Broken Tap Removal

[NarrowGauge]

Whilst using a 10 BA tap to clean out a thread in a blind hole I have managed to break the end of the tap and wondered what options there may be to remove the small part left at the bottom of the hole.

The tap I was using had been broken previously, some time ago and I had ground the end off square to make a plug type tap.

The hole is 1/4" deep and I would estimate there is approximately 1/8" of broken tap remaining in the hole.

Do I recall hearing somewhere of using some sort of pickle to dissolve the tap? The work piece I was making is a cylinder made from Ph. Bronze.

Any suggestions would be welcome.

Thanks

Dave.

[ridleyian]

Get some alum from the chemist (used for bed sores!)
make a saturated solution , immerse the part in it and wait. The hotter you can get the solution the quicker it will work. As you approach boiling point you will see a stream of small bubbles issuing from the hole showing that the ferrous material is being dissolved but leaving the non ferrous metal untouched other than an easily removeable surface discolouration. I find that the occasional poke with a bit of (preferrably stainless) wire will remove the black residue and speed the process. Not that I have ever broken a tap of course! Yea Right.
Ian
Radnage
Bucks

[NarrowGauge]

Ian

Thanks for the tip, I have ordered some Alum today. Tried several chemists, but they did not stock the stuff, just hope the one who I have placed the order with manages to get it ok.

Dave.

[Allan Waterfall]

I wanted some Alum a while ago,none of the chemists I tried even knew what I was asking for,all I could say was that it was called Alum,I never did get any.
It seems to be on grocery store shelves in the States in the pickling section,so it must have a proprietary name.
If you get some could you post a reply as to what you get.?

Allan

[Tel]

Aluminum Ammonium Sulfate

[Allan Waterfall]

Thanks Tel..

Allan

[NarrowGauge]

Allan

I tried the larger national chains and an established independent chemist in my nearest large market town, but without success. They too, looked puzzled and asked what it was. I then tried a small chemist in a small market town, who at least knew what it was and offerred to order a 500g pot. I will keep you posted as to whether I actually get the stuff.

Thanks Tel for the chemical name, may prove useful.

Dave.

[3405jimmy]

A company in Sheffield took a tap out for me by spark erosion it cost a tenner, well worth it I thought.

Jim

[SteveW]

Guys,

There is a very simple spark eroder in No 104 MEW (out now). It uses a bit of electronics but this is no more than a couple of DC power supplies. The eroder uses a 100 ohm series resistor, a capacitor, bridge rect. and a 40..50 volts 4amp transformer. The rest is just a solenoid, micro switch and clamp. The solenoid rattles the electrode against the target metal and the sparks do the rest.

The article quotes a 6mm hex hole in 3mm steel in twenty minutes.

QED. (Quite Easily Done).

[NarrowGauge]

I finally sourced some Alum; my first order having failed. It certainly seems difficult to come by. I gave up trying to establish an account with BDH, who did at least , list the item.

Mixed up some saturated solution and dipped the cylinder. It became apparent that to get any action, the solution had to be kept boiling, rather than just warm. In fact when the solution cooled, the solution crystalised. It was a slow process, but after approximately 4 hrs, the thread was clear. I was very pleased and thanks for the advice given.

For those who may also be trying to get some Alum, mine was obtained from:-

S&C Reavley, 124 High Street, Burford, Oxon. OX18 4QR.
Tel: [phone].

I believe they had some small pots still available, but I bought their last 500g pot. However, they were confident that they should be able to re-stock and they will supply by mail order.

The label on the box confirms the producer to be:-

JM Loveridge plc, Southbrook Road, Southampton, SO15 1BH.

www.jmloveridge.com

Thanks again
Dave.

[Allan Waterfall]

Thanks Dave,at least I shall know where to get some now.
Can't really understand why it's so hard to come by when it seems so readily available in the States.

Allan

[chrissyvine]

I don't know if this is useful, Jewellers use alum as their pickling agent for removing flux after silver soldering operations.

A Jewellers supplier would almost certainly be able to sell some to a model engineer.

Chris.