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 Jan 25, 2022 9:45 am

I will be interested to hear how you get on with the 31/2 inch gauge boiler.

That is beyond my experience!

There are lots of people in the model engineering world who would be much better placed to offer advice for that. However one of the best things is to have a go. It is only by overcoming problems that our skills get better.

Trevor

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

Post by -steves- » Tue Jan 25, 2022 12:50 pm

Trevor Thompson wrote: Tue Jan 25, 2022 9:45 am I will be interested to hear how you get on with the 31/2 inch gauge boiler.

That is beyond my experience!

There are lots of people in the model engineering world who would be much better placed to offer advice for that. However one of the best things is to have a go. It is only by overcoming problems that our skills get better.

Trevor
I am dreading starting that boiler, I have looked at it loads of times and then just put it back in the box. It's to go in one of these, a nice little Canterbury Lamb "Invicta" :thumbup:


Canterbury_Lamb_001.jpg
Canterbury_Lamb_001.jpg (19.18 KiB) Viewed 5367 times
The buck stops here .......

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

Post by Scrat » Tue Jan 25, 2022 3:11 pm

-steves- wrote: Tue Jan 25, 2022 12:50 pm
I am dreading starting that boiler, I have looked at it loads of times and then just put it back in the box. It's to go in one of these, a nice little Canterbury Lamb "Invicta" :thumbup:

Canterbury_Lamb_001.jpg
Wow, I am still looking for one of those.
I already have a Rainhill and two Tiches.

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

Post by Trevor Thompson » Tue Jan 25, 2022 9:12 pm

I understand the feeling.

You have a suitable torch - just go for it!!!!

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

Post by Trevor Thompson » Mon Feb 21, 2022 9:55 am

I have made some slight progress on the boiler.

I made a wooden former for the end caps. It consists of a rectangular block and a circular block cut in half and each half glued onto the ends of the block. It has worked so far - but I really need to remake it from a solid offcut of hardwood which I found in the workshop.
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A piece of copper sheet, cut oversize, has been repeatedly annealed and bent to get to the point where it is almost the right shape:
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It needs trimming to size and a final few attempts so get the curved ends just right.

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

Post by -steves- » Mon Feb 21, 2022 5:11 pm

Someone has been very busy with all these updates to 3 projects, love it :thumbup:
The buck stops here .......

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

Post by Trevor Thompson » Mon Feb 21, 2022 8:20 pm

It is good to have something to do when the weather is as bad is it has been the last week or so. We were lucky not to lose power or phone on a number of occasions!

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

Post by Peter Butler » Mon Feb 21, 2022 8:36 pm

Trevor Thompson wrote: Mon Feb 21, 2022 8:20 pm It is good to have something to do when the weather is as bad is it has been the last week or so. We were lucky not to lose power or phone on a number of occasions!

Trevor
Unfortunately we did lose power on Friday... all day and evening, so no chance of any modelling then... (sorry for thread drift)
The best things in life are free.... so why am I doing this?

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

Post by SimonWood » Thu Feb 24, 2022 9:00 am

I did lose power daytime on Friday - ended up working in the shed. And I don't mean working on the railway which I might normally do in the shed, I mean the what-they-pay-you-for work, i.e. trying to use MS Teams on my phone because the shed was the only place with a mobile signal when the wifi was off...

When power came back I was cocky enough to assume it was back for good - and started printing some wheels! Only just completed before the power cut out again for the rest of the evening. With cuts all weekend, I didn't try printing again until things died down on Monday!

(Also I still haven't assembled my 4420 chassis, the ABS rafts either stick to the bed or the the model, either way it takes a long time to separate and sometimes the process is so destructive I have to reprint! Should probably have gone for PLA, printing ABS is particularly difficult when the weather is cold. Nearly there though...)

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

Post by Trevor Thompson » Thu Feb 24, 2022 9:38 am

Simon

A tip.

Always lift the model 1 mm off the bed before adding supports.

Then when the print is finished you can separate the model from the raft easily. Then you can carefully remove the raft from the bed. This way you don't have to try to avoid damaging the bed and the model at the same time.

Stick with ABS. Its a better quality plastic.

I have solved another problem with printing in ABS which I will describe later.

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

Post by SimonWood » Fri Feb 25, 2022 11:09 am

Trevor Thompson wrote: Thu Feb 24, 2022 9:38 am Always lift the model 1 mm off the bed before adding supports.

Then when the print is finished you can separate the model from the raft easily. Then you can carefully remove the raft from the bed. This way you don't have to try to avoid damaging the bed and the model at the same time.
Thank you - I have reprinted the inner frame using this tip and the damage is much more minimal (and easily repairable).

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

Post by Trevor Thompson » Tue Jul 05, 2022 9:36 pm

I have done some more on the boiler.

The inside parts of the two tubes have been ground down to allow the flanged end plate to slot in:
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The flanged end plate is finished, and drilled and it fits (where it touches):
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The large hole is for the burner tube, the small one for a stay, and the other for the steam take off. Yes there are gaps at the sides - but the curved parts which fit properly were silver soldered. Then it was pickled to clean the flux off and the gap gently closed up with a hammer. The sides were then silver soldered:
IMG_2265.JPG
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I think that looks like a good soldered joint. So on to making the front flanged plate.

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

Post by Old Man Aaron » Thu Jul 07, 2022 11:48 am

Beautiful work as always, Trevor! :salute:

This loco really is something special.
Regards,
Aaron - Scum Class Works

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

Post by Trevor Thompson » Thu Oct 20, 2022 8:03 pm

I'm back to working on this one again. I think it is time to see if it can be made to work.

The boiler is finished, a second flanged plate for the front end, the tube for the burner inserted, the stay in, and the bronze bushes in place. I have made up feet to support the boiler clear of the plastic footplate. All soldered up ready to pressurise it to see if it holds water:
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You can see the PTFE top hat bushes between the boiler feet and the footplate in the first photo. I am hoping that there will be enough room between the motor and the boiler to get the jet out when it gets blocked.

I have drawn up the bodywork and printed out the parts. It is s strange looking beast for a steam locomotive!
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The body is just sitting there loose at the moment. I wanted to get some sort of attempt at the bodywork so I could make sure that I was fixing the boiler in the right place. I think some adjustments will be needed for the smokebox end of the body to make sufficient clearance for the flue.

And that is 4415 sitting in the background - which shows the similarities and differences between the two locomotives.

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

Post by SimonWood » 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?)

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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!!!

Trevor

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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.
Regards,
Aaron - Scum Class Works

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