Tap Extractor

Hello All,

Had to happen eventually with clumsy fingers.

Finished with taper tap, just started to remove the plug tap, and a careless move and it was broken off flush. In cast iron.

7BA has a nominal size of 2.5mm.
There is a Walton's No 4 extractor that says 3mm, but there doesn't seem to be anything smaller.

Anyone know any solutions?

Pick it out with an old scriber, EDM, or make a hollow cutter and core it out

Yeah, still trying the scriber method.
Don't want to do more to the casting than absolutely necessary.
And 7BA is small.

Edited By The Real Ron Skingley on 14/09/2021 19:09:48

Maybe worth a try for the time it will take to make.

1/4 " dia. silver steel , drill 1/4" deep with a drill core size of tap, reduce dia. to core size of hole, junior hacksaw

to form three castellations on the end , gently try to drive it into spaces of the tap.

Try to turn it out.

Ah yes, a sort of DIY extractor.
See if I can find some silver steel.

Most if not all my 'stock' is mild.
Bits of old cut-offs.

Only three flutes on the tap, so some very careful work required with the junior hacksaw.
But certainly worth a try.

Thanks.

Edited By The Real Ron Skingley on 14/09/2021 18:52:15

Domestic sewing needles and pins are fairly tough. If they can get a point into a flute then 2 or 3 through drill holes in scrap with minimal stick-out?

pgk

or try pushing 3 pins down the flutes and wrapping them with wire then turning them out.

I did this recently. Managed to drift it round using a scriber and a little toffee hammer. Just little glancing blows so it starts to spin.

Not having any luck with scriber and small hammer.
Pins and sewing machine needles is a good idea.
There's hardly any space showing down the flutes.

I've taken broken 2, 2.5 and 3 mm taps out with carbide three flute centre cutting end mills without damage to the partially cut threads.

Machine was a Bridgeport with the end mills held in R8 collets. Pucker factor high!

Annoyingly I've mislaid the cutter details. Thing brand began with N----.

Clive

1: find someone local with a spark eroder

2: grind it off flush and drill/tap another hole adjacent

Were you tapping into brass or aluminium ? You can dissolve a broken tap by putting the whole thing in an Alum solution.

Edited By Brian John on 15/09/2021 04:59:36

.

From the opening post, Brian : “… and it was broken off flush. In cast iron.“

MichaelG.

You may get lucky with trying to move it by other means but short of spark errosion it's definitely best to make a hollow cutter - 7 Ba clear inner and about a 1mm wall section. Cut the teeth with a file for left hand direction. Harden but dont temper. Slow's the word with constant swarf removal from the teeth. Slow process but it works (believe me!!). Once out, clean hole with next size drill and turn cast iron plug to suit, loctite in place and carry on as before.

Good luck for an efficient recovery

Tug

Thanks for all the replies.
Yes, cast iron.
A spark eroder would be the logical thing. But no-one over here (Ireland) seems to have heard of them.
Drill another hole adjacent. I wish. But has to match up with other fittings.
Taking out with a carbide slot drill has also been suggested by a friend locally. But that means another couple of weeks wait as I haven't got any. Maybe a good investment for the future.
So think it's going to be see what can be done with an end mill.
Maybe even have to make the hole bigger and make a plug and re-drill.

My son, a boat builder, suggested grinding a drill for left handed and running the drillgun backwards.
He's been there before
But only in wood with broken drills.
So a hollow cutter I reckon is today's job.
Haven't got a pillar drill as I use my Emco vertical mill, and not sure that will run backwards.
Nor will the lathe.
Thinking cap on.......

Ron

A carbide drill is another possibility with everything held really rigid. I had one to hand and used it for the same purpose on the Marine Engine build earlier in the year with success but a hollow cutter is just as good if a lot slower. I advised left had as it has a natural tendency to loosen the tap 'if you are lucky' but it is not essential. Just cut the teeth with as deep a gullet as possible and don't let the gullets crowd with swarf. Little and often, brushing the swarf out of the teeth as you progress - again the part needs to be in a rigid set up, not done freehand,

With care you will be able to reclaim your part with little indication of doingg so.

Good luck with it - Tug

Thanks Tug,

Yes, everything will be held rigid as I drill on the Emco vertical mill.
Found a piece of steel that I think is silver steel as it's only slightly magnetic.
So going to have a go at a hollow cutter.
Best solution if I can make it work.

Ron

Silver steel is strongly magnetic so your piece is a cheap form of stainless.
If you look up DIY spark eroders, simpe ones, you will find they use a simple electrical circuit with a resistor and capacitor, then various levels of complexity for the mechanics.

However one of our club members found for a one off small item you don't need any of the mechanical stuff, just a thin electrode running up and down in a plastic tube held by the mill chuck to align it. You provide the up down movement by hand. Sow and laborious but for a one off not too bad. Any time the electrode welds to the tap try turning it.

I did wonder about it being silver steel.
Obviously it's isn't then.

Have you, ot can you get, a link to the circuit for that spark eroder?
Into electronics too, so might be interesting.