johnsmachines

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.

How to fix a Mac Laptop with a Toothbrush and Metho. and another Cannon Bit.

After a session on the model cannon yesterday, I sat down at home with a glass of red and my laptop.

I was awakened by a phone call, but my bum was wet, and the laptop screen was black. And the laptop keyboard, and presumably my bum, was red with spilt wine.

Dealt quickly with the call. Dried myself off. Wiped the keyboard dry, but it was stained red.

Turned the Macbook on.

DUMB!!! Turn it OFF you idiot!!! I didn’t find that out until later.

Screen remained black. Charge cable light not registering.

Turned the laptop onto its edge and some wine dribbled out.

Still would not turn on. (See previous “DUMB” comment .)

Opened up another computer. Looked up “MacBook Pro Wine Spill” on YouTube. Lots of videos. Obviously I am not the only person to kill a laptop with red wine. Quickly viewed a couple of them.

“TURN OFF THE POWER”. “DO NOT TURN ON THE POWER”. Ok. Didn’t know that. Oh Dear.

“Use a 1.2mm Penta Lobe screwdriver and remove the back as soon as possible. The longer the delay, the worse the problems due to corrosion”

I have a few sets of tiny screwdrivers. None of them had a penta-lobe.

Rang around my computer savvy acquaintances, but none there either.

WHY DO COMPUTER DESIGNERS SPECIFY SUCH WEIRD SCREWDRIVERS?

Oh, I get it. They don’t want end users to fix their own computers. In a pandemic there is not much help from repairers either.

So, next morning I visited JayCar, and bought another set of tiny screwdrivers. They had a few sets with “penta-lobe” screwdrivers. This was the most comprehensive set. $AUD50. Really nicely made, bits held in multi layer case with magnets. Feels quality.

Very happy with this purchase.

Removed the 10 tiny screws under a magnifying light.

This is the laptop innards after I had wiped off most of the red wine.

Didn’t photograph the clean up steps. I was feeling very pessimistic about a successful outcome. Wiped off the red wine. But there was a sticky, syrupy, residue. A great glob of it under the big T shaped label, and a lot more around the vent holes on the right. I guess that the wine got access through those vent holes, and the keyboard.

One YT video showed a repairer scrubbing the electronics with alcohol and a toothbrush.

Oh well, here goes. So that it what I did, using methylated spirits. It felt risky, but the congealed mess did seem to clean off. Then I patted the cleaned areas dry.

Next question. Do I remove more components, to hunt for more areas of spill?

No. I think that I will try it first, just in case my cleanup so far has worked.

So I reassembled the bits which I had removed. Plugged in the power supply. … and the little power supply plug light came on! Hope!

Turned on the computer. Took a while to boot up. But boot up it did. Wonderful.

Next step. Make a complete backup of all of those files which I thought that I had lost.

Next step. Brag about my success on johnsmachines.com using the aforesaid MacBook Pro.

Meanwhile back to the scale model Armstrong cannon. The next photo shows yesterday’s result. Can’t see any change? Look carefully under the protractor. See that tiny bit?

That little piece represents several hours of cutting, silver soldering, filing, and fixing to the cross bar with TINY 10BA screws and nuts. Later it will have a mark to line up with the protractor marks.

So, life seems good again. And more Covid restrictions are being lifted tonight. Yippee. But still cannot see my Melbourne family for another 2 weeks.

BTW. I found some more videos to delete. So I have some more space for posts. But sad about the videos .

Armstrong RML Elevation Protractor

2 days in the workshop, and not much to show…. just one photo.

Yes, the trolley wheel axles need to be shortened. Next time the carriage is disassembled. The recoil tube is just sitting there, for effect.

The curved brass bar is a protractor for measuring degrees of elevation of the barrel. I used High School trigonometry to work out the distance from the pivot point at the centre of the trunnion, to the pivot centre at the fitting under the barrel.

Then cut out the shape from 2mm brass with the CNC mill. That was the easy bit. Although it did takes 3 goes to get the radius of the curve correct.

Today, although feeling depressed after the Cats loss last night, I made the cross bar with the rectangular cutout, then spent a couple of hours bolting it into place. It all works smoothly. The rectangular cutout is 2.2mm wide and 7mm long. I chain drilled with a 2mm carbide milling bit, then milled the slot sides, then filed the corners square. It is stainless steel. Slow work.

