Set screw tool holder accuracy is down to how precisely the holders are made. A
lightly oiled tool should pop when pulled out of the holder. Where this type of
holder doesn't do as well as a collet is in heavy production work. They need to
be monitored for getting bellmouthed. A precision rod inserted into a holder in
a machine spindle should ideally have zero radial movement at the end of the
holder.
I wonder if any company machines set screw holders with the tool hole very
slightly offset towards the set screw side so that the screw pushes the tool to
perfect center?
On Friday, April 19, 2019, 12:27:37 AM MDT, Gene Heskett
<[email protected]> wrote:
On Thursday 18 April 2019 20:02:45 Ken Strauss wrote:
> Weldon shank is round with a flat on the side. A setscrew prevents
> pullout.
>
> I haven't done personal measurements but I've often read that Weldon
> shank is worse than ER collets for low TIR when using small diameter
> tools which are usual in a high speed spindle.
>
In that case the TIR can't help but be worse as the setscrew will force
it to the far side of any clearance. So TIR's in the .002" range are
not impossible. In the case of an engraving v bit, the flat should be
located such that this offset presents the cutting edge to the work as
opposed to the heel, which likely will just burn the tool and the
workpiece. We should be so lucky as to reliably get that timeing from
the tool venders. While etching circuit boards, I've been known to stop
if the cut is leaving a big burr, and rotate the tool a quarter turn in
the ER and try again. Usually I have been able to get a cleaner cut.
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