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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.

Tag: Armstrong RML

A Transom on a cannon. And a lost hearing aid.

 

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After a fruitless 3-4 hours searching for my lost hearing aid, I decided to make a bit of progress on the Armstrong cannon chassis.  At least I got the workshop floor swept clean for the first time since last winter.  The tigers should be hibernating in this cold weather.

In the above photo you can see that the rear cross member, which I have named the “transom”, is now bolted into place, with 14 M2 bolts and nuts.  Later these will be replaced with solid rivets.   I reckon that I had about a 70% success rate of inserting the tiny M2 nuts.  The other 30% are somewhere on my workshop floor… probably keeping the hearing aid company, wherever it is.

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When those connections were made, ensuring that the upper girder surfaces were parallel, I filed the angle brackets flush with the girder surfaces.  To ensure that the file did not scratch the girders, I rested the end of the file on a sheet of paper.

The next job is to make the front joining piece of the chassis.  It is a box construction, so will be more complicated, but should make the chassis  quite rigid.

It is a bummer having only one hearing aid.  About $2000 to replace the lost one.  I would have preferred to spend that sort of money on a tool.   Or a good drone.  But SWMBO is adamant.” get that hearing aid replaced!! ” (at least that is what I think that she said.)

 

Armstrong RML. A Little More Progress!

Only a half day in the workshop today.  Wednesday is my Model Engineering Society weekly “Zoom” meeting, and I would not miss that for quids.

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But, I did get into my workshop after that.  And this is what I made….

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I am trying to make a bracket to join the side girders of the Armstrong RML cannon to what I will name the “transom”.  The transom is the lump of steel joining the side girders at the back of the chassis.

“No big deal” you say?  Well, that bracket has angles of 90º, 4º, 6º,  and some indeterminate ones.   And must sit flat with 2 pieces.  And is a single piece of steel.

First I tried to bend a piece of 2mm steel.

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Even though the bender is rated only for 1mm, it managed 2mm thick plate.

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Plus some hammering in the vice…

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…but machining all of those angles and distances was just too difficult….   This steel effort was just not up to scratch.   Look at the gap under the bracket.  Yuck!

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I cut out some brass pieces, and used a vertical belt sander (the Radius Master), to get them to fit snugly…..

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then cut some separate pieces to complete the brackets and secure the transom…..

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checking the fit of the right angle piece…

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then silver soldered the pieces together.  The bits of steel are to keep the brass pieces in position during the soldering.

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That is the angle bracket being held to the transom by my rather dirty fingers.  But, it is all nice and tight, and will do the job. Rivet holes yet to be drilled.   Soldered joint? I hear you ask?  “As strong as the parent metal” I answer.   One made.   A bit of filing required.  And 3 more to go.  They will be painted the same colour as the girders eventually, so who will know that they are not steel.  Just you.  don’t tell, or else….

 

Armstrong RML Model cannon. Assembly -1

Not much happens in each workshop session.  I am still a bit unsure whether I should only post when some significant progress has occurred, or whether the minute daily progress is enough.  Whichever occurs depends on my mood.  At the moment I am posting daily progress.  If it is just too trivial and boring, well, hang in there.  No doubt there will be big significant gaps in the future.

Today I thought about how I would assemble the chassis for the Armstrong cannon.  And I decided to do some woodworking.

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So, I machined a block of wood, exactly the size to separate the chassis girders.

Wood has an advantage over aluminium or steel.  Apart from being cheap, it is slightly compressible.   Here, I have accurately machined a block of wood, and by adjusting the tension in the G-cramps, I can adjust the distance between the girders to exactly what I want.   And using the granite setup block to keep the upper girder surfaces exactly parallel.

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Getting those girder surfaces exactly parallel, on a granite setup block.

 

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Then I marked out one of the end pieces, filed out the girder flange recesses, and fitted it into place.

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The end piece will eventually be riveted into place, using an angle bracket.  The dented girder corner top right, occurred when I dropped the girder onto the workshop floor!  Or maybe it was a Russian shell hit.

So, not much to show for a 6 hour workshop session, but actually, some decisions made.  And more small steps.

And a BIG discovery!  Another  Internet search has shown some more of this exact cannon at Warnambool, Victoria.  And from the few photos on the net, those Warnambool cannons are more complete than the ones which I measured at Port Fairy!

Ah.  Fuck this virus.  I want to go to Warnambool.

 

 

Armstrong RML Model Cannon Parts

Firstly, on the subject of metalworking lubricants, I have previously mentioned my homemade mixture of kerosene and olive oil.   And here is my favourite lubricant…..posing with the not quite finished cannon chassis girders…..

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For this model cannon I need quite a few sheet metal parts.  At 1:10 scale the final metal thickness is 2mm and 2.5mm.  Having had a good experience with laser cutting the HSS cutters for the rifling tool, I decided to send an electronic file to the laser cutting firm, and see how the parts turned out.  I decided to not include the rivet holes, thinking that the final positions might not be completely predictable.  If all goes well I will probably include all of the holes in future orders.

