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How to redrill a hole?
Chaz - 12/8/13 at 02:54 PM

Hi, as you may guess from the title I'm relatively new to this practise.

I need to fill in a threaded hole on an alternator and then re-drill it about 5 mm offset from its present centre-point. I have heard people using words like, chemical metal and slugs. I need it to be load bearing, what should I do?

If you need pics to clarify, i can provide.

Thanks in advance.

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[Edited on 14-8-13 by Chaz]

minitici - 12/8/13 at 03:03 PM

Normally tap the existing hole and screw in a suitable plug.
The plug can be epoxied, loctited and/or mechanically 'upset' to stop it coming out.
Then mark the new centre and drill the offset hole.

Depending on the material, the existing hole could be welded up and re-drilled.

Also worth thinking laterally and see if the other part of the mounting could be altered to suit the existing hole position.

Chaz - 12/8/13 at 03:10 PM

quote:

Normally tap the existing hole and screw in a suitable plug. The plug can be epoxied, loctited and/or mechanically 'upset' to stop it coming out.


By suitable plug, do you mean a bolt and then saw/angle grind it off?

By mechanically 'upset', do you mean damaging the bolt thread to prevent it from unscrewing itself?

Thanks again...

Bluemoon - 12/8/13 at 03:11 PM

I would avoid altering the hole position, as replacement would then become a PITA, adjusting the bracket is probably easier in any case..

dan

minitici - 12/8/13 at 03:15 PM

quote:
Originally posted by Chaz
quote:

Normally tap the existing hole and screw in a suitable plug. The plug can be epoxied, loctited and/or mechanically 'upset' to stop it coming out.


By suitable plug, do you mean a bolt and then saw/angle grind it off?

By mechanically 'upset', do you mean damaging the bolt thread to prevent it from unscrewing itself?

Thanks again...


Try and use the same material as the original plate for the plug i.e. Aluminium.
If steel then a suitable steel bolt (low grade not high tensile) might do.

To 'upset' the bolt you can use a centre punch to put dings close to the thread on the plate once the plug has been screwed in.

[Edited on 12/8/13 by minitici]

nick205 - 12/8/13 at 03:47 PM

quote:
Originally posted by Bluemoon
I would avoid altering the hole position, as replacement would then become a PITA, adjusting the bracket is probably easier in any case..

dan



Ditto, I'd look at mounting it differently or making a bracket up to suit.

Post up some pics of the alternator and intended mounting position and we might be able to offer some more suggestions.

fesycresy - 12/8/13 at 03:53 PM

You may be able to Helicoil it, depending on position.

But I'd alter the bracket too.