Thin walled frames.

The prototype frames of a loco I am designing has each frame made of two 1" plates with a 1" gap between them with spacers at certain points. Scaled down to 3 1/2" gauge would give frames made of two 1/16" plates and a 1/16" gap between them.

Would these be strong enough or should I make the frames from 3/16" plate and forgo the gap.

I don't "do" locos, Eric ... but that's an interesting general question.

The stiffness [which is not quite the same as strength] should be very similar, and there may be manufacturing conveniences.

MichaelG.

Solid would have the advantage of being a bit heavier so increase tractive weight which depending on teh loco may be an advantage. Are ther any screwed fixings that go into one plate only? if so 3/16" would give good depth of engagement compared with 1/16"

There are no fixings that go into one plate . The mass of the cylinders/steam chest would be at the front of the loco (when are they not) providing weight over none driven wheels with the drive wheels towards the rear of the loco adjacent to the fire box.

Edited By Eric Cox on 02/01/2017 11:08:04

Looks like the frames will be very much on show so may be better to stick with the two 1/16" ones and spacer

What a fascinating loco! I wonder what the point of the double frame was? I know Jenny Lind had partial double frames with the front and driving wheels between the frames. I also seem to remember that sandwich construction with wood between 2 steel plates was also used. What sort of valve gear did it use?

Please keep us informed of progress.

Cheers,

Rod

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Rod,

I thought I had made that reasonably clear in my first response to Eric:

"The stiffness [which is not quite the same as strength] should be very similar, and there may be manufacturing conveniences."

Modern manufacturing [Aircraft; Caravans; Lightweight Doors, etc. etc.] uses comparable techniques.

If the prototype used 1" thick plates instead of 3" thick plates, I would assume this provided a lot of the aforementioned manufacturing conveniences. [and should probably be carried-over to the model in honour of the designer's sound engineering principles]

MichaelG

It doesn't have any valve gear and the prototype could only travel forwards.

If you have great confidence in your machining abilities you could use 3/16" and put a thick groove around the edges, even the cutouts with the right sort of cutter.

N..

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But then it would be an 'image' of the original ... not a model.

MichaelG.

But how many working model boilers are there that are NOT an "image" of the original?

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I neither know, nor care, Brian

My point is that the style of these frames is a defining feature of this locomotive.

... as I said originally, I don't "do" locos.

[and you have highlighted one of the reasons that few of them interest me]

MichaelG.

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I will bow-out of the discussion now.

Eric, do the cylinders pivot slightly as it looks like they would need to in order to keep the piston rod from binding up as the crosshead guides are not inline with the cylinder.

As Rod says it looks an interesting project, I found a couple more images on google that are a bit better than the sketch. Do you hope to have it pull you around the track or will it just get run on a test stand, if the latter then there should not be an issue with frame rigidity.

J

I would make a set of dummy side frames and do some basis testing on them. Just a couple of straight 1/16 strips would do.

Looking again I see the cross head guides are inclined to match the cylinder

I thought at first that this was a contender in the Semmering Trials-

https://en.wikipedia.org/wiki/Semmering_railway#The_Semmering_trials

-but I see it is a slightly later build.

It's still really nice to see an early locomotive being built in miniature; would you keep us posted on your progress please Eric? No pressure or anything!

Regards,

John.

I'll keep you posted but it will be a while before I cut metal.

" If you have great confidence in your machining abilities you could use 3/16" and put a thick groove around the edges, even the cutouts with the right sort of cutter."

Don't you mean 1/16" cutter.

I think Neil was suggesting using 3/16" plate and then simulating the gap buy running around the edges with a 1/16" wide woodruff or tee slot type cutter to create a central shallow groove.

Why would you not make this from three layers of 1/16" MS?

Presumably one could invisibly rivet the three together to avoid any hassle, but the middle piece would have a different profile to the outer ones.