Broken Tap in a Hardened Thread

[electrosteam]

A good mate of mine has broken a 5/16 W Sutton bottoming tap in a through thread in a jaw of a tapping chuck.
It appears the jaw was hardened, and my mate was trying to clean up the thread for a grub screw a bit too enthusiastically.
I have subsequently been told that it is always a 'bad' idea to try and clean a hardened thread with a HSS tap, no suggestion on how it should be done.

The broken end is below the surface.
Any suggestions on an EDM contractor ?
I am near Penrith, NSW.

The alternative is to make a replacement part, left soft will probably work OK for some time.

Thanks in advance for any suggestions,
John.

[Clubman7]

Maybe give this guy a call.
Just googled him from the yellow pages so have no idea about his abilities.
Worth a try though.
Good luck.

Spark Erosion Services Toolmakers - Minto, NSW

7 Pembury Rd, Minto NSW 2566, Australia
(02) 9603 6888

[electrosteam]

Thanks Clubman7, I will follow up in the morning.
John

[morrisman]

Hi'

After reading a web page on these little tools I bought one.

Its a little air powered tool, something like a dremel but thinner , it revs up to 40k rpm or similar .

I bought the 3mm carbide tips for it .

It goes through hard metals . It is slow but it works well.

You can grind out broken taps , and bolts .

They only cost about $30 on ebay , the 3mm shaft carbide bit sets are cheap. I have a diamond bit set too .

Because its air powered, it has heaps of grunt and it doesnt matter if you stall it .

Mike

This is it

http://www.ebay.com.au/itm/65000RPM-...item4603c79bca

The pink stones in the kit are useless , you buy the 3mm carbide or diamond bits and the tool works like magic

http://www.ebay.com.au/itm/3mm-Diame...item3cc5c54a0e

[beefy]

If it's of any help, I have quite often drilled hardened steel with masonary drills. I use the highest speed on my drill and FLOOD the bit with water. The principle behind it is that the hardened metal is annealed at the point of contact due to the high speed creating enough friction (some pressure is needed too), yet the water/coolant prevents the brazing in the drill tip from melting.
A few months ago I came across the Bosch Blue Masonary/Steel drilling bits in Mitre 10 (couldn't find them in Bunnings). They seem to drill hardened steel a lot better than standard masonary drills, but I'd still be careful with heat buidup causing the brazing to melt. I still used coolant on these too even though the promotional material says they can drill hardened metal.
There are tools specifically made to remove broken taps. Never used one but they basically have "legs" which go down the flutes of the tap so you can turn it out.
There's quite a lot of information if you Google (plus Youtube) for broken stud removal. See if any of the techniques could be applied to a HSS tap.

Keith

[morrisman]

This is the review

Air micro die grinder

[Dave J]

Good luck getting it out, and I mean that in a nice way.
I broke a M8 tap in one of my mild steel tool holders which broke above the surface. It was a good quality P&N tap and after putting a washer over it and welding to it and then welding a round bar handle on it, the tap just splintered again, I then tried the whole process a second time and the same thing happened. So I gave up, welded the hole up, then turned it over and tapped the other side. I was lucky because it was a blank one that could be turned around.

With yours if you need some steel that can be hardened to remake it, just let me know as I have some 25-30mm rod here you could use for it, and since you come up here ever once in a while you could pick it up

Dave

[Dave J]

I forgot to mention, it was my own stupidity the P&N M8 tap broke in the first place,
About 20 holes before hand I accidentally dropped it from the mill table where I was working, and with that it was in a large tap holder, I think fractured it slightly but I never inspected it.

I cant really complain about the tap quality, because I have had the same set of 3 x M8 taps for around 10-15 years and I had just finished doing 185 holes full thread depth through 12mm steel, and only had 5 holes to go, LOL

Dave

[Dave J]

This is the review

Air micro die grinder

Hi Mike,
I have got good quality strait and 90 degree air powered die grinders, and have often looked at those mini ones, but thought they wouldn't be much for the money. Thanks for the review, I might look at getting one myself now.

Dave

[DavidG]

I have drilled our a broken HSS drill bit with a cobalt drill bit.
Don't think a tap would be any harder.

[electrosteam]

Thanks guys for the comments.

The price to etch the tap out is $70, and can be done in an hour or so, I will discuss with the mate.
The micro air grinder sounds like a worthwhile investment in its own right, so it has been listed on the "Acquisition List", and it might come sooner if the mate is shy on the $70 and doesn't mind waiting for a bit.
Not confident on any drilling activity because of the woeful rigidity of my Chinese drill press.
Its nice to know that I am not alone in getting into strife !.

Happy machining,
John

[19brendan81]

Hey Morris,

Thanks for the link to the grinder review. I bought one of them ages ago with the intention of using it in the tool post on the lathe but havent done so as yet. Might pull my finger out now and give it a go. I got mine from CTC tools for a song.

Where do you reccomend I get the carbide burrs from? Ebay?

Brendan

[morrisman]

Hey Morris,

Thanks for the link to the grinder review. I bought one of them ages ago with the intention of using it in the tool post on the lathe but havent done so as yet. Might pull my finger out now and give it a go. I got mine from CTC tools for a song.

Where do you reccomend I get the carbide burrs from? Ebay?

Brendan

Yes the diamond and carbide bits on EBAY ..pack of 30 is less than 10 bucks ..cheap as chips from China