I have not worked out how to engrave the protractor marks, which are at 0.25º intervals for elevation, and whole degrees for depression. I could ask Stuart T to engrave it for me. The design and actual lasering would be straight forward, and I am sure that Stuart would help if requested. The problem would be to align the part on the laser machine, so that the engraving occurred exactly at the correct location. Actually, as I type this, I think that I have the solution. Watch this space.

I need to make a pointer next, and to determine the 0º position. The carriage sits on the chassis which is at a 4º slope. Not rocket science, or brain surgery. Just need to get it right!

Next Project?

I made a 1:10 model of this Ottoman bombard a few years ago. This one was made in 1465, and is thought to be a copy of the bombards which brought down the walls of Constantinople in 1453. This one resides in the Royal Armories Museum at Portsmouth, UK, and I photographed and measured it in 2019. It has a bore of over 600mm, and fired stone balls of over 350kg.

Last used in anger against the Brits in 1807, where it and others like it, were instrumental in preventing a British fleet from invading Istanbul (renamed from Constantinople). How many weapons have an active life of ~350 years?

…and the model turned out well. 550mm long, but, it is made of wood.

So I am contemplating making a model at the same 1:10 scale, like the original, in BRONZE. It will have the same shape and size, but will look like and feel like BRONZE.

I still have my original measurements and drawings of the model. So my plan is to print the cannon parts in PLA, taking into account my extra information from the 2019 visit, then to cast it in BRONZE.

I had planned to stop this blog after finishing the Armstrong RML, but maybe , if there is enough interest, I will keep it going for the next project. You will need to let me know if this project will be of interest. Because lately, comments and likes are few, and numbers have been discouraging. And the renewal date for WordPress is approaching. I get it that people prefer videos, but that is not my style. If this written plus photographs style is not wanted then I will not persist.

CNC Machining a Small Part

The part measures 20x12x7mm.  And it has some tiny details.

Not quite finished here. Still needs a shaft hole drilled and reamed, and the top holes to be threaded.

The design is simply and quickly drawn on V-Carve. A rectangle with rounded corners for the base, and a rectangle with 2 arcs on each corner of the column. Circles added for fastener holes.

This is where it ended up….

The part is a bracket for the shaft. It locates the shaft in 3 dimensions, so the height of hole above its base is exact.

There are many ways to approach the machining of the part, and this is the technique which I used……

The part is machined in the end of a piece of material which can be held in a vice for milling, and later held in a lathe chuck for parting off. The hole for the shaft was made after parting off. The parallel end faces permitted it to be held in a vice. The shaft hole could also have been made by holding the brass rod in a vice or chuck before parting.
Not quite finished. When the bracket comes off next time, it will spend some time in the gemstone tumbler to take off the sharp edges and improve the surface finish.

The control wheel for the elevating gears was found in my rejects box. It was made for the triple expansion engine. It looks pretty good? Cant remember why I rejected it for the triple. Maybe my standards are lower these days.

There are not many photos of these cannons on the net, and none of them show this wheel. Or was it a simple handle? The shaft has a squared end for a wheel/handle of some sort. So this wheel is my best guess as to what would have or could have been used. Virtually all of the cannons remaining of this type have had the small parts removed/souvenired/stolen which is sad. Some old photographs of bigger Armstrong RML’s show wheels of this type, so I feel justified in making this design assumption.

P.S. And after making that comment above, I rediscovered this photo a few days later. I think that it is the Armstrong RML at Portland, Victoria. Note the hand-wheel at the front, which will be for barrel elevation. This is a different setup from the gun which I am modelling, with the gears within the carriage, but the hand-wheel is similar to what I came up with.

Another design consideration. SWMBO likes the cannon without the chassis, as in the above photo.

But this is how it looks on the chassis.

…and there are many hours of effort in making the chassis, and movement gears/brake/big wheel/riveting etc. and still more to be added, such as the projectile loader, gunner platforms, etc.

The gun and its carriage have brackets which make separation from the chassis very difficult/almost impossible. So I am considering a design modification which would permit a choice of with or without chassis. What do you think?

(please note. this is a MODEL cannon, has no touch-hole/vent and is therefore not capable of being fired.)

Fitting the Barrel Elevating Gears.

Firstly the right hand carriage side was removed from the carriage.

This is a side of the model Armstrong RML carriage.

I turned a disk with a small hole to locate one arm of the dividers at the centre of the trunnion, and positioned the quadrant gear. Then super glued it, and its pinion, into position. Marked the locations. The super glue will be removed later.