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I ordered enough parts for 2 cannons, and some spares for the inevitable stuff ups.  (or should it be stuffs up?).  If I do not use the spares I might offer them for sale later, along with my plans.

The accuracy and quality of the cuts seems excellent.  All of the parts will require final fitting and drilling for rivets, shafts, etc.   I was pleasantly surprised at the modest cost of these 30 parts.

 

So next I can start assembling the chassis.  Lots of riveting.  About 500 rivets per cannon. Another skill to be acquired.  Fortunately for me, one of my model engineering club colleagues used to work in aircraft manufacturing, and he has spent a session teaching me the ins and outs of installing solid rivets.  And loaned me a riveting gun suitable for the 2mm rivets which I have chosen.  Thanks Neil!

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The gun is about 40 years old but it works well.  The snaps are all imperial, so I made one, and modified one to fit the metric 2mm size.

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The blank snap in the ER collet is an unhardened punch blank.  Here being drilled with a carbide ball nose end mill.  Not exactly the right size, but with some fiddling I got it very close.  Since I am intending to use copper rivets I will not harden the snap.

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My initial riveting practice run in aluminium was a bit unimpressive…..

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….but I did improve.  These are almost up to scratch.   In aluminium.

And finally for this post, I drilled some holes in the muzzle of the barrel.  Do you know why they are there?

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A staged photo, using the 3D printed barrel, to show the drilling setup.

 

Armstrong RML Chassis Girders

 

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Having made the decision to try to mill the girders from solid steel bar, I bought some 50x16mm bar and cut it into 400mm lengths.

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Then milled it to 46.4 x 14mm, then used carbide end mills to form the girder profile.  This process produced a large amount of hot, sharp chips, and took 2 full day sessions in the workshop.  Each evening I spent about 30 minutes pulling bits of swarf from the soles of my boots with pliers.

And I discovered the limits of my milling machine.  The 5hp spindle motor never hesitated.  Nor did the axis AC servos.  I did manage to chip the cutting edges of  a 12mm carbide end mill when it dropped onto the milling table.  And I blunted another one.  Not sure how that happened.  Maybe hit a hard bit in the steel.   No, the limit of the machine was the ability of holding the end mills in the ER40 collet chuck.  If I pushed the depth of cut or the feed rate too hard, the cutter would start to move in the chuck.  I managed to ruin one work piece in discovering that fact.

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There is virtually no distortion resulting from the milling.  The apparent bend in the photo is photographic distortion.

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The Vertex milling vices are within 0.02mm for height.  I picked up the second vice cheaply on Ebay a couple of years ago, with this exact purpose in mind. (milling longish workpieces)

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3 made.  One to go.  Plus the bottom 6º shape and the 4º ends.   Each 4.5mm deep pocket takes about 25 minutes, at 300mm/min feed rate, 1.5mm depth of cut, 2700 rpm.

I should be able to finish the girder shapes tomorrow.

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These milling marks are visible but very not finger tip palpable.  Any suggestions for a good method of improving the finish?

Then to mark out the rivet positions, and insert about 100 rivets into each girder.  In the model these will mostly be decorative.  In the original they held the components of the girder together.  Luckily for me, a fellow member of our model engineering society is a very experienced riveter, having worked in aircraft manufacturing, and he has offered to spend a session teaching me some basics.  In the original cannons, the rivets are superbly neat, regular, and obsessively carefully laid out.  I will try to do likewise.

Armstrong RML. The Chassis -1

 

I will start by making the main girders.  At 1:10 scale they will be 400mm long, 11mm wide and 46mm deep.  Some fabrication will be required.

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Many rivets required.  I will need to improve my riveting skills.  One issue to be decided. Do I use copper (easy) or steel rivets (authentic)?.  Whichever, they will be eventually painted the same colour as the girders.

 

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And another decision.  Your opinions invited.  2 methods for fabricating the girders.

TIG weld the flanges top and bottom (right).  Or, (left) join 2 pieces of angle iron, then TIG weld the bottom flange.  I don’t like the top groove to be filled.  I do not really want to paint the surface that the carriage wheels roll along.

It is a very long time since I did any TIGging, so maybe some practice runs first…

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And another option comes to mind….   just to machine the shapes out of solid bar.  I think that I will try TIG first.

Later….   just remembered.  I don’t have any TIG gas.  Easter.  Bum.  OK.  Back to square one.  Maybe I will try to mill the shape from bar…..

Model Armstrong Cannon. Machining the trunnions-3.

On my “reject” barrel the silver soldering was problematic, and one trunnion was subsequently glued into place with Loctite 620.  This proved to be so effective, clean, and controllable that I used the Loctite for the main barrel.  The following video shows the Loctited trunnions being machined, and showing no signs of being dislodged.

It also shows a possibly dodgy but successful method of rounding the ends of the trunnions.

