Sigh, practicing a skill I would rather not need

[Dave SParticipant @daves59043]

I have just snapped another M5 tap on my current project.

<Sigh>

Now I get to practice tap removal again.

That is a skill I wish I didn’t get the opportunities to practice.

Dave

[Dave SParticipant @daves59043]

[Roger BestParticipant @rogerbest89007]

Noooooo.

[Mike PooleParticipant @mikepoole82104]

Are you tapping a difficult material or just suffering from a wobble that snaps the tap? A difficult material can be made a bit easier by drilling for a less than full thread depth. To combat the wobbles it can help to use a drilling machine with a spring loaded centre to keep the tap true to the work, a mill or the lathe can also be used to provide the same service or a universal pillar tool if you have one.

Mike

[old martParticipant @oldmart]

The trouble is that good taps come in different guises, to optimise different materials. I had to tap a 3mm hole in Densimet which is a Tungsten Cobalt alloy and bought a green ring tap intended for hard material. It did not want to do the job, despite being new and industrial quality. I looked through the box of small metric taps and found one that tapped the hole easily and it looked very second hand. I might have been better off getting a tap intended for aluminium.

For hand tapping, you could make a tap guide that keeps the tap square to the hole, just a piece of metal with a hole drilled using a drill press or mill that the tap can just pass through.

[Rik ShawParticipant @rikshaw]

I have found that you are more likely to break a tap if it is blunt. I use good quality British made HSS (Presto, Dormer etc) but even these get blunt eventually.

As for carbon steel jobbies – I would not give them house room even though some swear by them.

Rik

[Bill PhinnParticipant @billphinn90025]

There are many reasons for tap breakage [here are just a few of them], but the most over-arching reason in hand-tapping is insensitivity on the part of the operator to what the tap is actually "going through" at all times during its use.

You have to develop a feel for the tap in the material and know whether the tap is liking or disliking what you are doing with it. Invaluable practice can be obtained without great expense by tapping many consecutive deep blind holes with small taps on a range of scrap pieces of material.

[Dave SParticipant @daves59043]

HSS from a reputable source. Nearly new, probably done under a dozen holes.

Just one of those things I guess, no difference in the procedure from how I’d normally work.

Some pics:

Carbide D bit:

Peck drill 1 thou at a time…

Then pick out the remains:

Rescued, thread ok and part usable.
It’s good that this is possible but a trick I would rather not need…

Dave

[Peter Ellis 5Participant @peterellis5]

Hi

Where did your carbide D bit come from ? (asking for a friend !)

Cheers

Peter

[Dave SParticipant @daves59043]

I made it from a snapped PCB drill. I have a Deckel S0 grinder.

Dave

[Bob WorsleyParticipant @bobworsley31976]

Is it just me or do the flutes look more than a little uneven?

[DMBParticipant @dmb]

My take on this caper –

1. I never buy 2 nd hand taps ( or drills) Only new, sharper.

2 Always use methods of guidance as outlined above by others.

3 Try to avoid tapping blind holes, only through holes.

4. If blind hole tapping unavoidable, don't use grease or any kind of tapping sludge, however good it's supposed to be. Only use thin oil. Much easier to wash out swarf from the bottom of the hole with say, paraffin.

5. If in any doubt, use next larger diameter tapping drill.

6. Consult a reputable drill and tap guide table and don't use the smallest drill sizes, look at the percentage clearances. Not normally necessary to go beyond 70-75%. Tight clearances put a lot of extra torque strain on the tap for very little gain in thread stripping resistance.

6. Frequently remove tap and clear out swarf then start again. Smaller the diameter, the more important it is, to avoid swarf compaction at the bottom of the hole. Compaction could break tap and certainly make it harder to remove said swarf.

Hope my notes prove useful to the OP and anyone else in difficulty.

 

Edited By DMB on 17/04/2022 22:17:36

[DMRParticipant @dmr]

Posted by Bob Worsley on 17/04/2022 21:10:24:

Is it just me or do the flutes look more than a little uneven?

Looks like an Acme tap to me. Good list of advise from my almost name-sake

Dennis

[old martParticipant @oldmart]

I was glad to have solid carbide drills when I snapped a 1/4" tap in steel, it was not very sharp and the hole was a bit small. The carbide stub drill made removing the tap look easy, although I was rather apprehensive of the outcome.

I agree with DMR, the remains of the tap do look strange.

Edited By old mart on 17/04/2022 23:00:52

[Dave HalfordParticipant @davehalford22513]

The thread on the remaining bits of the tap looks wrecked.

When a tap is going to stick it, goes stiff, then springy, then bang. The trick is to let the pressure off when it goes stiff and try to back it out. Springy means it is a 50/50 chance of me having to reach for the plasma cutter to blow it out the busted bits.

[not done it yetParticipant @notdoneityet]

Posted by Dave Halford on 17/04/2022 23:26:59:

The thread on the remaining bits of the tap looks wrecked.

When a tap is going to stick it, goes stiff, then springy, then bang. The trick is to let the pressure off when it goes stiff and try to back it out. Springy means it is a 50/50 chance of me having to reach for the plasma cutter to blow it out the busted bits.

Dave,

How small can you go with the plasma?

Without full details of what is ‘normal practice when tapping’, for the OP, it is difficult to give specific improvement suggestions.

I feel a lot of people only buy one tap of each size, when a set of three would be much less likely to end up with breakages. Indeed, a lot (most?) of cheap sets on the market only include single taps. If it is a through hole in relatively thin material, a taper tap may well be adequate, but certainly for deep tapping, starting with a second tap, at high thread engagement, is not such good practice.

