Thompstone Engine

[paul raynerParticipant @paulrayner36054]

Hiya Jason

Just made a start on this engine at last!

how difficult is it to silver solder cast iron if I used that for the cylinders?

bearing in mind i'm a novice.

thank you for your response in advance

regards

Paul

[JasonBModerator @jasonb]

It is possible but if you have not done much silver soldering before it may not end well. Basically you need to preheat the parts to bring as much carbon to the surface as possible and then wire brush it off. Then flux with HT1 or Tenacity No5 and solder the parts together.

Another option if you want to use cast iron would be to use JB weld to bond the parts together, you could reduce the number of joints if you made the cylinder and it's flanges from one piece of 40mm nominal CI bar and just stuck the valve & exhaust blocks plus the feet on.

[paul raynerParticipant @paulrayner36054]

How does Jb weld fair with steam?

I do intend only to run on air but you never know.

methinks it could be tricky machining the slot for the valve and exhaust blocks with the flanges on.

mmm.

[Nigel Graham 2Participant @nigelgraham2]

If by the "slot" you mean the ports, that's not a great problem. In fact you can use the flanges to advantage.

Engine cylinders like these are normally cast with the flanges in place, and once those are faced parallel with each other, they can be used to align the cylinder on the mill, e.g, between angle-plates, for machining the feet, valve-face, ports and the valve-chest's mounting surface.

Other builders of similar engines may use a different, valid approach, which is fair, but that's how I'd do it.

[paul raynerParticipant @paulrayner36054]

Hiya Nigel

I know what you mean, but this cylinder isn't as straight forward as that, The valve flange and the steam passages are in one "T" piece soldered to the side of the cylinder there is a picture of Jasons cylinder halfway down the previous page, or the drawings are in ME vol 226 no 4662 page 491 if you are interested.

I Think the only way round it would be rather than milling a slot into the cylinder, to mill a 10mm flat on the cylinder, that way I could machine the cylinder, flanges & decorative bands.

soldering it could be a problem for me though!

or part with some cash.

thoughts anyone?

[JasonBModerator @jasonb]

Instead of machining straight along the cylinder with a 10mm bit use a much smaller one, 3mm ideal or 4mm would do. This would leave a radius in the corners as you get to the flanges, just file the corners of the valve block to suit and you will be able to fit the valve block OK. If that is not clear let me know and I'll modify a drawing to show it.

You could also reduce the width of the 6mm passage slots in the valve block to 5 or even 4mm to get a bit more area for the JBWeld to bond to, just don't use excess and have it oose into the passage and block it.

As for steam it will be fine, If you have seen any of Ramon's steam launch with a JBWelded twin cylinder block you will see it runs fine and he has also tested JBW joint(cold) to over 500psi.

[JasonBModerator @jasonb]

Nigel, we are talkning of how to build up the cylinder "casting" in particular the flat along the sid eof teh cylinder where the valve block and passages fit see this drawing

This engine like several of mine does not have slotted ports, they are drilled as shown on this drawing

 

Edited By JasonB on 27/02/2022 08:09:20

[paul raynerParticipant @paulrayner36054]

Thank you Jason, I think I will have a go at soldering some cast iron first.

Then maybe it will make up my mind!

regards

Paul

[geoff walker 1Participant @geoffwalker1]

Hi Paul,

If you are using cast iron I wouldn't bother with silver soldering.

JB weld is great and perfect for your application.

Good advice from Jason, leave a small radius at the end of the slots, have a narrower channel, and don't get carried away using to much adhesive.

Photo is of a cast iron cylinder I made recently, similar to the thompstone design.

Geoff

[paul raynerParticipant @paulrayner36054]

Jason, Bugger me I've got EF flux! so that wont do, JB it is

Geoff, thanks for that, a picture is worth a thousand words as they say.

Thinking about it I will try Jason's suggestion, use a smaller end mill and file the corners.

Now back to the shed with coffee in hand

thank you all

regards

Paul

[JasonBModerator @jasonb]

The reason for suggesting HT5 was that you may be heating for some time and this flux won't get exhausted, it doe snot contain anything that helps it solder CI though it does have something in it so it works on stainless steel.

[paul raynerParticipant @paulrayner36054]

That's correct, with it being cast iron it will take quite some heat and time to get it to temp.

Where as I don't think my EF would cut the mustard.

