Broken Tap Extraction Fluid

[mickeyw]

Found this on fleabay. Apparently it can dissolve hardened steel taps etc in non-ferrous materials.

Experiences???

[Phil Hancock]

I cant remember what the actual chemical used is, but in model engineering circles it is a common problem when you are dealimg with taps that are 10BA and similar sizes in bronze castings. It apparently does work.

Upon checking up one method is a solution of 'Alum' the other that was also suggested was a solution of 'phosphoric acid' to disolve steel taps in non ferrous workpieces.

[simonr]

Looks like a great idea if it works! Just found myself a victim of the tap breaking thing on a part which took 3 hours on a CNC lathe (made up of a dozen or so operations) - I didn't half swear when I had to make it again!

Si

[MrKev]

With taps breaking off in aluminium, dunking the part in 20% Sulphuric acid will get eat away the steel, but not harm the aluminium. I've been experimenting with anodising small aluminium parts at home, and found this to be quite effective.

Kev

Edited June 23, 2010 by Mark
Chemistry Correction

[integerspin]

I tried alum, think it came from Tesco's, I was told about this years ago by an old

bloke who used to cast his own heads and stuff before the war. I never tried it till I

needed to remove a roll tap from an engine adapter casting[i didn't drill a hole deep

enough], think where I went wrong was not supplying enough heat, I was warming it with

a blow torch every now and again. After a few hours and no visible difference I used acid.

Like the bloke said, anodising is a good way of removeing ferrous parts from ali. If you send

soemthing for anodising, with Helicoils in[how do I know this?], it comes back minus the Helicoils.

So battery acid and a battery are needed. I bolted some aluminium tubing to the part, with a gasket between them

and filled the tube with acid, I connected the battery charger to a bit of ali welding rod and clamped

that to something so it was almost touching the tap. It took about a week to burn the roll tap out, but

the castings and heat treatment were something like £90 plus the time machining, so was well worth while;

when the tap was burned out the thread was still perfect. Only sign it had been done was the little circle of

anodising. I will try just hydrocholic acid next time, if there is ever a next time.

I have a vintage gearbox someone has tried drilling bolts out of, and made a major mess off, if

I have any alum left I will give it a proper try and take some pics.

If you do the acid thing do it well away from stuff that rusts, I had acid condensation all

over the filing cabinet the casting was on top of while the tap was being eaten away. I ended up throwing

the cabinet away, it rusted like hell.

[zim]

So this would work with trying to get out a broken manifold stud in a v8 head....hmmmm

[MrKev]

Edit: I meant 20% Sulphuric Acid solution. Don't use Hydrochloric Acid!

[mickeyw]

@ Zim

In theory, I suppose it would. Trouble is you wanted to immerse the whole head, you would have to strip the head of steel parts. Err... valve inserts..no so simple.

I guess if you could provide a means of local immersion, I'm thinking of a plastic tube sealed against the face of the head in the problem area - perhaps use silicon sealer, or plastiscene???

Sounds like it's a slow process, but if you could leave it for a few days to get on with it...

Does the volume of solution make a difference in the performance/time it takes?

Just my ponderings.