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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.

Category: Trevithic Dredger Engine

Trevithick Dredger.. attaching the flywheel and driving gear to the mainshaft.

The flywheel and driving gear both are attached to cranks which join the connecting rods to the mainshaft.  It is important that both cranks are attached with the same angularity.   Seems simple.  The cranks are identical.  But small taper holes, through brass and silver steel.

Drilling the 2 holes took most of the day.

Figuring the setup was the biggest challenge.

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This is the setup on the milling machine.  The mainshaft is cramped on parallels, and ends of the cranks are resting on smaller parallels.   The square sections of the cranks have been centered.

First problem was that the 2.5mm drill bits were not long enough for the chuck to clear the gear.   I did not have adequately small ER collets (would have required ER8’s), but I did have a Dremel chuck which was small enough.  But no spindle for the Dremel chuck.  The Dremel chuck has a really odd thread.  I measured it at 40tpi, and 7.05mm diameter.

So I made a spindle.   Thank goodness for CNC threading.

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The Dremel chuck and the shop made spindle.

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Dremel chucks are convenient, but they are not very accurate.  Fortunately, once the hole was centred, the drill bits and reamer seemed to follow the centred start.   Here I am about to ream the hole which has 3 steps   2.5mm, 2,8mm, and 3mm.   The shop made spindle is held in the milling machine drilling chuck.

I took the reaming very gently, not wanting any broken bits of high speed steel stuck in the workpiece…. and all was well.

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And here is the gear crank pinned to the mainshaft.

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And this is the setup for the flywheel end.   Fortunately, by good management or good luck, I was able to remove the flywheel, leaving half of the crank insitu, for drilling reaming and pinning.

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I spent some time assembling the cranks and testing the rotation movements.  It does rotate, but there is still some sticking on the guides, the cause of which I have not identified/isolated.

So I sat back and enjoyed one of my Xmas presents.   Ah!   Bliss!

Making a Lead Ball for the safety valve

The deWaal plans for the Trevithick Dredger Engine call for a 30mm diameter lead ball for the safety valve.

I considered substituting steel or brass, and turning the ball, but lead is almost 50% more dense than the other metals, and that could be detrimental to the functioning of the safety valve, so I worked out how to make the ball in lead.

I have previously cast lead balls 14mm diameter, but this is significantly bigger.  I did briefly consider making a plaster of Paris mould, but I could find no balls of the correct diameter for the POP mould, so I decided to mill the mould.

On rummaging through my big milling cutters, I discovered that I have a ball nose cutter, 31.75mm diameter.  It was part of a package of cutters which I had purchased years ago, and almost forgotten.  I had bought the cutters BY WEIGHT.  I think that I paid $US5 per pound, and I bought 20lb.  Mostly the cutters were resharpened end mills, but one of them was an unused 31.75mm ball nose.  Pretty close to perfect for this job!

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First I cut off two 25mm lengths of 40mm square solid alu bar.

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Then milled them pretty close to square and identical.

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Then used the 31.75mm end mill to make a hemisphere in each alu blank and drilled and tapped for a 5mm cap screw in each corner. 

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On the left is the mould, screwed together, with a hole drilled into the spherical cavity.  Here I am heating it in a frypan, ready to accept the molten lead, which is being prepared in the cast iron saucepan on the right.  I hasten to add that SWMBO knows nothing about this.  Those utensils are part of my workshop gear, and will never be used for human consumption.  SWMBO does not read this blog, so I am safe.  I hope.

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From my previous experience with lead castings, I have decided that the mould should be 250-300ºc so the lead will not solidify in the small entry hole, and also to minimise the formation of voids in the casting.

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Here is the molten lead after pouring.  It is still liquid.

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And after cooling and splitting the mould.  The hemispheres were not exactly aligned.

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And there was a big void.  I could have filled it.  But I decided that if I made the mould even hotter, it might work better, so I made another lead sphere.

