Kerr Stewart 4420 - Live steam and 3D printing

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

Post by Trevor Thompson » Tue Dec 14, 2021 6:10 pm

Having finished all of the basic machining I have made a jig to make sure that all of the steam ports in the cylinders and port block align properly. It is basically a dummy cylinder and connecting rod. There are holes along the centre line for the pin on which the cylinders rock, and a hole for the crank pin to fit through. There is also a hole for each of the steam ports - each 9mm from the pivot pin hole, and again on the same central line:
IMG_1995.jpg
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You can see it here as it is intended to be used to drill two of the holes in the port block. I have made the sides of the jig the same width as the cylinder so I can use the same jig to drill the corresponding holes in the cylinder.

I did make a mistake of course - I read the wrong dimension from the drawing and drilled the holes for the ports in the wrong place before realising. So I tapped the holes 10BA and filled them with 10BA brass studding. Then I drilled them in the right place!

If all goes to plan the holes in the port block should align with the holes in the cylinder perfectly.

(It isn't my idea by the way - I got the idea from watching one of Tony Bird's videos).

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

Post by Trevor Thompson » Tue Dec 14, 2021 6:43 pm

So drilling the steam ports in the cylinders:
IMG_1996.jpg
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I fitted the jig on the pivot pin and lined it up parallel to the edge of the cylinder. Then drilled one hole as in the photo, removed it all from the vice, put a clamp on the other end before removing the first clamp, putting it back in the vice and drilling the other end.

That was repeated for both cylinders. Transferring the jig to the port block and drilling the first pair of holes in that:
IMG_1997.jpg
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Having drilled 2 holes the jig was moved to the other extreme of the cylinders movement, with the crank pin moved through 180 degrees, and the other 2 were drilled.

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

Post by Trevor Thompson » Tue Dec 14, 2021 6:51 pm

So the result with the jig removed:
IMG_1998.jpg
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The cylinders needed the recess in their face recutting because it had been lost in making the inner faces of the cylinders thicker. So that is the cylinders ready to assemble and test.
IMG_2003.jpg
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I went back to the port block to look at what else needed doing to it - such as making the holes to mount it onto the locomotive. I tried compressed air down all of the ports partly to clear out swarf, but also to try to detect air coming out of the correct holes. When drilling the ports I could feel the difference in pressure on the drill feed, on three of them at least. One of the bottom steam holes didn't seem to hit the steam ways as I drilled it, so I was trying to work out if it has connected or not. I have come to the conclusion that it isn't connected - because I didn't drill that steam way deeply enough. Something to sort out another day!

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

Post by Trevor Thompson » Thu Dec 16, 2021 8:43 pm

I have been thinking about the boiler (well the steam motor is almost finished), and of course that led me to the bodywork which is going to hide it all.

So this is a the outline of the bodywork in place on the chassis. The detail is not added yet, and I was contemplating adding the panels and rivets onto the surface, as separate pieces printed on the resin printer (to get the surface finish). Anyway the body:
Screen Shot 2021-12-16 at 20.27.40.png
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and with the boiler cover removed:
Screen Shot 2021-12-16 at 20.28.17.png
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So the boiler. The plan so far is to use 2 pieces of 11/4 inch OD copper pipe one on top of the other. Put slots in the bottom of the top one and in the top of the bottom one (where the cross stays will go). Add flat plate sides to give the outline in the photograph. Fit flanged ends front and back, with a 15mm tube running the length of the boiler to take a poker burner. All of this from 1.6mm thick copper. This would be strong enough for a boiler pressure in excess of the 40 psi I will use.

I calculate that 3mm diameter copper stays will be needed, on 20mm centres. Hence all the stays in the sides and ends.

Perhaps there isn't as much water volume as I would like but it comes down to what diameter pipe is available.

I have also thought about a vertical boiler and even a rectangular boiler - but simple is probably best.

