On Wednesday 07 March 2018 06:42:26 andy pugh wrote:

> On 7 March 2018 at 04:05, Gene Heskett <ghesk...@shentel.net> wrote:
> > So the only way is to buy R8's with square bores,
> I don't think that is the only way at all.
> You could make solid ER32 "collets" with grub screws in the end.
> (getting the extractor flange right would be a challenge).
> Bored true they would hold the tap true, with drive from the grub
> screws on the square.
> Needs one per tap size, but it's an easy CNC turning job.
I think the 3/4" brass rod idea, bored thru for each tap, with grub 
screws to grab the square butt, and a key slot cut in a 3/4" R8 to lock 
it to a cap screw seated in the side of the 3/4" brass rod, one per tap 
size, might be the best idea.

> I recently (and accidentally) bought a pair of floating tap holders.
> There is no reason that those would not work for rigid tapping, and
> they add a bit of relaxation to the process in the event of a problem.
> Those take a DA collet and have a pair of grub-screws to grip the
> flat.
> ER collets specifically for tapping exist (with a square in the back)
> https://www.ebay.com/itm/Techniks-1-2-ER25-Rigid-Tap-Collet/1221226735

Price is scary, and still leaves the collet free to slip. I think I'd 
rather sacrifice an R8 by grinding a key slot into it for a cap screw in 
the side of a brass tap holder, to lock it from slipping in the R8, and 
make a dozen or more, about an inch long. Like you said, once the code 
is written, it can make as many as I have brass on hand. I now have the 
Sheldons bent spindle corrected, and an ER-40 kit that sits in the 
shop-made 5C adapter, and running within a thou several inches away from 
its collet. I'll have to measure, but I believe it can pass a 3/4" rod, 
length arbitrary to about 3 feet as theres a storage shelf to the left 
of the lathe it will hit. If I add the rear spider I made, I should be 
able to maintain it pretty true.

Now, to find the 3/4" brass in 3 foot hunks.

> You could add a pair of drive grub-screws to a standard round R8
> collet. You might need to soften it off to allow tapping, though.
> At which point you might as well make your own, again it's a simple
> turning job. You wouldn't need to heat treat for your volume of work.
> It would not need to be a split collet. Bored for the tap diameter and
> relying on screws for grip and retention it ought to be fine.

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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