Metalwork ...HELP!

[Bean]

Alf
Cobalt drills as hard as they are! are no match for a HSS Tap. A company I worked for some time ago aquired some drills from the MOD for a project, now these would drill out a tap, but they were on a loan only basis as they would also drill Safes and Armour Plate. The best suggestions are to heat the tap to soften it then drill out but the winner has to be Spark erosion as it will not damage the surrounding material or surface finish. I belive that around Leicester it costs upwards of £20 per hour. Maybe less if you are lucky.

Bean

 

[Alf]

Thanks Bean, as I feared. No easy/cheap solution then. :roll:

Cheers, Alf

Going to take extra special care when tapping from now on...

 

[Dewy]

I had 30 years in a machine shop & broken taps was one of the jobs we hated. Spark eroding them out was the easiest but the spark erosion machines were in use 24 hours a day. As the tap had broken while biting into the steel, getting it started to unscrew was hit & miss. More often than not we ended up using punches to shatter the tap. The chances are that it is broken in a couple of places Unlike you, we used much larger taps & that 4mm one is too small to get a punch into.
Best of luck.
In future, never more than half a turn then reverse it to ease the tension. Use something to lubricate the tap (I found washing up liquid & water works). Best tapping aid I ever used would be illegal now as it was a carbon-chlorine mixture similar to carbon tetrachloride or trichlorethelene. It breaks the surface tension of the steel as well as lubricating it & makes tapping much faster & easier.