The Framers Forum

Hi all, just wondering what peoples opinions are on whether to use glass or pespex for a big (40x30") frame? Where is the cheapest place to get perspex cut to size? Seems to be more expensive than glass.

Is there a way of strengthening the corners on such a large frame apart from biscuits/proper joinery? I have glued and underpinned five times in each corner. I think I have seen bracing bars across the backs of frames before. Any ideas would be great.

Cheers,
Gareth

I wouldn't think twice at using glass.

If the frame is substantial enough gluing and underpinning is fine, if you don't think it is you could use a strainer to take the weight, the frame would then just sit on the strainer.

That's not big and smaller than a standard sheet of glass so no problem. As above though as long as he frame is substantial enough and well made then it's not a problem but if it wasn't I would be just as much of a problem for acrylic as glass.

How big is the frame profile? If there is enough meat in it to give a decent gluing area and your cuts are true then It's no problem. If it's a bit skinny then you might have to add extra strengthening measures.

One thing you could do is add 3" steel 'L' mending plates on the corners. A bit of belt'n'braces never goes amiss IMHO.

Plastic glazing is used more in situations where safety regs call for it. Schools and other public places. You don't really save a lot of weight at this size as generally you have to use thicker glazing to maintain rigidity which tends to negate any weight advantage.

Glass is tougher than you think. As long as it's cut clean with no chips on the edge and there are no lumps and bumps under the frame rebate, 40x30 is nothing to worry about.

Please excuse my ignorance but what does a strainer look like?

Nice Robo..

Wish I had made as many frames as visits to the loo! I 'd be a millionaire.

You can normally use 2mm float glass for sizes up to 1 square metre. (I say normally as public places can result in added legal requirements). If you wanted to use perspex for that sort of size you would need perspex of adequate thickness to avoid any concerns about the perspex not remaining flat. I can't tell you what thickness this would be, as I always phone up Wessex and ask them.

So for the sake of example if we said 4mm perspex (just an arbitery thickness you understand), then 4mm glass would still be cheaper than 4mm perspex and 4mm glass is very hard to break. So don't automatically assume that perspex is always required.

If the picture will hang in a public place then there are legal requirements to consider and the choice is then between laminated glass, or Perspex. As always one will be a better price than the other, so talk to your supplier before you decide.

I quite often make frames of this sort of size with Simons Oak/2 and 4 wedges in each mitre and it is more than strong enough. If it is only an obeche moulding, it will need to be of an adequate size for the neccessary rigidity.

On your basis of using 2mm float upto 1sqm then why at 0.774spm are you sugesting 4mm glass it simply doesn't need it. Even in public areas unless requested I would use glass on that size, its only on pieces larger than a standard sheet of glass or those which are box frames or with a spacer would I use acrylic and in most cases i use 5mm as it is very rigid.

Graysalchemy wrote:are you sugesting 4mm glass

No, he used an arbitrary thickness to make a point.

Gotcha

Not your average framer wrote:If the picture will hang in a public place then there are legal requirements to consider

What are these and why don't our glass suppliers make us aware of them..... not least of all to cover themselves?

I have been supplying frames for public spaces for nearly 20 yrs and 99% of my work goes out with glass. It is only the larger stuff which I insist on being perspex. Very rarely does an architect or designer specify it. The only times I do get asked is for schools hospitals and Prisons .

Mirrors is a different mater they are always specified as being safety backed by the designers. Funny how they do for one and not for the other.

4mm glass was not a recommendation, I was merely pointing out that thicker glass is usually lower cost than perspex and in some cases the thicker glass is so much more difficult to break that it could be considered as a possible safety improvement when compared with thinner glass.

Buildings where the level of public access requires mandatory fire inspections can have legal requirements specified by the fire inspection officer and I have encountered this where large frames with normal glass are not permitted in passage ways used for fire exit routes.

In some cases insurance companies will stipulate their own requirements, although I have not to date encountered this myself. The mention of architects, or designers is a new one to me, so I don't know if this has anything to do with building regulations, or what.

I've always considered this whole area as somewhat difficult to adequately address and there are times when I suggest a total overkill solution, so that it can be recorded that the customer rejected by original suggestion, so that there is no come back at a later date.

I use theplasticman for my cut to size acrylic. Although the postage us quite expensive I find the price pretty keen especially for multiples.

I'd use glass at your size as long as you haven't got a glass spacer, then I'd use acrylic.

A small note regarding perspex/acrylic.
It expands a lot more than glass. So ensure there is breathing space in the rebate.

The workshop done work for a client in Ibiza, left the the UK fine but once in the warmer climate the very large acrylic sheets expanded so much that they popped all the corners on the frame.

Mark most of my work goes in new builds or refurbs hence the involvemnent of interior designers and architects. The point I was making it is their job to know what are the legal requirements for what is to be used in a public space and any insurance stipulations etc should also be known before they start the design.

Your statement about legal requirement seemed to come across as a bit of a sweeping statement as if you knew what the legal requirement was as with the case of mirror glass.