple stages in the machining.
But before I started on the valve rods I made myself a new spanner for the collet chuck on the CNC lathe. I had been using an adjusting spanner, which was continually going out of adjustment and causing angst. The tool merchants did not have anything suitable (46mm opening, and thin profile), so I made my own.
The 46mm spanner being cut from 6mm steel plate.
It is a bit prettier after this photo and being painted. The rounded jaws facilitate easy application to the collet chuck.
Tightening the ER40 collet chuck with the new spanner. It works very well.
So then I got on with the new valve rods. Some end of day photos follow.
The valve rod is the silver coloured rod. Actually stainless steel. This photo shows the high pressure cylinder valve and valve chest. There are 2 other valves, one for each cylinder. All different sizes.
The high pressure valve chest and valve, the valve rod and guide. On the right is the Stevenson’s link, yokes and eccentrics which control forward and reverse. This setup is repeated for each of the 3 cylinders. This is hooked upto the worm and gear which was shown a blog or two ago. There are 22 components for each, not counting fasteners.
The low pressure setup.
And thank you to those readers who responded to my whinge about likes and comments. I will continue this blog until the triple expansion steam engine is finished, and hopefully running. Not sure after that.
“Underbelly” has a particular resonance for readers who know what the Yarra is and that Collingwood is a place and not a British admiral.
In the instance of my triple expansion steam engine, it refers to the bits and pieces underneath the cylinder block. The glands which prevent steam leaks from the con rods and steam valve rods, the and valve rod guides. These unsung heroes of the steam engine have taken 2 entire days to make. And here they are….
This is the cylinder block, upside down. You can see the valve rods. the valve rod guides, the valve rod glands, the piston rods, the cross heads (unfinished), the piston rod glands, and the cylinder bases. Give yourself 2 marks for each correctly identified item. The 6 hex plugs on the side are temporary, until I get around to making some cylinder drain valves.
I started to count the number of holes drilled and tapped in this view, but gave up at 100 and still not half way. This engine better bloody work!
Note the letter stamped into the cylinder base. Many parts are similarly stamped. The studs in the intermediate piston gland are temporary.
Just a different view.
I have decided to replace the valve rods which are made of brass, with stainless steel ones. That will take an extra day, which might exceed my second, self imposed, deadline. But if it does, well too bad.
By the way…. I am considering whether or not to continue this blog. It does take time, and is not free. If you read this and are not totally bored, the odd “like” would not go un-noticed. A comment would be even better.
I had made a worm drive and gear using an M14 x 2 tap, but it did not look the part, despite being functional. The problem was that the threads were sharp triangular and they did not look correct.
So I made a worm drive and gear using Acme specifications. The teeth have a chunkier squarish look. More authentic.
I ground a lathe cutter and used it to make the worm drive in gunmetal, and another identical thread in 14mm silver steel (drill rod). The steel thread had cutting edges formed, and when finished it was hardened by heating red hot and quenching. After hardening, a file would not mark it. I did not bother to anneal it, since it would be used only to cut cut brass or gunmetal. The hardened tool was used to make a gear in gunmetal. Unfortunately I did not take pictures of those steps.
Showing the handwheel, worm drive and gear. the shaft is mounted in gunmetal bearings which are bolted to the columns with BA8 bolts. The thread is Acme. 2mm pitch. The handwheel will control forward-reverse of the triple expansion steam engine.
In order to determine the position of the bearing bolt holes for the worm drive, I used SuperGlue to tempararily join the worm and gear.
When the position of the bearings was determined, the holes were drilled 1.8mm and tapped. the taps were BA8, about 2mm diameter. The engine is held vertically on the milling table, being cramped to a large angle plate. The holes were drilled accurately on the mill. The threads were made using a tapping head made by me from plans published in “Model Engineer” by Mogens Kilde. The double parallelogram of the tapping tool keeps the tap vertical. The tap did not break.
Close up photo of tapping the BA8 threads. Showing the bearing, shaft, worm drive and gear. Note the Acme thread. The bearing is Super Glued into position to facilitate the drilling and tapping procedure. The Super Glue will be removed later.
The final step for today was to make the handwheel. It is 1.5″ diameter. The rim is 1/8″ brass and the spokes are 1/16″ brass. I made 4 of these, with each being better than the last. I softened the 1/8th brass before winding it around a 32mm pipe to form the rim. The join in the rim was silver soldered. Then the rim and the hub were drilled using a tilting indexing head on the mill. I soft soldered the spokes on intital handwheels, but the final (and best) examples were glued with Loctite. Loctite allows a few minutes for adjustment of the spoke lengths, whereas there is only one go with the soldering.
It is looking interesting, Yes? And there are 3 spare handwheels. The rest of the reversing mechanism components were made several months ago. Almost ready to install them.
The triple will not be finished by Xmas. No chance of getting into the workshop while we are looking after 2 grandchildren. So the new aiming completion date is Jan 6, in time to run the triple on steam at the Geelong truck show. If I don’t meet that deadline, the next access to steam will be the end of 2017. I really do not want to wait that long.
So the next component to produce out of a chunk of gunmetal is the water pump.
There are two cylinders in the water pump. The gunmetal castings appear to be good quality.
Most of the machining will be done on the mill. But I need a datum surface, and have decided that the attachment plate is the most appropriate.
I do not need the small cylindrical protruberance, but that chunk of gunmetal might be handy for something else (eg as a bushing), so I parted it off and saved it. Lovely parting tool is from Eccentric Engineering.
Then turned a flat surface. On the mill I machined it to a rectangle. Diamond tool is also from Eccentric Engineering.