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The finished trunnions and shoulders.  Resting on a 3D printed platform which is quite handy.

Click on the arrow to see the 5″ video.

Armstrong RML Cannon Trunnions – 2

Silver soldering the trunnions into the barrel and the squared blocks did not go well.

For a start, I did not know the composition of the steel of the barrel.  The trunnions were/are silver steel, and the blocks were mild steel.  So it is possible that I did not use the best flux.

And the barrel is quite hefty, so I knew that it would require a lot of heat to get it to temperature, and to keep it at soldering temperature.  So I used a large oxy-propane torch, and heated it to dull red heat.

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The steel pieces fluxed and wired together, ready for heating

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It was a cool day, but the heat output from the red hot barrel was ferocious.

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Soldered, but one side was not good, and a hammer blow dislodged it.  Damn.

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The good side, partially machined.

I dithered about how to deal with the faulty side.  I was not enthusiastic about re-soldering it, expecting that the good side would fall apart.

So I cleaned up the pieces, and used high strength, high temperature, Loctite 620, to join the pieces.  The machining will test the strength of the joins, so I will give it the full 24 hours before testing it.  This is the “reject” barrel.

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Still pondering how to join the trunnions of the “good” barrel (front).  I will discuss it with my colleagues tomorrow when we have a Model Engineering Society meeting on “Zoom” video link.  The 3D printed barrel at back is a handy “how it should look” example.

 

 

 

Armstrong RML Cannon Trunnions 1.

cannon from above front

The 80lb Armstrong RML cannon trunnions were probably heat shrunk into the sides of the barrel.  The squared off barrel sides would have been part of the original wound and welded steel rods, and machined to shape before the trunnions were inserted.

The hole above the trunnion is to hold one of the 4 sights.

For the 1:10 model I considered various construction methods. This is what I decided…

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The 20mm diameter trunnion is fitted into a milled steel block, and the 2 pieces on each side are then silver soldered into prepared recesses in the barrel.

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The the barrel is mounted in the CNC rotary table and tailstock.  15mm deep holes are drilled into the barrel….

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and widened to 20mm diameter (drilled then milled)……  (for cutting fluid I use a mixture of olive oil and kerosene.  It produces a lot of evaporated fluid but is very effective at keeping the job cool).

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….then complete the recess.   The bottom of the recess is 8mm clear of the bore.

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Next step is to make the blocks, the trunnions, and silver solder them all together.  Not entirely authentic, but compromises are required when scaling down.   Still on the reject barrel, as a trial run.

Rifling the Model Armstrong RML

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The HSS cutter is mounted in a tight 3mm wide slot in 16mm silver steel.  The 4 mm cap screw pushes the cutter up by 0.2mm per full turn of the screw.

The following video shows an air cut of the rifling cutter in the CNC rotary table on the CNC mill table.   Then some actual cuts in a 1:10 scale cannon barrel.  This barrel was a reject, and was used to practice the rifling cuts.

You can click on the arrow in the box below, or see the video full screen in YouTube.

 

3D Printing is FUN! (but still slow)

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My 3D printer.  Bought from Amazon on a special offer.  $AUD279.  Worked straight out of the box after minimal assembly, and using the supplied plastic filament (PLA).  You can see the large gear on the platten which I drew up using a CAD program.  I used the software (Cura) supplied by the printer manufacturer (Creality).   The printer is a Creality CR -10S.  The “S” refers to a “filament out” sensor which I have not yet installed.  I read some reviews of the printer before spending my money, and so far I am very happy with it.  You might notice some bracing bars which I bought separately on Ebay.  Not sure if they are necessary, but they might improve the print quality by reducing vibration in the printer.

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These gears and shafts were printed.  They were used to check the sizes of parts for my next model cannon build.  I used a program called “Gearotic” to plan the gear module, teeth numbers, distance between centres etc.  Gearotic is also great fun.

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The printed gear and pinion quadrant on a background of a photo of the real cannon.  On my model the gear and pinion will be made of steel or brass, machined from bar stock.

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Another part sitting on a photo of the original.  This demonstrated that I had got the corner chamfer a bit wrong.  Much better to discover the fault at this stage! 

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A half size print of the barrel.  This was just for fun.  The final part will be ~300mm long, and will be machined from steel.  This print took almost 4 hours.

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A print of the centre column which the cannon chassis sits on and traverses around.  It is ~60mm tall.  It will be tricky to machine from solid bar.  Could be fabricated in pieces and silver soldered together, but I am considering using the printed part to make a mould and cast the part in brass or bronze……   The original cannon column has an 5-600mm extension into the concrete base which my model will not need.

So far all of these prints have been made from PLA filament, which I read is easy to use, tough, rather brittle, and has a low melting point.  It is also inexpensive (about $20-25 for 1 kg).  I am still on the supplied small roll which came with the printer.  Future prints will be in colour!

The weather is a bit cooler today, so I might get back into the workshop and make some metal swarf.

 

 

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