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Holdridge 8D Radii Cutter Setup


Nov 21, 2023
Hey guys, I'm having a bit of an issue trying to figure out this radius cutter.

I have to cut a 2.250" radius along a shaft. The shaft O.D. is 4.671" and it needs to be 3" diameter at the bottom of the radius. The width of the radius on the shaft overall is 3.5".

I set up my tool how it said to in the box instructions. 4" gage blocks, the .425" spacer and the 3" depth micrometer. Set my micrometer to 2.250, then got the tool set back up on center and started cutting, but the radius wasn't matching up with my radius gage -- I CNC'd a gage out of a piece of aluminum so I could check the part as I cut it. I thought my tool length may have been off, so I measured the diameter of the straight yoke that I was using (1.556"), divided it by 2, and found what the length of stickout my tool needed to be to make a 2.250" radius (1.556/2 = .778) (2.250 - .778 = 1.472). I adjusted the length of tool stickout from the front of the yoke to 1.472 and the radius cut perfectly and lined up with the gage I made. However, when I got the center of the radius down to the 3" diameter, I was only at around 3" in width.

Am I setting up my tool length wrong? Am I supposed to take into account the .425" spacer somehow?

Thanks in advance!