Snapping taps

Sounds like a black art to me but i'll give it a shot one day.

Michael W

Hello Michael.

Re your original question regarding broken taps, Can I ask were all the taps from the same manufacturer?

The reason I ask.is that I have recently tapped over 100, 5BA blind holes ( with reccomended drill size) in cast iron with the same set of carbon taps from a British manufacturer and the taps are still very usable.

I subsequently bought some 5BA HSS grnd taps for another job from the same manufacturer and they didn't seem sharp at all in fact were virtually unusable

Do you think you may have bought a duff Batch.?

Kind regards

Anna

Hi Anna,

It is a good point as they were not all from the same manufacturer, i do have some taps where the grooves along the pitch look as though theyve been smoothed over and not sharp, they get tight very quickly and i'm wary of using them.

I have changed from using HSS to M4 carbon taps from tracy's and haven't had a problem since, the shanks of some small HSS taps look so thin for how brittle a material HSS can be when the neck is too thin, this rule is often obeyed with turning tools, you wouldn't grind a neck too thin for a parting tool so why do it for a tap? it's not enough to support the forces involved. So from now on i generally go 0.1 over the stated size for tapping if i'm using those particular taps, the moment it starts to snag, i back the whole thing out and get another one.

Michael W

Having a loose adjustment screw on one of my Dickson tool holders I decided to clean out the thread & tap a deeper thread, I used a set of 5 mm HSS taps to start the process as there only seemed to be aprrox 3 threads of engagement so tapping deeper was a logical progression.

I only managed to get a turn on the 2nd tap when guess what ! yeah there is a broken tap in the hole, admittedly it''s not the first time I've broken a tap but it's annoying when its an expensive HSS one. I poured a few drops of some citric acid pickling solution into the hole & left it overnight, this morning it looks as though there is some reaction with the tap as it has started turning black, question is; has any one used this method of removing broken taps?. I don't have access to an EDM machine nor have the right size solid carbide drill ( expensive ).

Having looked back through previous posts I came upon the above article describing the use of Alum so have ordered a sachet ( 100 gms ) via link & will try that, so the next questions are..

What ration of alum powder to water is best ?.

How often does it need to be heated ?

Has /does Citric acid work as well ?

Any other information would be very much appreciated.

TIA

George.

Alum is only really suitable for when the tap is stuck in non ferrous metal as it does not know the difference between a steel tap and a steel tool holder so will attack both. Same with most of the other acids

Toolholders are hardened so that is what is the likely cause of breakage

I can vouch for the efficacy of Alum solution to remove broken taps. Even when the tap is in steel the solution works to loosen the broken tap so that the core of it falls out, there is no need to disolve it completely but it may be necessary to retap to a larger size if the thread is at all critical. In copper or brass there are no such worries.

Brian

I am probably an exception to the rule. The taps I have broken have always been HSS. I have never broken a carbon steel one (asking for trouble next time I use one!).

Like Anna, I find that the carbon steel variety are sharper and cut more easily. My HSS taps are of reputable manufacture and most of my carbon steel ones are from Tracy Tools.

Andrew.

This what Citric acid does to steel and as Jason has noted it can't tell the difference between toolholder and tap.

To remove the tap from the tool holder;......use a small stone on a Dremel to level up the broken tap then drill down gthe centre with a carbide drill,.....then slightly larger bits until just the outside of the tap is left in gthe hole then carefully use a scriber to break the remaining 'shell' of the tap and remove bits from hole.

One advantage of carbon steel taps over HSS is that they it can be softened by heating up the whole thing to say 400C (hotter than "blue" but not as hot as "cherry red" . The offending tap can then be drilled out.

Having said that, I have great confidence in spiral flute taps which I now use confidently down to M2. The evacuation of the swarf makes them much less likely to sieze

Rod

Edited By Roderick Jenkins on 21/04/2021 15:33:19

Thanks for the tip Bob, have done this method waaaaay back in the past & remember seeing the carbide drill glowing , have also used carbide tap removal drills as in pic..

**LINK**

**LINK**.

Both exhorbitant price; for the price of one of the Walton extractors I can buy a new toollholder. Thanks again.

George.

There is no substitute for having a number of different taps in the same size. Unfortunately this is too expensive for most people. I have some Densimet which is a heavy sintered tungsten alloy. It is useful for making heavy, stiff holders for carbide inserts. It can be turned and milled, and even threaded for holding the inserts. I had to tap some 2.5mm threads in it, so I bought a couple of Europa tools green band taps. They are premium quality, but I had great difficulty tapping the densimet. There are several types of tap available in any size, and I chose the wrong grade. An old unidentified tap from the box of 2.5's tapped the densimet much better.

I’m with Rod spiral point or spiral flute both types have front geometry that is different to conventional 1 2. 3 taps. The angles at the front of the tap are such that the cutting load is greatly reduced, that’s why industry uses them ( less breakages)

Probably the best way to go, have drilled out studs etc in similar fashion. I do have spiral flute /spiral point taps but didn't want to risk snapping these, as said it's probably 'cause the holder is case hardened & I was a bit over exhuberant with the tap, one of those instances when you know it's going to happen but seem powerless to stop giving it that 'bit extra' & all I wanted was to put a couple of extra threads into the holder.

I'll let the citric acid do it's stuff untill I get the Alum then try that; more a case of lets see what happens, it's not that I 'need' the holder as I've got 18 in all with various tools set up.

George.

The use of serial taps significantly reduces the tapping torque. Also using the second serial tap as a finishing tap gives a nice tighter fit on a std fastener - useful for stud holes.