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The next one, on the left, worked perfectly.  I heated the mould to 300ºc, and no voids at all.   I also reversed the bolting positions which removed the hemispherical misalignment. Drilled and tapped for the supporting ring.

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And here is the weight in its final position.   I dropped it, resulting in a Death Star indentation, which I kind of like.  A little bit of polishing will remove the latitude lines.

Only one part for the day’s work again.  But it was a LOT OF FUN!

 

 

 

How Many One Off Parts Can You Make Per Day?

Obviously it depends how many machining operations are required per part, but these days I find that one or two parts per day is about all that I can manage.  That includes deciding on then finding the material,  drawing up the part in CAD, mounting the material and the cutter(s), then machining and finishing time.

Take today for example.  My aim was make a steam pressure valve for the Trevithick Dredger Engine.   It consists of a lead ball weight 30mm diameter, a lever arm with a hook, a simple stand with a M6 male thread, a movement restrainer, and the seat and valve.  6 fairly simple parts.  I thought that I might get it all done in one day.

But at the end of the day, all that I had made was the arm, stand and restrainer.  3 simple parts.

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The pressure valve arm, stand and restrainer in place.

Admittedly the arm is stainless steel of unknown grade.  I broke 2  (4mm) cutters before I had slowed the milling feed rate to a snail’s pace 40mm/minute.  Machining time for that part was over an hour!  Then at least another hour of hand filing and finishing.

It is just as well that the worst day in the workshop is better than the best day of working!

And next will the interesting job of making the 30mm diameter lead ball weight.  Still thinking about that one.

Boxing Day in Oz

So, Xmas day was great.  Perfect weather, middle daughter’s home and vegetarian cooking thanks to her husband and all guests, and limitation rules for presents so that aspect was not gross.  And SWMBO agreed to be designated driver home.   So I could freely partake the lovely Aussie big reds.   And whiskeys.   And best of all… cigars.

Don’t remember much about the trip home.   But apparently we made it because I woke up with a dry throat but no headache. Must have been good reds and single malts.

Then best of all…. Boxing day!   Means that it is all over for another year.

A slow start to the day, then a half day in the workshop.

I spent several hours measuring various dimensions of the build to date.  Although I had been careful to keep the dimensions correct, the cross head was sticking and jamming on the slides.   Some dimensions were out by up to a millimetre…   mainly due, I suspect, to movements during the big silver soldering sessions.

So I tried various permutations and commutations to minimise the aberrations.  And started introducing brass shim strips to remove the aberrations.

And It gradually started to improve the situation.

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Shims under the base, and between the base pieces and the boiler.

Then I installed the valve timing mechanism.

But…..  it fouls the domed end of the boiler.

What to do?     After a lot of messing around, trial and error, swapping components around, I have decided to remake a couple of components AND to ease the fit between a couple of the others.    At least the cross head has stopped jamming so I am winning.

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Close up shot of the valve switching mechanism.

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The photo shows a vertical mark where the mechanism is scraping along the domed boiler end.

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where I left it for the day.  Will give it a miss tomorrow…   very hot day predicted.

 

Trevithick Dredger Engine.. the steam valve operator.

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I did not know what to name this assembly.  It attaches to the cross head, and pushes the handle of the steam valve up and down each revolution to admit and release steam from each end of the cylinder.

It uses the U shaped metal strip which I cut out and bent yesterday.   It is 230mm long, and I made it from brass, including the filler strips which actually contact with the valve lever.  I made the filler strips a few mm longer than necessary, so I can file them as necessary when the engine is timed.

Trevithick Dredger Engine.. the firedoor fittings. Or silver soldering tiny pieces.

Another day in the workshop.

Yesterday I  bolted the latch to the door.  But how to attach the catch to the surround, and the restraint to the door.  The plans call for tiny screws, but that method did not appeal.  I decided to silver solder them in place.  Silver solder is immensely strong, and does not require tapping and threading minute screws into position.  The problem with silver solder is that some parts of the firedoor are already silver soldered, and I did not want to risk undoing that previous solder.

So, I used a heat sink.