Alignment, in deeper tappings is, very important as one side of the hole will be equivalent to tapping with increasingly less than the proper tapping size until the tap is cutting 100% of its depth on one side while trying to bend the tap as it cuts.

M6 (in that section ) would be my choice, if at all practicable.

[Dave SParticipant @daves59043]

Whilst I mostly just wanted to moan to a group of people who would understand there are a lot of useful

comments here.

The holes are thru, drilled with the tapping drill I always use. Whilst I only need a couple of diameters of engagement the back of the hole can poke through. I try and avoid blind holes if possible it just adds to the pucker factor…

The taps are serial ones – so the taper tap is actually smaller diameter, then the 2nd and then the thread is fully formed by the last tap. I have been using this style for metric holes for a long time, purchased from Arc.
That’s one of the reasons the thread look shot – they are not full depth.

The green goo is Trefolex. I find it helps loads.

I would have used M6, but the linear rails are designed for M5.

I managed to get the rest tapped using the older set of the same taps.

Dave

[Thor 🇳🇴Participant @thor]

Hi Dave,

You are not the only one that has broken a M5 serial tap. I have never seen a carbide D-bit used to remove the broken tap, only a tool that was triangular in shape.

Thor

[BazParticipant @baz89810]

Thor cannot understand a word in the link you posted but they look like stellite drills, great for drilling anything hard but have to be run hot, no coolant. Unfortunately stellite is now difficult to get hold of.

[NealebParticipant @nealeb]

Looks very like the job I did building my CNC router. Lots of M5 holes in steel tube. The tube was nominally 3mm but backed inside with 4mm strip for more thread depth. I used a spiral-point machine tap in a cordless drill, Trefolex, and straight through in one pass. Can't remember how many holes now but there were two rails 1800mm long so quite a few. Was I lucky? Have to say that in general I use machine taps these days even tapping by hand.

[Thor 🇳🇴Participant @thor]

Posted by Baz on 18/04/2022 11:35:01:

Thor cannot understand a word in the link you posted but they look like stellite drills, great for drilling anything hard but have to be run hot, no coolant. Unfortunately stellite is now difficult to get hold of.

Sorry Baz, I used an example from a Swedish supplier I use, just to show the shape. They are used to drill out broken taps much the same way the D-bit Dave used. They are made from tungsten carbide and ned 1500 to 3500 RPM and a steady feed.

Thor

[Dave HalfordParticipant @davehalford22513]

Posted by not done it yet on 18/04/2022 07:43:26:

Posted by Dave Halford on 17/04/2022 23:26:59:

The thread on the remaining bits of the tap looks wrecked.

When a tap is going to stick it, goes stiff, then springy, then bang. The trick is to let the pressure off when it goes stiff and try to back it out. Springy means it is a 50/50 chance of me having to reach for the plasma cutter to blow it out the busted bits.

Dave,

How small can you go with the plasma?

So far 7BA on a steel through hole. The tips have a cross cut in them, all you do is draw a cross over the hole centre and align the tip and work crosses with each other and give it a quick PSST and the busted tap comes out as sparks. The Plasma jet is about 1mm dia and so far the thread has survived untouched.

[Dave SParticipant @daves59043]

Managed to complete the second part without any mishaps  The “backing” is 30mm square, so hopefully adequately rigid.

The D bit technique is one I got from James Harvey’s Machine Shop Trade Secrets. It’s a good book of short tips and tricks. I misremembered it slightly – he uses a ball nose, which presumably is a better geometry. He also likes to make the cutters hexagonal rather than round for some reason.

The important bit tho I’m sure is having a rigid setup and pecking a thou at a time:

Mods – if there is any sort of copyright issue then feel free to remove the pictures- I think it’s ok for educational sharing.

I’ve used this truck a couple of times on taps, but also to rescue a watch case where I snapped a tiny carbide drill in 316 stainless. In that case the cutter was bigger and I sleeved the hole, but the D bit did the job, with the tiny drill shattering as the pecking happened.

Dave

Edited By Dave S on 18/04/2022 14:44:00

[Simon Williams 3Participant @simonwilliams3]

I've learned quite a lot out of this saga, only sorry that it has to be at the expense of progress. But it does strike me that there is the makings of a magazine article in the art of tap removal/carbide drilling here.

I look forward to it.

Rgds Simon

[not done it yetParticipant @notdoneityet]

Posted by Dave Halford on 18/04/2022 14:39:00:

Posted by not done it yet on 18/04/2022 07:43:26:

Posted by Dave Halford on 17/04/2022 23:26:59:

The thread on the remaining bits of the tap looks wrecked.

When a tap is going to stick it, goes stiff, then springy, then bang. The trick is to let the pressure off when it goes stiff and try to back it out. Springy means it is a 50/50 chance of me having to reach for the plasma cutter to blow it out the busted bits.

Dave,

How small can you go with the plasma?

So far 7BA on a steel through hole. The tips have a cross cut in them, all you do is draw a cross over the hole centre and align the tip and work crosses with each other and give it a quick PSST and the busted tap comes out as sparks. The Plasma jet is about 1mm dia and so far the thread has survived untouched.

Thanks Dave. Another possible use for the recently acquired plasma cutter.🙂

I have broken a couple of taps in the last couple of years (none for a long time before that). One grabbed deep in brass (possibly not quite threaded straight enough?) and was dissolved away, with alum. The other (caused by not resetting my electric screwdriver to the appropriate torque setting🙁 ) was bypassed with a fresh hole drilled close by.

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