Then drilled and reamed the pinion hole.
The location of the barrel fitting was determined after reassembly of the carriage, with the quadrant gear still glued into position. Very tentatively drilled and tapped the holes for the bronze fitting into the barrel. That cap screw will be replaced by a shop made countersunk screw.

The bevel gear case was located through the pinion gear hole, and keeping the control handle shaft level. The case was drilled and bolted into position. The control handle shaft will be replaced by one of smaller diameter, in keeping with the 1:10 scale.

starting to look like the real thing….
That cap screw is temporary.

A couple of days in the workshop working out how to position those parts and drilling, tapping, and reaming. The other cannon will take less time.

Barrel Elevation Gear

This photo is the original Port Fairy cannon, and the 3D printed 1:10 model size copy. The original is ferrous and the guide is bronze or gunmetal. I decided to make my scale model versions from brass, for ease of construction, and to avoid rusting because these parts will not be painted.
I did not have a piece of brass big enough and thick enough to cut a 360º disk. It would have been 182mm diameter and 2.5mm thick. So, I made this fixture, and attached an aluminium plate.
Bolted on some bits of brass bar the correct thickness, using holes outside the gear, plus one which will be incorporated into the gear.
Then cut the teeth, using my CNC rotary table.
Then used the same fixture held in the milling vice, and cut the interior contour, and a rebate.
The ends still need to be shaped.
Showing the curved guides, rebates, and the bronze castings which secure the gears to the barrels

Making brass fittings is always a nice and enjoyable part of a modelling job. Making “bling” as my GSMEE friend John B characterises it.

More Bronze Pour Problems and Cheap Spanners

BRONZE POUR.

I had 3D printed another tree with 4 cannon parts. Brackets. The complete tree fitted into a steel flask 100mm diameter and 120mm high. So I repeated the steps of the last successful pour, and painted the tree with investment slurry, mixed the main investment, degassed it, poured it, and degassed the entire flask, investment and all. That method had worked well before, so I repeated it.

But I was a bit concerned because the investment was only a few mm thick at the bottom of the flask. Would it hold up? Read on.

So then commenced the drying, burnout, and baking cycles in the potters oven. Normally it is about an 8 hour process, and I did not get to start until 12 midday. So I was in for a long day.

But then the oven started to play up. It would suddenly switch off. The temperature gauge would swing wildly. And would not heat above 400ºc and it needed to reach 710ºc.

I did not know the source of the problem. Thermostat? Wiring? Controller? Power supply? I did know that the thermostat wire was not rated for temperatures above 600ºc, but it had worked OK previously. So I turned everything off, and removed the electronics compartment. Changed the thermostat wire to the proper grade (thanks Stuart!), then found a loose main heater element join, so fixed that too. It all took another 1-2 hours.

Started up the oven again. The temperature had dropped to about 200ºc, but the the temperature started rising slowly, so maybe the problem had been fixed? By this time it was 4pm, and there were still 7 hours of heating required, so it WAS going to be a late night in the workshop. Made my peace with SWMBO. She was happily watching the footy, and not too worried about about my travails. (and our team won convincingly!)

To finish this story, I eventually poured the bronze, and my earlier concerns about the thin layer of investment at the bottom of the flask were realised. The bottom fell out, and molten bronze poured out through the breach. I normally rest the flask in a tray of sand when pouring, and fortunately, the bronze seemed to harden when it hit the sand, and the outflow ceased.

This was the result….

Amazingly, the parts seem fully formed, with no voids or bubbles. The ugly lump underneath is the bronze leak through the bottom. Note the length of feeder sprue. And the funnel. If you zoom into the photo you will see that the fine detail of the 3D printing has been reproduced. I will cut the parts off and finish them tomorrow. I got home about midnight. I needed that shot of single malt.
The bronze brackets, after sawing them from the tree. I will add a photo after another session of machining and finishing them.
After some more tidying. The investment powder can be persistent.

CHEAP SPANNERS.

I have several machines which use 40ER collets. I have enough collet spanners, but only one locking spanner for the chucks, and it is always on the wrong machine. So I decided to get some more locking spanners, and I sent my drawing to the laser cutting company. I picked up 4 spanners from them a few days later. Cost $AUD55. (cheap!)

My Colchester, with ER40 chuck. And one of the new stainless steel locking spanners. Drawn up as a dxf file, which was emailed to the laser cutter. The square hole is to lock the carriage to the bed. A few moments on the belt sander removed the sharp edges. Not elegant, but works perfectly.
2 spanners are required to tighten the ER collet. Here I am making a jig which will be used to cut the quadrant gear which elevates the cannon barrel. More about that in a day or 2.

