@mikep
Yeah, that doesn’t look like 6061 to me. The bottom corner cuts and the broken edge on the corners of the block look like a much softer grade. You can try feeding faster (bigger chip, better cut in this case) but I would try a sweet spot test first (can find the link in Will’s page posted above). Possibly the bigger issue though is going to be chip clearing. ANY material getting recut is going to be a pretty big issue. Cutting fluid would buy you some forgiveness but I don’t know if you have the ability to use any. You could also try keeping compressed air on it to blow the chips out as you cut.
Assuming a grade in the 5000 series I would probably be looking at feeds in the 40+ IPM range to get a decent cut (depending on tool geometry and quality). That’s of course assuming the machine and tooling you’re using can keep up. To be clear I’m not trying to beat up on anything. I just honestly don’t know the machine well enough or what tooling you’re using to have a good guess.
@Qwkpony
Composites are what diamond cut bits were designed for. As they have more of a grinding geometry than a cutting one they are usually used full plunge. You can reduce the plunge depth or feed if you are getting deflection in the cut.
The 2 flute tooling is a whole other issue. They don’t handle composites like this well as they have very little cutting surfaces compared to the diamond cut routers. If you have to use them try to keep the depth of cut low (.010) as it’s going to have a hard time with the glass in the FR4. Also keep in mind that you will dull these VERY quickly so if you need a decent number of them I’d look at getting some different tooling.
One last thing. As I mentioned above FR4 is glass loaded. You need to be VERY mindful of the dust as you don’t want to get the glass in your lungs. Make sure you have proper vacuum, dust collection, etc.