NEED HELP - Material and Bit

I need some advice/ help on a project I am working on.

I am wanting to CNC what is approximately a 30" x 40" piece of .0125 Polypropylene with a hex pattern similar to what you might see in a perforated plastic the hex pattern is 0.25" hex that is staggered on 0.375" centers.

I have broken several 1/16" End Mill Down Cut bits attempting to machine this.

The reason i was using the down cut bit is that the up cut bits seem to pull the material up off the table.

the material is held on the machine by a neat method i found on youtube where you place painters tape on the bed and on the material and use superglue between them to hold the pieces in place. IT seems to work well as long as i use a down cut bit, but i am worried that if i use an up cut bit it will pull the material off the table.

The precision of the hex pattern is fairly important and the 1/16 End mill does give a beautifully cut pattern once i get it all cleaned up - before i break the bit anyways.

how would you experts in this forum tackle this job? and or any jobs in the future where I cut thin plastic type materials?

You might try a single-flute, or "O-flute" bit, which is optimized for plastic. https://www.amanatool.com/51515-k-so...outer-bit.html

With material that thin, PC-board bits might work too, and they're a lot cheaper (which is good if you're breaking them rather than wearing them out). Look at the Kyocera brand for instance.

To hold your parts down, you might look at a vacuum pod, instead of the glue and whatever. If you can get it held firmly to the spoilboard, you can use an up-cut bit which helps keep chips out of the cut and might help with the breakage problem.

I guess I might pre-drill the holes with a 0.239 drill then finish with the end mill. This takes out most of the material, reduces the load on the end mill

I like carpet tape for holding thin parts.

What speed and feed rate are you using?

I like Jim's idea for roughing it with the drill to get the bulk of the material removed

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Originally Posted by Jim Dawson

I guess I might pre-drill the holes with a 0.239 drill then finish with the end mill. This takes out most of the material, reduces the load on the end mill

I like carpet tape for holding thin parts.

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Thinking about it a bit more I think that no matter what bit i use I may use a drill or some other means to remove most of the material, it should just help give me that better finish hopefully. Also, i never thought about carpet tape, I'll have to try that!

Thank you all for your help!

Quote:

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Originally Posted by LorenBMS

What speed and feed rate are you using?

I like Jim's idea for roughing it with the drill to get the bulk of the material removed

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My speed I cant remember off the top of my head but it would be the same recommended settings for acrylic for the 1/16" bit from Amana Tool.

Quote:

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Originally Posted by awerby

You might try a single-flute, or "O-flute" bit, which is optimized for plastic. https://www.amanatool.com/51515-k-so...outer-bit.html .

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I got some plastic bits on order! Thanks!

Do you have any plastic building up on the cutter before it breaks or any on the cutter shank? I lean towards the low end on RPM and the high end on feed per tooth to try and keep things cool.

Quote:

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Originally Posted by LorenBMS

Do you have any plastic building up on the cutter before it breaks or any on the cutter shank? I lean towards the low end on RPM and the high end on feed per tooth to try and keep things cool.

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yes I was seeing that on one of my bits.

That is indicator the the plastic is melting. Maybe a combination of lowering rpm and increasing feed rate. I would lower rpm first.

Another thing you can try in order to keep the plastic from melting is a vortex chiller. This hooks up to your air compressor and generates a blast of cold air which you direct at the cutter. It keeps things cooler, which makes a big difference with plastics. https://www.exair.com/products/vorte...-products.html