[tenaja]

I need to cut a .25" deep slot that is tapered down (1* per side) to .041" wide at the bottom.

Should I use a .040" mill with a tiny left for the finish pass, or a .031" using HSM toolpaths? My spindle only goes 5k rpm, so I know it won't be truly high speed, but I am more thinking of the shape of the toolpath, tool rigidity, and chip clearing.

Any other thoughts would be appreciated. I have not spent much time below 1/16", especially at this large depth:width ratio.

Thanks.

[ERUS]

I would use a .031" Personally. If you use a .040", once you reach the bottom the cutter is going to be fully engaged. The side of the tool that is cutting in a conventional direction is going to pull the tool into the cut. The climb cutting side will push away. The tool isn't going to cut where you think it will. It would be off to one side slightly. The more flex in the setup/tool/machine the worse it will be.

[tenaja]

Thanks for that tip, that was one of my concerns. I guess I will give the 1/32" a shot.

[tenaja]

FYI, I tried both the 1/32" tapered and the .040" ball, and as you would expect, the tapered mill had nicer looking sides, but the ball had nicer edge chamfers and bottom. Even the scallops left on the edge chamfers with the square 1/32" end mill cleaned up nicely with the bead blaster.

I ran at 5 to 7 thou z steps and feedrate about 4 ipm. Not really rocket science at all.