The two water pump cylinders are bolted to the air pump. BA7. A broken tap is entombed in the air pump forever.
When I get back into the workshop I will machine the rest of the pump parts.
Today I made the rest of the drag links for the triple expansion steam engine, and just for fun I made one spare.
I ran out of BA10 nuts. Ordered more. 1.6mm thread, 3mm overall diameter, 200 of them weighs nothing. But if I drop one, that is another 25 cents down the drain, because individually they are invisible.
The weighshaft, supported on its brackets. It will be pinned with taper pins to the shaft. Also finished the reversing lever and reversing arm. The reversing arm has gunmetal bushes. About 2 x 8 hour days in the workshop to make these bits. Just as well it is a fun hobby.
It seems months since I made any progress on the triple expansion steam engine. It is such a complicated build, at the limits of my abilities (or maybe beyond the limits), and many components have been partly made and put aside to be completed later, that I was unsure just where I needed to resume.
But, Xmas/Saturnalia, New year, several exhibitions, several competitions, and an intervening Stirling engine build all conspired to “force” me to put aside the difficult triple build. Then it was just too bloody hot to venture into the workshop. But we now have some milder weather, and I have some free time, so back into the workshop to inspect the triple and see where to resume.
I decided to do some easier components, to ease back into the build. So I started by making some of the steam pipes, CNC’d the flanges, and silver soldered them. Only to discover that there was inadequate access to tighten some of the flange bolts. So a quick redesign of the flanges to use only 2 bolts per flange, CNC’s some more flanges, removed the bad’uns, and silver soldered the new ones. All good now, except that I need to fill some unused threaded holes in the cylinder castings, and drill and tap some new ones.
Checking the fit of the copper pipe, prior to machining and soldering the flanges
The pipes with flanges all made and ready to be fitted. Except that these 4 hole flanges had to be replaced with 2 and 3 holers.
Inadequate clearance to fit the bolts. So the flange was replaced with a 2 holer.
Today I made the bearings for the yokes on the Stephenson’s reversing mechanism. These are made of gunmetal, quite small (9.5x8x4.7mm), need some precision drilling and reaming, and there are 12 of them.
After considering the “how to” options, I decided to use the recently installed 5C collet chuck on the lathe, having machined the gunmetal to fit neatly into a 3/8″ square collet.
The following pics were uploaded and the order was totally mixed up in the process. From previous experience I know that trying to re-sort them will result in chaos and losses, so I will leave them as is.
This is the final photo. The 14 bearings (including 2 spares) are threaded onto a bright steel rod and the side decorative waist is milled.
Showing one of the reversing mechanisms, with 4 new gunmetal bearings bolted into position.
The square 3/8 x 3/8 lathe collet, about to accept the bar which has been accurately sized, drilled and reamed. I used a parting tool to cut off the bearing at the correct thickness.
Parting. The blade is only 1.5mm wide.
One of the yokes, with bearings bolted in place, and 2 loose bearings about to be fitted to the other yoke.
precision drilling the bolt holes (1.8mm diameter) using the high speed spindle on the mill, at 6000 rpm.
The three pairs of valve eccentrics, and reversing mechanisms.
This should be the first photo. It shows the gunmetal bar machined to size, drilled and reamed, ready to be drilled for the bolts, then parted on the lathe.
I accidentally damaged a gunmetal casting (an end plate of the condenser unit) of my triple expansion engine. I considered soldering a piece of brass or gunmetal and filing it to shape, but decided instead to try one of the 2 part epoxy repair kits. There are plenty of these with iron/steel coloured material, but for a long time I could not find a copper coloured repair kit.
The damaged, machined casting. I have punched some indentations to increase the adhesion of the filler, then washed it in acetone to remove all traces of grease.
Then I spotted this epoxy repair kit at an Aldi supermarket. So I decided to give it a try. Cost $AUD5
DYNASTEEL, Copper Repair. And this initial blob applied to the defect.
An hour later, after some paring with a knife and filing.
Next day, after some more sanding. Appearance not too bad. More shaping of the casting is intended. The epoxy repair is meant to tolerate temperatures up to 200 c. If it proves unsatisfactory I will solder in a patch.
The next step in making the Stephenson’s link reversing mechanism, is to make the yokes for the links. See the previous blog. I decided to drill and tap the BA10 holes, while the bar stock was still rectangular, for ease and precision of clamping the pieces.
BA, in case you are not familiar, stands for British Association. BA threads were standardised in 1884, using imperial measurements (fractions of an inch), but to metric specifications. All very confusing. BA threads are rarely used these days. Model engineers, instrument makers, and restorers of ancient British cars and motor cycles being the exceptions. Builders of model engines often use them, because the bolt heads and nuts are nicely scaled for the models.
BA10 bolts are only 1.7mm diameter. If a BA10 nut falls on the floor, it is gone forever. I can barely see the thread of a BA10 bolt. I shudder to think of using the even smaller BA12’s.
The tapping drill is only 1.4mm diameter. A bit thicker than a human hair, (OK, many times thicker), but very delicate. And the holes needed to be at least 5mm deep. I do not possess a drill press capable of drilling such fine holes. Any run out of the chuck, or excessive pressure would just destroy the drill bit. Also, on working out the feeds and speeds of the drilling, it was apparent that the optimal drilling rpm’s would be 12,000 . Twelve thousand.
So, once again, CNC to the fore.
I reattached the high speed head to my CNC mill, worked out the XYZ co-ordinates, and did a practice run on some scrap. No problems! Worked like a charm. 12000 rpm and feed 100mm/min. Then to the actual job. Centre drilled all pieces. Then using the Pro-stop by Edge Technology vice stop, repositioned the work pieces and deep drilled them using the 1.4mm twist drill, using CNC peck drilling at 1.4mm intervals.
