Author Topic: Cnc speed feeds in plastics and grp  (Read 1428 times)

Offline raynerd

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Cnc speed feeds in plastics and grp
« on: February 24, 2016, 02:57:28 PM »
My brother in law and I have been having some fun cutting plastic (Perspex) and grp on the lathe. The grp literally worethe cutter down from a end mill to giving it a rounded polished end within 10 minutes. The Perspex cut nicely but quickly clogged the cutter by melting on the cutter. This also caused the melted hard plastic on the cutter to scratch the top edge of the cut as it moved past.

Has anyone ever cut grp or more likely cut Perspex, what sort of feeds were used. If the Perspex is melting, is it suggesting my cutter speed is too quick?

I've ordered some titanium coated PCB chip breaker cutters for the grp... This may help!?

Any help appreciated.
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Offline chipenter

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Re: Cnc speed feeds in plastics and grp
« Reply #1 on: February 24, 2016, 03:40:46 PM »
We had to cut 1/2" perspex with a circular saw and used wd40 on the blade and that helped , one the blade got blunt nothing would stop it building up , getting hot and melting the chips into the blade .
Jeff

Offline PK

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Re: Cnc speed feeds in plastics and grp
« Reply #2 on: February 24, 2016, 06:34:40 PM »
We cut both on the router. For acrylic, the key is faster feeds and moderate speed. So we'll spin a 6mm two flute at 19,000 rpm and cut at 4000-6000mm/min (100um/tooth). As with all cutting you are aiming to take he heat out with the swarf so you have to move faster than it can.

For fibreglass/carbon, we use a diamond cut bur, spun as fast as we can and cut fairly slow, 60KRPM and 500-1000mm/min

PK

Offline Pete W.

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Re: Cnc speed feeds in plastics and grp
« Reply #3 on: February 25, 2016, 05:11:43 AM »
There was a time when I was regularly turning batches of Perspex blanks for a friend.  I found that, on my ML7, a sharp HSS tool was better than carbide.

There's lots of information on-line about machining Perspex (aka acrylic), for instance  http://www.theplasticshop.co.uk/plastic_technical_data_sheets/perspex-design-guide.pdf .

You need to be careful what you use as a cutting lubricant, stuff like WD40 or just about any organic volatile risks long-term surface crazing.  I found that, if I got the HSS tool angles and turning speed & feed right, I didn't need lubricant.  (Except that I would give a final polish with a damp mutton cloth.) 
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Pete W.

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