when does glass become too heavy?

[AJP]

hello everyone

i have to frame a full-size OS map but the client wants "thinnest moulding possible".

is there a scientific method for working out glass weight to moulding width? at what point do i opt for acrylic?

any wise words gratefully awaited!

AJP

[Roboframer]

glass to moulding formula.jpg

[prospero]

You forgot to carry the 3 John.

The best way IMHO when you have to use a minimal frame on a heavy item is to make a sub-frame out of timber that goes behind the backing. The frame has to me deep enough to cover the edge of this frame though......

Say the glass size was 3'x4'. Get some 4" x 0.5" timber (or thereabouts) and make a 4'x3' frame. Plenty of glue area. You can beef it up as much as you need to using biscuits in the corners or even make half-lap joints if you are kitted up for carpentry. The back/art/glass lays on top of this frame. The outer frame can be as diddly as you like as long as it has a deep rebate. It serves no part in the strength of the package: it only holds the sandwich together. You can even fix small mirror plates between outer and sub frame to stop in pulling away when people try to pick the frame up by the outer frame. The hangings go on the subframe, or you can hang the whole thing on a wall batten that fits under the sub frame.

That's how I did my bathroom mirror anyway.

[Jonny2morsos]

Have you considered an Aluminium frame?

[JFeig]

I simply tell my clients...... "In order to guarantee the engineering of a frame that large so it will not fall apart, I have to use a frame that is --- X ---" A superstructure skeleton behind the visible portion of a frame is great engineering. It hides the real strength of a frame. They can either be screwed or nailed to the visible frame. I call that inner skeleton a "strainer frame" or "internal frame".

[AJP]

thanks everyone - good advice, and that equation will come in handy in future ...