window frames

Need to make some brass window frames for a 1-1/2in scale loco, they will be hinged to open, and will have clear acrylic for the 'glass'. Windows are rectangular (about 50mm x 35mm) with rounded corners of about 5mm radius, and the outside face of the frame would be about 2mm wide. Any suggestions on how to do this? I thought of using some Code100 model railway rail but it's a bit hard to bend to such a small radius without heat and i'm not sure how much heat to use. All suggestions welcome!

... Sounds like a 'mill from the solid' job to me.

But that would depend on your tools, and your preference.

MichaelG.

Depending on a number of factors you could also consider lost wax casting.

You could try slitting thin brass tube along one side, annealing it, and forming it mostly by hand.

Geoff,

Could you post a sketch of the window, please ?

MichaelG.

Thanks for the feedback. I don't have suitable milling facilities or the necessary raw materials for that option, so i need to fabricate from stock sections.

After looking a bit more closely at the drawings and comparing them with photos, it seems like the window openings in the cab sheets have rounded corners but most of the windows don't.

I could therefore probably make them up from straight sections and just add infills in the corners for those that are rounded. A photo of the windows on the actual loco is provided below:

I'll have a go at making them up using the materials i have and see how they look. Will post another photo if it works

Geoff,

Please disregard this if you think it sacrilegious, but:

Have you considered using plastic sections to build the frames ?

**LINK**

http://www.model-dockyard.com/acatalog/Plasticard_I_Section.html

MichaelG.

Or 3D printing them

Thought about plastic sections as i have plenty of prior experience using plastic in scratch-building model railway stuff, but don't think it would be robust enough to survive long, hence original thought of using Code 100 rail with the flat-bottom being the outside, the rail head the inside, and the acrylic sheet sitting within the recess between rail head and base.

Did not consider 3D, there are few places in this part of the world offering this service in metals, but a friend has recently had some small brackets made in brass by this method so i'll check it out.

Thanks all for the feedback.

I'll make myself a hostage to fortune, just starting a print of a 35 by 40mm frame, 4mm thick, 5mm radius corners for 2mm acrylic. Obvioulsy you can't fit acrylic into such a frame without breaking it... it will be interesting if the unsupported top run prints OK, but the main interest is the bottom half, as obviously the way to do a usable frame would be two halves with open tops that you fit together around the glazing.

I imagine a number of practical problems with such thin sections, not least that very thin sections can be printed as two parallel surfaces with no fill in between, I'm not sure that 3D printers are normally expected to do thin sections. But it's fun to explore the envelope and we'll see how it goes.

In the past I have purchased brass section at very small cross sectional sizes from Mainly Trains mainlytrains.co.uk but they are sadly no longer trading. According to the labels on the bits I have, they seem to have been supplied by specialshapes.com here.

Ed,

Well as I feared, 1mm is too thin for wholly reliable sections, at least with this printer and PLA, but not far off succeeding.

You can see that (a) the bridge at the top was too long and (b) the 1mm thick section of the sides was OK on eth long runs at the bottom but caused some upset on one side of the uprights.

I have had consistent results using 1.4mm though, but that would be too thick for your needs.

Neil

Nice try, Neil

Maybe worth getting a quote from somewhere like Shapeways

**LINK**

https://www.shapeways.com/materials

MichaelG.

Neil, I have no practical experience of 3D printing so maybe talking a load of rubbish But would it be possible to print the lower layers, stop the print and insert the acrylic window and then resume printing. The acrylic might support the final layers. Of course there is always the chance the acrylic would buckle with the heat I suppose. But I would be interested in your views.

Keith

It would work very well if you could be sure of pausing it at the right point - with the dremel you would have to guess it.

I've found another print with excellent walls just 0.8mm thick, but done at standard setting, but they were longer and not 'dead ends'. The test piece above has actually cleaned up OK except for the upper part, so as long as you don't mind a bit of manual finishing I think this approach would be OK. Laser sintered brass would be great though, if more costly!

You could turn up a ring in the lathe for the four corners and braze in straight sections to form the frame.

.

... Certainly a better bet than bending profile.

MichaelG.

You can get small square section brass tube from model shops, leastways you used to be able to.

Have you considered picture frame glass/