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strange taps

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Rich250226/05/2014 11:45:13
65 forum posts
2 photos

I picked up a box of assorted taps from fleabay, the 2 in the picture have no flutes, are they gauges ?

The large one is marked " mercury" and is more triangular in form not round .

Russell Eberhardt26/05/2014 11:49:38
2728 forum posts
86 photos

They form the thread rather than cutting it. Commonly used on softer materials.


Andrew Johnston26/05/2014 11:51:13
6577 forum posts
701 photos

I would have expected more of a lead, but they look like form taps. These taps do not cut the thread, but form it by deforming the metal. They work best on ductile materials like aluminium and some stainless steels. The tri-lobal form is similar to thread forming screws used in production. When the screw is inserted it forms its own thread, thus saving a tapping operation.



John McNamara26/05/2014 14:33:46
1336 forum posts
125 photos

Hi Richard

If you decide to try them, they use a different tapping drill size... As they do not remove metal the hole will be bigger than for a cut tap. to allow for the metal pushed up by the swaging. If they are marked check the manufacturers site. They work well on thinner sheet.


Rich250226/05/2014 19:52:45
65 forum posts
2 photos

No use to me, if anyone wants them on here you can have them for nothing if you send me an sae.

Small one is marked "5/ ? Drill 7.4 mm Goliath"

Big one is "3/8 BSF Mercury"

Nigel McBurney 127/05/2014 09:43:19
999 forum posts
3 photos

Yes they are thread forming taps,they require larger tapping holes ,ie about 65% thread ,the threads are stronger due to the forming action,

Advantages virtually no swarf,less tap breakage ,high operating speed ,ideal for cnc work particularly with electronic solid tapping with pitch control,reduced cnc machine downtime and very few scrapped castings. needs high performance soluble oil with regular control of lubricant strength.

No good for any other work,they are a high speed production tool

Ian S C27/05/2014 10:21:11
7468 forum posts
230 photos

Here's a page from my little book of taps and tapping. Ian S Cdrill sizes for threadflow taps (548x640).jpg

John Stevenson27/05/2014 10:38:32
5068 forum posts
3 photos
Posted by Nigel McBurney 1 on 27/05/2014 09:43:19:

No good for any other work,they are a high speed production tool


I disagree with that statement. I have to tap some 3mm holes in drawn aluminium bronze and this stuff is so grabby it ought to be in politics. With normal taps you hear the squeal 1.3453765 seconds after the tap breaks.

Using fluteless taps stops all that and tap life is up by 3,000 % as a broken tap is useless.

Neil Wyatt27/05/2014 10:48:50
18994 forum posts
734 photos
80 articles

I might struggle to turn a normal tap holder that fast...


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