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David Billington[_2_]

On 16/04/15 19:04, wrote:
All-
I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws. So I need to make a groove tool to do the job. A straight
groove tool won't work because the sides of the groove are curved. I
have made tools like this before but this is a small one and I'm
machining 304 SS so I need carbide and only want to make the tool
once. So I think to find out what radii to grind the sides of the tool
can be determined by drawing the screw head with the groove in it.
Then extend the sides of the head until they meet. Then mirror the
drawing around that point. Then I can directly measure with the cad
program the two different radii of the sides of the groove. Am I
correct?
Thanks,
Eric
I wonder if you could use a rotabroach type cutter as used in magnetic
drills, I have quite a few and they go down to 10mm hole size in metric,
maybe 3/8" in inch as that is close. The pilots are 1/4" IIRC so they
may be ideal if the end geometry is suitable and you can control the
depth. They are available in carbide but the only ones I've used are
HSS. I cut 304 with my HSS ones frequently and they go fine but I
haven't cut anywhere near 500 so couldn't comment on longevity. I
suspect a maker of the cutters could comment on the likely lifetime
before re-sharpening if required.