Then to tap the holes. The BA10 tap seems even more delicate than the 1.4mm drill.
I attempted to hand tap the holes, in the belief that holding the tapping handle in one hand, and the work piece in the other, would be the most sensitive system. But these hands, which once performed microsurgery, were not up to the job. It was inevitable that the tap would break in the job, so I abandoned the method before disaster struck.
The work piece was repositioned on the mill, again using the vice stop, and I used the CNC positioning to centre the tap fairly precisely squarely above the holes. I made a spring loaded point to apply light pressure to the tap, and to keep it centered. (see photo below). 24 holes and about 2 hours later the threading was completed. No breakages!
Tapping the BA10 thread. Note the Prostop vice stop, and the spring loaded centering tool.
BA10 bolts OK. Now to shape the yokes. (seen in the background.)
I had made a video of the CNC drilling, but the broadband downloading speeds here are so slow, that you will just have to imagine the excitement of the drilling.
OK, the video finally uploaded. It is pretty crappy. To see it, click on the link which follows.
Progress on the triple has slowed lately, partly because I am spending spare time on the Colchester lathe commissioning, but mainly because the plans for the Bolton 9 triple expansion steam engine are fairly vague and hard to interpret with respect to the Stephenson’s link reversing mechanism. I think that I have finally got my brain around the workings of the mechanism, partly thanks to the many Youtube demonstrations, but mainly thanks to a series of articles in “Model Engineer” in 1985 -6, to which a colleague directed me. (thanks David).
The author of those articles has taken the trouble to document improvements to the original OB Bolton plans, and the improvements are much more comprehensible. (unlike this blog.)
My uncertainty was compounded by finding castings missing from the kit of parts which I had purchased. I had taken the precaution of taking photographs of all of the castings when they were originally unwrapped, so I know that they were never there. The supplier was not interested in rectifying the problem, so I am making the parts out of brass bar stock.
The following photos are the situation to date.
The eccentrics. These are all split, and joined with M2 bolts.
The components of each eccentric. The brass “halves”, the bolts and the grub screw.
The eccentric straps, also made in 2 pieces, joined with M2 bolts. A groove is turned in each circle, and a corresponding ridge is turned in each eccentric. All very precise and fiddly.
Six valve rod “yokes” need to be made, but there was only one casting, so I have decided to make them all from bar stock. The dimensioned bar stock (10x16x55mm) is seen here, with the “Model Engineer” article on the subject underneath.
I will machine the yokes next week some time. Space ships found in the Kazakhstan desert much more interesting, no?
The eccentrics are turned from 2 bits of brass, which are separated later. It was a trial and error effort, mainly error.
I tried soldering the parts initially, but mistakenly used silver solder. All was well until I tried to melt the solder, and so much heat was required that the thin brass parts were wrecked.
Next time I used Loctite, but during turning, the parts flew apart and were again damaged.
Finally, I Loctited the parts, then bolted them with the final bolts, then turned the disks. This method worked, but the 6 disks required almost perfect dimensioning on the milling machine during drilling, then the lathe for turning and parting. Altogether, very demanding.
Attempt one, showing the brass rod blanks which I soldered then turned, then separated, then discarded.
Final run, showing the glued and bolted brass rod, and the turned and part parted disks
Parting the disks was nerve racking, due the fine tolerances, and the eccentrically placed crankshaft hole. But it occirred without disaster
Final cosmetic facing in an appropriately small Unimat hobby lathe.
The finished eccentrics, stored on a piece of 10mm silver steel. There is less then 0.5mm between the bolt head and the machined edge. Hooray!!!!
The Bolton 9 triple expansion steam engine has 6 eccentric cams which drive the steam valves, 3 forward and 3 reverse.
The cams are each made as a split, offset disc. The disc is machined after 2 pieces of brass are soldered together (soddered if you are north American), then the solder is melted so the eccentric discs can be attached to the crankshaft.
I spent a day machining the brass pieces and soldering it, and turning the discs.
The brass rod with the soldered join, and the discs turned to accurate size
Another view of the eccentrics, still soldered together, ready for insertion of screws then melting of the solder.
Today I spent a couple of hours setting up the threaded holes to joins the disc pieces after the solder is melted away.
In the process of doing this I hit a wrong button, and fu**ed the whole job. So I turned off everything in disgust, and spent the remainder of the day cleaning up my Quorn tool and cutter grinder, in preparation for an exhibition next weekend.
Sh*t happens when metalworking. At least it will be quicker when I repeat this exercise in a day or two, if I can learn from the mistakes.
I have made the steam chest valves, the valve buckles, and the valve rods have been commenced.
The three steam chests, with valves and valve rods
The low pressure valve and buckle. Steam chest behind. The machining on the buckle did not quite remove all of the casting roughness.
And on a different subject, regarding last week’s post about making toys, this is the setup on my milling machine for CNC cutting of MDF. I am using the new high speed head running at 20,000 rpm with a 2mm cutter. There is a sheet of sacrificial MDF attached to the mill bed, and the material is attached to the sacrificial bed with double sided tape. I hand held a vacuum cleaner nozzle to suck up most of the MDF dust, rather than breathing it, or having it settle on my machines and causing rust.
CNC’ing MDF on an industrial scale machine.
The MDF after 20 minutes of CNCing. This turned into a raptor.
Today I spent a couple of hours drawing CAD elevations of the high pressure cylinder steam passages, then generating some G codes for the CNC centre drilling, drilling, and tidying up of the steam passage connection to that cylinder.