Cannon Update

Not much happening to show visual impressions, so fewer posts, but lots of hours making bits function.

The three main gear shafts now have brass end caps. They will have oil cups drilled into the 12 0’clock positions next time the caps come off.

The adjustable parallels do not get a lot of use, but they are very handy to align parts in horizontal positions, like the holes in the end caps above. Especially when the girder is at an odd (4º) angle, and even the bottom of the girder is at 1º.

Currently I am planning the making and installation of the barrel elevation gears. Here is a PLA version, paper clipped into position.

Very handy having plastic versions to decide drilling positions etc. In the above photo is a plastic version of the main elevation gears, printed at the correct centres. The little bronze bit is the casting which is screwed to the barrel.

And just to demonstrate the current appearance of the cannons….. Lots of bits yet to be added, but it is exciting to see the size and form of the models.

Tension Drilling.

Do you know what tension drilling is? Well, read on.

Having made the gears which position the carriage on the chassis of the Armstrong RML model cannon (I assume that regular readers will know by now that RML stands for “rifled muzzle loader”), I had to drill the chassis for the gear shafts.

There are 3 shafts, 8mm, 6mm and 5mm diameter. I knew the theoretical distances between the shaft centres by applying formulae taking into account module and tooth numbers. And also by using “Gearotic” software.

(I tripled checked with a lash up and direct measurement.)

But! I did not know the distance between the big gear and the rack gear. Because, the rack is attached to the base of the carriage, and the big gear is attached to the chassis. Considerations such as trolley wheel diameters, rectangularity of chassis and carriage, and position of the trolley wheels on the carriage all come into play. I will not bore you with details, but determining that measurement involved a lengthy, tricky, and complex setup using a surface plate, height gauge, adjustable parallels, straight edges, and averaging the errors. Amazingly, it turned out OK.

Then came a decision. To drill and ream straight through both girders at once, or to measure and drill/ream them individually. Luckily for me, I had a visit from GSMEE member Swen, (to borrow a tool), who is a retired ex-army Warrant Officer artillery fitter/turner. When I explained my dilemma, he was in no doubt. Measure them and drill them independently, he advised. So I did just that.

But, having invested many, many hours to date in making the chassis’, drilling a big (relatively) hole in the chassis girder was a very tense moment. (hence “tension drilling”).

Before drilling any more of the 6 holes required, I tested the fit between the rack and the big gear. Amazingly, it seemed pretty good. Maybe a little bit tight, but not too bad. So, I drilled and reamed the remaining holes.

Collars, splines, pins, bronze bushes and brake fittings yet to be made.

That photo represented a very long day in the workshop. I think that I arrived home about 9pm.

And there was a problem.

The big gear and its partner would rotate freely in one direction, but were catching and lumpy in the other direction.

Closer examination revealed that the teeth of the pinion appeared to be bent, allowing free movement in one direction only. Hmm…. how could that have happened? And how to fix it?

Root cause analysis of the issue concluded that the mill Z axis must have been bumped when I cut the teeth on that gear, causing them to be slightly off centre, producing the “bent” appearance. (the top photo shows the faulty gear. Can you make out the distortion?)

Solutions? Make a new gear. Or fix the distorted one. I decided to try the second option. I was not wanting to make another ratchet. So, I filed and tried, filed and tried, filed and tried…. you get the picture. And gradually the lumpiness disappeared. Several hours later, with blisters appearing, it seemed quite good, and will not be visible to casual inspection. You, dear readers, will be the only ones to ever know.

Yesterday I drilled the second chassis. I completed the task in only 2-3 hours. A fraction of time compared with the first one.

Small Pliers

One of my readers made comment about the pliers which I used to hold the domes of 2mm copper rivets while I threaded them.

The pliers are worthy of comment, so I decided to say a bit more about them, and also some other pliers which are often used when I am working with tiny fasteners.

These are the pliers which started this line.

They are Japanese, not as expensive as some German brands, but beautifully made. And not inexpensive. “Engineer” brand.
And these are the jaws. Note the transverse, and longitudinal hardened grooves/ridges. The longitudinal grooves are in cylindrical contours, so they will grip cylindrical objects such as screw heads and small cap screws, with ferocity. And not let go. These are the ones which I use to hold copper dome head rivets, with plastic tape covering to protect the copper.
They come in various sizes. I purchased the two smallest. They are indispensable. Behind them are two other small pliers which I also use frequently.
These are Maun parallel pliers. They also come in various sizes. These are the smallest. Incredibly useful. Do not damage tiny nuts or bolt heads. And will hold sizeable objects.
……..and tiny objects.

