On 2019-09-21, Jim Wilkins wrote:
"Bob La Londe" wrote in message
...

[ ... ]

I have to be honest. I've never really had an issue with using
carbide round tools in set screw tool holders, but I am told that
set screw tool holders "should only be used for tools with a flat."
I do put the tool holder in a fixture and tighten the set screw with
the maximum tool pressure I can put on a long arm hex key without
stripping the screw (and sometimes stripping the screw LOL).

So, is it what I have been told true? Should I only use tools with
a flat on them in set screw tool holders? If I do that then am I
reduced to finding a way to put a flat on those tools? How would
one go about that?

I'll probably ignore all that and just keep doing what I am doing,
but I thought I'd ask.

P.S. I use almost exclusively carbide tools except for drills. I
even have some carbide drills in sizes that see a lot of use. I
have a few HSS mills, but I rarely use them.

In my experience with mostly HSS, grinding a flat reduces mushrooming
on the end of the screw because it doesn't need to be as tight, and
the screw makes area instead of line contact.

If I can't easily surface-grind the flat or dog-point the screw on the
lathe, hand grinding them is usually good enough.

If you can remove a mushroomed setscrew through the center hole it may
not matter.

With the standard "Weldon flat", not only does the flat end of
the setscrew contact the flat on the tool (typically end mill), but
there is a 45 degree bevel on the end of the setscrew, and that contacts
the bevels on either side of the flat, to adjust the extension of the
end mill as the setscrew is tightened. Of course, this does not make
the practical extension right on an end mill which has been resharpened,
but it makes it consistent for that one end mill, and prevents either
the end mill pushing back into the tool holder, or pulling down with the
forces of the spiral cutting edge. So -- the extension will not change
during the cutting process.

With sold carbide end mills without Weldon flats, the extension
may be different each time you put the end mill into the holder, and it
may change during the use with cutting forces.

My experience with the Weldon flats and the setscrews is with
NTMB 30 or 40 tapers -- to fit either directly into my Nichols
horizontal spindle milling machine (40 taper), or into the quick-change
spindle on the Bridgeport BOSS-3 mill (30 taper). I also have the
adaptor from 40-Taper to 30-taper to let me use the smaller end mill
holders in the Nichols mill.

Just some thoughts.

Enjoy,
DoN.

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