Coach Building in 1:32 Scale

[JimG]

I've started building a rake of 48ft coaches in 1:32 scale using styrene sheet. Basically I use the David Jenkinson method of construction with and inner box holding the external detailed sides. But the main difference from his methods is that I CNC mill all the exterior detail in one action on the outer sides. I'll start with a trial run I did last summer using a 48ft First as the prototype.

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This is a compartment machined from 80thou styrene sheet. Also drilled are all the pilot holes for door hardware - the missing third, lowest hinge socket has been added to my current output. The bolections are machined in situ and replicate the cross section that I gleaned from a good GA.

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On the rear of the side, recesses are milled behind the quarterlights to get the correct depth and also to provide a slot for the glazing material.

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Closest to the camera is a part of the machined inner side which forms the side of the Jenkinson box. This is machined from 120 thou styrene and includes the recesses to hold the glazing as well as the raised area to support the outer side with tumblehome.

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These are the parts for a complete side - three outer parts and two inner parts. The joins on the outer sides are on door lines.. The offset inner and outer joins are to give the most strength in the sides. The main reason for machining the sides in sections is that my CNC mill can only handle parts up to around 250mm long.

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The tumblehome is heat formed in my oven - 25 minutes at 100C - and you can see the cross section of the outer and inner sides put together.

To be continued since I've fallen foul of the five image rule.

Jim.

[JimG]

...and now the completed side

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The side went together quite well although I ran into problems aligning the outer sides on the curve of the tumblehome since the heat forming is not an exact size. A slight variation in the curvature of the tumblehome gave some misalignment which was difficult to adjust, But I have since machined supports to go under each joint in the tumblehome to provide a definite support for the joint which should help alignment (I hope ).

And the recent work is...

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...enough outer sides to do a full first, a full third and two brake thirds. There's also a set of inner sides for the full first outer sides. This was about three weeks work on the mill - not quite nose to the grindstone all the time, but fairly continuous work throughout. It takes about two hours to do one outer section and about two and a half hours to do one inner part. At least with CNC machining, you can be doing something else while the machine is cutting - you just have to be around to change cutters when required and five cutters are necessary to do all the detailing on each of the outer sides.

The test full first side done last summer will become a test bed for painting and lining and I think I will need plenty of practice at that.

All the data was taken from the GA drawings available from the NRM/OPC Microfiche Archive and the chapter in Mike Williams' carriage book added a lot of useful detail. The temptation with that book is to go on and build a lot more coaches - maybe some fifty foot stock next. I even get the occasional thought about a Grampian rake. But it will take a year or more to complete the four 48ft coaches so my enthusiasm for more coaches may be tempered by time.

Jim.

[Dave John]

Impressive. At that scale they will be quite a sight as a full train.

[Alan K]

These look great Jim. I'm curious about the CNC process and how it's used on styrene. Is it done wet ie with a lubricant/coolant? Any chance of a pic of the machine?
And are you building a loco to pull them?

Alan

[JimG]

These look great Jim. I'm curious about the CNC process and how it's used on styrene. Is it done wet ie with a lubricant/coolant? Any chance of a pic of the machine?
And are you building a loco to pull them?

Alan,

The machine I have is the Sieg KX1

http://www.arceurotrade.co.uk/Catalogue ... y-CNC-Mill

When I retired, I closed my company down and after a good, final two years of trading, I had a bit of cash to splash, so the KX1 appeared. I had always been intrigued by CNC but the cost of the hardware had put me off previously.

The styrene machines dry but you have to use carbide cutters. These cutters do not create any heat so you get very clean cuts. HSS cutters do create heat and styrene tends to melt under the cutter and you get a poor finish. The main problem with styrene is that the material will tend to give and distort under heavy machining loads so you have to take things easy. But the finish can be superb.

I haven't started a loco for the coaches as yet. My first loco in 1:32 scale is a 782 tank and the work on that is still very much at the early stages. I always start with the wheels and here's the a wheel centre having being milled on the CNC mill.

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I particularly wanted to represent the much deeper wheel bosses of the Caledonian wheels since most available model wheels have much shallower bosses to allow for outside motion. I cut the centres from thick brass sheet since I find that's the easiest way to hold material.

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Here's the start of the machining if the rest of the six centres on the sheet. The bits of unmachined brass between the wheels will be used for other, smaller, wheel centres.

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...and all the centres cut. After release from the sheet, these still had to have the square section of the spokes scraped and filed by hand to get to the finished cross section and that work has now been done, but I don't have a picture handy.

As you might have guessed I've been thinking about something to pull the coaches and I think it will be a 4-4-0 of some sort. My other option is one of the larger 0-6-0s in passenger blue but I think a 4-4-0 might win the argument.

Jim.

[Alan K]

Thanks for that Jim - very interesting. Presumably you can also produce steel tyres for the wheels with the same machine, but will a lathe not be needed to form the profile? I expect the milling machine can be used for frames, connecting rods and all the body parts in the same way as an etched kit but in a much thicker gauge. I'm sure I'll not be the only one to want to see further progress...!