Finally, the most expensive tiny pliers which I own……and probably the best…

Knipex Miltigrips, holding a 2mm nut. Parallel jaws. Incredibly strong. Beautifully made. Very expensive. totally indispensable. You should save up and buy a pair.

All of the above tools, and many others in my workshop, were purchased over many years at Qualitool Tools, 77a Mercer St, Geelong 3220. tel 035221 8915. David, the proprietor/owner is incredibly knowledgable and enthusiastic about tools, and was a supplier to the aircraft industry, and also to auto mechanics. He stocks only good quality tools. I often pop in there to ask “what is new?”, and invariably he will demonstrate some fabulously useful (read “expensive”) tool which I cannot continue to live without buying. If you are in Geelong, you should visit for a wander around Qualitools. David has no idea that I have given him this rap. Nor do I have any pecuniary interest in his business, except that I hope that it continues. I am happy to support it.

Ducks in a Row and Bevel Gears.

Another small bronze pour yesterday, and it was my best one yet.  No bubbles.  No voids.  And excellent surface definition.  What did I do that was different?

First, the 3D parts were printed already attached to the tree.  So the trunk and branches were 3D printed with the parts attached.  That meant that I could determine more accurately the bronze flow, the gaps, the spaces.  The only “failure” was that I added some wax air vent sprues as an afterthought.  And those wax parts were the only part of the pour which failed.  Fortunately, the absence of the gas vents did not seem to matter.

The 3D printed tree. There are 9 PLA brackets ready to be replaced by bronze. I increased the height of the trunk for extra melt pressure. The air vents failed, and were not needed anyway.


Next, I painted the tree with a slurry of investment. The slurry was much more watery than the normal investment, but it was thick enough to leave a thin layer of investment on the surfaces, paying particular attention to the corners and internal edges.

Then I used my new, 1 hp vacuum pump to degas the investment mixture. It took about 15 seconds to reach maximum negative pressure, compared with about 1-2 minutes which the 1/4 hp unit was taking.

Then, after pouring the investment, I placed the full flask containing the tree and investment, and degassed the entire unit. I was shocked at how much extra air bubbled out.

The rest of the process was as usual, drying for 4 hours (except that this time it started at 6am, having put the process on an automatic start timer), burnout 2 hours, and baking 3-4 hours.

The cast tree was looking hopeful. And not much surface oxidation to see. (I had given the 15% phosphor copper a full 2-3 minutes to work this time.)
….and there are my brackets. 9 ducks in a row. They need a bit of filing, and some time in the gemstone tumbler.

BEVEL GEARS

Top is a bevel pinion as it arrived, and a mandrel which I made. Middle row is an unmodified bevel gear which is too big for the case. Bottom row is a machined bevel gear which now fits into the case, and a pinion on shaft, which also fits into the case.

While the investment flask was cooking, I experimented with the bevel gears which move the cannon barrel elevation. I had cast some bronze gears, teeth and all, some weeks (or was it months?) ago, but was not happy with the result. So, I had bought some bevel gears on Ebay. They are spare parts for an RC model car. Not quite the correct size, but close. The metal is HARD. Sintered? But, machinable with carbide cutters. (ps. added weeks later. Even carbide cutters struggled with machining these gears, so for the second set I used a tool post grinder on the lathe. That worked well, and produced a better finish.)

It all now fits.

Now before you all start shouting at me to make the bevel gears from scratch, let me just say that I might do just that. Not yet decided.

Ratchet Gear.

This was a feature of the model Armstrong RML cannon that I was not looking forward to. (to which I was not looking forward. Plogies to W Churchill. Something about split infinitives).

It is small, cannot be CNC’d with my degree of knowledge, and requires a lot of stuffing around. Which means filing. Or in my case, use of a Dremel.

This is the result after 5-6 attempts. It will have to do.

It is 11mm diameter, and 9mm long. Small and fiddly. And tucked under the cannon carriage out of site. As I said, it will have to do. 2 of them have taken several half days in the
workshop. A bit of a tumble in the gemstone tumbler should pretty it up. (?should up it pretty?). The ratchet on the right slides on a spline. The gear spins freely until it engages with the ratchet.

Occasionally I have a good idea, try it out, and after it works, I think “I should have taken some photos of that for the blog”.

Today I had one of those moments.

