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Threads... 750 crankcase studs

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K2-K6:
Ash, I'll go with Trig on the spark eroder. We ran one in the toolroom I was in and it was a godsend for removing this sort of thing, the only limitation was the size of the workpiece you could get into the liquid bath it operates in (don't know if they still have that requirement).

The method is similar to drilling in that you have to basically romove the core of the stud leaving what is in effect the thread (like a helicoil) remaining which you can pick out with something like a scriber.

Seamus's way is as good as you'll get for a home remedy and should get you there but you need to "contain" the core drill size as he says to keep it central to the stud.

If I had to do that with a drill i'd get a steel plate to lay on the crankcase face with two other holes to locate and bolt down on two of the other studs, giving good location and a tube of something like 20mm height over the stud you are drilling to provide a guide.

One of the problems of first drilling a pilot hole is that the larger size drill has very little self centering effect which is provided by the tip of a drill in the material. if you take that centre material away then the drill tends to grab on it's outer edges and is hard to hold central to the stud, It's this effect that using a steel guide should avoid.

An engineering tap set usually comes as a set of three, a taper tap, intermediate and a plug tap to gradually form full threads if used in succession. if you tapped just using the taper then the stud would bind up tight before reaching the bottom of the hole.

Trigger:
If anyone wants to know what a spark eroder is, I have found a vid that explains >> https://www.youtube.com/watch?v=YbeKxFBZrF8

AshimotoK0:

--- Quote from: trigger6969 on October 14, 2014, 09:26:27 PM ---If anyone wants to know what a spark eroder is, I have found a vid that explains >> https://www.youtube.com/watch?v=YbeKxFBZrF8

--- End quote ---

Watched it Trig and now understand how it works. Looks more like a 50+ quid job to me though but if it's the only way then so be it !!

Cheers for all of the good advice..... Ash

Trigger:
It was a American vid. He chatted at least 70% of the time. 3 minutes max to do this job :)

tom400f:

--- Quote from: trigger6969 on October 14, 2014, 09:56:00 PM ---It was a American vid. He chatted at least 70% of the time. 3 minutes max to do this job :)

--- End quote ---

It's always razamataz with them isn't it? Reminds me of my visit to the Kennedy Space Centre. There's a feature called meet the astronaut scheduled to last 30 mins. First 20 mins is warm-up act with the audience  ::)

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