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The catch is held in position by pressure from the latch.  I did NOT want to melt the solder of the hinge, so I rested a sizeable block of brass on the hinge.  Pure copper would have been even better.  Then, as I was soldering the catch, any heat travelling toward the hinge would have been absorbed into the brass heat sink.

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A staged shot, after soldering the catch was finished.  I was careful to keep the flux just in the joint which was to be soldered, to avoid the solder running into other areas.

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A close up of the soldered catch.  The iphone camera is pretty good hey?  That catch is only 3mm wide.   A bit of filing and finishing needed.

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And the finished door.  Looks OK IMO.

The next job for today was to machine a strip of metal 6mm wide, 2mm thick and 600mm long.  I decided to make it from brass because I have a sheet of brass the correct thickness, and I was already thinking about the tight bend which was going to be required.

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So, I bandsawed a strip of brass from the sheet, about 50mm wide.  Then removed the milling vice and universal divider from the milling machine.  I am amazed at how those items are becoming heavier with age!    Then cramped the brass strip to the table and machined the sawn edge with a 6mm end mill which protruded into the milling table slot.  Fortunately I managed to not enlarge the T slot during this procedure.

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Then moved the brass strip, and indicated it parallel.  Then used the 6mm endmill to cut off the 6.5mm strip.  Probably not very efficient, but it worked, and the strip was correctly sized and dimensioned.

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Finally, annealed the middle of the strip, and bent it around a 5mm thick piece of steel, with a rounded edge.   This will become the fitting which operates the steam inlet/outlet valve.

Trevithick Dredger Engine ….Con Rods

I had previously bent the brass U pieces which hold the split bronze bearings to the wooden connecting rods.  I had also made the con rods and the bearings.  Today’s job was to fit them all together.

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Bending the U pieces on my shop made bender.

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And the Jarrah con rods.  The U pieces need to be shortened.

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With the bearing in place, measuring the amount of shortening required (approximately).

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Using an end mill to shorten the U piece arms.  Note the paper between the workpiece and the vice jaws.  That reduces the chance of the work moving.  How do I know?  Dont ask.

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The holes are carefully drilled M4 through the U piece and the wood.  Stainless steel square nuts on SS threaded rod.   Then the bearing was reamed again to the finish dimension.  I have yet to make the wedges which hold the pieces in position.

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The (almost) finished connecting rods.

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And a test installation on the engine.  A bit of workshop clutter to add to the atmosphere.

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And I had a bit of daylight on this beautiful summer day, so I made and installed the firedoor latch.

I am hopeful that I will have this engine running before I say goodbye as my subscription to WordPress finishes.  Not exactly sure when that will happen, so if I suddenly disappear, do a search on YouTube for the video of it running on steam.    Still a fair bit to do before that happens, but things are progressing!

 

Trevithick Dredger Engine… hinges for the fire door.

No big deal?  This “little” task caused me quite a bit of heartburn.

I had redesigned the flat face of the boiler, including the door and had not really thought through the door design and hinges.

Needless to say, the original hinges as designed by Tubal Cain and Julius deWaal, were quite incompatible with my redesign.

There are NO original drawings of Trevithick’s original designs of this face.  The Rees Cyclopedia drawings do not include this face, and it is hard to tell if the London Science Museum reconstruction is original in this respect.  I did read somewhere that the firedoor in his engines was a casting, so I did not feel bad about silver soldering components to build up the final parts.

In the end, after a failed effort at making a hinge, I decided to wing it, and make something which would work.

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This is my interpretation of a Trevithick fire door hinge.  No idea if it approximates Trevithick reality, but I suspect that no-one else knows either.

The tricky bit was silver soldering the 5mm brass tube bits to the appropriate base, and not getting silver solder into the hinge itself.

It was tricky, but it works!!

 

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The latch, the catch, and the movement restrainer come next.  The hinge pin is the cobalt drill which I could not release after the soldering.  Oh well…  cobalt steel should work well.   Incidentally, the stainless steel cap screws will be replaced with studs and square nuts when I around to it.    Now thinking about the propane burner and tubing.