This was the result….

This morning, at the GSMEE Zoom meeting, I asked my fellow members where I could obtain some rivets which I could NUT into position. The reason being that some rivets in my cannon chassis are located in impossibly small cavities. And the dome end of the rivets are visible. Apparently “rivet-bolts” are available, but I could not find a supplier by searching my usual suppliers. One GSMEE member had some spares in BA8, but I suspected that I would need more than his small supply. And I was concerned that the dome head size might not match my copper rivets already installed.

Then I had a brainwave! Why not put a thread on my existing copper rivets! So that is what I tried. And it worked!

The biggest issue is not damaging the copper rivet head while holding it and running a threading die down the shaft. The copper is very soft.

The rivets in the photo above have a shaft diameter of 2mm. And the head is easily damaged.

These are Japanese pliers, designed with longitudinal, and transverse grooves. Very useful. Beautifully made. And not cheap. But they do grip. The rivet at the bottom of the top photo is evidence of the gripping power.

So I tried this…..

A bit of electrician’s tape stuck to the jaws, resulted in minimal damage to the rivet head. See the top rivet in the photo.

And a 2mm threading tool was required…

M2 x 0.4 threading tool.

Holding the rivet like this does leave a 4mm non threaded length of rivet shaft, but it can be packed with washers, or something else. It works!

So that was my brilliant idea for today. HEY IT WORKS!

More Gearing Up, and more to come.

This was 4 days ago.
Today. Re the gears on the right, bottom row…. one was machined from bar stock, the other was cast, had the outer ring removed, and a new ring soldered on, then the teeth were cut. Can you pick which is which? And all of the round gears have spent 3 hours in the gemstone tumbler to remove sharp edges. The tumbling has reduced the surface oxidation on the large gear castings, but some more time required to totally remove it.
CNC milling the spokes in one of the intermediate gears. Neat job, but the internal corners with fillets are not really kosher. This gear is barely visible in the finished model.

And the gears with ratchets attached need 2 mates. I tried to make them yesterday, but we had a wild day with thunderstorms and high winds, and my machines were playing up. I might get back to them today. (the ratchets can be seen in the header photo).

In country Victoria we are out of level 3 lockdown! Hooray! Still can’t see family from Melbourne, and minor restrictions on visiting local friends, and need to wear masks when out and about. But things are on the improve. I doubt that we have seen the last of the virus however.

Rack Off

As in, not yet installed.

I spent few hours finishing the racks today. But not yet installed. Some photos.

Firstly the racks were surfaced…
… then drilled, then given an outline using CNC.
….then tested against their corresponding circular gears. But not yet installed.

For once, a job proceeded without a mistake. Hooray. Hmmm. Look at that big gear. Thinks… “I quite like that blackened inner area with the polished bronze hub and teeth”.

(p.s. For non-Australian readers, “rack off” is an expression sometimes used in Oz, when telling someone to leave or desist, in a forcible, but not quite foul manner. Used in the post heading in a hopefully, mildly humorous effort to be eye catching.)

On the RACK

The final gear in the cannon carriage positioning train is a rack gear. It is 198mm long, 7.2mm wide plus tabs for bolting it to the carriage of the model Armstrong cannon.

A rack gear is a flat gear, and it is cut with the same cutter (number 8) which makes a circular gear of 135 teeth or more.

The teeth of a circular gear are cut by dividing 360 degrees by the number of teeth. But the pitch of the teeth of a rack gear is determined by a formula found in Machinery’s Handbook. rack gear pitch = module x 3.1416. Which for my module 1.25 = 3.927mm. Hmmmm. 3.1416. That is a familiar number. Light bulb in brain switches on! A rack is just part of a circular gear of very large diameter.

At first I thought that I would use the same mill arbor which I had been using for the circular gears, but as soon as I started to set it up I realised that the stick out of the arbor would be ridiculously excessive. So, reluctantly, I set up the horizontal milling attachment of the mill. Reluctant, because the attachment is heavy, fiddly, and time consuming. Luckily, I had a 22mm shaft for the attachment, the correct diameter for the cutter. I had never used this shaft before, and it was missing the nut, and bronze bush. Bought it on Ebay years ago. Found a suitable nut and made a bush.

This is the setup. The 350mm shaft was not long enough to make the rack in one setup, and it took a bit of trial and error to work out the best compromise.

The horizontal attachment on the vertical mill. Setting it up takes me a couple of hours.
No CNC here. Just lots of calculations using 3.927.

