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This Instructable shows how I replaced a broken picture frame glass with a sheet of transparent acrylic. This was prompted when the glass of a picture frame I valued much was broken when we were moving house last spring.

What we call acrylic is actually the synthetic polymer of methyl methacrylate. It is an excellent replacement for glass in a lot of situations, like the picture frame being repaired here. It has an impact strength exceeding that of glass (meaning it is less likely to shatter), and has only half the weight. Its only disadvantage here is, it is much more easily scratched than glass. See the Wikipedia article on Acrylic glass if you want more details.

WARNINGS
  • Cutting small pieces of acrylic is not particularly dangerous, but be careful using the cutter knife.
  • Cut acrylic may have sharp edges

Step 1: Tools and Materials

You will need tools to take apart the frame, and tools to cut the acrylic to size (unless you can get it exactly the size you want).

My frame didn't need any tools to take apart, so I'm only going to list what is needed to cut the acrylic.

  • Pen - any ball-point or thin marker pen should do
  • Ruler or straight edge - better if it is steel, but wood or plastic is OK
  • Acrylic cutter or craft cutter - use one strong enough for the job
  • Cutting mat - to place the acrylic on when cutting
  • Sandpaper - to smooth the cut edges.

Step 2: Disassembing the Frame

My picture frame was made so that the picture can be easily replaced, so the glass was easy to remove. This step will vary, depending on what kind of frame you have. In the worst case, it will be a wooden frame nailed shut, and you will have to extract the nails to get at the glass.

Step 3: Measuring the Glass and Getting a Replacement

Once the glass is removed, measure its dimensions (length, width and thickness) in order to get matching a sheet of acrylic. This will be rather difficult if the glass is completely shattered, in such a case, you can measure only the thickness of the glass, and measure the inner dimensions of the frame.

Once you know the dimensions, get a sheet of transparent acrylic of matching size. If you like, you can even use a tinted acrylic. Make sure the thickness is as close as possible. If it is too thick, you won't be able to close the frame, and if it is too thin, it will rattle around in the frame, and the picture wont be held firmly.

Step 4: Cutting the Acrylic Sheet

Short lengths of acrylic can be easily cut by scouring the surface with a cutter and bending sharply.

Note: Do not remove the backing film when cutting, keep it on as long as possible to avoid scratching.

First, place the sheet on the cutting mat, and draw lines to mark where it is to be cut. Then, using the ruler and cutter, scour the surface along the line. Apply medium pressure to the cutter, do NOT attempt to cut deeply in one go, scour it 7 to 8 times until the cut is deep enough. One surface should be enough, but it is easier to make a clean cut if you do both surfaces.

CAUTION
Extend the cutter only one notch as shown, or you will snap the blade and injure yourself

Once the scour marks are made, place the cut on the straight edge of a table or workbench, so that the part to be broken off is overhanging the table, and place the ruler on top of it. Then, while firmly holding down the portion on the table, sharply push down the overhanging portion to break it along the cut.

Step 5: Cutting Off Short Edges

If the section to be cut is very short, as was with one side of my acrylic sheet, you will need to clamp it in order to break off. This is fine if you have a clamp, but I didn't, so I wedged the short side in between a door and the door-frame.

CAUTION
Be careful not to cut yourself on sharp edges when breaking off the acrylic

Step 6: Smooth the Edges

The freshly cut edges of the acrylic are rather sharp, and need sanding to finish off. Use a 200 to 400 grit sandpaper for the purpose (a rougher grit will be needed if you messed up when cutting the sheet). Lay the sandpaper on a flat surface (the cutting mat is ideal for this) and sand the straight edges while holding the sheet at right angles to the paper. Tilt the sheet slightly and sand again lightly to soften the edges.
Sand the corners also by holding them pointed down towards the paper and sanding lightly.

CAUTION
Do not try to scrape the edges with the cutter. I tried this once, and the sheet slipped and got scratched beyond recovery.

Keep the backing sheets on in this step, it is not clear in my photographs (because the backing was transparent)

Step 7: Insert the Acrylic Into the Frame

When you have finished sanding, take off the backing sheets and put the acrylic in the picture frame. Close the frame, reversing what you did when taking it apart, and you are done!

Step 8: Further Information

There are many ways to cut acrylic (or other types of plastic) sheet, you can see them here on this Instructable video. My method is the simplest one, which can be achieved with tools lying around the house.

This site also gives information about acrylic, and how to work with it.

Acrylic can be used in many more situations than mere picture frames, just use your imagination!
This is really helpful! I am hoping to cut down some big poster frames to fit some cheap art that I have. Thanks!
Glad to know you found it useful. Thanks for the comment!
gmarrs, Thanks for the information. I plan on cutting some for the old frames I found.
I like the idea of clamping the sheet in a door frame. Thanks.

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