Manged to pull the threads on some 2.5mm holes – tapping Aluminium

This topic has 11 replies, 8 voices, and was last updated 19 May 2017 at 15:02 by Steve Withnell.

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15 May 2017 at 21:12 #298322
Steve Withnell
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@stevewithnell34426
Steve

As per title. Being a bit clumsy, I've managed to pull the threads on a couple of holes I was tapping in aluminium block – blind holes. How can I repair the damage so I can tap the holes correctly?

Thanks
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15 May 2017 at 21:12 #8715
Steve Withnell
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@stevewithnell34426
15 May 2017 at 21:32 #298326
Emgee
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@emgee
Hi Steve

You could use a Helicoil thread insert or if your hole is now 2.5mm that'sM3 tapping size, or if you want less TPI go to 6-32 UNC, that's 2.8mm tapping size hole.

Or if you can drill a deeper hole and retap for the designed screw, but longer than designed.

Drill oversize and fit a plug with Loctite or similar, drill and tap to suit. I'm sure there are other ways but a lot depends on what the fixing is retaining.

Emgee

Edited By Emgee on 15/05/2017 21:36:15
15 May 2017 at 21:34 #298327
Michael Gilligan
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@michaelgilligan61133
Steve,

IF there is sufficient wall-thickness available, then a Helicoil repair would typically be 'better than the original design'.

… No doubt there are good reasons why you consider this a non-starter

MichaelG.
15 May 2017 at 21:38 #298330
Henry Artist
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@henryartist43508
Can you use a bigger fastener? The tapping hole for M3 is 2.50mm.

Drill out the hole much, much bigger, tap it and fit a plug. Then try again to tap M2.5.

Start making the part again from the beginning.
15 May 2017 at 21:43 #298332
David Standing 1
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@davidstanding1
Depending on the circumstances, another option could be to TIG weld the holes up and start again?
15 May 2017 at 21:43 #298333
Jon
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@jon
Holes probably 2.9mm now, if can get away with it don't bother enlarging just run a few M4 taps down, some will cut better than others plus need the flat bottomer better off ground flat.

Check screws not to long to bottom out.
15 May 2017 at 21:58 #298336
Emgee
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@emgee
Posted by Jon on 15/05/2017 21:43:38:

Holes probably 2.9mm now, if can get away with it don't bother enlarging just run a few M4 taps down, some will cut better than others plus need the flat bottomer better off ground.

Jon, M4 tapping drill is 3.3mm so it may be difficult to start a tap if the hole is at 2.9mm.

Emgee
15 May 2017 at 22:31 #298343
duncan webster 1
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@duncanwebster1
Tap M4 and make a stepped stud, short length of M4 one end, the rest 2.5mm dia
16 May 2017 at 11:13 #298397
Ian S C
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@iansc
Drill and tap 4 mm, make a plug of the same material with a 4 mm thread, fit the plug in the hole with thread lock (Loctite) and cut it off flush, redrill and tap to the original size.

Ian S C

Edited By Ian S C on 16/05/2017 11:14:32
16 May 2017 at 19:31 #298460
Steve Withnell
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@stevewithnell34426
Thanks guys, out of the armchair and into the shed…
19 May 2017 at 15:02 #298843
Steve Withnell
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@stevewithnell34426
So, I had just enough clearance to drill and tap 4mm, loctited in a brass screw, skimmed flush, tapped out 2.5mm. Perfect!

What is it? 23cm Bandpass filter to stop those cell towers wiping out 23cm receive front ends!

Edited By Steve Withnell on 19/05/2017 15:09:34
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