I need 2 racks, so I will split this one down the middle.

Did not have a piece of bar stock big enough for this job.

So I joined 2 pieces end to end with silver solder. Will that be strong enough? My friend Stuart T insists that a well made silver solder join is stronger than the parent metal, so we will see.
It meshes nicely. The mounting holes (which I did not use) will disappear when the outsides of the 2 racks are shaped.

A bit of a story about that heavy horizontal mill attachment. When I bought it some years ago, I put it in the rear compartment of my SUV. But on the way home my SUV was T-boned by an idiot at an intersection. No injuries, but a big expensive dent to the passenger side of my SUV. Air bags activated. And the rear window was smashed. I could not figure out why the rear window was broken. After the police and fire engines had finished, and the tow trucks arrived (my car was out of action for 2 months, the other vehicle was a write off), a by-stander approached me with a familiar object which he had found in the gutter on the OTHER side of the 8 lane highway. Yep! It was the horizontal mill attachment. Been flung through the rear window by the violent impact of the collision, and across 8 lanes of the road. It was scratched, but otherwise intact. And thank goodness, it had not hit me or anyone else in its trajectory!

Gearing Up

I have been making gears.

 

The big bronze gears on the bottom row were cast, had M1 teeth cut, had the teeth machined off, a bronze ring silver soldered on, and M1.25 teeth cut, which is what you see. They are almost finished. Above them are an almost finished M1.25 pinion and a pinion which will be parted from the stock bronze shaft tomorrow.

The right hand smaller gears are M1, with teeth cut. The right hand one started life like the ones on the left, but was a reject. I machined off the outer ring, and part of the spokes. and silver soldered on a new outer ring, and machined the M1 teeth. The similar solid gear has been made from bar stock from scratch. The spokes will be CNC machined, maybe tomorrow.

The bar at top has M1 teeth machined, ready to be bored for the shaft, and gears parted off.

The pinions for the big gears have a 4 tooth ratchet. This will allow the gear train for carriage movements to be disconnected for firing.

Gears. Modularity Counts!

Making the big spur gear which pushes the gun carriage up and down the inclined chassis has been a bit of a saga.

For a start, I decided that fabricating it with lathe and mill was going to be very difficult, and it was an obvious candidate for casting. In bronze. After making a model with 3D printing in PLA.

So, I drew up a 3D model, saved it as an STL file, and printed it. But did not take into account shrinkage of the PLA part. Or shrinkage of the cast bronze part. So instead of 58mm diameter, the blank gear was only 57.4mm diameter. By reducing the number of module 1 teeth to 57, I could get a reasonable gear, and the teeth were duly cut.

But, module 1 teeth looked skinny and pointy and not correct. Plus, 3 of the cast gears were total casting failures and were discarded (remelted).

So, I machined off the module 1 teeth, made some bronze disks, and silver soldered them onto the cast central hubs and spokes, and machined the blanks to 60mm diameter. By this stage I had decided that the big gear teeth should be module 1.25. Chunkier. Looked the part.

But I did not have 1.25 module gear cutters. And no-one in our club had them for loan. So I ordered a set from China. Delivery any time up to the end of November!! Then I found 2 of the set from an Australian dealer, but they were priced almost as much as the full set of 8 cutters from China. But, thinking that they would arrive more quickly I bought them. They were Chinese. It is a seller’s market.

Then today, at our GSMEE meeting Swen P said that he had a set! And I could borrow them! So, gratefully, I did. And I cut the teeth this afternoon.

The module 1.25 gears at bottom. The module 1 gear top. Please tell me that you can see a difference.

While the teeth were being cut, I tidied up another bronze T rex.

Two of them now face off on my Trevithick engine. They should amuse the kids.

Next to cut the M1.25 rack. Should be straightforward.

Blood Sacrifice

My brother Peter, on reading my tribulations regarding the making of the big gear in the Armstrong RML cannon, reminded me of a saying of our father regarding any difficult job. That the job would not go well until some blood had been spilt.

My brother has not responded to my invitation to visit, in order that some some blood be spilt.

And to be frank, I have many so cuts and nicks and embedded splinters, that Hephaestus, the god of blacksmiths, should be happy….And, I have made some progress on the big gear…

Today I machined off the module one teeth, and silver soldered on a bronze blank disk ready for the module 1.25 cutters when they arrive. Yes, it was painful. Not sure if Hephaestus will be satisfied. But the invitation to my brother stands. If he will risk the Victorian Covid 19.