Alan

[JimG]

Presumably you can also produce steel tyres for the wheels with the same machine, but will a lathe not be needed to form the profile?

The tyres are produced in a more traditional way. I got an introduction to a local engineering workshop and acquired some short ends of mild steel bar of a large enough diameter. And a nice man in the workshop, with a very big lathe, put a big drill through the middle of the bits of bar to save me a lot of boring (both meanings of "boring" ) work in my much smaller lathe. I model to ScaleOne32 standards and I've got a Mark Wood profile tool to do the finishing work on the tyres.

I expect the milling machine can be used for frames, connecting rods and all the body parts in the same way as an etched kit but in a much thicker gauge. I'm sure I'll not be the only one to want to see further progress...!

I intend to mill the frames - probably using 36thou nickel silver. The only problem I will have is that my milling machine X travel is not long enough to cope with most loco frames so I'll have to put a join in, more than likely behind the rear-most driver where it won't be seen. I'll be popping up to Eileens in Gloucester in a week or two's time to get some more large sheets of styrene and I'll get a sheet of the 36 thou nickel silver sheet at the same time.

Jim.

[Alan K]

Jim
Excuse my ignorance but why can't you make up some kind of registration for the edge of your blank so that 'extra' length can be slid along into place onto the bed to continue milling the rest of the length to avoid having a joint?

Alan

[JimG]

Jim
Excuse my ignorance but why can't you make up some kind of registration for the edge of your blank so that 'extra' length can be slid along into place onto the bed to continue milling the rest of the length to avoid having a joint?

Alan,

That is a definite possibility but the table on the KX1 is not much larger than its X and Y travels and it would be difficult to clamp and register the material. I often have problems just clamping material to the table because of the lack of room. I have to admit that I did buy a rather expensive sheet of cast alloy to attach to the table to extend its size but I haven't got round to doing the work necessary to allow it to be fitted. I'm quite happy at the prospect of having a joint in the frames since I can hide it behind a driver, and if that driver is the rearmost, then the reinforcing work on the inside of the frames will be hidden by the firebox and cab.

You've now got me thinking about fitting that plate. The only problem being that it will take up modelling time.

Jim G.

[Alan K]

Jim
It would surely pay dividends in the long term. Wouldn't it allow you to do your coach sides in one piece?
Of course the situation wouldn't arise if you opted for a smaller scale !!

Alan

[Dunks]

The only problem being that it will take up modelling time.

Surely setting up better tooling and improvi the facilities in your workshop is a reasonable use of modelling time?

[JimG]

Alan, Simon,

There's a well known danger in model engineering (rather than model railways) that people can start making tools with their tools and that's all they ever do - with a workshop full of tools, jigs and fixtures. I had something like that a while ago when I machined some 7mm scale resin cast loco and coach bodies, when I spent more time designing and making the jigs and mounts to hold the pieces than on the actual machining itself. I also scratchbuild almost everything, and not very quickly, so I try to keep on the straight and narrow as far as possible - heaven knows there are more than enough other matters to divert me.

As for being able to do much larger parts, I have found that it is better to do the machining of smaller parts since if there is a problem you have only messed up on something taking, say, two hours to machine rather than twelve hours. Machining styrene can have its problems because of its inherent flexibility and I also depend on double sided tape to hold the material down, which can also have problems. I also model in S scale and I did set up to machine both sides of a 48ft coach in one go, with a machining time of around twelve hours and I did get the worst possible case of getting a fault in the final hour which meant scrapping the lot.

Tough forum.

Jim G.

[Alan K]

Re that well known danger, I'm sure you're right Jim. And its not just in model engineering: I also do a bit of woodworking, and have fallen into the trap of making jigs (eg for the router), some of which never got used but seemed a good idea at the time! And there are others that I don't remember what they were for....!
Just carry on with the good work and enthrall us with your progress from time to time!

Alan

[JimG]

There's been a good bit of progress on the seven compartment first.

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The body is built with the partitions fitted. I've just got to do a bit of finishing off on the corners between the sides and the ends.

I'm now looking ahead to the two third brakes that I will need for the rake - especially the making of the brake ends.

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This is about the sixth attempt to get something acceptable. The problem has been cutting the bolections. There has been no problem on cutting them on the sides, but the larger window openings combined with similar recesses on the rear of the ends to get the correct depth of glazing seems to have made the part a bit flexible. I suspect my spiral cutters are tending to lift the styrene because of the flexibility and I'm getting grooves around the bolections. the attempt above, which worked well, utilises three layers which allows the top layer to have a flat back which can be stuck down securely when cutting.

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A close up of the outer skin with the bolections cut.

I did similar Drummond ends in S scale but in that case I built up an inner frame from Perspex to supply the structure and the glazing in one hit. But I thought that there will be too much to see through the windows in 1:32 scale so I'm trying to make the interiors believable.

Jim.