broken tap in aluminum casting

[mopar92]

I was taping one of many holes when the tap broke, the casting is only 1/2 thick and the hole goes through the casting. How do you get the broken piece out. Its a # 6 -32 tap any help.??

Mike

 

[Mcgyver]

if broken in AL, it will dissolve out in a solution of water and Alum, available at the grocery store

 

[Stan]

Many things to consider before taking action. Depending on how deep the tap is now in and how much load will be on the finished thread makes a big difference. If the tap is less than half way in and it it is a taper or plug tap, I just turn it over and stick a pin punch in the hole and use the BFH. Run a new tap in the hole and all will be well.

If it is almost all the way to the bottom of the hole, I would drop some A-9 tapping fluid in the hole and use a broken tap remover.

I have read all the posts on different chemicals to use to dissolve taps in different metals but I don't have enough patience to set it on the shelf and wait for nature to take its coarse. Big taps (3/8" and up) in steel in either through hole or bottom hole I just blow out with o/a torch.

BTW: The usual reason for me breaking a tap is that I was too cheap to throw away a worn tap.

 

[rake60]

We did have a thread here about dissolving a tap in any nonferrous metal.

It can be seen here: http://www.homemodelenginemachinist.com/index.php?topic=270.0

It does work!

Rick

 

[mopar92]

Thanks to all. BTW Stan I was thinking that I should go and get a new tap just before it broke . It was a new tap last month but I had used it a lot (20 holes) . I'm new at this model building but the aluminum seem to work the tap more than say cast or brass. I was using taping fluid when it broke. Were do you get alum? drug store

 

[Stan]

All I know about alum (I don't make pickles) is that municipal water treatment plants use it by the ton as a flocking agent to settle small particles out of the water. They would probably give you a lifetime supply if you asked.

 

[shred]

I found alum in small quantities at one grocery store in the spice aisle. Several other grocery stores and a brewers supply store all turned up nothing, so you might want to call around before traipsing off anywhere.

 

[rake60]

Alum is becoming more difficult to find these days.

The food grade can be found in the grocery stores, but the cost is rather high.
If your in the USA here's a source to consider.

The Great American Spice Company

Lots of other good stuff there as well, but that would take me WAY off topic! LOL

Rick

 

[joe d]

Here in Montreal i found alum in the local pharmacy. No idea if it was a good deal or highway robbery as I've never bought it before. I suspect that in the end my solution was not near saturation, after two days soaking of a 4-40 tap in brass I finally lost interest in watching nothing happen and drilled it out, plugged the resulting over-size hole, re-drilled and started over with a new tap. Also I may not have re-warmed things often enough... Some day when I'm bored and the part isn't crying out to be finished NOW I'll try again.

Joe

 

[DickDastardly40]

In the UK I could not find Alum (Aluminium Potasium Sulphate) on any shop shelf. I asked in a local chemist and they ordered me a 1/2 kilo bag in for the next day which cost about £3.50 (IMS)

I made an estimated saturated solution and 'melted' a 7BA tap out of a brass cylinder block over about 3 weeks. Patience is definitely required, there was a whisp of black in the solution that showed something was happening; occasionally I'd give it a poke with a tapping size drill and stir up the liquid.

When the tap was fully disolved a thread was left which was carefully cleaned out with a new tap. I have not tried the same trick in aluminium.

The broken tap had been maturing for some 8 years in the hole and was ripe for removal. ;D

Al

 

[Eric L]

if you have a mill you can use a .093 - 4 flute carbide end mill to ever so gently and slowly raise the knee to mill the tap out. The end mill will probably be junk when you are done and you will still have to knock the teeth from the tap out of the hole. Make sure you use lots of cutting fluid.

 

[rickharris]

The most common use of Alum in modern times is as a mordent in dying to make the dye fast.

Look at the dye section of a large store for small supplies.