 

More Trevithick, and Xmas

The last 20% of the build takes 80% of the time.  Someones law.  But SO true.

I should be Xmas shopping.  But frankly, buying stuff which costs money, is not wanted or appreciated, takes time, and should be donated to people who really need it….  irritates me.

At least the adults in my family have taken a sensible decision to randomly allocate one person to buy a present, for one person only, to a maximum amount.

But it does mean that the one present should be meaningful.

I decided on something that my allocated recipient might like.  A bit unusual.  Something they (he or she) would never normally buy, and should make an impression.  But there was a catch….  I had to drive to the shopping centre, park, find the shop, and buy.

So I looked up the shop on the computer, noted the address, drove there, parked, paid parking, walked several hundred meters, and could not find the shop.  Walked for about an hour.   The shop no longer exists.  It has closed and they have not changed the Internet info.  Bummer.

But at least I actually own one of the items.   It is a bit old.  Actually about 40 years.  But it is in good condition.  so I will wrap it and give it.  And hope that its aged condition is not  detrimental.

My allocated recipient is the au pair, from Italy, aged 19, who lives with and looks after some of my grandchildren.  She is a lovely girl, and I believe that she is really enjoying her stay in Australia, with my youngest daughter and her family.

The present is an Australian flag.  I hang it on out front gate every Australia Day.  I hope that she sees it as a compliment, and a memory of her stay in in Oz.

I will buy a replacement for myself.  It will probably be made in China, but so what?

So today I had a few hours in the workshop after wasting a half day in the shopping mall.

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And made and installed the water feed tube from the pre-heater to the boiler.  I had made the clack valve in my previous session.

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I find that it is actually quite tricky to make the bends in exactly the correct place, with exactly the correct angular bends, and to silver solder the flanges at the correct angles.   This one worked out well.   I usually bend a piece of aluminium wire to roughly the correct dimensions, on which to base my copper tube bends.

Finally, normally, I detest Christmas (actually it is Saturnalia, a pagan roman festival).  The commercialism, the waste on presents, the killing of turkeys, pigs, sea life.   It is all gross, and I hate it. Yes, I am a grinch.  Once, I just refused to take part in it, but the fall out was immense, and I am not strong enough to repeat that protest.  But this year, my adult children have made a decision which makes me immensely proud.  They have decided to limit adult presents to one per person, (the grandchildren still get heaps), and the meal will be vegetarian.  A step in an wonderful direction.

 

Trevithick Dredger Engine… No more aliens, just a gear

Another few hours in the workshop, and I made the spur gear which transmits power to the dredger bucket chain.

I chose bronze, because 1. It will not rust 2. It machines fairly easily 3. I had some in the correct size!

I did think about whether to CNC mill the gear, or make it on my lathe and form the teeth with a custom built cutter.  In the end, I decided to CNC mill the entire part.   The plans called for a tooth shape which looked like an Acme threaded part.  I decided that Trevithick would NOT have made it like that, nor would he have known about pressure angles, and parabolic tooth shapes, so I winged it and drew a shape on the CAD which was a bit between both.

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As you can see it is a blank of bronze which I bought at scrap price from a local supplier.  Here centering it on the CNC mill using a Starrett wobbler.

Roughing the shape was with a 6mm 4 flute carbide cutter.

 

And finishing, to impart the fine fillets, was with a 3mm carbide cutter, taking 1mm depth bites.  I broke one, but the next one, new, finished the job intact.

 

And here is the gear, still attached  to the bronze rod.  Now, how to detach it?

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The blank gear still attached to the bronze rod.

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So I started by using a parting blade, but I chickened out when it had plunged about 12mm.

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So then I parted the gear from the bronze rod on the bandsaw.  It was a bit tricky… became quite hot.

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After bandsawing, I counted my fingers, 9, hang on there’s another, so 10.

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Then I surfaced the back of the gear on the mill.  Actually, I tried gluing the gear to a silver steel rod, and turning the back face, but the glue did not survive.  So I resorted to this solution which worked fine.