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

Post by Trevor Thompson » Tue Dec 21, 2021 4:42 pm

I left the progress on the steam motor with the thought that a steamway wasn't connected to the cylinder ports. I mounted the port block in the drill and open out the plug in the end of the drilling. Re-drilling the hole established that it had been left just a mm too short. So with that corrected the surfaces of the cylinders and the port block were polished using wet and dry paper on the lathe bed (as a flat surface).

In the meantime the 7mm O rings had arrived so I made brass pistons with a groove for the O ring:
IMG_2025.jpg
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The pistons have ended up as an almost perfect fit. They slide freely in the bores yet when I cover either of the ports the piston acts as if it was an air spring - you can feel the pressure coming back as you move the crankshaft, and it springs back when you let it go.

Trial assembly identified that the crank shaft was touching the cylinder gland when the piston was at the upper end of its travel, stopping the crank rotating fully. So the cylinder was disassembled again and a millimetre taken off the top of the bearing housing on the crank. The same on both sides.

So I now need to take the piston off one shaft and shorten the shaft slightly. But we are getting closer to a running motor.

Trial assembly:
IMG_2026.jpg
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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by Trevor Thompson » Fri Dec 24, 2021 8:00 am

The steam motor is now assembled, tested and run in on compressed air:
IMG_2028.jpg
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The toolmakers clamp is temporarily holding the reverser tight against the port block. I have to organise a strong enough spring to keep it steam tight - yet allow it to rotate - and without leaking steam. While this type of reversing valve is used everywhere I don't really like it - I always find it hard to get it to stop leaking!

There is a short video of it running on the bench:

https://www.dropbox.com/s/adhh53inyqt4m ... 0.m4v?dl=0

Now I have to design the method of holding it in the cab of the loco, and linking the reduction gears to the chain drive.

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

Post by SimonWood » Mon Dec 27, 2021 11:04 am

Since I am going to follow in your footsteps with this project, I am by turns terrified and grateful for all the photos on this thread. It still looks amazingly tricky but the images to make everything really clear - including some parts that I have only seen completed/assembled.

Steam motor running looks great. How much have you slowed the video down by in the slow-motion segment?

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

Post by Trevor Thompson » Tue Dec 28, 2021 10:42 am

SimonWood wrote: Mon Dec 27, 2021 11:04 am Since I am going to follow in your footsteps with this project, I am by turns terrified and grateful for all the photos on this thread. It still looks amazingly tricky but the images to make everything really clear - including some parts that I have only seen completed/assembled.

Steam motor running looks great. How much have you slowed the video down by in the slow-motion segment?
I don't know how much that video was slowed down - its an automatic function on the iPhone. However it really will run that slowly! In fact I am amazed at how quickly it has run in and how well it runs. It is smooth and very controllable. Some time ago we talked about using this type of reverser as a combined throttle and reverser. In this case it will work - as long as the force required of the servo does not wreck the servo!

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

Post by SimonWood » Tue Dec 28, 2021 10:48 am

Trevor Thompson wrote: Tue Dec 28, 2021 10:42 am I don't know how much that video was slowed down - its an automatic function on the iPhone. However it really will run that slowly! In fact I am amazed at how quickly it has run in and how well it runs. It is smooth and very controllable. Some time ago we talked about using this type of reverser as a combined throttle and reverser. In this case it will work - as long as the force required of the servo does not wreck the servo!
I had a quick scan - it looks like iPhone do 1/2 or 1/4 speed depending on the model.

With regard to controlling on the reverser, I think it's essentially very similar to the oscillating cylinder on my Regner Konrad, albeit that's a single cylinder (with two cylinders, this motor should be able to self-start?) I can control it on the reverser, although in that case it has a throttle as well.

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

Post by Trevor Thompson » Wed Dec 29, 2021 7:38 pm

Oh yes it does self start and it doesn’t seem to matter what point in its cycle it had stopped at. It just starts every time. It will also take off very slowly and run on no load at something like the speed in the Video. Of course it also rushes around at high speed as well if asked to. It’s the ability to actually control that on the reverser that took me aback.

When I made my version of Idris I had problems getting it to run and particularly to get it to not leak steam through the port block/cylinder interface and particularly the port block/reverser interface. This one seems to seal well. I am sure that using a jig to drill the steam holes is the significant difference here.

