Help please - broken tap

[manofkent]

Hello all.
Yesterday I was tapping 7BA holes in the dome fitting of my Miss 10 to Eight boiler, and telling myself to be really careful not to break the tap.
Of course it broke, really close to the surface.

The material is copper. There is very little width of material to widen the hole.

My only plan at the moment is to
1. Soak in very thin oil
2. Warm it up with a hot air gun
3. Insert two tiny pins in the broken tap flutes
4. See if I can grip the inserted pins with pliers and twist.

Any advice gratefully received 

Many thanks 

John

[dhamblin]

If that fails you could always try the alum method as it shouldn't attack the copper.

Regards,

Dan

[ettingtonliam]

Try the alum method first, because if you've put oil on it you'll never clean the oil out well enough for the alum to penetrate.

[manofkent]

Thanks.
What is Alum and where do I buy it please?

John

[davewoo]

I've never tried the alum method, but I have successfully removed the remains of a tap from the bronze dome bush of a boiler. I used the method in Geo H Thomas's book making a small reservoir of plasticine around the broken tap and using sulphuric acid to eat the tap away, I believe the book says to use nitric acid but I only had sulphuric (used to use it for boiler pickling). Took a few days and repeated changes of acid but eventually the rusted bits of tap fell out. I seem to remember reading somewhere that Alum is available on Ebay, I think it has to be used hot but works faster than the acid method, as I said never used it but sort of filed it away for future use.
Good Luck
Dave

[weary]

Hello John,

further to Dave's post immediately above ->

you want Aluminium Potassium Sulphate available from ebay; or from your preferred supplier of course. You must have the 'aluminium' version as 'Potassium Sulphate' is also available and both are commonly called 'alum'. However, without the Aluminium it will not work for your use. I read on here somewhere that Aluminium Potassium Sulphate is also known as 'Potash Alum', so that gives you an alternative search-term.

Flood the area containing the broken tap by immersion or building a small 'coffer-dam' around the area and if possible keep hot. It is very slow (a matter of days not hours, despite the video linked to below!) but will work. You can always try and gently dig 'bits' out during the process to try and speed things up.

I found this relevant video on youtube. But a search is sure to turn-up others with more detail.

Regards,

Phil

[manofkent]

Thanks all for your excellent advice. 

ALum it is then. I will order it from eBay and hopefully be able to try it on Monday.

I will keep you posted. 

John

[martyn1936]

Alum is the first line of attack, I found it works much better warm/hot but if you don't have any success the last resort would be to take it to a firm and have it spark eroded out.
Good luck,
Martyn

[SteveW]

Guys,

Is it worth suggesting, perhaps reminding everyone, that carbon steel taps are notorious for breaking at a bad time, especially the small ones and usually in bronze or copper and most of all buried in a treasured life long project. Then again high speed steel taps can be twice or three times more expensive but much harder to break.

In my experiences, when doing multiple processes in any expensive piece there is a trend to get a bit more adventurous as the task advances and then it happens. A disaster when least expected.

What are the thoughts here for establishing a rule that one should push the boat out and buy high speed steel taps for the really important "it must not break tasks"?

[SteveW]

Nov 8, 2023 12:36:57 GMT SteveW said:

Guys,

Is it worth suggesting, perhaps reminding everyone, that carbon steel taps are notorious for breaking at a bad time, especially the small ones and usually in bronze or copper and most of all buried in a treasured life long project. Then again high speed steel taps can be twice or three times more expensive but much harder to break.

In my experiences, when doing multiple processes in any expensive piece there is a trend to get a bit more adventurous as the task advances and then it happens. A disaster when least expected.

What are the thoughts here for establishing a rule that one should push the boat out and buy high speed steel taps for the really important "it must not break tasks"?

It occurs to add and at the cost of quoting myself (above) ... given the price of our materials, the hours put into a piece and perhaps the impact on our newly discovered "Mental Health" the price of a single high speed steel tap for a special job is all but insignificant.

Not sure this applies to the eye watering cost of buying a complete set of high speed taps and dies.

(269)

[abby]

Never bought anything but HSS taps , but most of my threading and milling tool collection came from working at Clarksons.
Dan.

[peterk]

My son and I experimented with the use of allum to remove a couple of broken taps from phosphor bronze. We wrote up our findings (all very good) in Engineering in Miniature, in the May 2021 edition. I'm happy to PM a copy of the article, if this is helpful (and supported by the forum?). We heated the part/solution to just below boiling point and made sure that the end of the broken tap wasn't covered by a small bubble, thereby not allowing the solution to actually contact the tap (this stumped us for a while!). Once the reaction got going, it was very quick, with a stream of bubbles indicating that the reaction was working well. It took a few tens of minutes, once it was going, to remove the broken piece (and it was an HSS tap, albeit a very small one). I've tried to attach a photo of the reaction underway, but keep getting a message saying that the forum has exceeded its attachment limit (and the file is well under the 1MB limit stated). I'm a newbie here, so may be doing something wrong!

Regards

Peter

[mbrown]

Hi Peter,

I think most of us have been caught out by the "forum limit" message the first time we try to post pictures. There is a pinned thread called "Posting Photos" with full instructions. You have to upload the pictures to a hosting site like Flickr and then copy and paste the link.

Once I'd done it a few times it became second nature.

The video sounds most interesting...

Malcolm

[manofkent]

Hi

Peter,yes please do pm a copy of your article.
I assume the Alum is mixed with hot water?

Steve W - yes this was a HSS tap, from Tracey Tools as I recollect. Your advice is sound and HSS is my default for these tools.

Martyn, I do actually have an industrial spark eroder stored at the back of another garage, but the sheer hassle of getting out from behind loads of other stuff and recomissioning it means it is a very last resort. It is a Charmilles machine, and I had thought if I have to use it I could use distilled water as the electrolyte not great but would be easier on the boiler than the oil based alternatives.

The Alum powder is ordered,and should be used in anger over the weekend.

Thanks to all for your most helpful responses

John

[peterk]

I'll have a go at posting a pic when I have had time to read the 'how to' guide.

John - I will send you a PM.

Best wishes

Peter