Shaving a little off too-tight acrylic?

Echobelly

CGF, Certified Grumble Framer
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Just had a customer bring in an oversize print that had fallen off the wall and all four corners of the frame broke. I was able to shave a paper thin slice off each miter to give me a clean surface to glue, but was concerned this would shrink the frame just enough to make the customer's acrylic too tight. The print was framed with spacers so the acrylic was cut pretty tight. Luckily, it did fit back together fine, but I was wondering if it hadn't, how to trim just a hair (maybe 1/16") off acrylic. Scoring it would take too much. All I could come up with was taking it out to the sidewalk and taking a belt sander to it, but I thought there must be a better way. Any ideas?
 
Acrylic can be wet sanded. Messy but it gives a better result than dry sanding. Of course the best result is with a no-melt saw blade. If you have a table saw, a 7 1/4" saw or a cordless saw, they make no-melt blades for all of them.
 
It would probably be more cost effective to put in a new piece of acrylic, unless you have the set up already and it is easy to shave off a tiny bit of the acrylic.
Since I don't, I would have charged for another piece of acrylic
 
A good straight edge, and a small edging router with a straight cutting carbide bit. If you have a router table, that can work as well.
You will need to ease the edges after as they will be sharp.
Use strips of mat board so the router foot doesn't ride on the face of the acrylic, or, if using a router table, tape mat to the side that will be on the bed of the table.
 
It would probably be more cost effective to put in a new piece of acrylic, unless you have the set up already and it is easy to shave off a tiny bit of the acrylic.
Since I don't, I would have charged for another piece of acrylic
I didn't have that option, the customer needed it for Christmas and the acrylic I'd need to replace it would be 48x90, not a size we keep in stock.
 
A good straight edge, and a small edging router with a straight cutting carbide bit. If you have a router table, that can work as well.
You will need to ease the edges after as they will be sharp.
Use strips of mat board so the router foot doesn't ride on the face of the acrylic, or, if using a router table, tape mat to the side that will be on the bed of the table.
Good idea! I actually just bought an edging router to cover a counter with formica. That should work.
 
Another option with the router is to use a flush trim bit and clamp a piece of Mdf with a good edge on top as a guide. The router slides along on the Mdf and you don’t have to freehand a straight line. I keep an 8”x96” piece on hand for just such an occasion.
 
Get a straight edge carbide tipped router bit with a bearing that matches the cutting diameter. Clamp a straight boad onto the bottom of the acrylic set back as far as you wish to trim off. Adjust the router making sure the bearing hits the clamped bard and the cutting edge is cutting the full thickness of the acrylic. Run the router at top rpm's and slowly feed it along the edge. To avoid surface scratches it is a good idea to put tape along the acrylic surface that the router base is sliding along. Done this numerous times. Works perfectly.
 
I had to do that once. I used a Japanese pull-saw, which has a narrow kerf. This type of saw goes through wood like a knife,
but it struggled with plastic. Took me ages. Easier to widen the rabbet with a Dremel. :rolleyes:
 
Hi, Echobelly. How wide is the frame rabbet? If this comes from a 48 x 90 sheet, it needs enough space for significant shrinkage/expansion. Someone can correct me on this, but depending on relative temperature change, I think that a piece that big can change as much as 1/4". If the rabbet was only a quarter inch, there's a chance it could happen again. I'm sure that neither you nor the customer want to mess with routing out the moulding, but if there are future problems and they want to give it more room, perhaps adding a sturdy fillet and giving the acrylic more wiggle room would help. I'm also curious as to what kind of spacers were used. Were they glued on mat strips with foam backing, or plastic spacer strips that were butted, end to end? And if they were butted, were they solid strips, or hollow ones that had something hidden and glued inside to 'bridge' the joins? Thanks.
 