In fact with the reverser in the stop position I can feel the “air spring” effect when I rotate the cranks by hand. This indicates to me that there are no leaks anywhere which is amazing!

I have made a first stab at fitting it into the chassis. My efforts so far have led me to fix the motor to the back of the cab. I was trying to find a way of holding it firmly so that I can position the intermediate shaft. It isn’t going to lead me where I wanted to go. In that if I continue this way it will be difficult to attach steam pipes or service the motor. So I will persevere as far as using the back half of the cab to locate the motor temporarily. Use that position to fit the intermediate shaft and then remove the moto and cab. I can then make a permanent bracket which holds the motor to the chassis in such a way that the whole cab can be removed for access. I have a mental picture of a chassis with a boiler and motor attached, and a separate body which just slots over it all. Photos when I get somewhere!

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

Post by Trevor Thompson » Tue Jan 04, 2022 12:19 pm

I have been printing off components to mount the steam motor. So far I'm on the second iteration of the components.

I have been discussing off forum some issues with printing the components in ABS - which I thought I should share.

ABS has good heat resistance - which is particularly relevant for this model.

Firstly you need to know that Simon and I both have Flashforge Adventurer 3 printers. These come with a removable flexible plastic build plate, and an alloy underplate which is heated. The flexible plate has a replacable self adhesive film on it.

Initially when you have a new build plate ABS does not stick to it - or at least the components come free too readily to be useful. The accepted wisdom to solve bed adhesion problems with ABS is to wash the surface with a mix of acetone with ABS dissolved in it. That works - but if you do it you won't be able to get the model off the bed without destroying the self adhesive film. So a light wash of acetone should be sufficient. If not try a SMALL amount of ABS dissolved in it.

I have the bed plate on my printer nicely conditioned at the moment so that the raft comes free readily, and nothing comes off until I want it to!

So I have just mentioned using a raft. My experience is that I have to print ABS onto a raft. The photo shows 2 of the components for mounting the steam motor:
IMG_2033.jpg
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The part on the left I printed without a raft - but with a brim. Printing it ALMOST destroyed the self adhesive film.

The right hand part is as it came off the printer - with its raft still attached. It came free from the bed easily by bending the plastic plate (as you are meant to). The components will come free from the raft easily. The downside of this is that the underside of the component isn't a nice clean flat surface. You can see here:
IMG_2034.jpg
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However the remains of the supports sand off easily.

One thing I forgot to mention is that I raise the component by 1mm when I set things out in the slicing software. The software adds supports which you can see on the raft as a thread of plastic running back and for across the raft. By raising the component above the bed like this I make sure that it is easy to get the component off the raft. Not so much a problem with a small component like this but it is with something bigger like the sides of a building.

Trevor
Last edited by Trevor Thompson on Wed Jan 05, 2022 10:30 am, edited 1 time in total.

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

Post by Trevor Thompson » Tue Jan 04, 2022 7:06 pm

I have finalised the method of holding the steam motor on to the chassis. It uses a mounting bracket to hold the steam motor in place. The two holes in the port block are fitted with top hat bushes made of PTFE, 4 of them two in each hole. This should ensure that the heat is kept away from the plastic. Of course this is all experimental - so we will see if it works - when it gets hot.

The view from the top:
IMG_2035.jpg
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You can see that the steam motor is off set to one side. I did that to make the operating lever for the reverser more accessible for manual control, and to give more room to connect steam and exhaust pipework on the other side. I have modified the reverser control by making the bracket longer so that the lever can extend forwards into the cab - rather than out of the back of the cab.

The view from below:
IMG_2036.jpg
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Two printed bushes hold ball races (3mmID, 10mm OD, 3mm wide) and are bonded to the inside faces of the inner chassis. Lining up was by eye. The shaft is 4mm OD to suit the gear, the chain wheel was bored out to 4mm, and the ends of the shaft turned down to 3mm diameter. I have yet to tighten the grub screws on the gear - which will be done when the acetone bonding the parts together has finally evaporated, and the joints are secure. I await chain to complete the drive - but I will be able to test it as it is tomorrow.

