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From: Dave Baker
Date: 02 May 2004 02:57:58 GMT
Subject: Re: drilling a broken bolt
Message-ID: <>

>From: "Bob Paulin"

>If a bolt of a given diameter has corroded so badly as to break while
>attempting to unscrew it, a "stud extractor" or "easy out" of an even
>smaller diameter - and often harder and more brittle metal - is usually NOT
>the answer.

Agreed. It always amazes me how people expect that if an 8mm solid steel bolt
or stud has snapped right through without budging, that a 4mm easy-out is any
sort of a sure fire way to unscrew the remains. It keeps me in beer money
fitting helicoils after they've had a good old bodge at it and given up though.

>The end result is, often, finding oneself with the need to drill out
>something that is even harder than the original fastener - i.e. the broken
>portion of the not-so-easy-out which has spiraled itself into the fastener
>material - often expanding that same fastener even tighter into the hole.

Plenty of posts on here over the years to confirm that :)

>An old machinist friend once told me that the ONLY time he used an
>"easy-out" was when he broke a fastener while installing it himself.

I try them occasionally but only when the part is in the workshop and I can get
it on the mill for proper repair if the easy-out fails. Every now and then an
easy-out surprises me on a stud I thought would never budge but I use them with
very delicate feel and if it's clear they aren't going to work I stop trying
long before breaking them in the hole.

I would say that most easy-outs break because the top of the stud they are
being used in hasn't broken off square. That puts a side force on the easy-out
which snaps them off flush. First step if I ever use one is to mill the remains
of the top of the stud square, mill or drill absolutely centrally, give it a
damn good whack with a punch to shock it loose and then try the easy-out
gently. Maybe 3 times out of 10 I get lucky and the other 7 means drilling out
carefully until only the spiral of the thread is left and peeling it out with a

>He would NEVER attempt to use an "easy-out" on a fastener that he hadn't
>just installed, since he could not be sure exactly what condition - and
>level of corrosion - the threads are in.
>Careful, precision drilling is required. A skilled machinist can often
>drill the fastener out to the point where the fastener threads can be
>spiraled out of the hole, leaving the original female thread untouched.
>OR welding a nut to the remaining piece of the bolt will often work. The
>heat from the welding often serves the purpose of breaking the corrosion.

Also an excellent way to remove badly stuck oilway taper plugs in engine
blocks. They tend to made of fairly soft steel and round the allen key location
out before undoing. Drill right through, weld an old bolt into the hole and
they pop out like they were never tight in the first place. Always annoys me
that does :)

>People who are not skilled at this sort of thing, often end up with a hole
>that has progressed to the next standard size - at least.
>It is often easier and quicker to simply drill the fastener out to the
>proper Heli-coil size for the original fastener size, and install a
>Not trying to discourage you, but removing broken fasteners is not usually
>an easy project - which is why, after more than 40 years' experience, I am
>quick to heat fasteners that seem to offer even the slightest resistance.
>Bob Paulin - R.A.C.E.
>Race Car Chassis Analysis and Setup Services

All excellent advice. Sadly most amateur mechanics won't heed it and then we
get the posts on what sort of drill bit do I need to drill an easy-out out with
- lol.

I'd only add that a good swift belt with a hammer before trying too hard to
undo a reluctant bolt often makes a huge amount of difference.

Most really experienced engineers don't break fittings in the first place.
Anything that won't undo with the expected amount of torque gets a few hefty
whacks or some heat plus a decent 6 point socket instead of the usual 12 point
'designed specifically to round off anything tight or rusty' one and the
fitting comes out quite nicely.

Amateurs just tend to go at it until something breaks, either the tool or the
fitting, and then have a good moan on here.

Dave Baker - Puma Race Engines (
I'm not at all sure why women like men. We're argumentative, childish,
unsociable and extremely unappealing naked. I'm quite grateful they do though.

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