Kerr Stewart 4420 - Live steam and 3D printing

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Keith S » Sat Oct 22, 2022 5:28 am

This is brilliant. I have to admit I found the idea outlandish at first, but now I see it and that genius boiler design, I am firmly of the opinion that this thing is going to be a masterpiece.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Sun Oct 23, 2022 2:03 pm

SimonWood wrote: Fri Oct 21, 2022 11:38 am Fantastic.

How did you make the PTFE boiler feet? Turned on the lathe?

Really interesting to see the bodywork. It is a strange looking loco, but while it's hard to deny it looks like it's had an encounter with the ugly stick, it's actually far more appealing to my eye than drawings suggested to me.

I know it's not your plan to, but looks like there's lots of room in the tanks if one were to R/C it (reverser linkage running under the cab floor perhaps?)
Firstly the feet. Yes turned on the lathe from PTFE bar (readily available on the internet).

The room either side of the boiler was intended to take a gas tank down one side. There is clearly room for radio control on the other side. It would also be possible to mount the electronics inside a "box" mounted to the frame - to protect it from water steam and heat.

I am planning to run a pipe directly from the boiler to the motor - without a regulator in the middle. I am hoping the reverser control on the steam motor will work for both reversing and speed (something we have discussed in the past). So that would be easy to arrange with a single servo which could be mounted near to the motor at the back of the cab.

My plans for it to be a simple loco are slowly evaporating. I have bushes in the boiler for a water filler, and a water level sensor! So radio control can't be that far behind.

Trevor
Last edited by Trevor Thompson on Sun Oct 23, 2022 2:07 pm, edited 2 times in total.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Sun Oct 23, 2022 2:05 pm

Keith S wrote: Sat Oct 22, 2022 5:28 am This is brilliant. I have to admit I found the idea outlandish at first, but now I see it and that genius boiler design, I am firmly of the opinion that this thing is going to be a masterpiece.
Wow - I didn't think it was that good. It had better work!!!

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Sun Oct 23, 2022 2:21 pm

I have checked that the boiler is fit to use. This is my arrangement for checking it:
IMG_2540.JPG
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I am studiously avoiding the word "test" because it isn't an official test. The pressure gauge is not calibrated - and you can't do it yourself. But a tiny boiler like this doesn't need an official test (in the UK anyway).

So I have filled the boiler with water blocked off all the bushes except one and fitted the rig to the boiler. Pump it up to 5 bar in this case and shut the valve to isolate the pump from the piping (to avoid the slight leakage back through the pump).

The first time I did it was disappointing - a drip from one stay and a jet from another. So it was all dismantled and drained before re-soldering the offending stays.

The second attempt was much better. It retained 4.5 bar (about 75psi ish) for 5 minutes, with slight leakage from the thread connecting the pipework to the boiler.

I think that will work fine on 30psi - which is what I intend to run it at. (I don't think its fair to expect a steam motor with a simple reverser like this has to cope with more than 25 to 30 psi.

So the boiler is mounted into its final place on the footplate:
IMG_2541.JPG
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The top hat bushes sit under the boiler, and simple PTFE washers sit on top, and 8BA bolts hold it down. I can modify the drawings for the footplate later - but I just held the boiler in place with superglue while I drilled 1.8mm holes through the bushes. The superglue held for the first two holes, so I tapped the footplate 8BA and put the first two bolts in before drilling the last holes.

So I suppose it is boiler fittings and pipework next.

It feels like it is quite close to seeing steam!

I will add the bodywork files to the 3 D printing files shortly. I can't say they won't need modifying, but they would allow someone to make a battery driven version of the loco.

Trevor

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Old Man Aaron » Sat Oct 29, 2022 5:09 pm

Congrats on the successful boiler experiment! ;)

Need to go back and properly catch up on this thread (and the forum at large) but the project is looking superb as always.
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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Sun Nov 20, 2022 4:48 pm

Progress and a setback to report!

I have made the tank, control valve and burner:
IMG_2569.JPG
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It is a modification of the drawing for "Brick" from the 16mm Association website.

