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problems making wagon brakes

Posted: Mon Apr 08, 2019 5:10 pm
by andrewnummelin
At present I'm slowly making a model of a Rhymney Railway brake van and I've hit problems with the brake gear. Unfortunately there's no commercial product that I'm aware of that is a close match so it will have to be scratch building. (For a one off I think the costs of designing and etching one set of gear would be excessive and I think the components are too fine to consider 3D printing.)
1. operating rods are thin single strips with forked ends - so tedious fine metalwork, but I'm not confident I'll be able to drill the ends to pin things together. The V irons are wider than normal PO wagon ones but I think these should not be too difficult to fabricate, but getting the inner one properly lined up may not be simple.
2. pivot for the lever connecting to the brake column fouls the axleguard and springing etch (Masokits) so may be replaced by a blob of epoxy putty
3. the real problem is how to make the brake hangers - I guess the prototype were a casting but I haven't a clue how to achieve this in 4mm scale.

I hope the following illustrations will show the difficulties. If anyone has any ideas on how to approach these I would be extremely grateful. (I've rejected advice received so far - Punch's to persons about to get married and my wife's to take up cross stiching...)

brake0.png
brake0.png (114.73 KiB) Viewed 1295 times

brake1.jpg

brake2.jpg
brake2.jpg (300.05 KiB) Viewed 1294 times

Re: problems making wagon brakes

Posted: Mon Apr 08, 2019 11:37 pm
by David Knight
It depends on how fine a set of files you have but filing from the solid strikes me as being a possible way forward. I would proceed as follows:

Mark out all holes on a suitable piece of brass stock and drill

With magnification, fine files, possibly a fine bladed jeweler's saw and infinite patience remove stock to suit.

Do not remove from the parent material until the last possible moment in order to make holding the work possible.

Offer multiple sacrifices to the GCG before starting.

It might also be possible to make some of the bits up from plastic section material but the strength would be questionable.

Hope this helps.

Cheers,

David

Re: problems making wagon brakes

Posted: Tue Apr 09, 2019 7:36 am
by nigelcliffe
I wouldn't rule out 3D printing. I've been experimenting with iMaterialise.com, and their stainless steel option. Main cross-section limit is about 0.5mm by 0.5mm (can be less in some cases). Detail is much finer than that. Provided you can keep the total volume of component and supporting/surrounding sprues within reason, the price doesn't run away. One of my friends has produced connecting rods and other chassis parts for a working 1:160 scale narrow gauge locomotive through this method.

Nigel

Re: problems making wagon brakes

Posted: Thu Apr 11, 2019 1:30 pm
by andrewnummelin
Thanks for the encouragement.

David, I have the tools but these days I doubt whether or not I have the dexterity needed - I’ll have a go.

Nigel, at first glance a minimum thickness of 0.5mm seems to much for most bits of the brake gear but I might give it a try. I have another project involving unusual cross heads and guides and for this 3D metal printing may well be very interesting and I had not considered this technique before. Study is called for over the next few weeks.

Re: problems making wagon brakes

Posted: Thu Apr 11, 2019 1:51 pm
by Crepello
nigelcliffe wrote:I wouldn't rule out 3D printing. I've been experimenting with iMaterialise.com, and their stainless steel option. [...] One of my friends has produced connecting rods and other chassis parts for a working 1:160 scale narrow gauge locomotive through this method.

Interesting! Are there any photos in the public domain?

Re: problems making wagon brakes

Posted: Fri Apr 12, 2019 8:14 am
by nigelcliffe
Crepello wrote:
nigelcliffe wrote:I wouldn't rule out 3D printing. I've been experimenting with iMaterialise.com, and their stainless steel option. [...] One of my friends has produced connecting rods and other chassis parts for a working 1:160 scale narrow gauge locomotive through this method.

Interesting! Are there any photos in the public domain?


Not that I'm aware of.

Re: problems making wagon brakes

Posted: Fri Apr 12, 2019 10:07 am
by Guy Rixon
The problem part of this brake hanger, from the point of view of printing, is the 0.75" flat bit. Everything else can be brought (just) above minimum thickness for resin-printing, or is invisible and can be left off:

    0.5" flanges that wrap round the middle bearer: invisible, leave them out.

    Fork that spans the back of the brake block: to fine to print as separate part, but possible, I think, as a hole in a solid part if the shoe is printed with the hanger.

    0.5" trunnions in which the hanger swings: too fine to print to scale, but thicken the top of the hanger slightly and they would go. This thickening would not easily be seen.

    1" pin in the trunnions: too fine, but could be thickened to 1.5" or 2" without looking too bad and then I think it would print.

For the thin, flat part, it would might be possible to print it thicker and then to file back the flat part to nearer scale. This would have to be done very carefully, but seems possible.

Re: problems making wagon brakes

Posted: Sun Apr 14, 2019 7:44 am
by andrewnummelin
Guy,
Thanks for the suggestions that I’ll study carefully. I think your approach to 3D printed brake gear is great for working layouts, but may be a bit limiting for “glass case” models.
By the way, I can’t remember if you put the information in one of your posts, but how much clearance do you plan between wheel and brake block?

Re: problems making wagon brakes

Posted: Sun Apr 14, 2019 8:42 am
by Guy Rixon
The clearance between blocks and wheels in resin-printed brake gear can be whatever one wants, given that the prints are dimensionally accurate. Shapeways prints seem to be accurate. I've tended to larger-than-scale gaps to accommodate variation in wheel sizes (e.g. AGW are slightly smaller than Exactoscale IIRC) and for the axle-ends wandering a little in the cones if the end float is not perfectly set. It would be possible to print for scale gaps, which means no working clearance at all, in a practical model and to require the builder to thin the blocks to suit.