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View Full Version : Drill guide plates for drilling out sheared bolts and studs



bob ward
14th Mar 2018, 09:26 AM
I needed to remove/drill out 20 sheared off bolts and studs from tapped holes in an old engine (1935 Hudson 8), they were a mixture of 5/16" UNC and 3/8" UNC.

The eternal problems with this sort of work are:-
a)precisely finding the bolt centre
b)getting the drill to start on centre - bolts and studs never break off nice and smooth
c)keeping the drill on centre

Drill guide plates solved all of the above problems, I was fortunate on this job that the bolt layouts were measurable and I did have some clean holes that I could bolt the guides to. Using the mill and DRO I made few drilling plates, all from 12mm flat steel, to suit the different configurations of holes that were available for fixing and holes I needed to tackle.

Each drill plate had 2 sets of fixing and drilling holes. The first set of holes positioned a 6mm hole through which I firstly put a 6mm spotting drill 2 or 3mm into the offending bolt or stud, then I swapped over to a 6mm jobbing drill and drilled right through. After that the second set of holes positioned either a 6.35mm drill for the 5/16" threads or a 7.8 mm drill for the 3/8" threads and drilled right through. Those drill sizes are larger than the minor bolt/stud diameter and smaller than the hole tapping size. It goes without saying that you only use fresh sharp drills.

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After that its a matter of teasing the remnant of thread out of the block. Final score Bob 20, bolts and studs 0.

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Grahame Collins
14th Mar 2018, 08:27 PM
Hi Bob

I have a real soft spot for those big straight 8, motors Bob. My uncle had a Buick straight 8.
I thought it was one tough car.The kids could stand on the roof and watch the football from outside over the tin fence at the Brisbane, West End - Davies park footy ground in early 60's.

I can still remember the comment the uncle made."the b------d could pull a caravan up a cliff face in top gear"
It had big wheels, much bigger say, than a Holden of that time. Needless to say, it impressed me greatly as a ten-year-old of that time.

That drill guide plate is a wonderful idea.

The best of luck with your restoration.

Grahame

morrisman
14th Mar 2018, 09:45 PM
That's a neat fix. I have exactly the same problem, the water jacket cover on my 1930's Morris 6 side valve engine, the 6mm bolts sheared off . So are you using a hand drill ?

KBs PensNmore
14th Mar 2018, 10:13 PM
Hi morrisman, it was done on a DP, using a hospital bed???
You can read about it here, http://metalworkforums.com/f65/t140510-todays-tools-gloat/page-142 thread number 2127
Hope this helps a bit.
Kryn

bob ward
15th Mar 2018, 12:27 AM
That's a neat fix. I have exactly the same problem, the water jacket cover on my 1930's Morris 6 side valve engine, the 6mm bolts sheared off . So are you using a hand drill ?

This is my rotted water jacket which needed to be replaced, I guess its a similar set up to your Morris engine, this one is held on by 26 off 5/16" UNC bolts tapped through into the coolant, Despite my best efforts, a combination of gentle persuasion heat and violence only 9 off the little buggers unscrewed.

I did all the drilling with a drill press, it could have also been a job for a mag drill. Using a hand drill would have worked, very tedious though and a much higher chance of breaking a drill bit.

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