Thread forming taps

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?

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.

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.

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

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.

cheers

Bill Pudney

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

Harold

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

Thanks Ian

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.

Harold