Broken tap

[ian HoldsworthParticipant @ianholdsworth27760]

How do I get abroken tap out. The previous owner ground it flat and placed a dummy bolt on the face of a steam chest.

ADVISE PLEASE.

[noel shelleyParticipant @noelshelley55608]

First we need to know the size of the tap ? I would use a spark eroder but that’s because I have one. What metal is it in ? What engine. A steam chest with a missing stud or bolt in a working engine is not a good idea.

[Robert Atkinson 2Participant @robertatkinson2]

What is the material it’s stuck in and what size is the tap?

Robert.

Edit Noel beat me to it.

[old martParticipant @oldmart]

I broke a 1/4″ tap in aluminium after drilling undersize in error and after setting it up securely in a mill, used a solid carbide drill which got it removed easily. You have to be careful to have positive control of the feed, a drill press will be likely to break the drill.

[SillyOldDufferModerator @sillyoldduffer]

The classic chemical dissolver is Alum, specifically Potassium Aluminium Sulphate, as sold by Amazon here.  Plenty of other sources.

Watch out when ordering.  Other chemicals are called “Alum”, and they are more-or-less unsuitable compared with Potassium Aluminium Sulphate.  Ammonium Alum Aluminium Sulphate and the others are a waste of money.

Make up a strong solution and fill the hole with it.  Leave for several hours, possibly a couple of days.  All being well the tap will slowly disintegrate.

Potassium Aluminium Sulphate does not attack Aluminium, Brass or Bronze.  Can be used on steel, but it attacks the part as well as the tap, possibly causing unacceptable damage.  Keep an eye on it.  Not a problem if there’s enough meat to clean out and rethread next size up, but…

If Alum is too corrosive, EDM or a mechanical method.   I once removed a broken tap with three piano wires passed through a rod, something like this.

Though it worked, more luck than judgement!

Dave

 

 

 

 

[Dave SParticipant @daves59043]

I have drilled out taps with a single flute carbide cutter.

For this to work you need a rigid machine, preferably with a quill and a quill stop.

The problem:

M4 IIRC snapped in a part I had a lot of work in.

The cutter:

Made from a round piece of carbide on a single lip cutter grinder. Flat ended, with normal relief on the back

Chucked up ready:

Then peck drill 0.001” at a time, against the quill stop, and allow a bit of dwell.

The tap comes out as very fine chips:

Result 🙂

Once you are through then you can pick out the pieces and with luck the thread is good.

Dave

 

 

 

 

 

[SillyOldDufferModerator @sillyoldduffer]

I see Dave’s broken tap is coated with TiN.  Reminded me that coatings are likely to resist Alum…

🙁

Dave

[GazParticipant @gaz13336]

If it was working prior to your discovery, why not leave it as is. Let sleeping dogs lie as it were.

 

[bernard towersParticipant @bernardtowers37738]

Yes but the broken bit will not be coated!!!

[bernard towers]

On bernard towers Said:

Yes but the broken bit will not be coated!!!

Think about the practicalities.  Dissolving top-down through the break alone will take forever because so little metal is exposed.

And as the tap is jambed deep inside the hole, one might die of old age before a coated tap comes loose.  Dunno about Bernard, but my days are numbered…

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Another option [forgive me if this has already been mentioned] is to use a core-drill, and then Helicoil. Obviously this is dependent upon there being sufficient ‘meat’ in the job.

 

MichaelG.

[bernard towersParticipant @bernardtowers37738]

Sorry SOD but have done it and with elevated temp and agitation with a Hypo it goes quite quickly, last one was 2 days. All our days are numbered

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, yes all our days are numbered, I’ve clocked up a bit more than 26000 days so far, but not many of us will reach 42000 and beyond.

Regards Nick.

[duncan webster 1Participant @duncanwebster1]

You young whippersnapper, I’m at 27649 days

[John PurdyParticipant @johnpurdy78347]

Get in Line. I’m at 30608. I think we are getting slightly off topic here!

[Author]

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