Round holes with flat bottoms

mkoblic · 2010-10-31T23:58:48+00:00

I am sorry to ask something very basic. My excuse is that I am testingthe Forte Agent :-)I need to make round holes in steel, 1/8" deep, with flat bottoms. Thediameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is notcritical.I do these on my mini-mill. I pre-drill the hole to the required depthundersize and then use a 4-flute mill to square up the profile. All is well until I start getting near the bottom. The machine beginsto labour and there is a tendency for the table and/or the head towant to move in a circular fashion, clamping x and y notwithstanding.I assume that this is due to the mill beginning to remove morematerial, particularly the center portion of the hole.The end-mills are supposed to be centre-cutting. There are two flutesthat meet in the middle, the orthogonal two flutes do not. All thepictures I could find suggest that these are indeed centre-cuttingend-mills.So the question is: Is this a normal behaviour for end-mills in thissituation? If not, what is the likely cause? Is there a betterprocedure to do this?Michael Koblic,Campbell River, BC

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Jim Wilkins 15 years ago

My mill chatters worse on shallow holes than deep ones where the end mill has lateral support over a larger arc. Perhaps you could bore a through hole in a small steel plate and clamp it onto the work after starting the hole.

jsw

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Bill McKee 15 years ago

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My mill chatters worse on shallow holes than deep ones where the end mill has lateral support over a larger arc. Perhaps you could bore a through hole in a small steel plate and clamp it onto the work after starting the hole.

jsw

How about a plug tap?

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