Extracting a Broken Threading Tap

While tapping an M4 (4mm) thread in a 10mm aluminium alloy plate, the tap snapped off. I tried a few methods of removing it, but without success - apart from the difficulty of gripping such a tiny tap in any way (cutting a slot, sliding wires down the flutes, etc), the tap seemed to be very firmly stuck!

I also considered punching the broken tap out of the aluminium sheet, but thought that the forces needed would damage/distort the sheet.

This Instructable suggests one way of dealing with the situation, and covers the first step in the sequence below:

1. Create a 'core drill' and drill out the 4mm tap.
2. Enlarge the hole and tap it to a much larger diameter (eg M10 - 10mm diameter thread).
3. Create a plug by threading a scrap piece of aluminium bar to M10 using a die.
4. Screw the plug into the hole, use thread lock, then trim the plug flush to the sheet.
5. Re-drill the hole for the M4 thread and re-tap the hole - this time, being more careful!

I used a metal lathe to create the core drill, filed the teeth by hand with a triangular file and used a drill press to drill out the broken tap.

Step 1: Create the Core Drill 'blank' on the Lathe and Cut the Teeth

Core drill blank

Using a scrap of steel bar, I chucked it up on my lathe and drilled out a 4mm hole.

I turned the bar down to about 5mm diameter (giving a wall thickness ie tooth size) of about 0.5mm.

I took a small cut on the lathe to relieve the core drill behind the cutting edge. This would stop the drill from binding as it drilled down.

This was all done by eye - none of the dimensions seemed important!

Cutting the teeth

I cut the teeth with a tiny triangular file. I aimed the file at the centre of the hole and lowered my hand so that I was cutting upward and creating a tooth on the near side of the drill only. I left a very small flat on the top of the tooth, so that each tooth was the same height.

As this was for aluminium, I did not heat-treat the drill in any way.

Step 2: Drill-out the Broken Tap

Using WD40 as a lubricant, I aimed the drill to surround the broken tap, and slowly drilled down. I stopped fairly frequently to flush away the swarf.

On a couple of occasions, I re-sharpened the teeth. The drill stopped progressing at one stage - the core had broken off and clogged the inside of the drill. I punched the plug down inside the core drill and carried on!

The photo shows how the drill was left at the end of the process - not pretty. This is a one-off tool, I hope I never have to do anything similar again!

This seemed to be a successful strategy.

Comments

[gasify]

I held the aluminum and chisel joint in one hand (with glove) it gets very hot. the other end of the aluminum rotated the tap.

With small ones, I turn the work piece upside down if possible and hit it with lots of air before trying to turn the tap back out. Once you get some of the small chips out of the way the tap has room to move back out. Again, and aluminum punch (home made of course) works best because it catches the sharp edges of the broken tap.

[qthurtle]

Nice advice. Many thanks for sharing.

Best wishes

[gasify]

I've had to remove both large and small taps after they broke off at surface level. For the large one ( 1-1/4" bolt tap ) I used a very dull air chisel bit against a small piece of aluminum bar. And stopped several times to use compressed air to blow out anythingthat would come out.

[ndjalva]

Find some tap lube, WD 40 is ok but not the best. Blaster works great! 10wt for most projects (save the money) or bees wax for aluminum. 40 yrs machinist A&P [aircraft]

[jprobst2]

Someone above mentioned Tap Magic as a lubrication solution, and it is a very good one but make sure if you are teaspoonful aluminum to use the Tap Magic made for aluminum. When I worked at a plant that had primarily aluminum parts that's what we used, like I said, never broke one in aluminum. As others have said speed, torque, improper use of the tool in general, all contribute broken taps. I figured if you have a lathe and can machine a part you probably know exactly why the tap broke. Most of the time when I've broken one is because I was into much of a hurry, lacked the proper drill bit, or was using a Chinese tap.

[qthurtle]

I might well have been guilty as charged on all three. M4 needs a 3.3mm drill (I don't have one), my tap was cheap (and nasty?) and I was probably in a hurry/careless having successfully just tapped two previous holes. I was probably using WD40 as a tapping fluid (can't remember).