It works fine in the open. Nice flame pattern and blue flames. However inserted into the 12.7mm tube in the boiler and it doesn't work. The flame goes out, or it acts like a flame thrower! Tony Bird did say that he thought it was too small a tube - and of course he was right. So a bit of an adjustment. I used a stepped cutter to open out the tube, basically cutting it free at each end of the boiler and removed it. I have a 15mm diameter tube ready to silver solder into place.

So some adjustments to carry out - and this time I am sure the burner will work in place. We know 15mm tube works.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Wed Dec 07, 2022 12:26 pm

Progress again.

Modified burner control and:
IMG_2590.JPG
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Modified burner lit outside the boiler:
IMG_2598.JPG
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And you can just see the flames inside the boiler burner tube:
IMG_2600.JPG
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I can see on looking at this again that I put the burner into the wrong end of the boiler. It doesn't make any difference it was just a test - but you might wonder why there were bushes in the front of the boiler!

So that is a success. I will draw up the components and add them to the thread when I have it all working. On to the boiler fittings.

Trevor
Last edited by Trevor Thompson on Wed Dec 07, 2022 10:21 pm, edited 1 time in total.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by SimonWood » Wed Dec 07, 2022 3:41 pm

Very neat Trevor! Have I understood the orientation right - that the gas valve will be accessed from the cab opening (port side) and the gas filler vale will be accessed through the water filler chute to starboard?

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Wed Dec 07, 2022 10:18 pm

SimonWood wrote: Wed Dec 07, 2022 3:41 pm Very neat Trevor! Have I understood the orientation right - that the gas valve will be accessed from the cab opening (port side) and the gas filler vale will be accessed through the water filler chute to starboard?
I hope it will work out like that!

Trevor

PS One of the modifications I have made is to use an O ring to seal the gas valve. I have never been able to get those pointed spindle valves to seal properly - and I can get the ones with O rings in to seal fully every time.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Dr. Bond of the DVLR » Fri Dec 16, 2022 7:30 pm

Brilliant! What an excellent project. Looking forward to the next installments.
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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Mon Dec 19, 2022 2:18 pm

I am now at the stage of giving 4420 its first test under steam.

Firstly to show you the progress so far:
IMG_2646.JPG
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You can see that I have the gas valve control wheel in a place where it should be accessible from the cab doorway. There is a copper pipe connected between the steam takeoff ( no regulator) and the steam motor. Also a pipe from the steam exit on the motor to the front of the boiler. Boiler fittings at the moment consist of a safety valve, two blanking plugs and a steam takeoff. In due course the blanking plugs will be replaced by a filler valve and a water level sensor. The sensor will feed be used to drive LEDs - as per my other steam locos.
and from the other side:
IMG_2647.JPG
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On this side you can see the way the gas tank sits alongside the boiler. At the rear end there is a half support under the tank, and at the front a full support. Initially I glued the front support into place, but I have made a modified arrangement which will allow it to be bolted into place. The burner is removable - its just easier to take burner and tank off in one piece to clear a jet. That means that I can clean a jet without disturbing gas fittings and risking creating a gas leak.

and finally looking down on the cab area:
IMG_2648.JPG
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It is a bit cluttered - but it has developed as it went along. Note that at the moment there is no displacement lubricator. There is no smokebox - or its equivalent which will in this case be a sort of "T" piece directing the burner exhaust up and down. I have not fitted the body on - and it will need modifying to get it to fit. So first things first - lets get it working.

So here is a link to a short video of it running on my workshop test track;

https://www.dropbox.com/s/05of7zdn3vo8d ... 2.MOV?dl=0

Not exactly running properly yet - but I still have a big grin on my face!

There is a significant steam leak from the pipe where it goes into the steam motor. And the steam motor is letting steam out all over the place. That will be partly due to the lack of lubrication. So I am not really getting steam up properly certainly little evidence of steam around the safety valve which I have set to 30psi. I may yet fit a regulator - but I think there is an advantage in not having one on a simple locomotive like this.

So the next steps are to

Insulate the boiler.
Fit an exhaust / smokebox
fix a steam leak
make and fit a displacement lubricator

Those changes should have a big impact.

