Greetings all,

Got some time in the shop today and needed a couple of holes for the breeches of the Girandoni rifles we're making. Starting with a 1" square 12L14 bar, I need through holes .510" X .610".

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The corner and center holes are drilled.

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A .500" endmill enlarges hole and removes most material.

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A .375" square tool bit is ground with a 6 degree angle and mounted in an R8 mill holder with a brass shim to give a slight clearance. Here it is being set square with the bar before starting a cut. Note the face clearance. The mill spindle is locked at each side.

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The tool is stroked up and down, advanced ~ .002" each time, until the endmill cuts are reached. Wish I had a shaper! Note the slight groove on the far side from the endmill cut, also the brass shim on the back of the tool. A couple of more passes without advancing the tool cleaned up that groove.

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Here are the finished holes. The bottom is within .001" of spec with no taper. The upper was my first attempt, note the taper and remainder of the endmill cut, I forgot the shim which left no clearance on the face of the tool.

The second hole took ~ one hour start to finish. The first over twice that.

Hope this interests someone.

Martin

'It used to be only death and taxes; now, of course, there's shipping and handling, too.'

I been using a square file clamped in my vertical drillpress an getting slower and slopppier results every time!