On Wednesday 02 August 2017 14:09:09 Gene Heskett wrote:
> On Wednesday 02 August 2017 11:23:00 John Kasunich wrote:
> > On Tue, Aug 1, 2017, at 10:34 PM, Gene Heskett wrote:
> > > On Tuesday 01 August 2017 20:33:11 Ken Strauss wrote:
> > > > you can use a spiral point ("gun") tap to push
> > > > the swarf ahead of the tap and out of the bottom.
> > >
> > > I think that would describe the tap I am using except the flutes
> > > and cutting edges are straight.
> >
> > Then its not a spiral point tap. Sounds like a hand tap. Hand taps
> > are for hand tapping and shouldn't get near machines. In fact, I
> > don't even use hand taps for hand tapping. Spiral point taps are so
> > much better that I would _never_ actually buy a hand tap. The only
> > hand taps I have are ones I was given.
> >
> > Hand tap:
> > https://images1.mcmaster.com/mvA/contents/gfx/large/2521a773p2-a02cl
> >.p ng
>
> Thats what these are for sure. And they aren't even straight. Cheap,
> one of everything kit survivors. But they are sharp!
>
> > Spiral point tap:
> > https://images1.mcmaster.com/mvA/contents/gfx/large/2523a413p1-a02cl
> >.p ng
> >
> > Spiral flute tap:
> > https://images1.mcmaster.com/mvA/contents/gfx/large/2529a21p1-a02cl.
> >pn g
> >
> > That little notch at the tip of the spiral point tap makes a huge
> > difference!
>
> In those pix I can see that easily. Looks like I need to invest in
> some different taps when these are ~30~
And I seem to have discovered that in 8mm metric spiral flute coated
taps, there is not an 8mmx1.0mm tap to be had anywhere. Everything I
could find from ebay, mCmaster-carr, and banggood are only available in
metric coarse, or 1.25mm thread pitch if its priced below $50 USD a
copy. Zero 8x1.0mm to be found in spiral flute. WTH?
Unless I wreck this cat head, I won't likely need the fine thread version
again, but still...
============
Playing with that $12 diamond disk, it looks as if it will do a decent
job of shaping HSS tooling given time enough to do it. Slow and has the
wibblies even after I shaved the face of the arbor, which helped a lot.
I set my vice at 15 degrees, mounted a 1/4" HSS bar in the vice, mounted
the disk diamond side up, set a tomato juice can 2/3rds full of k2
beside it on the mill table, stuck a kerosene lamp wick in the can with
the tail laying on the disk, added 1/2 ounce of scrap alu laying on the
wick for additional contact pressure so the k2 would stay wet on the
disk, raised the mill head for first contact, touched off z, and told it
to turn the disk at about 150 revs while raising it 25 thou at .0002"
minute, put an m5 in the mdi buffer and came back when it was up about
15 thou, looks good. Turned off most of the lights for the night.
Patience and I'll have a better tool to cut the barrel threads with.
Needs to be around .0505" or .051" wide. I am hopeing that 15 degrees of
clearance on the left is sufficient, zero on the right since cutter
advance establishes that.
Cutting threads in SS, this will be scraping almost like a cutoff tool as
I'll leave the top flat, so it can be re-sharpened by just flattening
the face, so suggested tool advance per threading pass is?
I've got around 1.5 to 2 thou in mind. With some buttercutt or rapidtap
painted on it. I am not capable of coolant recovery yet. Or would K2 be
better?
It has to survive making a square thread just a hair over 50 thou deep.
And since I'm spooky about wrecking a nearly $500 barrel, I'll be
re-running the code, reducing the OD's till its a good fit in the
action. That has to be enough clearance the SS doesn't gall and seize.
Final assembly with a coat of milk of magnesia or maybe never-seize just
to assure it can be unscrewed again when this barrel is shot out. 5 to
30 years hence.
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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