Trevor

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by SimonWood » Mon Dec 19, 2022 3:28 pm

And now I have a big grin on my face too! It really is just wonderful to see this beast running. Fabulous.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Sat Apr 29, 2023 4:22 pm

I have been making progress on this project. Perhaps its worth admitting that I have carried out a successful steam trial outside with the body in place. That will be revealed shortly!

Firstly I have addressed the issues I found when I first steamed it.

I have made and fitted a displacement lubricator:
IMG_2942.JPG
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A simple arrangement based on the one in the drawings for "Brick".

I have created a "smokebox" or at least a functional equivalent:
IMG_2941.JPG
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and finally the boiler has 2 layers of wool felt wrapped around it. It is just held in place with insulating tape:
IMG_2962.JPG
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On to the next post.

Trevor
Last edited by Trevor Thompson on Wed Nov 08, 2023 8:58 am, edited 1 time in total.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Sat Apr 29, 2023 5:08 pm

I have had it in the garden and the result is in this short video which can be viewed via the following link :

https://www.dropbox.com/s/k8iszgsgwymct ... y.mp4?dl=0

Remember that this is an experiment. So this isn't a final finished loco - its just part way through the project. The first question we all want to know is how did the plastic bodywork cope with the heat. Here is a photo of the inside of the body so you can see for yourself:
IMG_2964.JPG
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So the answer to that question is that the body was only affected where it was touching the exhaust. The rest of it was totally unaffected particularly relevant in the cab area where there was a certain amount of steam escaping. I am reassured that the concept will work. You will see that I have been butchering the inside in various places with a Dremel to clear the various components.

So what were the next set of issues which came out of the test:

Firstly more detail of areas where it got too hot. The "smokebox" consists of a 15mm copper pipe "T" piece, with a length of 15mm copper pipe extending upwards. I used a hole cutter to make a hole in the footplate underneath it. Crude but I am experimenting. When I lit the burner the flame didn't move to the burner correctly - it went down out of the bottom of the "T" piece - charring the paper covering on the bench before I smelled it. Adding a short length of pipe on the bottom leg of the "T" stopped that. Of course the front buffer beam was damaged by the flame playing on it. With the pipe on the lower end that has not reoccured. I suspect the boiler is not quite square on the footplate - because the "chimney" isn't quite central in the hole in the bodywork, and that has resulted in the exhaust pipe touching the edge of the hole it passes through. I can correct that. I will make a turned "chimney" with a smaller diameter perhaps tapered to fit into the top leg of the "T" piece. The "T" piece was only "bonded" to the flue tube in the boiler with lock tight bearing retainer. That requires over 300 degrees to make it let go and it certainly hasn't fallen off so far!

When you look at the video you may notice that the body isn't quite down on the footplate. There is a gap os 1 or 2 mm in some places. Also it isn't sitting on the footplate squarely. So some components need moving slightly. The steam supply pipe, for example, could do with being bent to clear the cab side. The gas filler is probably touching the bodywork as well. I want to make rectangular blocks to bond to the footplate so that the body just drops over the blocks which will hold the bodywork in line with the footplate. I want the body to just sit there held only by friction.

The wool insulation works on the boiler itself. Wool is naturally fire retardant. However any insulation on the "smokebox" would have to be the type used on coal fired locos - totally fireproof. It might be better to do that to avoid accidental damage.

You might notice in the video that the loco seems to crab sideways - and it would not go forwards over the point without derailing. The back to back on the front axle was far too small. That is the problem with bonding the wheels to the axles. The superglue doesn't always hold. I find that making them a tight fit doesn't always work either!

Aesthetics. I will move the boiler back a couple of millimetres so that the safety valve is inside the cab. At the moment it is EXACTLY in the middle of the spectacle plate. When all of these things are finalised I can take dimensions from where things like the exhaust and water filler actually go through the bodywork so that I can make a finished version of the body - and paint it.

Performance. You can see that the loco is running at a suitably slow speed - and I have had it pulling a couple of wagons on the flat. The limiting factor is boiler pressure - it's nowhere near blowing off the safety valve. I have not fitted a pressure gauge but I think it is operating at about 10psi. I always have difficulty getting these simple reciprocating engines leak free - particularly the reversing block. I am sure it will get better as it runs in.

