Re: Extracting sheared bolts

Roger Martin wrote:
> I've heard of spark erosion machines used on very old and rare equipment
> which cannot be replaced or will cost squillions to have re cast if damaged
> beyond repair. Interesting process - like a spark plug I suppose. There was
> a UK based model magasine - Model Engineer's Workshop that had plans.
>
>
We bought a proper spark erosion machine here at work from an ad in
machine mart, and by the time we'd fixed it, rather wished we'd made our
own in the first place. Spark eroders are THE tool for breaking out
studs or taps, The ME article you refer to is quite good, but there is a
book available from Camden Books by Dave Gingery I thnk that tells you
how to make a rather more efficient unit - and one that can be clamped
over the offending stud and put to work in situ.

Our machine will break out a 1/2 UNF tap (HSS) in under 30 minutes.

Of course if any fellow 101'ers ever need anything sparking out, please
drop me an email !

Steve

"Steve Taylor" <[email protected]> wrote in message
news:[email protected]...
> We bought a proper spark erosion machine here at work from an ad in
> machine mart, and by the time we'd fixed it, rather wished we'd made our
> own in the first place. Spark eroders are THE tool for breaking out
> studs or taps, The ME article you refer to is quite good, but there is a
> book available from Camden Books by Dave Gingery I thnk that tells you
> how to make a rather more efficient unit - and one that can be clamped
> over the offending stud and put to work in situ.
>
> Our machine will break out a 1/2 UNF tap (HSS) in under 30 minutes.

Can you explain how they work? Do they just blast little bits out of the
offending stuck item? How do you erode the bit you want, and not all the
bits around it? Sounds interesting.

David

>
> Can you explain how they work? Do they just blast little bits out of the
> offending stuck item? How do you erode the bit you want, and not all the
> bits around it? Sounds interesting.
>
http://tinyurl.com/26alg

SimonJ wrote:
>>Can you explain how they work? Do they just blast little bits out of the
>>offending stuck item? How do you erode the bit you want, and not all the
>>bits around it? Sounds interesting.
>>
>
> http://tinyurl.com/26alg
>
>
Neat article.

Steve

David French wrote:

> Can you explain how they work? Do they just blast little bits out of the
> offending stuck item? How do you erode the bit you want, and not all the
> bits around it? Sounds interesting.

The neat bit is the "electrode" which constitutes the tool whose shape
will be imposed in the work piece. Burning out taps is a simple case of
using a cylindrical tube, with a dielectric (Paraffin works) passed
through it.

The REALLY neat thing is that the tool can be made of cheap, but
electrically and thermally conductive material, graphite or copper are
often used, and is of course a "male" part, much, much easier to shape.
mould cavities for exotic shapes in horrible tough alloy steels used for
injection moulds, or for punchtools can be made very easily. With the
right tuning, the tool wear is much lower than the removal of stock from
the job. Our machine needs periodic kicking in JUST the right place to
achieve this....years of training etc etc. And a mallet.

We used our EDM to make 4 pockets in the inside of a 1" bore, about 1/2"
square and 10 thou deep - 1 inch DOWN the inside of the bore. Absolute,
probably impossible, bastards to make anyother way.

"Wire cutting" EDM is also nice, where a contiuously reeled wire, like a
bandsaw, but not an endless belt is reeled past a workpiece while
under spark action. A cut of less than 0.5mm is easily achieved in X,Y
and two angles.

Steve

>Of course if any fellow 101'ers ever need anything sparking out, please
>drop me an email !

Hi Steve, small world!

No 101 but a 30 year old Rangie might produce some custom when the engine
strip/rebuild starts.

Nick