Hand taps with centring hole?

Hi
Does anybody know of a source for hand taps with a centring hole in the top of the tap. The holes are 60 degrees and used for hand
tapping using a mill or pillar drill with a centre point in the chuck to keep the tap square to the job when tapping. Also used on a lathe in a similar manner. I tried my local engineers merchant but their titex/dormer and lyndon taps do not have these holes. Just wondering if these taps have a designation or a particular name?
Cheers
Paul
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Paul,
    Have you actually tested one? I'd be surprised if the top was hardened. Check it by scraping very lightly, if the top's soft, just run a centre drill into it. Otherwise, just take apart and soften the top by heating and then center drill.
    Can't check my own at the moment, unfortunately. --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Looking through my collection of taps from umpteen different manufacturers there seems to be little ryhme or reason to the way they are made. Some do have the centre hole, and are thus ideal to use as Paul describes, some are flat ended and a few have a conical end that might fit a female centre.
Is my collection unique or do other have a similar mish-mash?
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1501 wrote:

My small ones do have a male cone, the bigger ones a female one. Depends on how they were ground.
Nick
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On or around Wed, 26 Sep 2007 17:41:48 +0200, Nick Mueller

I've seen pointy ones, not worked out what they were for though :-)
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Paul M wrote:

The center holes are an artifact of the manufacturing process, rather than a feature of the tool.
You pretty much have to find a maker that is still grinding their taps between male centers, rather than between female ones or in a collet.
Good luck!
Cheers Trevor Jones
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Most of my taps, and all of the small ones, have a 4 sided pyramid end. I find that using the drill chuck with the jaws open a couple of mm provides a sufficient recess for the end of the tap to hold it straight. It's not perfect but it's a lot better than I could do freehand
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Paul M wrote:

The tap wrench I use has its own dimple on the end - I also have a spring loaded point that is used to locate it. Some, but not all, of my taps have the dimple, but it doesn't matter, the wrench has its own.
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    Paul, I'm slightly red-faced! Since posting, I've actually had a look at my tapping chucks, I've got three different sizes, all Eclipse, of various vintages. All are fully hardened and three out of four have the dimple at the top. The body,with the flexible collet fingers at the bottom, is made from a single piece of steel, which is then heat treated to temper the fingers and this obviously hardens up the top too.
    If the need's important enough, why *not* try to soften the top. Others may have more creative solutions but one I've used before is to push the part into a good old potato, which will act as a bit of a heat sink. Just leave the top exposed and play a flame on it for a few minutes, to cherry red. Let it cool naturally, don't quench, of course. Not only will this probably do the trick, but you'll also have a tasty hot baked spud snack for when the job's done!
    Keep us posted! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Hi
Thanks for the replies.
I actually have one of the ratchet type tap wrench`s http://cgi.ebay.co.uk/DRAPER-45698-RATCHET-T-TYPE-TAP-WRENCH_W0QQitemZ290161430647QQihZ019QQcategoryZ64819QQssPageNameZWDVWQQrdZ1QQcmdZViewItem similar to above and I have centre drilled the back of the wrench whick works Ok. The main problem is height clearance when using the milling machine. When you add up the length of the tap wrench + length of tap + height of machine vice it takes up most of the space from spindle to table. By using a standard T type wrench it would give an extra clearance of around 60mm.
I also have a mixture of taps some with and some without the hole. The ones without do have a small dimple type of affair.
I might try the process for softening the top and then centre drill. Would it just be a matter of heating to cherry red and then quench to re harden?
Thanks again
Paul
On Wed, 26 Sep 2007 16:08:16 +0100, Chris Edwards

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[cut]

Most modern taps seem to be HSS and I for one have no idea how you soften this; I suspect it needs temperatures in excess of those achieveable with the usual propane torch.
In the case of carbon steel taps, you don't really want to soften the tap itself (unless you have decent heat treatment equipment). As was suggested, I too find potatoes ideal for this purpose (push tap into potato) and heat the exposed end.
You can grind a male centre on the tap quite easily (at least if it is small) using make shift equipment if you don't mind holding the tap in the lathe in a collet and using a tool postgrinder and then cleaning up the ensuing mess of grinding dirt from the lathe. I try and do it roughly first on the bench grinder using a drill sharpening type jig and then finish accurately.
Alan
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Paul, Given you are using a pillar drill / milling machine (presumably you drill the tappng hole then tap it?) why are you not simply using the chuck to hold the tap? you can drive this round by hand either (in the case of a drill) with a tommy bar, or with a suitable spanner. I avoid using hand tapping chucks where I can, I have *much* less tap breakage using the quill as a guide.
hth
Dave
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Hi Dave
The idea of using the machines own chuck sounds good. I will give it a try.
Cheers
Paul
On Thu, 27 Sep 2007 00:18:16 -0700, dave sanderson

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wrote:

I have one of those cheap aldi bench drills, I just take off the drive belt and slacken off the return spring for the capstan and in two minutes you have a tapping jig... I tend to drill with the mill, and tap with the drill...
Steve
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Paul M wrote:

http://cgi.ebay.co.uk/DRAPER-45698-RATCHET-T-TYPE-TAP-WRENCH_W0QQitemZ290161430647QQihZ019QQcategoryZ64819QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
An old tool maker friend of mine always used to tap under power on his mill fitted with a VFD. I subsequently fitted VFD to both my mill and pillar drill and now also tap under power with the tap held directly in the chuck. I was very worried at first, but now do it in preference to hand-held. Its also faster and more accurate.
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lemel_man wrote:

I recently had the joy of being allowed to use one of these: <http://www.microtap.de/Englisch/jobtap.htm Had to do 200 threads in brass, so I asked a friend who owns one whether I can come by and use his threader. Next time, I'll do the same! It took me about 15 minutes to finish all parts (and 45 minutes to go to him and back home).
Just push the tap into the hole and grab the next piece. Starts to rotate at a settable depth, reverses automagically (settable), checks torque, can beep if torque is out of settable limits, rpm can be adjusted, etc, etc.
Only the price tag is shocking!
Nick
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I got a set of these tap sockets, must be something similar available over there. http://buy1.snapon.com/catalog/search_keyword.asp?keyword=Tap+Socket+Set
__________ Andre' B.
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A carbide centre drill will fix any tap that needs a hole.
Wes
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