The module 1 teeth on the left gear has been rejected. So I have ground off the teeth on the middle gear and silver soldered on a blank disk ready for the module 1.25 teeth. Same with the gear on the right.
and these are the big winding handles, with the defects repaired. I silver soldered in some segments from the reject handle to replace the defects. Can you pick the handle which was perfect? Not quite finished, but looking pretty good?

Casting Bubbles

When bubbles occur inside a casting, the cause is probably in the design of the pouring system, or the way the melt was poured. If you watched the video a few posts ago by Prof. John Campbell you would think, as I did, that our pouring funnels and sprues should be more complex and more carefully designed. Difficult at an amateur level. I have made some changes in this direction, using a side reservoir to tip the melt into, and trying to avoid the gurgling and glugging.

With the sort of castings which I have been making for the Armstrong cannon, I am not so concerned about internal voids. The scaled down model always has an advantage in strength of the part, compared with the full size part, within limits.

But, bubbles which stick to the exterior of lost PLA/wax models are replaced by solid bronze, or whatever metal is used, and these metal bubbles can be tricky and difficult to remove.

I decided to remake the big gears, which were the subject of the last few posts, and the cause of a lot of bad language. I decided that the gear teeth were too skinny and pointy, and redesigned the part using larger module teeth. To compensate for PLA shrinkage and metal shrinkage I printed the PLA parts with a 2mm machining allowance.

The gears with the narrow pointy teeth.

I printed the PLA blanks, leaving the gears and brake drums as a blank lump which I will turn to shape after casting. But the internal decorative holes and ribs will be cast. And they are the site of many bubbles in previous castings.

So, to avoid the bubbles, I am trying something different in the current casting session. I am trying a method which was suggested by a GSMEE member, and that is to PAINT the first layer of investment material thinly on the tree components, making sure that no bubbles stick to the parts, then to pour the rest of the investment filling the cylinder. There might be some bubbles in the main volume of the pour, but they should not be sticking to the parts. That is the theory anyway. I am waiting for a bigger vacuum pump to arrive by post, which should be more effective at sucking out the bubbles, but meanwhile, I will try this…

The gear blanks, painted with investment, particularly in the bubble prone areas between the spokes.

Today, I heated 2 cylinders/moulds in the investment oven, and melted some bronze.

For the pour I tried the negative pressure apparatus.

I did not notice any change in the level of the molten bronze in the reservoirs when I applied the negative pressure, so I doubt that it added much to the process.

The results were like the curate’s egg… some good, some bad.

This was one cylinder. The reservoir/funnel at top, then 4 rather spindly round handles. The top one had a defect, the second was perfect, the third had a couple of small defects, and the fourth was unusable.
The bottom one will be used to repair the 2 with small defects. There were 4 tiny parts in addition. 2 were excellent, 2 must have broken free from the tree and disappeared into the ether.

There were 2 big gears in the other cylinder. The one at the top did not fill properly and is not usable. It will be remelted. The bottom one was close to perfect.
Note the absence of bubbles. I think that my pre-painting the investment into the recesses must have worked. The failed gear again was near the top of the tree. It seems that even bronze requires a bit of head to create filling pressure.
These are the tiny 20x19mm fittings. Some time in the gemstone tumbler should polish them up nicely.

I am waiting for a more powerful vacuum pump to arrive by post. The 1/4hp one that I am currently using is too slow, when time is critical. I have a 1hp pump on order. No more casting until it arrives.

And then got better….

When my workshop activities mainly involved woodworking, I realised that concealing mistakes was a major skill of the craft.

As an amateur metalworker/model maker, the same principle applies.

So, today, I took a long hard look at yesterday’s disaster. (and apologies for my bad mood, and worse language. Actually, I toned down the language for the post.)

It was pretty bad. Huge gash, bent brake drum, damaged teeth.

And what I did is as follows….. first, a bit of amateur blacksmithing to bend the bent brake drum roughly back into shape. Then….

I found a bit of brass, and roughly fitted it in the big gash. Some belt sanding improved the fit. Then silver soldered it into place. I rested the brass shaft on a piece of brass as a heat sink. I really did not want that join to let go yet.
… then bandsawed and belt sanded and turned it closer to shape…. then recut the teeth.
… and it turned out pretty well, no?

Still some work to be done on the reverse face, but it is looking useable.

This time I wrote my own CNC gear cutting program. And it worked perfectly. And I used the same program to cut another gear.

Repaired gear on right. Some further filling, filing and machining required. But, nothing can go wrong now. OK?