Milling GFRP Feed and Speed

[Burkhardt]

I need to cut out a few small parts from 1/16" FR4 glass/epoxy material. I have not done that so far because of the nasty dust but it is only a foot of cut length and I will make sure to have good dust collection. I am planning to use an 1/8" very coarse carbide bur end mill (diamond shape cut) that was recommended. This will not really make chips but mill to a coarse powder.

Now looking around on the web I find recommendations of very high speed (20krpm+) and very slow feed rates (e.g. 8ipm/0.13ips) but it was not really clear if that was for much smaller bits and how deep the cut can be.

Does anybody have a recommendation for depth of cut (full thickness or partial?), speed (I can do 24krpm max.) and feed rate? I have only 3 bits and don't want to experiment too much.

Thanks!

[Brady Watson]

Those suck. Since you are only milling a small bit, just use a 2-flute carbide end mill. 15k @ 1.00-1.50 IPS should be fine. Make sure it's held down well or it will flap up because of the upcut helix.

-B

[willnewton]

I have cut FR4 up to 5mm thick with a 1/16" chipbreaker bit at 18k and 1ipm feed and .5ipm plunge. Ramp your cuts a bit if plunging. Depth of cut should be a bit over half the bit diameter.

You will be fine with the 1/8" bit and Brady's recommendations, but I choose smaller bits for less dust.

Diamond cut bits work fine, I use them and spiral chipbreaker bits, the spiral bits seems to clear out the dust better. Not much difference on the surface quality.

Cutting FR4 is not a big deal, except for managing dust. It is easy to manage with a dust skirt around the cutter, but gets bothersome once your piece is done and you are maybe sanding the edges to remove sharp edges by hand. I sand in front of a fan or wet sand. The dust is literal itching powder, so wash your hands after handling!

[bleeth]

Getting rid of the itchies hint:

Make your shower as hot as you can possibly stand it and wash and rinse well.
Then before you get out turn it to cold and rinse well again.
Umpteen years building boats taught me this is the only way that worked for me.

[bill.young]

I found that it also helps to cover your exposed skin with talcum powder or baby powder beforehand...it fills your pores and helps keep the fibers from embedding themselves.

[scottp55]

Funny Dave,
I always did it the exact opposite:)

[Burkhardt]

Thanks All for the tips! That gives me a starting point. Since it is a small one-off job, efficiency does not matter but I did not want to break the bits.
I hope I keep the dust under control well enough to not need the special shower procedure or talcum :eek: But I will wear latex gloves and a mask.

[willnewton]

I have cut FR4 up to 5mm thick with a 1/16" chipbreaker bit at 18k and 1ipm feed and .5ipm plunge. . I can't go back and edit my post, but this should be inches per second, not inches per minute.