I recently met someone using a large CNC machine to cut whole sheets of plywood. Many of those are laminated on both ends. I asked him how does he diminish tear out on the edges. He pointed me to compression bits.
I have read many posts from people asking how to better their cuts and minimize sanding. I don’t think I had read about compression bits before. I just ordered one and will be testing it soon. He said that one bit lasts him about a year with weekly cutting. They sell them on Amazon. Sounds exciting. Anyone has any experience with these?.
They are still upcut bits until quite a large part is buried in the stock.
I have started using them and I’m in love. I was losing my mind trying to minimize tear out on thicker pieces of baltic birch using combinations of downcut and upcut spirals, and not getting good enough results.
Phil is right about the upcut portion, but there are some with small enough upcut edges to be used successfully on a shapeoko. They seem to be called “mortise compression spiral” or other ordering of those same words and the upcut area is as small as 1/8" long.
I’ve been using these, and the shapeoko cut edges look as good as the factory edges:
They’re expensive but save lots of time and failed parts, so easily worth it for me. For them to work as intended, obviously you have to ensure that only the right flutes touch the right edges of the piece. This is easy for simpler jobs but can require some thinking and planning for more complex jobs.
I finally had an opportunity to try my compression endmills in plywood, and I must say I’m quite happy with the results. Very little sanding required, no tearing on either the top or bottom of the piece.
Single pass profile cut at full depth (0.2"), 18.000RPM, 40ipm using this single flute 1/8" compression endmill:
Which one did you get? It does not look like an Amana.
Bought them here:
At 5 euros a piece, they must be chinesium and nowhere near as good as Amana’s, but for cutting plywood, good enough !
What feeds and speeds are you using with this bit in Baltic Birch ply? I’ve been struggling with getting a decent finish with minimal tearout, going to try this ASAP. I’m cutting thicker ply - 5/8 and 3/4. Carbide Create doesn’t have any compression bits in the tool library, so I’m wondering how I should set it up to optimize the feeds and speeds for the bit.
You would be surprised. I have the same hozley ones and push them pretty hard. Figured I’d treat myself to an Amana one and it won’t take the same abuse, makes an awful noise. I still have the Amana one but reach for the cheap one whenever I need to rip through plywood.