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Help identifying this tool


New member
image.jpgI’m not sure where I got these but I have no idea what they are. Markings are Madison and then some engraved measurements and maybe stock number. Can someone tell me what these are? Thanks


Active member
That looks like an adjustable "reamer" or "counterbore" cutter, intended to be driven by a arbor with a slot through it. The 4.166 scribed on it is probably the diameter of the job it was last adjusted to fit. The notches on one edge engage with a small lug on the driving arbor to keep it roughly centered with moving the tool in and out of the hole, but in operation it's supposed to be self-centering.


Active member
Found a couple of photos of a large-ish Madison reamer arbor on eBay. Notice the undercut in the slot. There's a matching thicker section on the reamer cutter, and that retains the cutter when withdrawing the tool from the hole.

While you can think of these as counterbore cutters, they are not intended for massive metal removal. I found some suggestions that the leading edge should have a taper of 1/32" or 1/16" at 45 or 30 degrees, depending on material hardness, and that taper represents the upper limit on how much the tools is expected to take off the radius.

The tool you show in your photos is obviously a slightly different style, but it's the same general type of tool.


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