I love that in both 3D printing and CNC routing I am still learning things.
Yesterday I was cutting a clamp, and doing multiple to check repeatability. I had 2 failures, haven’t had one in a long time but both led to a busted endmill.
In the upper right hand side of the inner circle I would get chatter and the endmill would snap and ruin the work piece, as seen below. I tried slowing down, heavier load on the endmill, lighter load, nothing seemed to resolve this issue in this one spot.
I played around a bit more and sat and watched a full cut. The depth didn’t seem to matter, but it did get worse the deeper I went around the entire work piece.
Looking into it, it wasn’t the first pass. The first pass is at 3.65mm width and .6 deep at 600mm/m, the total cut width (to give the chips somewhere to go) 4.05, so a .4 step over second pass. I like cutting like this as it leaves a finishing pass look on the final work piece without having to run a finishing pass. This was the issue.
I never had chatter on the full endmill load. The .4mm step over is where the chatter is. I was only using ~ 10% of total cut width. The load is not sufficient for the speed I was traveling.
I adjusted to a .6 step over and all is resolved. The odd thing to me is I cut .25" thick plate with .4 step overs all day, the .5" thick material is the issue. It seems it would be machining the same step regardless of depth?
