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

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

MichaelG.

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

Or 3D printing them

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.

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

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

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

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

Have you considered picture frame glass/