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And this is the gear, with the crank push fitted.  pretty neat hey!

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And the inside face.  Some filing required to remove sharp edges.  Or maybe I will put it in the gemstone tumbler for a couple of hours.

Hey, no aliens!  But watch this...

Trevithick Dredger Engine.. connecting the water pre-heater

A few more hours in the workshop today.

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The steam exhaust from the engine passes through a tube to the chimney.

Since this was the worlds first “strong steam” (high pressure) boiler, the water level in the boiler needs to be constantly replenished.

Trevithick thought that the water coming into the boiler could be preheated by the exhausted steam.  So he conceived a double tube, with the exhausted steam exiting through the inner tube, and the water being pumped through the outer tube….  A heat exchanger.  It was awkward to make using modern heat sources and silver solder.  I can only imagine how it was made 200 years ago, using castings and black-smithed iron panels.

The users noticed that the steam which was injected into the chimney improved the coal fire.

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The cap screws are temporary, until I replace them with square nuts and stainless thread.

The hardest part of these connection pieces was keeping the flanges square to the 1/4″ copper tube while silver soldering them.    Any clever methods out there?

Back to the Trevithick Dredger Engine. No aliens… promise.

OK, it is not just the fascination with Antarctica and whatever it is that is going on down there, and that they are NOT TELLING US!

But SWMBO has insisted that I assist with the renovation currently going on with an investment property.  Unfortunately, I am very handy with all sorts of skills which she finds useful, like assembling flat pack kitchens and laundrys, and welding broken windows, and winching crooked concrete steps, and removing rubbish in my ute (which is now fixed after the failed thieving attempt).

But I managed to grab a few hours in the workshop today, so I made the pre-heater for the boiler water feed.

This was another Trevithick invention, using the exhausted steam  to heat the water before it is pumped into the boiler.

It is a tube within a tube, and the inner tube (copper) has separate inlet and outlets, each with its own flange.

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It looks simple, but it has 10 parts.  All silver soldered.  Too many to solder in one heating session.  It needed several redos before it was satisfactory.  But seems good.

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There!  Did not mention aliens once.  But did you see this video…just watch it!

Trevithick Dredger Engine- the stays

 

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The stays appear simple but they took several hours to make and adjust.

When I arrived at my workshop today I discovered that someone had attempted to steal the Toyota Landcruiser tray which I leave parked there.   A window had been smashed, the doors were unlocked, and the cowling over the steering column had been removed and broken. (presumably in an attempt to access wires to start it.)  The driver’s door lock showed signs of being jemmied.   The ignition lock also showed signs of being forced.  The thief must have been an amateur, unable to get the vehicle started.

The police arrived soon after being telephoned.

Fortunately the vehicle is drivable, but repairs are required.  I am relieved that it was not actually stolen.  The police told me that these vehicles are in demand by thieves.  They are built like tanks, and useful in ram raid thefts.

So the dredger engine will be put aside while I install video cameras at my workshop.

(I have deleted a paragraph here.  It was written with exaggeration caused by anger.)

After the police left, I made and installed the stays which are visible in the photos.

 

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The lower end of the stays attach to the boiler flat plate end.

 

 

 

Trevithick Dredger Engine Progress

First day of summer in southern Australia today.  And it was very warm and windy.  Keeping my eyes open for snakes, but none seen.

I was pondering how to attach the crankwebs to the flywheel.  I had decided that I would not silver solder them together, because the heat would likely distort the thin flywheel.  And pressing them was not feasible because I had machined them to a sliding fit.  Whatever method was used, I wanted it to be reversible i.e. future disassembly possible.  So, in the end, I used small brass screws which will not be visible when the engine is painted.

 

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countersunk brass screws holding the assembly together.

 

I made 2 more U shaped bearing retainers to fit on the ends of the connecting rods (same as shown in last post).

Then made 2 shafts which will be attached to the cross head bar, to join to the con rods.  These are made from silver steel.

