broken tap in aluminum cranckase

[petertha]

Dangit! 2 holes away from completion & I broke an M3 tap. I really cant say how, the preceding ones went perfectly fine & I did all the holes & tapping operation identically. It was a brand new, good quality tap, chip ejecting style which I've had excellent good results with in the past. Lots of WD40, controlled tapping....

Anyway, I finished tapping the last 2 holes while it was all set up on the rotary then removed part to examine. I tried heating the CC up to expand a little & gripping the 1mm tap remnant but it just crumbled. Now its now essentially flush. I really don't feel in the mood to start another CC right now. Any successful experience or solutions you can recommend? The hole is 0.300" deep & suspect the tap is 0.250". I can't seem to locate prior threads, Alum or something? And no, I don't have access to EDM nor am I interested in building one.

 

[Foozer]

Aluminum Potassium Sulfate (Alum) A warm saturated solution will dissolve the tap. Broke a 1/4-20, took a couple days. Mixed solution in a glass container set upon one of those coffee cup warmers and changed the solution after 24 hours. Leaves a little soot residue on the part, comes off easy.

 

[goldstar31]

Probably the easiest way to obtain alum is to buy a styptic pencil. This was the thing that old wearies( me) used to stop bleeding when using old fashioned razors!

Having said that, your breakage could arise from lack of proper alignment of your tap or - ahem- it was blunt------or both!

The cure is possibly to follow a lot of my correspondence about such things as Universal Pillar Tools and using a shaped abrasive stone to 'tidy up' the lead on taps.

I must leave it for you to ponder.

Norman

 

[Cogsy]

Never tried the Alum myself but I have heard many stories of how well it works, albeit a little slow. Definitely worth a shot before remaking a crankcase.

 

[django]

You could try putting a couple of needles down the flutes and gently rotating the tap back and forth (with a pair of pliers) it works about 60% of the time but you must make sure that any bits of broken tap or swarf are blown out and use plenty of WD40. Remember gently does it. Good Luck!

Paul.

 

[Journeyman]

Alum works, I have used it. It needs to be hot, just off boiling, and a saturated solution. It wont work at room temperature I discovered after two days trying!

John

 

[mcostello]

Alum does not always work. I made a saturated solution and left it on a warm wood stove for a week with no result.

 

[XD351]

You may have to resort to a small carbide end mill .
Being so small using a 2mm carbide mill would be a delicate operation !
I have in the past given a broken tap a few very light taps with fine pin punch and a small hammer to try to loosen its grip - works sometimes .
Last ditch effort if all else fails is plunge a 4mm carbide end mill in and machine the whole tap out , then tap the new hole 5mm so you can install and loctite a threaded plug in then re drill and tap this plug for 3mm .

 

[goldstar31]

You may have to resort to a small carbide end mill .
Being so small using a 2mm carbide mill would be a delicate operation !
I have in the past given a broken tap a few very light taps with fine pin punch and a small hammer to try to loosen its grip - works sometimes .
Last ditch effort if all else fails is plunge a 4mm carbide end mill in and machine the whole tap out , then tap the new hole 5mm so you can install and loctite a threaded plug in then re drill and tap this plug for 3mm .

I've answered this SO many times but the few times that I have been daft enough to break a tap, I've either cracked the carbon steel tap or welded a stud on to the stump.

N

 

[Herbiev]

Alum has always worked for me

 

[ozzie46]

I broke 6-32 tap in aluminum piece and the alum trick did it just fine. Went to the grocery store ,bought some alum, it was in the spice section, did a saturated solution heated on the stove at almost boiling point.I had to add some water when it got to thick but it ate the tap in about 2 hours.

Ron

 

[ninefinger]

Alum does work most times, but it needs to be able to get to the tap - if the flutes are all plugged up with aluminum swarf it will take forever as its only going to be working on very top.
As also mentioned, it needs to be 1. Saturated solution and 2. hot - near boiling. 3. stir the part / brush with a toothbrush to help remove the oxides that form.
If you do this in a pot it either needs to be aluminum or as suggested use a glass coffee decanter and warmer. Stainless steel pots will be affected by this solution (it will stain it).

If you are lucky it will dissolve it enough that you can get it out without having to wait for the entire tap to dissolve.

Also, in my case it left the part (a crankcase ) with a dull finish.

Mike

 

[portlandron]

You can get Alum at a will stocked grocery store. It's used for canning.

 

[John S]

Send it for anodising. that will remove the broken tap and any helicoil inserts that are fitted.

Don't Ask.

 

[petertha]

What's an appropriate vessel to simmer the water/alum solution? An aluminum pot? Avoiding glass (don't ask).

 

[portlandron]

Glass container should be used with Alum.

 

[XD351]

I've answered this SO many times but the few times that I have been daft enough to break a tap, I've either cracked the carbon steel tap or welded a stud on to the stump.

N

I would like to see you weld something on the end of a broken M3 tap without melting the parent metal around it now it has broken off flush !

 

[goldstar31]

I would like to see you weld something on the end of a broken M3 tap without melting the parent metal around it now it has broken off flush !

I confess to being around with the dodos but the technology then was that it was possible to join metals with friction and again on a more
lowly bit of the firmament, people were sticking carbides to parent steel with silver foil. I suspect that they still are.

Again, having been retired for longer than I ever needed to work, my late wife was happily welding stainless steel wires and bracket to children's teeth. My little grandson orthodontic work is no longer routed (rooted?) to welds but is something rather simpler like these fancy glues with an accelerated gel done with UV light. Actually, someone used it on the dentine of my broken teeth. For a more approachable application, I have seen the stuff on sale to Joe Public and possibly a write up here.

As far as the other alternatives, in the days when I larked about as a manure student, we used Migs to fire wire through niobium steel and also stuck wires into dented metal to correct car bodies.

I thought the answer out which if you look at it rationally, only involves a slug of metal jammed in the wrong place.

Norm

 

[XD351]

And none of that will help the OP get the broken tap out !
If the alum is not working maybe there is some contamination stopping it like tapping fluid ?
Is the tap carbon steel , chrome steel or HSS , maybe the composition of the tap itself is inhibiting the chemical process?

 

[ozzie46]

I used a cheap teflon coated pan from "wally world". The teflon protects the aluminum pan from the alum

Ron