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Re: Breaking off a tap?!

To: "David Scheidt" <dmschei@attglobal.net>, <shop-talk@autox.team.net>
Subject: Re: Breaking off a tap?!
From: "Phil Ethier" <pethier@isd.net>
Date: Sun, 9 Mar 2003 00:59:43 -0600
From: "David Scheidt" <dmschei@attglobal.net>

> >Through holes, use a gun tap.  And don't back off.  The gun tap pushes
the
> >chips forward, so you you tap in one pass.
>
> That's a spiral fluted tap, right?

No, a spiral POINT.

See the pic at
http://industrialhardware.com.au/Gun_Tap_M3x0_5_Goliath_0001HG.html
where the description reads:
"Gun Taps also known as Spiral Point Taps or Gun Nosed Taps.

Gun nosed taps have straight flutes supplemented by angular cutting faces at
the point. These faces cut with a shearing action which propels the chips
ahead of the tap leaving the flutes clear for the free flow of coolant to
the point.

Primarily designed for use in through holes, these taps can be used in blind
holes provided that there is ample clearance beyond the threaded section to
accommodate the chips.

The advantages of a gun tap are, the shearing action of the angular cutting
faces which produce a fine finish on the threads and shallower flutes which
permit a stronger cross section throughout the tap."

Spiral futes are a different thing.  See the pic at

http://shop.industrialhardware.com.au/index.html?cat=00013500013600013B00013
J0001G2&prid=0000TD&it=product

where the description reads:

"Spiral Flute Taps are designed primarily for machine tapping of blind holes
and are used to the best advantage in materials which produce long stringy
chips. The shearing action provided by the spiral flutes produces a better
finish on difficult to machine metals and causes the chips to be drawn back,
eliminating clogging at the cutting chamfer."


> They don't work as well in
> non-ductile materials, which don't form such long chips.

Seems so.  I have seen sprial FLUTE taps, but don't recall ever using one.

> >Except in cast iron.  Always tap cast iron dry or the stuff can crumble
on
> >you.
>
> Hmm.  Many of the cutting fluids I've used claim to be suitable for
> tapping cast iron.  I don't tap many holes in cast iron, so I don't
> have any experience.

Have not done it lately, but I'd strongly recommend testing on a part you
don't need.

Phil Ethier  West Side  Saint Paul  Minnesota  USA
1970 Lotus Europa 65/2597, 1992 Saturn SL2, 1986 Suburban, 1962 TR4 CT2846L
pethier@isd.net  http://www.mnautox.com/  http://www.lotusowners.com

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