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Sigh, practicing a skill I would rather not need

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Dave S17/04/2022 16:54:50
367 forum posts
90 photos

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

Roger Best17/04/2022 16:59:58
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369 forum posts
56 photos

Noooooo. face 24

Mike Poole17/04/2022 18:12:39
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Moderator
3335 forum posts
73 photos

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 mart17/04/2022 18:25:55
3771 forum posts
233 photos

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 Shaw17/04/2022 18:29:49
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1483 forum posts
398 photos

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 Phinn17/04/2022 19:11:18
753 forum posts
113 photos

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 S17/04/2022 19:12:48
367 forum posts
90 photos

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:

9d62e235-5463-4f44-826a-1b18f11583f2.jpeg

Carbide D bit:

7496b5a0-e5d7-4314-9d53-a39d7b8b9d14.jpeg

Peck drill 1 thou at a time…

ae4a01c9-fc18-4cad-8b59-8bd16d4736ab.jpeg

Then pick out the remains:

84173f77-96b0-4359-8359-f93436dfeb1f.jpeg

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

Dave

Peter Ellis 517/04/2022 19:46:17
101 forum posts
11 photos

Hi

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

Cheers

Peter

Dave S17/04/2022 20:20:44
367 forum posts
90 photos

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

Dave

Bob Worsley17/04/2022 21:10:24
118 forum posts

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

DMB17/04/2022 22:13:24
1312 forum posts
1 photos

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

DMR17/04/2022 22:43:55
127 forum posts
14 photos
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 mart17/04/2022 22:58:40
3771 forum posts
233 photos

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 Halford17/04/2022 23:26:59
2047 forum posts
23 photos

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 yet18/04/2022 07:43:26
6809 forum posts
20 photos
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 S18/04/2022 10:45:20
367 forum posts
90 photos

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.
091a41a4-b610-4be9-90c8-8b16b386cd78.jpeg

Dave

Thor 🇳🇴18/04/2022 10:59:33
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1627 forum posts
46 photos

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

Baz18/04/2022 11:35:01
723 forum posts
2 photos

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.

Nealeb18/04/2022 11:45:32
80 forum posts

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 🇳🇴18/04/2022 12:44:55
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1627 forum posts
46 photos
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

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