Then I spent 30 minutes or so running the programmes.
All went well. No drill bits broken in the depths. No break throughs of dark passages into the cylinder bore, or into the bolt holes. Whew.
The steam passages now open into the top and base of the high pressure cylinder. Intermediate and low pressure cylinders to be done ? tomorrow.
This is the drilling setup. I used a sine vice, sitting on gauge blocks, to produce an exactly 5 degree angle, to avoid the cylinder bore and the bolt holes. The sine vice was held in the milling vice.
The 2mm end mills arrived, so I have started machining the steam passages.
The steam inlets are 2mm wide and between 12.7mm and 31.75mm long, and up to 12mm deep. I had planned to angle the passages, rather than placing them at 90 degree angles, but realised that angled passages would impinge on bolt holes, so I have reverted to the original plans.
First I marked out the steam ports.
The cylinder blocks, painted with marking out paint, ready for marking.
Milling the slots. Here I am using a 2mm end mill to cut the inlet ports. . Feed 60mm/min, 6000rpm, 0.25mm slices. HSS cutters were not up to the job, becoming blunted quickly and then breaking. The carbide cutters performed well, at 6000 rpm. Each slot took about 30 minutes to cut.
The condenser covers are attached to the condenser body with BA7 screws. The 4 inlets/outlets are drilled, surface machined, and screw holes tapped ready for the pipes.
An unintentional ding from the milling machine chuck will need to be repaired before painting.
Covers for the inlet/outlet perforations were made, to enable testing for leaks. No significant leaks found. Slight weeping from the right hand cover will be stopped when the join is sealed or a gasket installed.
In the previous post I described my attempt at silver soldering the condenser unit.
The 29 joins on one end were quite water tight, but the other end leaked like a sieve.
I decided to try to fix the leaky end, by doing the following….
1. I shortened the copper tubes which were protruding more on the leaky end, thinking that the deep narrow spaces between the tubes might not have become hot enough during the soldering.
2. I used a Dremel to enlarge the spaces between the copper tubes.
3. I watered down the flux to make it more runny, in an attempt to get it into the narrow spaces.
4. I used a larger oxy-acetylene tip, to deliver more heat onto the job. I think that maybe (as per reader John’s suggestion) I was getting intense heat at the soldering point, but maybe not enough into the base metal of the condenser. The condenser is a thick brass, heavy object, and maybe, maybe it just was not hot enough. With the bigger heat delivery, it did show the dull red heat which is recommended for silver soldering. Also, I used a lower silver content rod (45%), again reader John’s suggestion, because it melts at lower temperature, and is less viscous, than the higher silver content rods. Thanks John!
The condenser unit, after today’s soldering fix. Note: there are no air bubbles rising! It is air-water tight, at atmospheric pressure, which is adequate, because it is a low pressure unit.Then I glued the end covers onto the unit, using Loctite, in preparation for the next step, which is drilling and tapping the holes for the BA7 bolts which will hold the end covers in place.
The Bolton 9 triple expansion steam engine build has stalled, and it is all due to achluophobia
Achluophobia, in case you are not fully aware of the term, is fear of dark places.
The next step in the build, is to drill or mill the steam passages (the dark places).
These passages are slots less than 2mm wide, and up to 14mm deep. The plans call for 6 of these deep, narrow, dark slots to be made in the cylinder blocks, upon which many many hours of work have already been lavished. In addition, the slots have a 90 degree bend in the depths. And that bend is only 2mm away from the cylinder.
The thought of a broken drill bit, or milling cutter, at those depths in the cylinder blocks, fills me with apprehension.
So I have done what I usually do when facing a difficult task with potentially disastrous consequences…. nothing.
I am waiting, thinking, and hoping that some thought bubble will pop, and give me the answer as to how to accomplish the task with some certainty of success.
Any suggestions would be welcome.
Maybe it is not achluophobia. maybe it is atychiphobia.
Yesterday I turned the pistons for the steam engine.
The plans called for the pistons to be made in 2 halves, and the rings to be cast iron.
But the plans also showed the cylinders were cast iron, and my castings were all gunmetal.
So with gunmetal cylinders, I decided that iron rings were not appropriate.
I have used graphite impregnated packing for other steam engines, but after investigating the use of Viton O rings, I have decided to use them.
Viton rings are easy to install, cheap, easy to replace, and apparently work well. They would not be used in an engine doing serious work, but my steam engines are more for display and interest and education, and will do few hours under steam.
Also Viton rings are quite small. So if I decide later on that I want to change the Viton to packing or something else, I will simply turn larger grooves in the pistons to accept the alternative.
A day out of the workshop for looking after my grandson, and watching my daughters husbands eldest son from his first marriage playing football, and cheering him on for kicking 3 goals in the last quarter….!!
But back into the workshop today.
First I bored the big end bearings.
Bored on the mill, not CNC for a change. After some fiddling to get the measurement correct on the first big end, the next two took only a few moments.
Then some finishing turning and polishing for the con rods, and a decorative groove.
Then bored and reamed the the crossheads for gudgeon pins. For once, the 3 cylinders were the same, so measure the first then quickly repeat the process for the next two.
Then, for a bit of fun, I assembled everything done so far.
The crankshaft, con rods, crossheads, gudgeon pins. The big cylinder in the foreground is a handle which I use to turn over the crankshaft manually or in the lathe. It is also a threading handle (home made).
Close up of the engine guts.
The whole engine, so far. It is quite exciting to see it coming together. SWMBO is not impressed with it sitting on the kitchen table.
