Any advice on cutting the 1/4" polypropylene sheet would be appreciated. We have cut it with a jig saw in the past but are in need of more precision. We have a router and were wondering if it was safe or possible. We are willing to experiment, but have had bad experiences with cutting pvc and would rather not have a problem that could be avoided.
Thank you
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In the past, we have always cut it with a scroll or band saw.  The speed of the blade is very important.  If you cut too aggressively, it simply melts and then solidifies a bit behind the blade.  I don't think I would want to cut pieces with a hand held router, much less let the kids, but if you used a template, watched your spindle speed and were not too aggressive...  you MIGHT get decent results.  Definitely not my first choice though.

I quickly found this article  http://www.plasticsmag.com/routing.asp?fIssue=Mar/Apr-08&aid=4741 .  It focuses on CNC, but does address a few pertinent issues.

We are planning on experimenting with cutting it on a CNC router this year.  

Not to hijack your question, but it would be great if anyone has a few tips of their own tips for CNC with any of the plastics.... perhaps posted as a new thread to keep this one on topic
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I would suggest a bandsaw.

There are some useful general tips on kit material in the BRI File Manager if you have not seen them before.

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In addition to speed, the size of the teeth on the blade is critical. Larger teeth are more effective at removing material from the work area, thus inhibiting the self-weld process.

I have never cut the polypropylene with a router, but I have cut it on a mill, and have found that large (3/8 +) 2-flute end mills, with a low spindle speed (600-1200rpm depending on end mill size) and a high feed-rate, work really well. I would imagine that the router would work well under the same conditions, as long as your cut pattern isn't too intricate.
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