Hi, Echobelly. How wide is the frame rabbet? If this comes from a 48 x 90 sheet, it needs enough space for significant shrinkage/expansion. Someone can correct me on this, but depending on relative temperature change, I think that a piece that big can change as much as 1/4". If the rabbet was only a quarter inch, there's a chance it could happen again. I'm sure that neither you nor the customer want to mess with routing out the moulding, but if there are future problems and they want to give it more room, perhaps adding a sturdy fillet and giving the acrylic more wiggle room would help. I'm also curious as to what kind of spacers were used. Were they glued on mat strips with foam backing, or plastic spacer strips that were butted, end to end? And if they were butted, were they solid strips, or hollow ones that had something hidden and glued inside to 'bridge' the joins? Thanks.
The actual frame was 42"x45", not huge, but necessitating the extra large acrylic. The strips were wood, finished to match the frame. Luckily I was able to pry them out without them breaking, they had been attached with rubber cement. The piece had been framed in the 80's, the frame was flimsy, and the materials weren't archival (plywood backing which at least gave it some strength). The print (valued at 20-30K) had been adhered to the wood pulp mat board with double-stick tape all around. I expressed my concerns to the owner, but she said she just wanted it put back together like it was so she could hang it for Christmas, and would have a conservator look at it later.
 
The actual frame was 42"x45", not huge, but necessitating the extra large acrylic. The strips were wood, finished to match the frame. Luckily I was able to pry them out without them breaking, they had been attached with rubber cement. The piece had been framed in the 80's, the frame was flimsy, and the materials weren't archival (plywood backing which at least gave it some strength). The print (valued at 20-30K) had been adhered to the wood pulp mat board with double-stick tape all around. I expressed my concerns to the owner, but she said she just wanted it put back together like it was so she could hang it for Christmas, and would have a conservator look at it later.
Makes sense. You might get comments about how you should have insisted on restorative measures, but in reality, that's not what she wanted. You gave good advice, did what she asked, and thankfully, it wasn't damaged while in house.
 
I'm late to the party, but a block plane takes care of this really quickly and with much less mess than sanding. Use one you don't care about.
Good to know... I've saved myself once before by going nuts with a woodfile, but it looked like Christmas afterwards.
 
I'm late to the party, but a block plane takes care of this really quickly and with much less mess than sanding. Use one you don't care about.
I've used the modern equivalent of a block plane (jointer) with great success before. More to make the edge look pretty after cutting it with a table saw, but same principle.
 
I just finished taking 1/8" off 2 pieces of acrylic . Scored it 6 times with the Fletcher plastic cutter, then used the glass nipping pliers to snap the little buggers off. If you nip it in the right place, close to the previous nipping, the result is pretty smooth. I am very glad it worked. I had it delivered, pre-cut, and it was cut 1/4" bigger than the requested size. Whew!
 
I just finished taking 1/8" off 2 pieces of acrylic . Scored it 6 times with the Fletcher plastic cutter, then used the glass nipping pliers to snap the little buggers off. If you nip it in the right place, close to the previous nipping, the result is pretty smooth. I am very glad it worked. I had it delivered, pre-cut, and it was cut 1/4" bigger than the requested size. Whew!
I've done the same, but flipped the acrylic over and scored the opposite side 6 times and the bead just peels off with finger pressure. We actually have to do this fairly often since the stock sheets of acrylic tend to come 1/8-1/4" over sized, and we do a fair amount of pieces in the 48" X N sizes.
 
What a PITA.
:coffeedrinker2: Rick
It doesn't have to be. They make no-melt plastic blades for cordless/corded circular saws. Or if you want to go the full monty.........

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This is 100% dedicated to cutting acrylic; both the panel saw (cutting down 4x8 sheets) and the table saw for precise cuts. I can trim 1/64' with ease.
 
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I have shaved acrylic with a hand planer. There's some mess involved. A plexi blade on a table saw would be option #1, if possible.
 
Would love to have a panel saw, but no can do.
:coffeedrinker2: Rick
I built that one from a kit from Rockler circa 2001. Sadly it is no longer available.

The kit consisted of the metal parts and plans for all the wood parts. I used high quality plywood and some cherry or walnut to build it. It has moved twice since I built it. I modified it a bit so that the circular saw can be swapped out and have two saws for it; one dedicated to acrylic and one for wood. I seldom use the wood one.

While a little bit different than mine, I found this one: https://www.widgetworksunlimited.com/Panel_Saw_Deluxe_Free_Standing_Kit_p/ww-panel_saw-dfs.htm Deluxe Panel Saw Kit - Free Standing Version - Build your own panel saw accurate to 1/32''. Cut wood and plastic sheet goods quickly, accurately, and safely. WidgetWorks Unlimited This kit includes all the wood and is $740. I don't remember what I paid for mine but being the metal parts only, it was far less than $740.

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I love all of these tips on shaving acrylic but I probably would have considered running the moulding through a table saw to make the rabbet a 1/16" wider before re-joining it.
 
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