Best method for cutting sintra

[andre]

I am new to sintra and cut a sample of sintra sandwiched between two sheets of formica. One small piece 10 by 10 with a .375 straight bit. I am sure .25 would work better but thats what I had in the collet. My question is for cut throughs what is an optimum feed rate and rpm so not to melt and gum up the bit?

[Brady Watson]

Not sure what the Formica adds to the mix being phenolic plastic, but...the best results can be had with a double spiral O flute (Onsrud 52-series) and a move speed of 2 to 4 IPS. You'll need good hold down, such as vacuum or carpet tape. I run between 13,000 and 15,000 when I cut it.

-B

[elcruisr]

I cut a lot of sintra with a 52 series .375 tool from Onsrud. That's about the best I've found. Like Brady I run at about 15,000 and 4 IPS. I've done some with the Formica and that does throw a wringer in the deal. To get a clean, chip free top and bottom cut means a compression spiral which is not the best plastics tool as it tends to pack and melt the chips. BTW I usually cut 3/4 or 1/2 stock.

So the best solution I arrived at was an Onsrud 60-121 single flute compression. Did a single pass leaving on about .06 outside final cut at around 14,000 at 6 IPS. Then a finish pass. Not ideal for the sintra but gave a good cut on the laminate. BTW, the laminate will rapidly dull your tooling!

[elcruisr]

One more hint I forgot to add! Bigger diameter is almost always better for plastics. Better chip removal and less melting of chips.

[andre]

Eric and Brady
thanks for the advise. I have a good vac hold down and the large bit makes sense. Sounds like I need to slow down the rpms and feed rate a bit.
Eric did you mean you offset by .06 your first cutand then came back and cut to the original vector? or was that what you left for the final depth of cut through?