316 stainless threads locking up solid

[srp]

Cut some M10 threads in some flat stainless bar the other day (part of my new engine beds). Got the bolts today and tried them all by hand, no problem. Fitted them into position and used my cordless drill to fit them - one of them locked up solid, apparently welding itself to the thread in the bar. When I eventually got it back out the thread on the bolt was completely stripped, stuck in the tapped hole in the bar. I've cleaned it out again with a tap, so not a problem, but three questions:
1. I seem to remember hearing about this before (but didn't believe it as I've never had it happen to me) - is it a known phenomenom?
2. Can I prevent it happening again, maybe by greasing the threads?
3. Was it caused by using the cordless drill instead of turning by hand? Seems a bit unlikely as it wasn't very fast, but who knows.

 

[Evadne]

Galling is a problem on stainless steel. It is prevented by careful cleaning and greasing of the threads: you want absolutely no metallic or gritty bits in there. Otherwise, you have my sympathy, I, too have been there and got the T-shirt, you live and learn. /forums/images/graemlins/frown.gif

 

[srp]

Galling - that's the word. Thanks - I've found a load of useful information via Google now thanks to your reply.

 

[Norman_E]

I was told by someone to use "Copperslip" (spelling?) which is a grease containing copper particles. Is this wrong for stainless? I know it is good for ordinary steel.

 

[VicS]

[ QUOTE ]
"Copperslip" (spelling?)

[/ QUOTE ] Actually spelt "Copaslip" but even the manufacturers, Molyslip, acknowledge that is more often spelt incorrectly than correctly.

I know no reason for not using it on stainless. Website: http://www.molyslip.co.uk/antiseize.html

Personally I use a antiseize grease called PBC (Polybutyl cuprysil) Made by K.S. Paul. It did googlle for it a while back. It contains an organic compound rather than metallic copper. I only use it because that was what i was able to scrounge when I wanted something. I think I've got Copaslip as well.

 

[yoda]

Seen the same on a frigate rudder nut and it wasn't pretty! Clean and slow and you should be OK.

Yoda

 

[Birdseye]

We used to copper plate stainless steel wire when we produced it for nut and bolt manufacturers in order to prevent welding of the stainless to the die under pressure. As an alternative, stearate loaded with moly disulphide.

Totally clean and lubricant free is what you dont want if you are to prevent problems.

 

[ronniewood]

Part of the probelm is caused by using stainless steel of the same grade for the nut and threaded bar. Use a different grade for the nut and it will reduce the problem.

 

[TheBoatman]

Go to Halfords and by some Copaslip - its what is used on the backs of car disc pads - 1 small tin/tube will last a life time.

Peter.

 

[srp]

Thanks for all the replies. With your help, and some Googling, it would seem that I caused this by cleaning the threads (to get rid of the Trefolex cutting paste) and then using a cordless drill to wind the bolts in. Most of the information I've read suggests using compounds containing molybdenum as a good prevention.
I also found that using different materials for the bolt and the threaded bar would also help, but they have to be significantly different (304 and 316 grades aren't different enough apparently).
Copaslip would also undoubtedly work, and I used it on my last boat, but discovered that it can cause electrolytic corrosion problems.
I'm glad this happened on the workshop bench rather than on the boat - it would have been difficult to sort out in-situ.