 

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The concave end had a radius of 10mm.  Fortunately, I had a 20mm end mill which worked well to produce the curve.  A bit of finishing required for these parts.  I will probably run them for a while in my gemstone tumbler to knock off the sharp edges and polish them.

 

 

 

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They will be pinned in place at the ends of the cross head bar.

 

Woodworking for the Steam Engine

The connecting rods on the Trevithick dredger engine were wooden, presumably to save weight.  I used to do a lot of woodworking and still have radial arm saw, bandsaw, thicknesser and planer, etc, and too many scraps of wood and left overs from previous furniture projects.

The con rods are 16x10mm and about 320mm long.  Lignum vitae was recommended by Tubal Cain, and “hard wood” by Julius deWaal.  I looked through my piles of offcuts, and eventually settled on West Australian Jarrah.

 

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There are 2 con rods, but I cut enough sticks for 4, just in case.  One was immediately rejected due to a split.

Jarrah is hard, remains stable during machining, is dark and becomes darker with aging, and is relatively resistant to rotting and warping with water.  In Oz it is often used for outdoor decking.  The figuring tends to be quite wavy rather than straight, so very sharp tooling is required to avoid teatouts.

 

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Using a shell end milling cutter to make the end rebates.  It is really sharp and heavy, and quite scary to handle.  But does leave a beautiful finish.

I try to avoid machining wood on my metalworking machines.  The dust gets everywhere, and if not removed attracts moisture, and rust.

But, the metalworking machines are far more accurate, so that is what I used after the initial roughing cuts.

Next was the metal U shaped metal strips to hold the bearings at each end.  I chose brass, because I had some 2mm sheet, which was the specified thickness, and I imagined that it would be easier to machine and bend than steel.

 

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This is my bender, with a test strip of annealed brass.  I made this bender last year to bend copper pipe, and my advisor, Stuart, suggested using it to bend the brass ends for the Trevithick.  So I turned up some aluminium cylinders and a brass pusher to the appropriate diameter, leaving a 2mm gap for the brass strip.

 

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Worked like a charm.

 

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I will make the bearings before I trim the U strip to final length.

So that all went very nicely.

Hang on.  There are 2 connecting rods, with 2 ends each.  I need FOUR U pieces, not TWO.  Shit.

No time to make the other 2 today.  Got to get home to clean up before visiting my hearing specialist.  Should see a brain specialist too.

 

 

 

 

 

 

Dredger Engine- Crankweb and Firebox Door

Power is transmitted from the dredger engine to a cog on the crankshaft which is held in place with a crank-web.  It is similar to the crank-webs which secure the flywheel.  Similar, but more complex and more difficult to make.

 

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More finishing required, but the basic shape is done.  Note the 2º wedges securing the bearing housing and the oil tube.

 

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The firebox door is shaped.  Hinge, catch and latch coming soon.  The wooden front support is also seen.

The engine is really taking shape.  I am looking forward to seeing it run.

 

 

Scale Trevithick Dredger Engine- the Supports, and crank-webs.

Some photos of progress.  I have been busy, but the results are not particularly photogenic.

The support under the chimney end was in the plans as this:

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…and many models of the dredger engine are made along these lines.

…but the rescued Trevithick engine in the London Science Museum is different..

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The shape of the front support is appealing, but it is unlikely to be original.

….and this is the drawing of the dredger engine from the Rees Cyclopaedia of 1819..

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Look.  The front support is a block of wood!  And the rear support is quite open, showing most of the mainshaft.

The Rees drawing was made at a time when many Trevithick engines were operating, and it is likely that the drawing is representing an actual engine.  So that is what I have based my scale engine supports on.

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This is the rear support for my engine.  5mm thick steel, silver soldered.  Quite a bit of tidying up to come.  And you can see the wedges which hold the bearing housings in position.  The bushes are bronze.  And the vertical tubes just visible are oilers.

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The rear support before I milled out the middle section.  It was supposed to be 5mm mild steel, but the carbide end mill became red hot while plowing through, then broke.  Something really hard encountered there!

