Removing Broken Tap

It was bound to happen. Usually I'm very good at tapping threads but tapping M5 using a taper tap into stainless steel seemed to go OK but then didn't seem to sound or feel right and just before unscrewing the tap - thought I would give it just one more 1/4 turn and the tap broke right at the entry point. So no available tap to clamp to to extract. So need best way to get the remaining portion of the tap out - only about 5mm.

On a related issue - is tapping stainless steel any different to tapping aluminium or mild steel? This is the 1st time I've tried into stainless Steel - would like to know whether it was my method or just a poor tap I was using.

Totally different to aluminium and steel! I usually drill for a maximum of 50% thread engagement and always use a tapping compound plus quality, and sharp, taps.

Andrew

Know anyone with a spark eroder?

Depends upon the grade G303 is easy almost like steel, G304 might expect problems, G316S11 done many 5 times diameter depth with full contact ie not oversize hole but are a bitch putting it mildly.

Easy way out break whats left of the tap up in the hole. Sooner or later one of the three flutes will crack or chip away, just keep going. Might then thread out, if not break the rest of tap up, short sharp blows with suitable sharp tool.

9BA are a bitch 3 times blind hole depth.

Hi Colin,

If your tap is imbedded in stainless steel you can dissolve it with strong acid. The acid should not affect the stainless.

Peter.

At that size you might manage to unscrew it with electronic type pliers - they have longish pointed noses. Or you might be able to make something with 2 dowels sticking out / hand filed. I'd use silver steel and harden and temper it - dark straw.

Somebody I believe mentioned a carbide drill - wish you luck. The favoured way is spark erosion. I have heard of stellite being used but suspect it wont do the hole much good. The drills are also expensive.

Real stainless is a pig. The free cutting stuff which is slightly magnetic is a lot easier. The real stuff, marine grade seem to work harden. Last time I used it 3 drills to drill 2 holes. One went ok the other didn't and none of the drills were any good when I had finished it.

John

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I have previously bought taps specifically for Stainless steel, using them never gave a problem. Bought from Bruetsch Ruegger in Switzerland. Surely they must be available in the UK. I understand Rape oil is good for Stainless tapping.

Clive

Edited By Clive Hartland on 02/06/2015 20:34:29

Tapping stainless calls for sharp taps. Tapping lubricant is a must. Oversize tapping drill size helps a lot. Using serial taps reduces the amount of metal removal with the 1st tap.

A simple internet search will reveal lots of information on "removing broken taps".

Edited By Dinosaur Engineer on 02/06/2015 21:41:32

Edited By Dinosaur Engineer on 02/06/2015 21:42:00

Dormer Taps are available for stainless steels and other harder materials their web site even has an online selection route, I have used more general purpose dormer taps on stainless steel 316 and Dormer ones specifically for stainless and they like chalk and cheese.

As for removing taps left hand carbide drills is one option, left hand as it will tend to unscrew the tap rather than screw it in or a diamond burr in a Dremel.

BTW left hand drills do not work very well in keyless chucks for obvious reasons.

Bob

Hi Collin

Suggestion to remove the tap....

Go to the dentist!

Mine keeps diamond burrs for me sometimes. He throws them out when they are only slightly worn. They work fine for my needs and will cut hard metal or carbide no problem . You will need a high speed handpiece preferably Air driven, Fairly inexpensive on the net these days if you do not have one.

Its a pity we cant charge as much as the dentist for work on a small hole.

Regards
John

Industrial type Handpiece (I have a couple of these the small pencil type is nicer to use)

**LINK**

Gee dentist types as well (I guess you would also need some sort of regulator they don't have a valve)

**LINK**

Perhaps someone can enlighten me as to the Stainless Steel I am using. The short length I have left has the following imprinted on it (probably not all of the code).

...307/X-2 CR NI 18-...

Now I can't find a 307 in the USA AISI coding - it skips from 305 to 308 but I'm guessing its Austenitic (it is non-magnetic) and contains Chromium and Nickel

Did it! Thanks guys - the diamond burr trick worked just fine. Took a little time - but tap now dust and minimal damage to the hole - just waiting for my serial taps to arrive in order to have another go. I'll be more careful this time.

I have just been trying the warm alum solution method of removing a broken tap from a piece of aluminium.

After 2 days I can see no sign whatsoever of any change in state of the tap. The tap has letters 04 CPB 4-4k and AFS marked on it. I wonder if the tap is of a type of material unaffected by Alum or if the Alum I bought was of the 'wrong type'. (Ammonium Sulphate or Potassium Sulphate, other versions of Alum maybe?)

Perhaps this method only works for carbon steel taps? Does anyone know for sure?

I should like to persevere with this recovery method but not waste time exploring blind alleys.

I've got broken drills out by the following method. Boiler pickle [ dilute sulphuric acid] injected into the hole. Then warm it with a blow lamp. You have to do it a few times but the drill just pops out with the fizzing action of the bubbles! Works great in copper or brass, I don't know if the acid will attack the stainless. It will dissolve the points of the tap and it will probably then unscrew.

Colin, just be aware that the part-tapped hole may have work hardened at the point where the flute which caused the breakage (Yes I know you broke it) snapped off. Go real easy with that new tap - may be even better if you take Andrew's advice and drill a bit over size.

Bob

Colin - a bit late I know, but looks like 304L aka 1.4307 aka X2 CrNi 18-9 though none of the specs will be exact equivalents for each other.

Colin -

There is a huge raft of stainless-steel alloys developed for all sorts of different properties and applications, and their designations if not the alloys themselves vary a lot around the world.

You may well need more than just one country's standards tables to identify any of these alloys. The USA is only one country and favours its own specifications, so if it's not listed in the AINSI it may well be in the BS: EN, German DIN or other; but finding them is accordingly as complicated!

307 grades seem a bit odd though. It looks as if it's very much a welding grade, as the only references to it I found without spending half the morning, are as welding wire and rod.

Pretty sure you have the wrong Alum - several different chemicals are called 'Alum'. You want Potassium Aluminium Sulphate aka Aluminium Potassium Sulphate aka Potash Alum.

Dave

What do I know... but I think it is bad practice to use serial taps in Stainless. Parts of the unfinished threads get work-hardened, and then good-bye...

Just now I have 48 tubular 'thingies' in the workshop, at least 3 different grades of stainless steel (scrap from the merchant), diameter 16 mm, which should get a M12 thread at least 20 mm deep, I drilled 10.5 instead of the standard 10.2 mm, and will do the thread in one swoop with a machine tap. Can tell the outcome in a couple of days, if it still interests someone...

Kind regards,
Hans