# Jig Suggestion Please



## slackline (Jul 15, 2010)

I have a little different issue. I use my router for plastic work and am having a problem getting a straight edge on my finished piece... I bend acyrlic and when I do, it "flares" out on the edges of the bend. I need the edges to be very even and smooth so I can weld them to another piece of plastic. Does anybody have any suggestions for a jig that could help me?


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## Wood-Chuck (Aug 12, 2005)

Is there anyway you can bend it and then rout it flat? I really don't completely understand your problem - just guessing.


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## RJM (Apr 11, 2010)

slackline said:


> I have a little different issue. I use my router for plastic work and am having a problem getting a straight edge on my finished piece... I bend acyrlic and when I do, it "flares" out on the edges of the bend. I need the edges to be very even and smooth so I can weld them to another piece of plastic. Does anybody have any suggestions for a jig that could help me?


Without a picture, this is hard to address but assuming that the bulge is only on the concave side of the bend, you might be able to use a pattern bit (bearing on shank) in a router table with the bearing riding along the part of the edge that's still square. See picture of cross section below.


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## slackline (Jul 15, 2010)

Thanks for the input! Here are a few pictures to show you what I am talking about. The corner "flares" are the things that need to smoothed out so they can be glued. Sometimes they will flare out and sometimes they will flare in and sometimes they will do both with the inside of the bend going out and the outside going in...I hope that makes sense... The first one just shows what I am working with.


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## slackline (Jul 15, 2010)

Here are some pictures of the flares. Sometimes they bend in, and sometimes they bend out. I just need to have an even, smooth edge for welding so I have to clean up the edges. The first one shows the type of thing I am working with and the rest show the corner issue I am dealing with.


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## slackline (Jul 15, 2010)

I just uploaded and posted four images but when they didn't show, I realized they won't show because I still have under 10 posts...UGH.


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## jschaben (Jun 21, 2009)

slackline said:


> I just uploaded and posted four images but when they didn't show, I realized they won't show because I still have under 10 posts...UGH.


Hi Scott - Double ugh on the pics, they would help.
I don't know how you are bending it but wonder if you could design a "bending jig" that would hold that edge square during the bend. I don't recall ever having to address the issue, but then, I've never had to bend plastic very precisely either. :blink:


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## slackline (Jul 15, 2010)

I wonder if this will work:


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## slackline (Jul 15, 2010)

Well it didn't...but at this rate, I'll have my ten posts!


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## slackline (Jul 15, 2010)

Let's try this:


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## istracpsboss (Sep 14, 2008)

Ok, If I'm understanding it correctly,you want to clean up the edges?

Why not clean up as carefully as you can with a file one of your pieces, primarily to ensure flatness, then nest the next one of your pieces outside the other, using some thin card as a spacer, one piece say,1/2" above the other (depending on the size of your cutter). You could then use a bottom cutting pattern bit.The spacer is to keep the bit from scratching the master piece.

Does this make sense? I think you would need to keep your speed down, otherwise the plastic could melt.

Cheers

Peter


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## slackline (Jul 15, 2010)

That would work but the bends are not always exactly the same and I use a ton of different bending patterns. Some have suggested a horizontal mount but I've never used one of those and have no idea how they would help me...I'm sure they would help, I just don't know what bit or how to use the mount.


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## RJM (Apr 11, 2010)

slackline said:


> Let's try this:


I don't see anything except a red X. My company blocks sites like facebook, photobucket, etc (if I remeber, I'll look again when I get home tonight). I usually save (to my desktop) any picture I want to post, then upload it.


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## slackline (Jul 15, 2010)

Yes these are photobucket so they will probably be blocked.


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## bill strop (Oct 26, 2009)

Don't have a suggestion but an explanation. The plastic is of the same thickness on the inside as on the outside edges. That being so, when you bend it the inside radius, being smaller, must displace the "excess material somewhere. Therefore it "pooches out" and creates the flare. Short of sanding off the flare I guess you're left with paring off some of the inside of the bend area before making the bend or afterward.

