Help Framing a very large work with acrylic

EcoFrame

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Oct 23, 2024
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Christchurch, NZ
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Eco Frame & Mirror Company
Framing a very large Egyptian papyrus in to a 76 x 40" frame (1940 x 1018mm). At that size, I think acrylic would be better than glass due to weight and safety concerns. Will 3mm acrylic be too thin at this size? I can source 4.5mm acrylic but the price difference is enormous - $600 for 3mm conservation control acrylic or $6,000 for 4.5mm museum-grade acylic. Also, I've read that acrylic will expand and contract, will that make it unsuitable for a work this size? Any advice appreciated.
 
Welcome to the G.
Yes to acrylic.
3mm would work, but 4.5mm would be more rigid, so less bowing and distortion. Tough call there.
Acrylic does have a higher coefficient of expansion and contraction than glass and wider rebates with more generous allowances are recommended. At that size, off the shelf profiles will work, depending on the environment. Both temperature and humidity variations are in play. Environmental conditions are crucial to choices here.
 
To accommodate the greater expansion/contraction cycles for acrylic, you could use a standard moulding with a slip or fillet to extend the width of the lip.
 
"To accommodate the greater expansion/contraction cycles for acrylic, you could use a standard moulding with a slip or fillet to extend the width of the lip."

Yes, to this, it's also important to have a large lip on the moulding because acrylic is very bendable, flexible, and can pop out of the edge if mishandled.
 
You are not comparing identical products. "Conservation control acrylic" is the name of one manufacturer's product. There are other manufactures of Ultra-Violet filtering products.
 
You are not comparing identical products. "Conservation control acrylic" is the name of one manufacturer's product. There are other manufactures of Ultra-Violet filtering products.
Unfortunately, where we are based there are not many options. The customer is wanting UV-protection. I can't source conservation control in 4.5mm, only the museum-grade is available to us at this thickness, hence the big jump in price and why I was hoping we could get away with 3mm. From the advice I've had from my suppliers 2 out of 3 opinions said to go for the 4.5mm.

I read online that acrylic sheet can expand up to 6mm per linear meter. The rebate of the moulding we were going to use is only 6mm so I don't think this will work. Now the issue is finding a moulding the customer will like with a bigger rebate. A fillet would be an easy option but not the 'look' the customer wants!
 
Welcome to the G.
Yes to acrylic.
3mm would work, but 4.5mm would be more rigid, so less bowing and distortion. Tough call there.
Acrylic does have a higher coefficient of expansion and contraction than glass and wider rebates with more generous allowances are recommended. At that size, off the shelf profiles will work, depending on the environment. Both temperature and humidity variations are in play. Environmental conditions are crucial to choices here.
Thank you for the advice, very helpful!
 
Did you search for general industrial sources as used by display box manufacturers or just the picture frame suppliers?
The picture frame suppliers we have in NZ don't supply acrylic or even glass. I have contacted the acrylic display specialists around town, a specialty plastics importer, signage suppliers as well as our glass supplier who are stockists of the TrueVue range.
 
I read online that acrylic sheet can expand up to 6mm per linear meter. The rebate of the moulding we were going to use is only 6mm so I don't think this will work. Now the issue is finding a moulding the customer will like with a bigger rebate. A fillet would be an easy option but not the 'look' the customer wants!
If the moulding is wide enough, and not easily marred, another option is to rip out some width, to make a wider rabbet.
We use a table saw to do it, and I think Hubby also uses a planer, sometimes.
 
Hubby typically uses a table saw and prefers a square end on the moulding over a mitered end when ripping (provides a more reliable surface for pushing material through the saw - cut the miters after expanding the rebate). Hubby has also used a router table when Hubby didn't plan ahead well enough and needed to expand the rebate after the frame was joined. This technique can be more exciting.

Thermal expansion depends on the expected temperature range. Multiply the size of the acrylic in meters by the expected range of temperature in degrees C and multiply that product by .065. Answer will be in millimeters.

Thus, the greater the span of temperature to which the piece may be exposed, the greater the change in dimension you should expect.
 
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