When I have this working I want to try the same principles to make a live steam version of my battery powered "Welsh Pony" - using the same printed components of course. It could be "Little Giant" as running in the 1890's with a full cab to hide the steam motor.

Trevor

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Old Man Aaron » Sun Apr 30, 2023 3:41 pm

I was wondering how you were going with this. Just wonderful to see it run.
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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Tue Nov 07, 2023 6:21 pm

It is a while since I have worked on this, but I have made significant progress over the last week or so. Rather than explain how I have modified it first, I will share the outcome so you can see the result - and then I can explain what has made the difference, and what has yet to be improved. The video of 4420 running on the Railway in the Valley of the Mill:


https://www.dropbox.com/scl/fi/sys0bgjc ... z6cfs&dl=0

Perhaps it is worth noting that the train it is coupled onto is heavier than it looks. The two coal wagons are full of coal - real coal - and are actually heavy.

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Tue Nov 07, 2023 6:43 pm

So what have I changed since it was last videoed on the track?

Firstly I have "fettled" the steam motor. One piston was a bit stiff in its cylinder, the cranks were hitting one of the bearings on the layshaft, and actually hitting the layshaft at the bottom of their motion. It is running more smoothly now. The reverser was leaking steam - which had the effect of limiting the steam pressure in the boiler. So I have changed the spring holding it onto the port face:
IMG_3434.jpeg
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Originally the spring (an O ring) was on the back face interfering with the steam pipes. I have tapped out the hole in the centre of the port face 6BA, and drilled a clearance hole right through the reverser block. I made a washer to hold the spring and cleaned up the hollow mounting disk which holds the lever. So when assembled a much stiffer spring significantly increased the force stopping the steam escaping. When assembled:
IMG_3435.jpeg
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The gas tank I had made wasn't really big enough, so I started again and made one from two lengths of square section hollow brass. Run time is much improved:
IMG_3433.jpeg
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You can see that there are two outward facing brackets on the bottom ends of the tank. They slide under the plastic brackets (there is a cut out in the bottom to each bracket). That holds the tank firmly yet allow it to be removed easily by sliding it sideways. That works well - I will use that idea again! In the photo you will see one error I made. The "o" ring on the gas filler valve sits on the surface of the gas filler bush. I really should have counterbored the bush when I made it so that the "O" ring is supported on the outside and it can't be forced out by the gas pressure. I was reluctant to un-solder the bush to modify it with the risk of ruining it in the process, so I counterbored it VERRY CAREFULLY in the milling machine. Thankfully that worked OK.

Trevor

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Tue Nov 07, 2023 7:02 pm

So I am much more satisfied with the way that is working, however there is room for further improvement. I noticed as I was recording the video that oil and steam was escaping from the lubricator cap - so I will have to look at why, perhaps it wasn't screwed down properly?

While the reverser is sealing well and the boiler is able to generate more steam pressure, there is still steam swirling around the cab. You can see it in the video at times - and no sign of steam from the chimney even though it was fairly cool outside that day. I will try stronger springs on the cylinders to see if that reduces the steam escaping.

At the end of the video the loco was struggling to move both up and down the hill. Note that the bridge and the track beyond it has a slope of 1 in 60 - so it should have struggled up hill and raced off downhill which it clearly does not do. I tried opening the gas valve slightly but that made no difference - so I think it was running out of water. So lots of gas and probably running low on water so I now need a filler valve and the water level sensor.

I have been running on the track a few times now with the body in place - and broadly speaking the body is withstanding the heat well. The only signs of melting are near the "smokebox", firstly where it passes through the footplate and secondly where the other end passes through the top of the body. It doesn't to it all the time - its just when I get impatient and increase the gas flow - and probably its low on water and the extra heat goes into the smokebox rather than the water.

I am going to make a different "smokebox" to reduce the diameter of the top and bottom pipes - increasing the clearance between hot metal and plastic.

At least the body as it is is just a prototype. In due course it can be remade.

Trevor

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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by SimonWood » Thu Nov 09, 2023 6:13 pm

I was delighted to see how well 4420 is running! Really interesting to see all the change you made to get it from running a few feet light engine to hauling a respectable train up that steep bank. The slideable in/out gas tank is very neat.

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