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Thread forming taps

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RJKflyer27/02/2012 16:26:17
49 forum posts
3 photos

I have an opportunity to acquire some of the above quite economically.

At present I use hand taps, albeit in the mill with an excellent Walton pilot handle.

Given i do quite a lot in aluminium, wondered if it was worth trying some thread forming taps - any thoughts/guidance? Is this practical to still do by hand - I'm thinking M3-M6 only?

colin hawes27/02/2012 17:08:28
552 forum posts
18 photos

Thread forming taps are best for ductile metals, especially copper and soft aluminium, in sheet form .They are stronger than fluted taps and are usually used for machine tapping. Not suitable for tapping castings.As they work by deforming the metal a stronger thread should be produced Note the different hole size and lubrication required. Colin.

RJKflyer27/02/2012 17:33:49
49 forum posts
3 photos

Thanks Colin - yes this is what I figured - potentially ideal for ali where one can tend to get a rougher thread from 'cutting' vs. forming.

Ian S C28/02/2012 00:33:58
7468 forum posts
230 photos

I'v got a few of these taps, the only one I'v used is 6BA , in aluminium, and brass, (I don't do little BA) they work very well. IanSC

Bill Pudney28/02/2012 03:45:05
587 forum posts
24 photos

When I had to work for a living we had to make some satellite bits out of grades 2 and 4 Titanium. The parts had lots (dozens per part) of M1 threads. Conventional very high quality cutting taps were lasting maybe two threads, they usually broke after two, so we developed some expertise in getting the bits out! Someone suggested thread forming taps. They were imported from Germany, and they worked a treat, but they were very, very expensive. Taps would typically last 30 to 40 threads from memory.


Bill Pudney

Harold Hall 128/02/2012 10:28:48
418 forum posts
4 photos

I use M4, 5 and 6 in my controlled feed tapping stand in mild steel without a problem, have also hand fed them.

With there not being any swarf produced the finished thread is clear of such and screws just slide in which is a nice bonus when it comes to assembly.

Also,they are very good for thin parts as there is a full thread through the material and the process adds a degree of work hardening.

The cheap alternative is to salvage Taptite screw from items being disposed of as they have the same form as the rolltap and produce standard thread forms. One screw will be good for at least 20 holes in thin material, more if in aluminium


Ian Welford29/02/2012 17:09:34
299 forum posts

What size tapping drills should one use? I have M3, M4 , M5 and M6 forming taps?

Thanks Ian

Harold Hall 129/02/2012 20:33:42
418 forum posts
4 photos

As per my Metalworkers Data Book Ian, the values are-

M3. 2.8mm

M4. 3.7mm

M5. 4.6mm

M6. 5.6mm

I have been known to up M5 and M6 to 4.7 and 5.7 where load on the screw was not that great, or where depth of engagement was at least twice the diameter. They do though benefit from lubrication of some form, but not cutting oil.

The data book also includes other metric sizes as well as Unified fine and course, also BA sizes.

If I can give the book a plug, 220 pages of data for just over £5 is the best value book in the Workshop Practice Series, size wise that is. See here for more details.


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