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Discussion in 'CAD Corner' started by mickoo, 11 March 2014.
Thanks Steph - I'll check with them (PPD).
The limitation on the etch feature size has to do with the thickness of the resist. Most etchers use a film resist, which is relatively thick. There are liquid resists but only Chempix of the etchers used by modellers used them. Probably some of the engineering etcher will use liquid resists but they will be very much more expensive than PPD.
I don't think the thickness of the line will make a difference if the phototool is made by a photoplotter. Instead draw the piece you want at the size required +/- the etch tolerance. That really shouldn't fail.
Many thanks John.
I would say that all the information you might want on drawing tolerances is contained in Mike Clark's article in MRJ 228 pages 18-25.
That's what we were presented with on Alan Buttler's course at Missenden Abbey and it has worked well enough on a couple of 4mm etched locos and a few 0gauge Mk1 derivatives.
The only issue I might have with the article is that Mr Clark doesn't seem to like 2D CAD very much and prefers to use coloured pens but apart from that , the info in the article works.
I managed to get hold of a copy from the wonderful GW Watts at Reading last weekend. It’s certainly useful, especially combined with some of the web resources already quoted. Thanks for the ‘steer’!
Apropos of nothing whatsoever, I was speaking to Piers at PPD this morning regarding minimum thinness of box to half etch.
I am doing some new body sides for an OO scale Pullman bar car which has the vertical "washboarding" below the waistline. PPD's max camera resolution for 12thou NS [0.3mm] will allow them to half etch rectangular boxes [i.e., a fill box] whose walls are 0.13mm apart. Whilst clearly that is no use as a 1/2 etched "line" for folding purposes, it will certainly work as a representation of 4mm Pullman whimsy.