Bill Strop


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## LexB (Apr 12, 2010)

slackline said:


> I have a little different issue. I use my router for plastic work and am having a problem getting a straight edge on my finished piece... I bend acyrlic and when I do, it "flares" out on the edges of the bend. I need the edges to be very even and smooth so I can weld them to another piece of plastic. Does anybody have any suggestions for a jig that could help me?


I have only worked with plastic a couple of times, so I'm certainly not even close to being an expert, but I would flatten it after bending using sandpaper attached to a flat plate (like using the "scary sharp" method to sharpen chisels and plane irons.)


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## almosta7ftr (Jul 29, 2010)

Hello Scott. About fifteen years ago, I worked for a company that built aquariums and filtration for the aquariums and I spent all day bending acrylic sheets. We used a custom router set-up for the job of trimming the bent sheets to final width. This was done specifically to elimiate the distortion created at the bend. If the pieces you are trimming are huge, like the aquarium stuff - let me know and I will take the time to describe the set-up. If your pieces are small, you might be able to get away with using a jointer, but that depends on whether your pieces are bent past 90 degrees.

Since I no longer work for the aquarium business, but I still tinker from time to time (too often if you ask my wife) - I have used the following technique with good results.

You might try a table mounted router and a fence that is tall enough to handle your pieces. By looking at your photos - about a 4" tall fence should work.

If it were my project I would start with the plastic cut about 1/4 to 3/8 wider than your finished width because you are going to trim off 1/2 that much from each side to get rid of the distortion.
I would mount a straigt bit in the table and set the fence away from the bit so that you will trim about 1/16" off at the most when you pass the piece through. For instance, if you want your piece to finish at 4" wide, cut it to 4 3/8, then bend it. Then set your fence at 4 5/16 from the bit and start the work into the cutter. ( I would set the bit with about 1/2" of the bit above the table). Start your work into the bit by laying it flat on the table with the bent leg of the work standing vertically. When you get to the bend, it gets a bit tricky, but use the tall fence to stabilize the work as you lift the horizontal leg while moving the piece forward into the bit. Keep both legs of the work tight against the fence and the bend firmly down on the table as you rotate the bend into the bit. The trick is to get the work past the bit so that when you begin to cut the leg that was vertical, it will be horizontal when you clear the bend.

Sorry for the dissertation, but I don't have a picture, so I used 1000 words. Good luck Scott. PS - If you ever need to trim the end of acrylic tube square, I've done that too, but that will probably be 2000 words.


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## paduke (Mar 28, 2010)

*use ******* router table*

Its physics. stuffing proverbial 10 lbs into 5lb sack. The material on the inside of the radius has to go somewhere. Post bending surfacing is required but a flush bit with bearing will mar your acrylic and your inside radius is very tight. Attached is a pic of a ******* router table. Depth height is done by adding blocks to table under material:moil: maybe you can clamp a fence at material thickness or mount ******* router table horizontally and use as a quasi planer


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## johnk (Aug 29, 2008)

I've seen someone cut plastic to size with a fine tooth band saw blade and then sand the edge if needed. These were not large pieces.


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## dapetersen (Aug 23, 2010)

*router as a horizontal mill*

Scott,
You might try cutting the plastic oversize(i.e. +.25") and sand/file one side flat. Mount the router horizontally and get both sides of the V to cut level which they should do if the other side is flat. Repeat at final "height" on the side which was filed flat. Be sure to leave enough stock to get the bend "in" flat. Be sure to hold it against the fence good and tight.

Dave


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## DonnWalter (Sep 7, 2010)

One trick you can try to even out that bump - Build a simple "V" shaped jig to hold your piece of plastic with the bend at the bottom. Set the jig up against the fence with enough space to allow room for the expanded corner. Then it is just a matter of trimming the corner flush with the rest of the side. does this make sense?

Donn


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