Feeling very lucky.

[bodrighywood]

I was in the process of buffing some work when there was a bang and I felt somthing hit my chest. Stopped the lathe to find that the screws on two of the chuck jaws had sheared. The buffing wheel went in one direction and the jaws came at me. I was doing about 1000rpm at the time. Fortunately it hasn't done any damage other than tomy nerves but if the jaws had hit me in the face or head it would have been serious, doubt the face shield would have protected me against the jaws. They were screwed on tight and everything was in balance so I can only put it down to metal fatigue though two sets of jaw screws at the same time? Seems odd. This ever happened to anyone else?

Pete

[GBF]

Glad your are OK
I wonder if they were over tightened

Regards George

[bodrighywood]

Could be George. I tend to make sure eveything is well tight, perhaps too much so. This is a pemanent set that I use a lot and so if overtight could have been ready to go any time. Just glad it happenned when it did not with a student or at a demo. I'll be going round checking all my other ones, that's for sure.

pete

[Paul Hannaby]

Are they the the right type of screws? I think they are supposed to be high tensile screws rather than standard ones so if you've bought some extra screws were they high tensile?

I think if it was me, I would replace all the screws on that jaw set just in case.

[bodrighywood]

They are the proper screws as far as I know Paul but probably old as it's a 2nd hand chuck and I have had it for some years. I will take your advice about changing them all though just to play safe.

pete

[Les Symonds]

Are they the the right type of screws? I think they are supposed to be high tensile ...

It's an interesting point that you raise, Paul. I too, had a jaw screw sheer off this week, but fortunately it was just the one. Like Pete, mine was a second-hand chuck. Might well be worth buying a full set of HT screws from my local engineer's merchant.
Les

[Bryan Milham]

Pete, I've had screws fail on me, only on my 1" long jaws though, I put it down to them being over stressed due to the length they had to hold against.

I now change my screws on a regular basis.

As I've posted before, if you buy 'branded' screws they are about £5 per 8, down at the local tools and fixings I can get a dozen for £2. That's a new set and spares in case I drop one in the shavings.

[The Bowler Hatted Turner]

The other thing to remember is if you buy second hand you will not know the history of it, it could have been dropped at one time and landed on the jaws which would aid this happening.
       As a wood machinist  I am always "aware " of my machines and the tooling that goes with it.
 There is a phenomenon in the armed forces, when you throw a hand grenade the base plug 9 times out of 10 is blown back at the thrower  and no-one knows why (and yes there was a study done about it) in machine tools, if something breaks, 9 times out of 10 the broken piece or bits of it always hits the operator. Be safe people. Murphy's law exists.
Pete, glad you are OK.

[edbanger]

Well that must have made you jump Pete, glad to hear that you just bruised and nothing worst.

The problem is that these little countersunk socket screws are suppose to be 10.9 grade high tensile steel, but once someone replaces the screws you have no idea what they have replaced them with. Most of these screws are made in China now and people import millions of them and don't look at the spec just the price.

Ed