# Flush trimming Lexan for an offset router base



## MarkJ (Nov 16, 2007)

I'm working on making an offset router base out of 3/8" lexan. I started of by making a template out of MDF. I then stuck the template to the lexan with double stick tape and trimmed the lexan close to the template with the bandsaw. I'm now moving over to the router table with a flush trim bit and this is where I'm having problems. I'm use a starting pin to rotate the piece on to the bit but as soon as I touch the bit it kicks the piece back with a bang. I'm using a 1/2" straight flush trim bit. I tried switching to a shear cut 1/2" flush trim bit but it's just as bad. I do also have a 3/4" pattern bit, but that would then put the bit up above the work piece and with it kicking back this bad, that doesn't seem like a good idea. I've done this sort of thing plenty of times with wood, but this is the first time using a router on lexan.

Any ideas why it's doing this and how to prevent it?


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## TrBlu (Mar 19, 2011)

A spiral bit with a pilot bearing will work better with Lexan.

If you are using a variable speed router, try slowing the router speed.


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## JoaoAraujo (Aug 22, 2010)

Hello,

Lower the speed of your router to 10k RPM and use a spiral bit, if you don't have one, stick with the shear cut bit.

Take care,

Joao Araujo


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## NiteWalker (May 7, 2011)

I do this all the time. The key is to make sure you cut away as much waste as possible. I typically leave around 1/16"-1/8". No special bit needed, though a downshear leaves a smoother cut.

The kicking of the piece when it hits the router bit is a sign of trying to take too much at once.


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## MarkJ (Nov 16, 2007)

Thanks everyone. I trimmed down to about 1/16" on the bandsaw and slowed the router down but it still kicks as soon as I pivot the piece into the bit. Maybe my bits are dull. I'm going to borrow a spiral flush bit from a friend and see how that does.


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## DS (Oct 10, 2011)

Plastic and dull bits don't mix. Had this issue with a dull saw blade. It would slam the workpiece as soon as it touched the material.
Also agree on slowing the speed down. At too high speed, plastic melts and grabs before it cuts.


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## NiteWalker (May 7, 2011)

FWIW there's a single speed 690 in my router table (27,000 rpm). I use a plain flush trim bit and don't have the issue you are when trimming lexan.

Here's how I do it:
- Trim as you have been.
- For the pivot pin, I use the fence set about 1/2" behind the bit. 
- I pivot the workpiece in from the right side of the table and once the bearing makes contact with the template I rotate the disc counter clockwise.

Where is your starting pin position?


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## Fuzzy (Jun 25, 2007)

How far is your pivot pin from the bit ??? The further the pin is from the bit, the less effective it is. You are correct in your assumption that dull bits accentuate the problem … dull carbide tears away the debris and it then sticks to the face of the cutter, causing even more tearing … etc … etc … etc.


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## Bluepine38 (Dec 14, 2009)

Not sure if this is a fact, but I was told by a local plastic company that while lexan can be bulletproof, regular
plexiglass is actually stiffer, and would make a better insert.


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## MarkJ (Nov 16, 2007)

Fuzzy, the pin is about 2 1/2" from the bit. I haven't had a chance to mess with it anymore but will hopefully be able to borrow a spiral bit flush trim bit tomorrow and see how that works out. It's definitely something unique with the lexan since I've never had this problem template routing hardwood using the same bits and technique as I'm doing here.

NiteWalker, I'll try your fence trick as well to get my pivot point closer to the bit and see how that works out.


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## Fuzzy (Jun 25, 2007)

I think 2 1/2" is a bit much for a "grabby" material such as LEXAN … I hope moving the pin to within an inch or so helps you out. You'll still need a sharp, clean bit.


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## MarkJ (Nov 16, 2007)

Borrowed the sprial bit and it still caught. Used the fence to pivot from and it worked great and finally got the thing flush trimmed! Thanks for the help here.


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