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Flush trimming Lexan for an offset router base

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Forum topic by MarkJ posted 02-15-2012 08:19 PM 2954 views 0 times favorited 11 replies Add to Favorites Watch
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MarkJ

52 posts in 3305 days


02-15-2012 08:19 PM

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?


11 replies so far

View TrBlu's profile

TrBlu

379 posts in 2086 days


#1 posted 02-15-2012 08:33 PM

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.

-- The more I work with wood the more I recognize only God can make something as beautiful as a tree. I hope my humble attempts at this craft do justice by His masterpiece. -- Tim

View Joao Araujo's profile

Joao Araujo

25 posts in 2294 days


#2 posted 02-15-2012 08:35 PM

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

View NiteWalker's profile

NiteWalker

2735 posts in 2037 days


#3 posted 02-15-2012 10:26 PM

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.

-- He who dies with the most tools... dies with the emptiest wallet.

View MarkJ's profile

MarkJ

52 posts in 3305 days


#4 posted 02-15-2012 10:39 PM

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.

View DS's profile

DS

2151 posts in 1881 days


#5 posted 02-15-2012 10:46 PM

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.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View NiteWalker's profile

NiteWalker

2735 posts in 2037 days


#6 posted 02-16-2012 02:42 AM

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?

-- He who dies with the most tools... dies with the emptiest wallet.

View Fuzzy's profile

Fuzzy

297 posts in 3448 days


#7 posted 02-18-2012 03:01 AM

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.

-- - dabbling in sarcasm is foolish … if you’re not proficient at it, you end up looking stupid … ... ...

View Bluepine38's profile

Bluepine38

3341 posts in 2545 days


#8 posted 02-18-2012 04:13 PM

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.

-- As ever, Gus-the 77 yr young apprentice carpenter

View MarkJ's profile

MarkJ

52 posts in 3305 days


#9 posted 02-19-2012 12:36 AM

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.

View Fuzzy's profile

Fuzzy

297 posts in 3448 days


#10 posted 02-19-2012 04:01 AM

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.

-- - dabbling in sarcasm is foolish … if you’re not proficient at it, you end up looking stupid … ... ...

View MarkJ's profile

MarkJ

52 posts in 3305 days


#11 posted 02-19-2012 07:37 PM

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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