ER40 collet nut seized

This is bugging me! I set up an M10 screw in my ER40 lathe collet chuck using a 9-10mm collet & nipped it up using moderate force on the ball bearing collet nut. After turning the screw I released the collet nut and took out the part. Now the trouble starts, as I continued to turn the nut everything locked up and no amount of force CW or CCW would budge the nut, the collet itself was free.

I had to resort to Mr Angle grinder to nearly sever the nut in half to undo it, in all my years using ER collets I have never lubricated the threads or had any problem such as this.

My question is has anyone else come across this problem? I am at a loss as to why it just all locked up.

Tony

Only on cars, undo two turns then lockup I always blamed a bit of thread breaking off and jamming.

Thanks Dave for that insight! Definitely felt like something had jammed or sort of 'cold welded' together?

Sounds to me like picking up or cold welding. such a part should have a light lube oil to try and stop it. Some metal seems very prone to it if dry and under load. Noel.

Hi Tony,

First time I have heard about an ER collet nut that has locked up. I do apply a drop of oil to the threads and have never had any problems with the ER chucks I have.

Thor

Isn't it galling when that happens?

They can do this if the inner thread is not cleaned out before putting the next collet or cutter in the chuck. Even just changing cutters in the same collet size, you really should should take the whole nut off and clean it all out and check that the body thread is all clean too.

+1

I have never had any trouble, but I think the threads are very slightly oily.

Personally I don't believe that oil will stop a thread jamming or galling when not under load. Sometimes you can undo a bolt enough to spin the washer under the head then continuing to removing the bolt begins to include removing the thread as well.

The trouble is the process is so destructive you can't tell what caused it.

Hi Tony, Guys,

It only takes a sliver of metal to jam up a thread ! It can get down the slots in the side of the collet and into the threads.