When I recently cut a pocket with a downcut bit and followed up with a finishing pass on the walls with a compression bit I noticed that the finishing pass actually cut slightly deeper (a few 0.01"). I thought it was an error on my depth setting, so I set up a quick test and was able to reproduce it.
I re-cut a pocket with a downcut bit and followed up with the exact same cut just with a compression bit, and it cut deeper again. (See pic, not that it shows much)
G-code (attached) seems fine. Is this a common behavior of downcut bits because they don’t have an upcut portion to cut the bottom of the pocket flush? I don’t recall having this issue in the past but I also haven’t needed to fit parts to a precise depth in a while.
I have not cut much plywood, but I have noticed a Downcut bit will not cut well at the bottom.
It is trying to stuff the chips back into the part.
Why not use the compression bit for the whole cut ? It will bring the bottom material up and still give a nice cut on the top, so long as your DOC is a long as the min for the compression bit.
A Cadence Jenny requires a .125 ( I think ) DOC in order for the bit to work as intended.
I used to use compression bits for everything but the 65mm spindle doesn’t like it much through baltic birch. It can be done, but I burn through spindles much faster. A downcut roughing/chip bit is awesome at initial pocket clearing and much less demanding on the spindle (it seems). I’ll look into the Cadence, most compressions I’ve seen were 0.2-0.25" minimum. 0.125" is very attractive.
When I use my compression bits it’s on the finishing pass, unless I have the stock elevated off the spoil board and am machining the top/bottom surfaces at the same time. I use the Golden Boy for all roughing, works very well.
