I don't have any spiral taps and can't remember the last time I broke a tap. Set of 3 standard Volkel ones from Rotagrip should do you OK

Edited By JasonB on 01/05/2017 07:58:15

Bucking the trend here, but… I have a set of spiral taps bought from Cromwell on special offer. Still not cheap though, but very good value for money and work very well indeed especially in blind holes.

John

^^^^^ +1 on all of this. Tubal Cain's Model Engineer's Handbook also has all his charts for correct drill sizes to get 85 per cent, or even 65 per cent, thread engagment, which still gives full strength threads but cuts WAAAAAY down on broken taps in these smaller sizes.

Breaking taps may be more down to technique rather than brand…

Using a slightly larger tapping drill can make a real difference e.g. for M2.5 I would use a 2.10mm – 2.15mm drill in preference to the recommended 2.05mm depending on the material. YMMV.

Using a lubricant like Trefolex can also help.

Spiral taps every time for preference, they are a one-pass job, without the necessity to start taper, then 2nd and then plug/bottoming.

Rule 1 – Buy decent HSS taps from professional suppliers

Rule 2 – Drill the tapping hole for partial thread engagement, for M2.5 in steel I'd be drilling 2.2mm

Four flute? I've just looked at a selection of my small taps (<6mm) and they are all 2 or 3 flute. I wouldn't expect to see a 4 flute tap much under 10mm. Four flutes simply doesn't give enough room for the swarf.

Spiral point and spiral flute taps are intended for machine tapping. Spiral point are for through holes and push the swarf forwards. Spiral flute are for blind holes and push the swarf backwards, out of the hole. In a ductile material you will often get spirals of swarf exiting the hole. Despite being intended for machine tapping both SP and SF taps can be used by hand without a problem.

I have a few spiral point taps but I tend to use spiral flute for my most common threads, blind or through hole, machine or hand. I'm with KWIL on this; you only need to buy one tap, they cut easier than hand taps, the swarf tends to get ejected rather than jamming and they cut to within a pitch or two of the bottom of a hole in one pass. I seem to end up tapping a lot of blind holes where drilling deeper is not an option due to design contraints.

Here's the tap I will be using this afternoon, 3/4" UNF:

This is for the pipe connections for an experimental heatsink. The pipe bore needs to be a minimum of 12mm, but the heatsink also needs to be as small as possible, so 1/2" BSP is out. Of the common threads UNF is the finest pitch in 3/4". I already have a set of 3/4" UNF hand taps but the hole isn't deep enough to allow them to be used.

Andrew

Hi Perto1head

from someone that uses taps everyday for work….

As Andrew says – Rule 1 – Buy decent HSS taps from professional suppliers

both Bergen and Clarke taps are cheap carbon steel and don't compare to decent HSS

Spiral fluted taps clear any swarf far better than straight fluted ones.

Hi Sillyoldduffer

I vaguely remember a similar product – was it a wax crayon ?

I Use spanners / sockets etc every day and snap on tools are far superior to cheaper options, they are more comfortable to hold for longer periods, usually fit better, wear less and are stronger than many other premium brands and of course the biggest thing is if you break it they give you a new one .

Theses days Halfords ​are doing a nice professional range of tools with a similar guarantee but you need to show the receipt, I also find them good tools for the money and ideal for a newbie or someone wanting good tools at reasonable money.

Tony

Edited By Antony Powell on 01/05/2017 12:28:45

I have both carbon steel taps and HSS, I can't tell the difference in use and I have yet to wear out any carbon steel taps. For hobby use I don't think it matters as long as they are decent quality.

Tubal Cain's tapping drill sizes are the way to go, Using the manufacturers chart's suggested hole size, is a recipe for breaking taps.

Andrew.

Not at all – I learned a few things too. (Thanks chaps)

Don't be surprised to break small taps, it's not that unusual. How to remove a broken tap from the hole is a popular forum topic too!

Painful experience has taught me that a gallon of patience is needed for every teaspoon full of cutting fluid. I'm not a natural in the workshop and find that the problem is often me rather than the tool. I improve slowly with practice. I'd suggest starting with inexpensive new taps (provided they're sharp) on brass. M4 is big enough to take a bit of abuse: if you break one it's probably bad technique. My taps mostly come from Tracy Tools and have met my hobby requirements well.

It's useful to experiment with different sized holes. Unless it's critical I usually drill tap holes a tad bigger than recommended in the tables, e.g 3.5mm rather than 3.3 for M4. This weakens the fastening slightly, but reduces the strain on the tap enormously. A trick learned on this forum.

The metal being tapped makes a big difference too. Tapping M4 in a 3.5mm hole is brass is easy. Tapping M4 in a 3.2mm hole in steel is much harder. Aluminium is deceptively soft but the swarf tends to stay in the hole and jam the tap, snap! Copper is horrible – it tears.

Take care to remove swarf and always apply lashings of cutting fluid, CT90 works for me.

Dave

Edited By SillyOldDuffer on 01/05/2017 15:14:27

No, you will have a set of 3 good quality M2.5 taps that will cut well. Given that the hole you intend to use them for is to take a Torx screw for an insert I would not go larger than 2.1mm for the tapping drill as there is not much length to these screws and we tend to wind them in quite tight.

You will also be able to use them in situations where you cant assure there is support for the other end directly above the work which is where a taper tap will be easier to start true into the hole.