Next on my list, the pistons and piston rods. Big decision. Rings. Cast iron or packing.
ps. Neither. Cast iron rings in gunmetal cylinders not a good idea. Gunmetal would wear excessively. Graphite impregnated packing would be OK, but I am probably going to use Viton O rings. Easy to install, fairly inexpensive, and quite suitable in an engine which is unlikely to see any serious work.
The con rod shafts have a taper of approx 1.5 degrees. I turned the shafts between centres, using a tangential tool.(a Diamond tool holder from Eccentric Engineering). The HSS cutter has a round cross section which gives a good finish, and automatically fillets the joins.
Of course left and right hand tools are required to do the whole taper.
Another jig! The con rod casting is difficult to hold accurately for milling, so I made a jig to assist. 10mm aluminium plate, with a cut out section to accept the con rod casting.
The jig had to be made as accurately as possible. So it was milled square and parallel, then centre pins were installed to hold the casting by the previously drilled centres. A further pin with a sharp point was installed to stop the casting from rotating during the drilling and reaming for the gudgeon pin. That gudgeon pin hole was continued through the jig, so a large pin could be inserted to really hold the casting securely. It also allowed an accurate 180 degree rotation of the casting.
A bit clearer with the swarf swept away!
You can see the gudgeon pin in place, while further surfaces are milled.
Close up of the jig and my metal workers’ dirty hand. Just as well there is no more gynaecology.
Not a clear shot, but here I am using the flutes of a milling bit to smooth the flat section under the gudgeon pin. Not ideal but it worked OK. Tomorrow I plan to round off the external surfaces and mill the slot for the cross head. Not much to show for a full day in the workshop, but it was fun…
Each main bearing consists of 2 gunmetal halves which fit into a slot in the base, and a cap which bolts to the base. There are 6 of these.
I machined the gunmetal castings, and made the caps.
Before I finished the machining or drilled the holes for the bolts, my phase changer failed, so I finished the job on my (single phase) drill press. Not ideal but adequate.
The Phase Changer has failed at least once every year since I bought it 5-6 years ago. It is the least reliable machine in my workshop. Repairs to it seem to take at least 3-4 weeks on each occasion, which is frustrating. I will borrow a 3 phase diesel generator to keep the workshop in action while waiting (again) for the repairs.
One of the 6 main bearings and caps. The hole has been roughed out, ready for accurate boring
The 6 main bearings sitting in their slots. The hold down bolts are ready to be installed. The bearing surfaces will be bored when I have some 3 phase power again.
This is the first big end bearing. The bearing surface was roughed out on the mill (held between centres using the dividing head), then the excess around the flanges was removed on the mill (with the workpiece held in the milling vice), then the bearing surface was finished in the lathe. There is a crankshaft buried in that lump of steel. I just have to remove all of the bits which are not crankshaft. (apologies to Michelangelo).
Making a start on the second big end. There is a block of steel loctited in the first big end so it is not bent when the workpiece is compressed between centres while the other big ends are machined. The second big end is yet to be finished on the lathe.
A slightly different view showing the block glued into the first machined big end, and the almost finished second big end. This is the milling machine setup.
My first attempt at making a crankshaft for the triple expansion steam engine involved turning the workpiece between centres.
It worked in a fashion, but only at 200rpm. At that speed, not great finish. And frankly it was scary and hairy!
Then I discovered that I had made a 3mm mistake in the position of the middle big end bearing, so it all had to be done again.
The first method of making the crankshaft. Slow, not a great finish, and fairly hairy, despite the 2 tonne lathe.
So today, with some new steel, I decided to use the vertical mill instead of lathe. Actually, I turned the cylinder to size on the lathe, after drilling the centres on the mill. I tried to turn the big ends on the lathe, (eccentric turning, using counterweights this time) but I was still not happy with the result from the intermittent turning.
So I tried a different method, using the vertical mill, and rotary table, set up as in the photos.
Setup on the vertical mill. The rotary table was turned by hand… rather tedious. The 8mm end mill was run at 1600 rpm, taking off 0.5mm on each revolution. A slow process, but it felt safe, and the finish was excellent.
The rotary table setup.
Only 10mm of material remains, for the big end bearing. Before excavating the material for the next 2 big ends, I will glue (Loctite) blocks into the gaps to provide support. The mains will be turned or milled last. I might still finish the bearings on the lathe. Not yet decided. Watch this space,
After my initial problems with making the crankshaft, I asked and obtained advice from my Model Engineering Club colleagues. That resulted in the decision to machine the big ends first (thanks Stuart) and counterweight the turning when doing offset turning (thanks Malcolm). Also thanks to Peter V, for double checking my measurements this time, and jollying me along.
Still a lot to go to finish the crankshaft, but I can see that this method will work. I might motorise the rotary table before I start any more of the 8 remaining bearings.
p.s. 7 December 2019 (4+ years later) I did eventually motorise the rotary table, with a stepper motor, and it is CNC controlled, along with the XYZ axes on the mill, by Mach 3. The triple expansion engine has been running on steam for over a year, and is virtually finished except for some optional small fittings (like cylinder waste drains, builder’s label).
Apart from contending with fauna in my workshop (a tiger snake) , I did actually make some progress today.
All three steam chests are now attached to the cylinder block. This photo shows the high pressure cylinder steam chest. All of the screw holes are threaded and ready for the screws. More BA7 screws on order.
The time which I have had spare in the past few days has been spent tidying up the workshop, sorting tools and putting them away. Today I spent a few hours making a start on the intermediate and low pressure steam chests.
Roughed them out and CNC’d a boss on the bottom of each chest. Then roughed out the steam chest covers.
This is the progress to date.
