Dissolving a Broken Tap in Aluminum or Brass

[rake60]

I had read several notes on this subject and decided to try it for myself.
A broken tap really can be dissolved from a non ferrous part.
It’s a simple but time consuming method of simmering the part in a
saturated solution of alum in water. My test piece was a scrapped aluminum
flywheel with a 2-56 tap broken off in an angled hole through the hub that was
intended to accept the set screw. After simmering in the alum solution
for about an hour and a half the outer edges of the tap turned to a rusty sludge
and it pushed out of the hole without any damage to the part.

For the size of the stock and time it took to make my test piece this process
would have been more or less a waste of time, but I had to see for myself
if it would actually work. It does quite nicely.

 

[Hilmar]

Hi Rake,the tap was it HSS or Carbon. Will it make a difference what it is?
I heard it works with carbon only
Hilmar

 

[rake60]

I honestly don't remember what that tap was.
It was broken off some time ago. I did find another piece of
aluminum that I know for sure has a HSS tap in it.
I'll try it when I get a chance.

Rick

 

[Bogstandard]

Hey Rick,
You got a supplier of bits with broken taps in them?
If so, can you give us the web address so I can get some, and try out the process.
(Just jokingly rubbing it in a bit).
BTW, what the hell is ALUM, you have some funny names for things in the US, there must be a UK equivalent name.

John

 

[rake60]

Alum is "aluminum potassium sulfate"
Here it’s commonly used as a pickling agent in, well pickles.
This post from a UK clock site, suggests using it to remove broken screws
from brass. Removing Broken Screws
It says that in the UK Alum is used to treat bed-sores.

My chemist son was home from college for the weekend and I was
discussing this with him. His explanation was it causes a rapid oxidation
reaction in ferrous metals. My reply to that was, "Oh I thought it made
it rust away real fast"
That drew his usual "I give up" grin..... :lol:

As for my source of broken taps John, of course they are purchased.
Why I’ve never broken a tap in my life!

What No Lightning Strike??? LOL

Rick

 

[Bogstandard]

Thanks for the info lads.
It seems like you use it for pickling vegetables, we use it for pickling people. That explains our government then, they must have all got bed sores on their heads.
Just got to get some bed sores now so the doctor will give me a prescription to get some.
I get free medication, so why pay for it.

John

 

[sidecar_jon]

I've got it from a normal high-street chemist before now, small packets of white crystals. I was using it to grow bigger crystals for my own amusement.

 

[J. Tranter]

Can you tell me wat the mix ratio for alum to water is. I broke a tap in a part that I have allready made three times and I really dont want to make it again.

 

[rake60]

It has to be a saturated solution.
Boil the water and add alum until you can't get any more to dissolve.
You only need enough water to keep the part submerged.
You do have to keep an eye on it and add water as it simmers off.

Rick

 

[ChooChooMike]

Daaaaaaaannnnnnnnnnggggggggg :'( Wish I'd know about this tip 5 mos ago. I busted off a tap in a brass block. My fledgling attempts at EDM'ing it out gave less then stellar results. Hole came out too big (copper probe I had made was too wide) and not deep enough.

I wound up trashing the part after some other dismally-related tries and pathetic fixes.

I could have used this technique and saved the day !!! So-to-speak ...

Mike

 

[kellswaterri]

Hello all,
check out my post on ...

http://modeleng.proboards20.com/

to my knowledge this process works with any ferrous material embedded in non ferrous material, broken taps, drills, screws, e/t/c...quite why, I have not been able to find out...
John.
(SEARCH under post...REMOVING BROKEN TAP...reply no 7..2/21/06)

 

[Swede]

Interesting and useful tip. One thing you DON'T want to do is to try a DC salt/acid type of setup. I don't remember where I read about it, but essentially it involved using DC power and some sort of acid (I believe diluted nitric) in an attempt to dissolve/erode a 5-40 HSS tap from a precious aluminum crankcase that had already seen perhaps 40 hours of work, and was near completion. The process eroded the tap (slooowly) but it also egged and eroded the aluminum.

I finally got rid of the tap this way: I chucked a new 1/4" carbide center-cutting end mill. Centered over the hole, I then moved the table slightly less than 0.125" to present the flutes, rather than the center of the cutter, to the broken tap hole. I plunged that end mill straight down and was amazed when that carbide end mill cut through the remnants of a HIGH SPEED STEEL tap like butter, with little chatter or fuss. I ended up with a .250" hole which I then plugged with a press-fit aluminum slug in a press, and redrilled and tapped the hole. The repair was invisible.

One way I've found to get through noxious materials like stainless, some aluminums, inconel, etc, is to alternate a taper and plug tap until you are through. Start with the taper, and when the forces get borderline scary, back it out, and then use the plug tap. Go back to the taper tap, and repeat. The two profiles complement each other, and while tedious, it beats a broken tap anyday.

Now all I need to do is find some alum for a rainy day!

 

[Steve J]

tried it today and it worked fine. 2 oz of alum in a 6 x 6 pyrex pan and about an inch of water. three different sessions of about an hour and a half each time and kept it at just a simmer. you could see the bubbles coming out of the hole as it simmered. little sludge in the pan and the tap (4-40) is gone! saved me about 3 hours to make a new one. the part is an aluminum connecting rod for a panther pup 4 cyl. thanks guys.steve

 

[gilessim]

Swede, thanks for that tip about the stainless!, I'm just encountering that one today, just off to replace one broken tap that I managed to get out with a centrepunch!.

Giles

 

[alan2525]

I'm feeling more at home here by the minute!

It's good to know that there are others here with draws full of odd shaped pieces of brass festooned with the remnants of broken off taps sticking out like a hedgehog!

I'm always under the impression that if you muck something up it's because it's a little difficult and if it was too easy every joe would be doing it.

If you run out of space in the draws, for smaller components you can always push them into a potato and throw them over your neighbours fence!

 

[kvom]

Today I went to the drugstore to get "alum" for dissolving a broken tap in a brass piece. What I got was ammonium alum. Will this work the same as potassium alum?

 

[Holescreek]

Thanks for the tips guys! I just sent a link to a friend of mine with a freshly broken 6-32 tap in a chunk of aluminum. I have never tried the chemical route before. Last time I took a tap out of alminum I did it with an arc welder. I wrapped tape around the sides of the rod and stuck it down into the hole and let it attach to the tap. The initial blast of heat loosens the tap then I unscrewed it with the welding rod. I have also done this with a mig welder. -Mike

 

[Holescreek]

I waited a bit to see if my friend would post about trying the alum but I guess not. He went to the local grocery store and picked up a box of alum in the spice aisle, mixed it it water to saturation and immersed the aluminum part with the broken off 6-32 tap in it. Next day, nothing had happened. He went back to the store and found another box marked "pure alum", same process, nothing.

Any one else tried to use the store stuff yet? -Mike

 

[rake60]

This is what I buy:

It has to be a saturated solution left on a simmer over low heat.
It usually takes 10 to 12 hours.
I do that on an old electric hot plate on the back porch
since my wife isn't real happy about her kitchen smelling like
alum.

Rick

 

[shred]

I've used that same stuff from the spice aisle on a #50 drill that snapped off in some brass. It took a couple days to get it loose enough to pick out, but I didn't heat it beyond the initial over-saturation part (loose alum crystals hanging around in the liquid doesn't seem to hurt anything and that way you know it's saturated)