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Brian H16/08/2019 15:18:33
2218 forum posts
113 photos

As is the 8BA Plug tap that is broken in a 1/8" inch deep blind hole!

Any (sensible) suggestions welcome, as is an offer of spark erosion near Mansfield with a financial contribution from me.

Please don't suggest heating it to red (it's a carbon steel tap) because it's in a silver soldered assembly!


Edited By Brian H on 16/08/2019 15:25:43

Dave Smith 1416/08/2019 15:43:57
187 forum posts
28 photos
This comes up on an internet search.
Meden Square
NG19 7SQ
United Kingdom
KWIL16/08/2019 15:51:05
3414 forum posts
66 photos

You do not say what metal the tap is in.

GoCreate16/08/2019 15:54:49
386 forum posts
119 photos

I broke a 7 BA tap in a blind hole the other day, I managed to grind away the tap using a small diamond coated burrs with a Dremel. I basically ground away the centre portion of the tap after initially grinding the top surface reasonably flat to get a good start. I used a fine pointed burr and a very small spherical burr, alternating between the two.

I did this with the aid of a desk illuminated desk magnifying glass.

It took 15 - 20 minutes and I was surprised how well the it went. 8ba is a little smaller though but I think manageable by this method.


old mart16/08/2019 16:04:57
3317 forum posts
203 photos

Take the offer of spark erosion and cough up the money.

Trevor Drabble16/08/2019 16:19:54
257 forum posts
5 photos

My suggestion would be either carbide drill from M A Tooling on Attercliffe in Sheffield on 07973843152 or a carbide burr from J B Cutting Tools in Dronfield on 01246 418110 . I got some minature burrs from J B at last year's Midlands show , and they are very good . Also , if you visiting Meadowhall in the near future , Took Shed in The Lanes has a small stock of Proxxon carbide burrs . Hope t all helps . Please post your progress so we may all learn . Trevor.

Brian H16/08/2019 17:57:24
2218 forum posts
113 photos

Many thanks for the suggestions all. The material that the broken tap is in is a mixture of brass and gunmetal.

I seem to remember that there is a chemical solution that has been mentioned before on here, that disolves the steel, but I can't remember what it is.


Rod Renshaw16/08/2019 18:05:13
301 forum posts
2 photos

Memory suggests that the chemical is alum, as used in cooking, but I can't remember the details. I seem to remember it takes quite a long time.

Roderick Jenkins16/08/2019 18:21:38
2122 forum posts
582 photos

With respect, you wouldn't need to heat the fabrication up to red heat in order to soften a carbon steel tap. Tools are usually considered to be spoiled if they get to blue, which is about 300C. You've another 300C to play with before the silver solder starts to soften - and that's ignoring any liquation effect which will raise the solder melting temperature even further.



Tomfilery16/08/2019 18:45:46
131 forum posts
4 photos


The chemical you mention is Alum, however, I managed to get a broken small drill (1.5mm dia) out of a brass item by leaving it soaking overnight in citric acid. The next day the drill had basically turned to rust and could be poked out with a scriber.

If you use clean citric acid, rather than some which has had copper in it, you won't get a deposit of copper on your item.

Good luck.

Regards Tom

Samsaranda16/08/2019 19:44:20
1193 forum posts
5 photos

If you need Alum it is readily available on the internet, when I ordered some it took only a day to arrive, can’t remember where I ordered it from but there are plenty of suppliers..

Dave W

ian j16/08/2019 19:48:01
304 forum posts
278 photos

broken tap remover.jpgremoved broken drill.jpgrecently I broke a No. 50 drill in a block of Aluminuim . Some time ago I bought a product called BTR-10-broken tap remover, (Translunar technology Ltd , Bucks) it contains 33% aluminum sulphate.

The instructions say to dissolve a quantity in water in a aluminum /glass container and simmer the part . It states no action occurs at a lower temp.

After approx 1 hour enough of the drill had been dissolved and it just fell out.

removing broken drill.jpg

norman royds 216/08/2019 20:41:09
48 forum posts

the chemical I use is hydrochric acid it dissolved carbon taps the problem is tirying to buy these days regards norm

John Reese16/08/2019 21:18:18
972 forum posts

Is alum safe on copper alloys?

peak416/08/2019 22:38:31
1469 forum posts
159 photos

BrianH, whereabouts in Derbyshire are you?

If you're in easy reach of Buxton, I had some Alum arrive a month or so ago off ebay, You're welcome to a bit.

I bought it ready for when I brake a tap in a bit of motorbike one day.


Ian S C17/08/2019 08:24:37
7468 forum posts
230 photos

Alum is usually available in garden shops, and the cooking dept of the super market.

Ian S C

Mick B117/08/2019 08:50:05
2005 forum posts
116 photos

Have you an option to move the hole and drill and tap elsewhere?

You can see the attempted expiation of my sin in the position of the LH bearing strap retaining bolt (also due to a broken 8BA tap) here:-



Anthony Knights17/08/2019 08:52:33
556 forum posts
233 photos

Hi Norman. Hydrochloric acid is the main constituent of B&Q's Brick Cleaner.

Brian H17/08/2019 14:38:32
2218 forum posts
113 photos

Many thanks to all on here for the suggestions and offers. I've now managed to secure a small amount.

I first came across alum as a young apprentice with Crossley-Premier Engines. One of my first jobs was to pressure test valve guides which where hollow cast iron castings with water passages to cool the valves on diesel and gas engines.

They were tested to 25psi (as I remember) and any porosity or leaks were fixed by the addition of a teaspoonful of alum which VERY quickly rusted any defects so that a second pressure test could be carried out to ensure no leaks.


Brian H17/08/2019 17:47:31
2218 forum posts
113 photos

Just discovered that I needn't have made the holes blind! They will just go through without leaving a witness in the mating parts.

Also realised tht the two holes that I broke a tap in,needn't have been put in at all.

Must get my brain in gear next time.


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