So far I have drilled, tapped and inserted ~180 BA7 screws and studs. And there are a lot more to go. The steam chests and covers are sitting on the base.
Attaching the cylinder block bases to the cylinder blocks was tricky. I drilled the holes with the bases glued to the blocks using Loctite, and then tapped the holes and inserted the screws. I will apply some heat to break down the Loctite.
It is quite difficult to insert the screws to the underside of the block. Many are quite inaccessible. There have been multiple tear downs of the model, with many more to go, so only a small number of screws are currently inserted. I will have to work out an order of assembly, to make the assembly process as logical and easy as possible.
I am starting to consider which method I will use to make the crankshaft. It has 6 main bearings, 3 big end bearings, and locations for 3 valve eccentrics and an oil pump. It is quite complex. Fabricate or turn from the solid. I am tending to the latter, but we will see.
The 56 bolts which attach the cylinder heads, were installed today.
First, the heads were bolted into position with a jig.
The work is held in position on the milling machine table, using 4 hold downs, and 2 T slot locating fixtures. The jig also helps to secure the work to the table.
The jig fits into the milling machine T slot, and the bolts are exactly positioned in the centre of the heads.
The bolts hold the heads in place while the centre drilling, through drilling and thread tapping takes place.
That is 4 processes for each of the 56 holes. Even semi automating the process using CNC, it took 6 hours, including setting up, making the jig, and finally installing the bolts.
Drilling the relief holes in the heads, after preliminary centre drilling. Those holes are only 2.5mm diameter, and 12mm deep. Despite the tiny drill size there were no breakages. The drill was set at 2500 rpm, feed rate 50mm per minute, and with pecks set at 2mm. A cutting lubricant was used.
The head bolts in place. The bolts are BA7, which is pretty tiny, but they look the part, yes? The highest “density” of bolts is on the smallest cylinder head, which is on the high pressure cylinder. The threaded holes in the centre of the heads are for the pressure relief valves.
I have left the set up intact on the milling machine, until I am sure that there are no further processes I can perform with the block in this position.
Turning these fairly simple pieces should have been a doddle. Trouble was that they are relatively thin and soft and holding them in a three jaw chuck on the lathe was OK, until the rather sharp tool got pulled into the work. The cutter jammed, the workpiece was pulled out of the chuck and thrown across my workshop, with a a lot of superficial damage to the workpiece.
Fortunately, there was enough material remaining to machine out the dents and cuts. Also, it forced me to make a jig to hold the workpiece securely. Since the head caps are all different sizes, I had to change the jig dimensions after each head was machined, which was time consuming, but the method worked well with no further hitches. Also, I changed from a tangential, sharp, high speed steel cutter, to a neutral rake carbide (and therefore less sharp) one, and no further dig ins were experienced.
The jig for turning the reverse side of the cylinder heads, and the underside of the low pressure head (the biggest one)
Next I will drill and taps the holes for the small bolts which secure the head caps. All 56 of them. I sense some more CNCing in my near future.
Today I bored the cylinders on the triple expansion engine.
Most model engineers would perform this task on a lathe, bolting the work to a faceplate or possibly using a large 4 independent jaw chuck.
The most accurate machine in my workshop is my CNC mill, so I decided to use the mill.
The setup is as depicted in the photo below.
The cylinder boring setup.
Cylinder boring complete. The setup took a couple of hours. The boring process also took 1-2 hours.
Of course, the high pressure cylinder needed to be center drilled, then drilled to 6, then 12, then 15mm, then bored to size 22.23mm.
Doing the job on the mill, I can be confident that the bores are all on the center line, all parallel, and the centers all correctly located. The intermediate cylinder finish was not acceptable, due to some chatter on the final cut, so I bored it out an extra millimeter to rectify the problem. The extra size will not matter. The piston (and rings?) will be made to fit the bore.
At the end of the session, I have left the setup intact, so I can check whether further processes can be performed using the same setup.
The heavy chunks of brass which form the cylinders, and the intermediate cylinder valve chest, have been machined externally, and bolted together.
The low and intermediate pressure block on the left, the IP valve chest (with the round boss), and the high pressure cylinder block on the right. All bolted together. Almost ready for cylinder boring.
The IP valve case cavity has been machined, but 3mm too wide. I think that this error will not matter, but if it does I will silver solder some extra material to get to the specified dimension. (the external dimension of the steam chest is deliberately left too big at this stage. It will be blended with the cylinder blocks later.)
Now that these pieces are together, I can do the cylinder boring and complete the external dimensioning and finishing.
I read an expert treatise on making a double expansion steam engine, and I imagine that the comments applies to triples also. One aspect emphasised the importance of accuracy in making the cylinder bases. The parallelism of the surfaces, the concentricity of the piston rod hole and the other circular elements, and the thickness. The usual method for making these items is to turn them in a lathe with a 4 jaw chuck, then to reverse the item in the 4 jaw to turn the other face. It is possible, but very fiddly and time consuming, and relies on expertise, patience, good eyesight, and a good lathe. All of which are in short supply around here. A triple expansion steam engine requires 3 of these base plates, and while there are some common dimensions, the cylinder bores are all different. Many of the screw holes are common to the 3 plates. The thicknesses are all the same. To shorten this rather boring epistle, I decided to have a go at making the base plates on the CNC mill. Given my previous muck ups, broken bits, crashes, this was a courageous decision, as evidenced by having to bin the first effort. But the next 3 all seemed to work OK. First I studied the plans and noted the common elements, then I made a jig, with holes drilled at the common positions.
The underside of the jig, showing the 5mm centre hole and the counterbored holes at the attachment points.