Then the bearing housings were made, and the main bearing bushes.  Straight forward machining.  Inserted the mainshaft (12mm silver steel).

The flywheel had been previously water jetted from 6mm steel plate.

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I chose water jetting in preference to laser cutting, in order to minimise heat distortion of the rather thin piece of steel.  Even so, it required some cold pressing to flatten it.  No olive oil appeared.

Then made the crankwebs.

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CNC milled from a chunk of brass.

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The crank webs sitting in position.  I have not yet decided how to fasten them.  Soldering is specified by Tubal Cain, pressing by deWaal.  I will probably use Loctite and a taper pin.

Next are the wooden connecting rods, and the driving spur gear.

Still thinking about the stand.  Wooden box? open metal structure similar to my beam engine? masonary block?  Wait and see.

Note that there is now an option to “like” these ramblings, at the end of each post.  Up to you the reader of course, but a tick of approval would be nice.  Your comments are always appreciated.

 

Trevithick Dredger Engine Guide Bars

I was discussing the guide bars with a very experienced modeller, and he finished with some advice….  “make them either very accurately, or very sloppy, otherwise you will have problems!”

The guide bars and cross-head

Well, I decided to shoot for “very accurately”.

I made the cross-head bar, and silver soldered it together.

All seemed good.  Just the guide bar bushes to be made and Loctited into position.  After a soak in sulphuric acid and tidy up.

So I made the bronze bushes, drilled them in the lathe to 9.5mm, then reamed them to 10mm.  Or so I thought.

But when I fitted them to the 10mm guide rails, they were very, very sloppy.   Checked the guide rail diameter… 9.99mm.  Checked the reamer 10.07mm!!  Chinese reamer.

So I searched my reamers and found 2 more.  Another Chinese one measured 10.04mm.  Another was a Sutton, made in Australia.  It measured 10.00mm.  I reamed a test piece, which fitted the guide posts perfectly.   So which reamer did I use?   Guess.

I made some more bushes and Loctited them to the cross-head.  Then drilled and reamed them, carefully, accurately.  This time the fit on the guide bars was snug, perfect.

Is there a point to be made here?  You better believe it.

Trevithick Dredger Engine Guide Bars and Crosshead

 

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As you can see from the photo, I have made the vertical guides, the curved top bar and the crosshead.

 

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The curved bar was bent in the motorised ring roller which I made years ago.  Bending 3.2mm steel was easy.  I have bent steel bar up to 10mm thick in this machine.

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Parts of the guide bar.  2mm thick.  I confess that these were CNC’d.

 

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A few more parts required for the crosshead, but a test fit was quite good.  It is just pushed together at this stage.

 

 

 

 

 

Trevithick Dredger Engine- Valves

No workshop posts for a while because I have been making parts for the internals of the engine, and when installed they are not very photogenic.

Since the last post I have made the piston, piston rod and installed soft packing to seal the piston, made the valves and valve handles..

 

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Stainless steel piston rod, bronze 20mm dia piston, and soft packing inserted into the machined groove.

Also made the throttle valve and steam direction valve.

 

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This was the third attempt at making a steam valve.  I went slightly undersized with the first, totally buggered the O ring groove on the second, but the third one looks OK.

 

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Good one (I hope) on the left, and destroyed one on the right.  The lathe tool bit into the bronze.

 

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From left to right.  The bush, the undersize, the buggered, and the OK I hope.  and the plans.

And after all of that, and also making the throttle valve, I discovered a mistake in the plans.  A 1mm discrepancy, which I suspect was an arithmetic mistake on the part of the plan maker.  I decided to modify the valves, bush and valve block rather than remake the valves.

 

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I machined 1mm off the faces shown in the photo, then spent some time prettying it up.  Then took 1mm off the valve lengths, and the valve bush.

 

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This is what it looks like now.  All fixed.  Waiting for Viton O rings to arrive.  Looks OK IMO.

 

 

 

 

 

 

 

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