I think that the moving parts will clear everything.

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

Post by SimonWood » Tue Jan 04, 2022 10:12 pm

This looks really good Trevor! Very neat, sturdy and suitably insulated where needed.

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

Post by Trevor Thompson » Wed Jan 05, 2022 12:16 pm

The steam motor is now firmly located on the chassis and it runs on air. The drive shaft rotates freely, although one crank just catches the ball race and the other may well touch the chain when its fitted. To be rectified when the chain arrives.

The reverser is tending to leak as expected. I didn't use a spring to hold it onto the port block but an O ring:
IMG_2038.jpg
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I thought it would provide more pressure. So you can see the red O ring, and a spacer which has a slight depression in its inner face to take the O ring. Two nuts are locked onto the stud with lock tight and by locking the nuts against each other. The faces on the other side are well coated in steam oil. The arrangement for controlling the reverser is shown here:
IMG_2037.jpg
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A brass ring, with a saw cut top to bottom, and 10BA bolts pinching the cut section onto the reverser. A long stainless bar protrudes forward, to control it by hand.

I will add the components to mount the steam motor to the 3 D printing files section.

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

Post by Trevor Thompson » Fri Jan 07, 2022 12:34 pm

I now have a running chassis. The steam motor is easily removable by undoing two nuts and bolts, and the chains are all connected.

I have added video of it running on compressed air at 20psi. The reverser does allow good control of both direction and speed - and I am sure could be controlled by a servo. Both videos are taken at actual speed- in other words that is the real speed its running at:

https://www.dropbox.com/s/q7xrh0ebhlmqc ... 0.m4v?dl=0

https://www.dropbox.com/s/71dm31z5hh50x ... 1.m4v?dl=0

Im now waiting for materials to arrive so that I can start on the boiler.

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

Post by Lonsdaler » Mon Jan 10, 2022 12:32 pm

That's very impressive Trevor and far beyond my skillset. It's an interesting idea to combine 3d printing and live steam - fingers crossed for you that it works.🤞
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Re: Kerr Stewart 4420 - Live steam and 3D printing

Post by SimonWood » Mon Jan 10, 2022 7:37 pm

Trevor Thompson wrote: Fri Jan 07, 2022 12:34 pm I now have a running chassis. The steam motor is easily removable by undoing two nuts and bolts, and the chains are all connected.

I have added video of it running on compressed air at 20psi. The reverser does allow good control of both direction and speed - and I am sure could be controlled by a servo.
Terrific! Very controlled. This whole project just gets more and more exciting.

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

Post by Trevor Thompson » Tue Jan 11, 2022 9:59 am

SimonWood wrote: Mon Jan 10, 2022 7:37 pm
Trevor Thompson wrote: Fri Jan 07, 2022 12:34 pm I now have a running chassis. The steam motor is easily removable by undoing two nuts and bolts, and the chains are all connected.

I have added video of it running on compressed air at 20psi. The reverser does allow good control of both direction and speed - and I am sure could be controlled by a servo.
Terrific! Very controlled. This whole project just gets more and more exciting.
Simon

How are you getting on with the chassis?

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

Post by SimonWood » Tue Jan 11, 2022 12:39 pm

Trevor Thompson wrote: Tue Jan 11, 2022 9:59 am How are you getting on with the chassis?
Got my replacement print-bed stickers (also got a new plate just to have a spare) and now printing without issues. Will post a pic once I have it assembled!

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

Post by Trevor Thompson » Thu Jan 20, 2022 7:35 pm

I have started to build the boiler.

An unusual design I know. Two tubes one on top of the other with slots to allow steam and water to pass through, as well as to allow for the cross stays:
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Rather than cut the copper tube longitudinally as per the drawing above I decided to make 6mm slots across the tubes, to allow for the cross stays etc. Just seemed a "better" way to do it. The end plates are not shown in the views above, but I will describe those later.

Starting with two tubes.

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