TAPS, spiral or std

i am currently making a steel ball turning tool for my lathe.

I need to tap two 2.5mm hols to hold the tool bit.

I recently bought a set of Bergen taps, 3 taps per size, but to be honest on small holes i.e. M3 or M4 I often end up snapping the tap even though I use lube and back feed every 1/3 turn . I also have a set of Clarke taps which do seem to be more robust.

I appreciate you get what you pay for and realise that the Burgen and probably Clarkte taps are made in China.

So I then read up and hear about spiral taps, the advantage being they clear the swarf better.

So, to me question, am I better getting a m2.5 spiral tap or std 4 flute tap for this job?

Edited By petro1head on 01/05/2017 07:57:22

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

I've used a set of Clarke taps for 10 years and never broken one. If yours have 3 taps per size, are you using then in the right order?

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

petrol1head,

If you are regularly breaking taps you are probably using a too small tapping drill. I recommend that you buy the book Drills, Taps and Dies by Tubal Cain. He explains all about selecting appropriate tapping drills and include comprehensive table at the back. An excellent book for the price of one good quality HSS tap!

^^^^^ +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.

I am using the taps in the correct order and I have bought specific drill to suit the tap. It's more likely that I was being ham fisted

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.

Ensure the tap is started upright to the hole, go up say 0.1mm on tapping size drill and you should not break a tap. I always tap on the mill and bring a tapping guide down on to the tap when starting. Sometimes this is just a small threaded shank cutter held upside down in the collet/chuck to use the centre. I use the upside down cutter when I can't find the spring loaded guide I made 50 years ago. For taps with a centre in the end and not a point a simple pointed piece of silver steel will suffice. On bigger taps I hold them in the chuck and turn the first few threads in to the job by hand rotation of the machine. I've not broken a tap for 20 years but do always buy quality high speed steel taps.

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

Where the job allows ( which the one in question does) I just drill the blind hole deeper than needed to get a good thread length that way you can tap a blind hole with just a taper tap so still a one pass job.

Comparing the Clarke and Bergen taps the Clarke ones look noticably sharper.

I have bought a set of 2.5mm Volkel taps from Rotagrip for this job though and will buy a 2.1 drill as advised by Henry

At the Midlands exh. last year I bought a set of spiral taps plus tapping drills from Greenwood Tools, and they are excellent! On this basis, and also having a couple of other spiral taps, I thoroughly recommend them. I also now usually tap in the mill under power, setting the VFD to 5 or 10 Hz. One is only tapping for a few seconds so there's no downside to this. I drill the hole; replace the drill with the tap; bring down to the hole using the lever quill feed (as for drilling); hold the lever so the tap is just bearing on the job, switch on the spindle in forward so the tap cuts the thread, still holding the feed lever; stop the spindle when cut enough and reverse to back out the tap; all the time keeping pressure on the feed lever so the net axial force on the tap is zero. If it's a blind hole I just get the tap started; stop the mill, lock the quill, loosen the chuck; then raise the quill and complete the job by hand. So far no broken taps in dozens of holes.

Also I second the Tubal Cain book and technique. You almost never need full engagement, much better to use the minimum you can, it hardly affects the strength of the thread and actually since I got the book and started using his methods I have never broken a tap.

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

The other thing is to make sure the tap goes in straight. I got on much better after making a tap-stand and/or holding the work and tap in the lathe. Small taps are delicate and the cheap ones (carbon steel?), are particularly brittle.

I've not been able to find the product since, but at school I remember a stick of plastic or wax being pushed into the hole first. As the tap went in the stick was squeezed out like toothpaste taking the swarf with it. Anyone know what that was or am I dreaming again?

Funny you should mention 'Bergen'. I bought a set of their small metric spanners last week; they're 'fit for purpose' but have a poor finish. I have a hobby-horse about the foolishness of blindly trusting Brand-name purchases so I did some research. It seems that the original 'Bergen' were a US company selling expensive tools. They ceased trading many years ago. The name is now being applied to a range of what I suspect to be re-badged generic economy tools.

I have a motorcycling friend who has spent a fortune on Snap-On tooling, very nice. Every time I see him he tells me that they are worth it because they last for ever. I haven't had the heart to tell him that both my cheapo Japanese spanner sets are still going strong after 40 years. (It doesn't prove much because we're both moderate-use hobbyists, not professional mechanics.)

Dave

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

Well I have assigned my Bergen set to the bin (well actually given to a pal) and have purchaced a Volkel set

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.

When I first started work, after a period of being self employed, I bought a set of 1-10 BA carbon steel taps and dies as I just getting interested in model engineering and the inspection department that I worked in had a Boxford lathe.

Now, 50 years on I still use the set and only 2 taps have had to be replaced due to wear.

I think the previous comment about using the correct sized tapping drill and not aiming for 85% engagement is absolutely correct along with the use of lubricant.

Brian

So have I wasted my money now