6 replies to this topic

[Northernpower]

I need to thread the end of an 8mm stainless steel bar. Do I need to do anything different than I would for mild steel, i.e. different lubricant?

[Ethel]

I've managed it with Trefolex. Wouldn't say the results were brilliant though - Can you even get cobalt taps 'n dies ???

[Spider]

Some grades of Stainless cut nice and clean, others want to tear as they coff coff,,, cut

Use a new Tap or Die, HSS will be fine, and a decent cutting lubricant. Like Ethal, I tend to use Trefolex on S/S.

[DeadSquare]

Stainless doesn't cut, it tares, so it is essential to keep backing off the die every half revolution. because with anything up to 6 mm, it is easy to block the die and twist the thread off, not so likely with 8 mm but it can happen.

 

The thread pitch for 8 mm and 9 mm is the same, i.e., the same number of threads per inch.

 

When threading 8mm Stainless, I used to use a 9 mm die, that when crushed in its stock would cut about an 8.666 mm thread on an 8 mm rod as a first cut.

 

I'd then switch to the 8mm die and rundown the thread again with the die fully open, which was about 8.333 mm. before taking two further cuts.  (And people moan about the cost of "one off" precision engineering)

 

The imperfections in a stainless steel thread, between the shank and are nut, a well-known fatigue points.

[bikewiz]

As Spider says it depends on the type of stainless. A-2 aka 304, threads pretty easily A-4 aka 316 is a bit harder but makes a nice thread. I use Castrol Variocut C Moly Dee on stainless and titanium, it smells horrible but works really well. For the best result make sure you use at least a HSS tapping die (generally round) and not a "threading die" (generally hex) 

This is a 316 shaft I single point threaded on the lathe for my boat trailer.

 ssthread.jpg   40.9K   2 downloads

[Northernpower]

Thanks all for the comments. I'll change my lubricant.

[Ethel]

Has anyone tried annealing it first? Trying to think of things a lowly botcher could do, you might stand a chance of getting the surface of the end of a bolt sized rod  hot enough with MAP gas.