Milling Carbon fiber Sheets - Need Help

Hello Fellas machinists.

As the title states, I need some guidance about cutting Carbon fiber sheets. I will explain my problems as much as I can, and if I have forgotten something, please point it out.

Intro:

I have been cutting CFRP materials for some time, and there are differences in results between each job.

For example, when I was cutting without any coolant, I have had best results so far. Holes are on spot, round and there were no quick tool wear.

As I wanted to remove the dust from my workshop, I have started using water as coolant. Well, not coolant as more of a dust blocker. And not, After a single plate, tool wears out pretty quickly.

Tools in question are not cheap ones: Carbide Diamond pattern Router bits, Diamond pattern and Diamond Coated. with 3.175 mm of diameter.

Machine setup:

Fully rigid machine which is designed for machining aluminium and steel. Problem is not in rigidity.

Spindle speed is on 5500 RPM and feed speed is on 650 mm/min.

DoC: 0.75mm

Problem: Tools wear out very quick, and therefor tolerances become a problem very quickly. Required holes are also not circular as more of a ellipse. Small but noticeable ellipse.

When using no dust blocker (Water), end bits last much longer, which is so strange to me, and the tolerances are much much better using just a vacuum cleaner as a dust removal.

As I cant afford to have my workshop be full of dust, can anyone give me an advice on how to optimize milling, to prolong the end bit life, while keeping the dust at water control.

Thank you

Marko

Don't tell anyone my secret... (15 years experience with the stuff) I get the best result from the cheapo $10 carbide tipped wood router bits you can buy at any hardware store. Run a slow RPM +-2000 and a speed of about 40ipm. Leave a generous stock and do a finish pass at the same speed. You will ALWAYS have fuzz from the fibers but it can be sanded out. Running the RPMS this slow and a slower speed will create minimal dust. The diamond patter cutters create a lot of dust and I don't use them because of that. The cheapo $10 cutters are so cheap you can throw them away without worrying too much. Even better, I would just grind down the dull parts of the tips and have it be good as new. I have tried all the fancy cutters from Onsrud and nothing worked as well for the sheet I cut. Tailor your feeds and speeds to the sheet specs. Different weaves and binders will yield different results so do lots of tests.

As for holes that is from the bidirectional strands. Interpolating a round hole with a smaller cutter will give you a better result.