Just out of curiosity I went on CUP's site and notice they have a flux for bronze!

regards

Paul

[James Smith 24Participant @jamessmith24]

Hi Jason

I started building this engine as a first project and really enjoying it so far. The instructions and drawings are really helpful to me as a beginner, but I am stuck on one point.

On the eccentric strap the drawings show a 2mm hole, to join the two halves together, but the material list does not show M2 nuts of sufficient quantiy, and looking at the pictures of your finished engine it looks like you have used a bolt with nut and locknut. Can you enligten me as to what you used and the correct size.

Thanks

James

Edited By James Smith 24 on 07/11/2022 20:45:03

[JasonBModerator @jasonb]

I'm just off out but will get back to you later today.

[John RutzenParticipant @johnrutzen76569]

Hi Jason, lovely photos and very interesting , especially for someone like me who fabricates nearly everything. I hadn't considered JB welding cast iron together for a cylinder. Does it stand the heating/cooling cycles and the moisture? Also , I'm pretty sure that you can silver solder cast iron though I haven't tried it.

[JasonBModerator @jasonb]

James, having refreshed my mind by taking a look at the finished engine it looks like the bill of materials is wrong and that I have the nuts and the two bolts listed as M2.5 rather than M2.

But I also notice that in my text I said to thread one half M2 and the other half to be drilled M2 clearance.

So there are a couple of options:

-You could tap one half M2 and then use some of the 2mm studding material to make studs and then you would just need two M2 nuts.

– As above but with nuts and locknuts

– Do as I did and drill both halves 2mm for M2 clearance, use a 10mm long M2 hex head screw or bolt and retain that with a nut and locknut. Note Photo 54 in the article shows cap head screws and a nut which were just use during construction.

– You could also drill through both M2 clearance and make up a couple of M2 studs and retain these with a nut at each end.

I hope this error won't set you back too much and please post some images of your build.

[JasonBModerator @jasonb]

John the JB Weld was an option for those that may not have the facility to silver solder but yes it is possible to silver solder CI, usually needs a pre heat to bring the carbon to the surface which is then cleaned with a fine wire brush before heating again and soldering.

Although my own engines that have been bonded with JBW have only been run on air others here such as Ramon have built engines that do get steamed and have had no problems. Ramon has also tested joints to several 100psi both hot and cold and they hold up well. Do make sure to use the "original formula" (red and black tubes) not the rapid or marine as they don't have such a high temperature rating

[James Smith 24Participant @jamessmith24]

Jason,

Thanks for the comprehensive reply, I had drilled the holes 2mm as the drawing so will probably go with the M2 studs with a nut at each end.

Below are a couple of pictures of where I am up to, I am not totally happy with some of the parts so may yet remake but will see. It has been an interesting project and have learned a great deal from it.

James

[John RutzenParticipant @johnrutzen76569]

Thanks Jason, that's interesting to consider as an option. The design of the joint would also obviously have a lot to do with it. I've only ever used it to make fillets when I fabricated the flywheel for my Rumely tractor.

[JasonBModerator @jasonb]

That's looking good James and you don't look to have too many bits left to make.

[James Smith 24Participant @jamessmith24]

Finally completed my version of the engine so thought I would upload a couple of photos.

I repositioned the steam inlet so I could recess the valve cover.

[JasonBModerator @jasonb]

That looks to have turned out rather well, the slightly larger flywheel does not look out of place and the colour is nice and subtle plus it makes a change from the usual dark greens and crimsons.

How does it run?

[James Smith 24Participant @jamessmith24]

Thanks Jason,

I was inspired by your use of muted colours for my choice.

The flywheel was not ideal, but what I could get hold of reasonably easily at the time, I don't think it looks too bad, but when I compare with yours I do like the slimmer smaller design.

It runs okay, though have only been able to try on air.

I have to decide on a next project now !

[Dave WoottonParticipant @davewootton]

Nice work James a very good job and the flywheel looks fine to me, the grey colour suits it well. good luck with the next project i'm sure it will turn out as well as this one has.

Dave

Edited By Dave Wootton on 12/02/2023 13:23:41

[paul raynerParticipant @paulrayner36054]

Hi James Love the colour.

As it happens I've just pulled out my bits this weekend, hopefully I should get some time over the next couple of weeks to do a bit more.

Paul

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