Extending thread on stainless steel bolts

Hi All,

A friend has asked me to extend the thread on some M12 304 stainless steel bolts. 98 bolts by 20 mm and 98 by 80 mm. So I'm looking for a quick method. Any advice on the best method would be appreciated. My experience with stainless is that it blunts cutters quickly.

Cheers

Bill Pascoe

Decent sharp die also use cutting fluid.

Tony

Politely say no.

You'll probably spend more money on replacing multiple worn-out HSS dies than the favor will be worth, you'll also end up with hands that are blistered for weeks and wrists that are too sore to even raise a pint glass.

Hiding-to-nothing is a phrase that immediately springs to mind.

Peter

That sounds like a significant favour - more of a production run.

Check if the bolts are to be used for anything critical, especially if likely to be subjected to cyclic stresses - cut threads won't match the fatigue performance of the original rolled threads.

Check the shank dia they may have been rolled so there won't be enough metal to cut a thread

Im with Peter Neil.

The threads would have work hardened when they were made and running a die down them again will blunt dies quicker than anything, even with the best of fluids.

Sounds like a good earner, but their will be tears.

I'm with Peter and Jason, it's unlikely that you will get a serviceable bolt, might be ok if you want to hang a gate. Get some stainless "all thread", and put a nut on each end. If one end must be a bolt, Loctite the nut on that end(shaft lock).

Ian S C

Thanks ever one. Thinking about this I also came up with the thread rod idea which I have put to my friend.

Cheers

Bill

Invite him into your workshop, hand him a tap wrench etc. also have a price list for quality dies on the bench and see how long he lasts.

My bet is 5 min............

Before he runs off get the cash for the die he's wrecked........

Shaun

Edited By Involute Curve on 07/12/2015 10:31:36

You will ruin your dies. Colin

I'm with Peter & Ian SC... politely refuse.

George.

Just persuade him to buy hex head set screws, they are threaded to the head.

Perhaps they are all bolts to him!

Are you sure they're 304 ? Has someone made them because the majority of commercial bolts are A2 or A4. If they're A2 then it's no problem to add thread if the shank is the right diameter if they're A4 then forget it. Done loads of rethreading A2 when I needed the right length of plain shank of a longer bolt, a decent HSS die lasts a fair bit on A2. Just get your mate to do it under your supervision though for that many.

Mick - A2 is 304 and A4 is 316, and quite frankly I've always found 316 easier to machine than 304 at any time.

Without casting aspersions, a lot of 'stainless' fasteners these days come from China, and I have seen some terribly soft metal used there, as well as some that behave as expected. But re-threading a stainless bolt is not an easy task, so I'll have to beg to differ with your view of 'no problem'

Peter

Thought A2 was 304L not just "plain" 304 as I've never had a problem with reworking A2 fixings compared to machining/threading 304 barstock.

The 'L' when added to stainless always means low carbon (for easier welding) not added lead, so 304 is just 304 and not easier machining like the free cutting mild steels with lead added.

I reckon you must have had the Chinese A2 bolts Mick

Most stainless bolts are(in my experience), 316, as this is the grade use in marine work, you might find suitable bolts at a Ships Chandler's.

Ian S C

I have extended the thread on large bolts, high tensile and stainless, over 8mm I always screwcut and finish off with a die.

Thanks for all your help. The thread rod suggestion has been excepted.

Cheers

Bill