Bits bits and more bits

I have question about bits…so far in the CNC world I have experimented with cedar, pine, and red oak. I got my hands on some Walnut and Cherry, which are hard wood. With all the other wood I’ve been using I have used an array of bit, end mills, ball nose, vbits all various sizes, up / down and so on…
so every now and then I will read posts about compression bits for hard wood…can someone explain the difference between the others and compression bits…also I use Sienci and precise bits for bit purchases…I don’t recall seeing compression bits…so where should I look? And should I get?


@chapklc - Kari, as you are probably aware the different bits perform a little differently from each other. When you use a upcut end mill you will get fuzzies on the upper surface of your material. Just the opposite with a downcut, clean on top and fuzzy at the bottom (for cut throughs). A compression bit is part upcut and part downcut and will cut both surface and bottom cleanly. You would normally only need a compression bit for cutting all of the way through your material. Hope this explains it a little. Enjoy.


@chapklc As Heyward said, Kari, compression bits are only for cutting all the way through the material, and generally, all in one pass. If the material is too thick for a one-pass cut, you need to at least get down deep enough in the first pass to bring the down cut part of the bit into play. If you don’t do that, you will get fuzzies on the top surface from the upcut end of the compression bit.

Sienci has both 1/8 and 1/4 compression bits in their store.

Since I am cheap, I use a combination of downcut and upcut bits to achieve the same result. If, for example, I am cutting through a 1/2" thick material. I create 2 toolpaths. The first one cuts down to 1/4" in one or two passes, using a downcut bit. Then the second toolpath starts cutting at that 1/4" and cuts through the material. The second toolpath uses an upcut bit.

Doing it this way is more time consuming than using a compression bit, but I’m in no hurry. :grinning: If you try this, remember that you need to reset Z0 when you install the upcut (second) bit. Don’t reset X0Y0.