The topside of the jig, after the first and second baseplates were drilled, thicknessed and shaped. The jig needed to be made very accurately, to retain position of the workpiece after it was reversed, so both faces could be milled. I am told that CNCers build up a collection of jigs over time. They are rarely used again.
CNC milling the central boss. 20.48mm diameter, and accurate. Note the red positioning device, enabling the workpiece to be removed to check measurements, then replaced exactly in the same position.
The cylinder baseplates screwed to the columns. Some trimming of the column tops is required. The baseplates are centered accurately, as far as I can measure. Note that the central jig separating the columns has been removed, and the baseplates are now holding the column tops in position. The columns appear to be lining up correctly.
The next example of using the CNC mill to perform a task which is normally done on the lathe. The mill cutter is travelling in diminishing circles, producing a central boss, and a flat surface.
The boss finished to size (10mm dia) and flat surface.
BTW. In a previous post I mentioned a 1 mm inaccuracy in a CNC milled part. It happened again when I milled the first base plate, which ended up exactly 2mm smaller than programmed, and had to be re-made. This time I discovered the cause of the inaccuracy…. I had used an 8mm milling cutter, but had forgotten to tell the CNC computer that I had changed from using the 6mm cutter. The CNC machine did not notice the change, and cut the part exactly as instructed, very accurately, 2mm smaller than intended. CNC machines are incredibly clever, but very very dumb. They do exactly as instructed, even if the instruction is wrong.
Today I assembled the base, columns and Jig, intending to mill a flat top to the whole assembly.
To my surprise and dismay, it was apparent that one of the columns was one mm out of position. Dont know how that happened. A typo in the CAD drawing or CNC program? It could not be a zeroing issue, because all 3 columns on that side would be out of position.
What to do?
I decided to turn the 2.5mm holes in the column base into slots 3.5mm long. The bolting position on the jig was exactly correct, so I used that to zero the position, found a 2.5mm end mill, and gingerly milled the slot. holding the column upside down in the milling vice.
Fortunately, that seems to have worked. The columns are now all correctly located. The tops of the columns are the crucial plane and position, and they seem good. I doubt that the slots will be an issue in the finished engine. They are invisible under the column feet. If necessary, I will make a couple of locating pins and drill them in position right through the base from underneath. I doubt that will be required.
After that, I did take a milling skim off the column tops, to create a dead flat plane, to which to bolt the cylinder bases, when I have made them.
Not tomorrow though. I am off to Ballarat Victoria to a swap meet on the aerodrome. In previous years there have been approximately a thousand stalls. Some are shed clean outs, some commercial vendors and dealers, and lots of ancient cars and machinery and parts. The best stalls are the ones selling used tools. I seem to come home after each meet with a heavy pack full of tools and materials, and a lighter wallet. But it is always interesting and fun.
Today I made the BA7 studs for the columns on the triple expansion steam engine. I decided to use 25mm bolts, then trim them to length after they were installed into the threaded holes. Why not use threaded rod or make my own studs on the CNC lathe I hear you asking? Well, I could have made my own studs. In fact I did make 2 studs, quite succesfully. But it was time consuming. Cutting up threaded rod would have worked, but it turned out to be less expensive to buy over length bolts which are threaded right down to the heads, and trim them to length, than to buy threaded rod. Plus, the trimmed bolts are now quite useable 12mm bolts. Also, it was easy to use the bolt hex head to screw them into the threaded holes.
I did manage to break off one stud and spent a half hour or so digging the stub out and renewing the stud. But no permanent damage.
The BA7 25mm bolts are screwed into place, and held there with with a nut. The saw blade was attached to a 200mm long arbor which was shop made for the job, shown here about to trim the bolts to length, on the milling machine.
The studs are trimmed to length, and the columns are sitting in place, temporarily held with 4 nuts each. 9 studs and nuts is total overkill, over- engineering, but it looks the part, no?
After fiddling with the minute BA 7 studs and nuts, trying not to go nutty myself, I had some fun rough machining the lump of brass which is to become the low and intermediate pressure cylinders.
To see the YouTube video, click on the link below. Sorry about the shaky image. I was holding my iphone in my right hand, while hovering my left hand over the emergency stop button, just in case. But it all went perfectly.
The triple expansion engine legs will be bolted to the base, with 9 bolts each. That is 54 holes which needed to be precisely drilled so the columns are accurately positioned. Each one of those holes needs to have a mating hole made in the base. The base hole will be threaded to accept a stud.
Normally one gets accurately mated holes by drilling through both objects simultaneously, but that was not possible in this situation due to obstruction from the columns themselves.
So the solution?? CNC of course!
The hole positions were known from the CAD drawings, and were entered into the CAM program. The resulting file was too big for my old CNC mill (1997 model), so I attempted to drip feed the information as the machining operation was taking place, but without success. Several phone calls to my expert friend Stuart did not resolve the problem, so Stuart kindly came to suss it out. A couple of hours later he had the drip feeding working as a result of a serendipitous error.
We knew that the largish file needed to be drip fed into the CNC mill, but it eventuated that we had to try to enter it directly, and produce an error message first, before drip feeding it. A bizarre system, originating from the land of Manuel of Faulty Towers.
A test run in scrap wood.
Heart in mouth, center drilling in progress
And 2.5mm through drilling
And the mirror image holes in the base. 2.05mm diameter, ready for BA7 threading. See how the holes line up exactly with the marking lines. Now to make 54 BA7 studs.
Deep drilling using CNC. The last hole was drilled manually, with problems. CNC rules OK!