This highlights a typical problem I have (as a real armature/beginner). I want to 'get on' so I can't wait for days to purchase exactly the right kit. In addition, often I can't afford/justify purchasing exactly the right kit. Hence I 'work around' tasks, using what I have to hand and improvising. Many of my difficulties can probably be traced back to this handicap!

Best wishes

[jprobst2]

Teaspoonful?? Auto correct you are the bane of my existence! Should be tapping.

[jprobst2]

I've broken many taps (never in aluminumn) and have always ended up punching them out our breaking them into smaller pieces. I like your solution, a bit time consuming, but for what you were working with, probably the best solution at hand.

[qthurtle]

Why do taps seem to break in the most annoying circumstances? It is always a one-off item which has already had lots of work done to it, or it happens when you are in a hurry, etc!

Perhaps taps should have a 'maximum torque' value on them, then we could use a special tap wrench which had a torque setting on it - no more broken taps!!!

Thanks for your interest.

[nextuz]

The drilled hole is to small
Not enough lubricant
Only turning the tap clockwise <--- that the most common problem.
You should turn cw a little bit then ccw to cut of the grinded metal. Continue that way in small steps and u will never broken a tap again.

[Chipper Bert]

As my late Dad used to say "Slolee slolee catchee monkee! Slolee slolee tappee holee".

Aluminium is a b.... to tap...

[ReeceS6]

I love the"outside the square" thinking you have shown here. There are not enough people applying their mind like you have. Well done.

[qthurtle]

Thanks for your kind comment. I think this is just an example of "Necessity is the mother of invention."

Best wishes.

[RichardW110]

That is an interesting method, but the best possible advice is don't break your tap ! Overdrill the hole by one size, make sure your tap is fresh and cuts well, make a little chamfer to help aim the tap, use a tap guide to make sure it goes in straight, use a good tapping product(tapmagic, etc.) to help you, and clear the chips regularly. If you DO have a problem and can't burn it out, drilling a hole and plugging it is a good repair. One more thing - know the difference between gun tap and plug tap and bottoming tap and use the appropriate style.

Yes, I've broken a few :)

[qthurtle]

I was surprised how 'sticky' the aluminium alloy seemed to be. The chips didn't break off nicely, like they do in steel. I was using a cheap tap - probably not sharp enough?

Thanks for your interest.

[imcp1024]

This must be for a very good cause. a very eloquent solution.

[qthurtle]

Many thanks. I didn't want to throw away the plate and start again. Too mean!

[johnip4]

Nitric acid will dissolve a tap without damaging the aluminum.

[qthurtle]

To be honest, I'm frightened of concentrated acids! Also, I'm not really convinced that this is a practical method. I have seen very successful tap removal from stainless steel, but the jury seems to be out as to whether this would work well. I think the exact composition of the aluminium alloy has a major effect on this technique. Pure aluminium forms an aluminium oxide layer which is resistant to nitric acid, but other metal ions present in aluminium alloy might permit the nitric acid to eat the aluminium alloy!

If you don't mind bad language, you might look at this video, which suggests that alum might do the trick.

The following video shows what happens when aluminium foil is placed in nitric acid:

Thanks for the suggestion.

[dadsaid5x]

NICE HOME MADE SOLUTION HOWEVER, A SPECIAL TOOL IS AVAILABLE TO SOLVE. THE BROKEN TAP PROBLEM. SOME TAPS HAVE 3 WHILE OTHERS HAVE 4 FLUTES SO YOU'D NEED TO PURCHASE THE CORRECT ONE. BASICALLY THE TOOL HAS 3 OR 4 "FINGERS" THAT SLIDE DOWN THE FLUTES OF THE BROKEN TAP AND WITH A WRENCH YOU'LL BE ABLE TO UNSCREW SAID TAP SAVING THE PART AND TONS OF TIME. WORKS ABOUT 97% OF THE TIME.