A warm day today. Too hot to wear a shirt in the workshop. But no metal splinters from machining the brass and aluminium, and only one hiccup, which will be described.
The jig which I started yesterday, needed 9 more accurately positioned holes drilled and tapped M4.
So I programmed the CNC mill, only to discover that there is a limit of 8 holes able to be programmed. So the final hole would have to be separately positioned, and that was the cause of my problem.
Firstly, the 8 holes were deep drilled (30mm deep, 4mm diameter) after centre drilling. All done with the CNC.
All went beautifully. 2mm pecks, some cutting fluid brushed on.
Then I used the CNC to position the last hole, and centre drilled it manually, AND BROKE THE CENTRE DRILL IN THE JIG!!!
I did not want to remove the jig from the vice, because it was all accurately set up. But I could not see the broken high speed steel tip, so I removed the jig, and tried to dig out the broken tip. Unsuccesfully.
So the next method was to use an old carbide end mill, 4.5mm diameter, to drill into the hole and to break up the high speed steel fragment. That method worked, but at the cost of enlarging the accurately placed but incompletely drilled hole. Next step was to reposition the jig in the milling vice, then deeply countersink the hole, then complete the 4mm drilling operation. It seemed OK, but it later became obvious that the hole had moved about 0.5mm from where it was intended. I eventually used a carbide end mill to enlarge the entire hole, in the correct position, at 4.5mm diameter. All a bit messy, but not fatal.
The jig halves opened up, and the drilling positions which were entered into the CNC instructions.
Then the columns were drilled and tapped. 2 attachment points per column, so with 3 holes per column in the jig, there are 2 possible positions for each column in the jig.
The columns to be attached to the jig.
A column on the wedge in the milling vice, ready to be drilled and tapped.
The columns screwed to the jig.
2 columns are integrated with the condensing unit.
Re “Titanic” engine heading… I get a lot more hits on this blog if I include the word Titanic. OK?
Now that all columns are attached in their final position on the jig, I can start hacking into them to produce some flat surfaces
The columns sitting on the base in their correct position, using the jig.
LP is the column for the low pressure, biggest cylinder. HP is the column for the high pressure, smallest cylinder. IP is intermediate. C is for the steam condenser.
A day on the steam engine. SWMBO went to Melbourne to choose marble so I was free!!
After discussing my problems with machining the triple expansion engine columns with the senior members of the GSMEE (Geelong Society of Model and Experimental Engineers), I have machined a JIG to assist with this issue.
The JIG thickness is precisely the width between the columns (30.05mm). It is made in 2 halves so I can bolt the columns from their critical surfaces which are the con rod slides.
I will use the CNC mill to drill the holes in the jig, and the matching columns, then finish milling the columns which are attached to the JIG.
The jig for machining the columns. Not yet finished.
Bottom left is X=0, Y=0. The photo shows the 4 countersunk M4 screws.
The holes will be centre drilled then through drilled 4mm. The columns will be drilled 3.3mm then m4 tapped.
Hopefully that will happen tomorrow if the workshop is not too hot.
You will see what I am intending with the next post.
Today I drilled and tapped the holes for the bolts which secure the crankshaft main bearings. I had accurately marked the bearing mounts in the previous session (see previous photos), and calculated and recorded the DRO (digital read out) position for each hole. So going back to that position for each step in the process was easy and quick. The steps today were centre drilling, drilling the 3.3mm holes, and tapping the 4mm threads to a depth of 20mm.
Centre drilling is done with a centre drill bit in an accurate chuck in the milling machine. Centre drill bits are inflexible and will not wander over the work like an ordinary twist drill bit, The centre drilled hole is deep enough to create a chamfered edge to the hole. All 12 holes are drilled with the centre bit, then all 12 drilled with the 3.3 mm bit, then all 12 are threaded. The DRO positions the work within 0.005mm each time, and the repositioning is very fast, much faster than going to a position doing all 3 processes, changing the bit for each one, then moving to the next position.
The threading was done with a Tapmatic 30 tapping head in my milling machine. See photo. This takes about 10 minutes to set up, but the tapping process for the 12 holes then took about 5 minutes. I use Rapid Tap lubricant for tapping, even in brass. I guess that manually tapping the holes would have taken about the same time, but it was so satisfying to see the Tapmatic do its stuff. I use the Tapmatic for any tapping job involving more than about 8-10 holes. Fewer than that it is quicker to do them manually. The Tapmatic has a adjustable clutch. I have never broken a tap in the job using this machine.
Incidentally, I have decided to use nuts and bolts and screws and studs in preference to metric cap screws for this model. The appearance wins out over practical expediency. So why the metric threads for this job today? The specified thread was 5/32″ which is 3.96mm, so I decided to go with the 4mm metric, for which I have the tools already.
Tapping the main bearing blocks using the Tapmatic and Rapid Tap.
The base, with 6 pillar mounting areas machined parallel & coplanar, and the crankshaft mounting blocks after an initial skimming. Slots for big ends roughed out. 2 hour first machining session. 2998 hours to go?
After carefully examining the base casting, and scrutinising the plans to discover all of the dimensions of the base, I commenced machining on my King Rich mill (Bridgeport clone, NT40 with DRO, an excellent machine). Since the base dimensions are scattered over 3 pages of very complex plans, and I am still relatively unfamiliar with them, I am approaching the machining with great caution. At this stage I am aiming to create some flat and coplanar surfaces, with a margin of material remaining, so I can hold the base flat, without rocking, roughing out the shape, and leaving finishing to dimensions at a later date. I intend to attach the base to a rectangular piece of aluminium, so the aluminium can be clamped or held in a vice, rather than risking damaging the brass casting.