Thread cutting on 316 round bar

[ajlelectronics]

I have a vintage caravan which has a brake pull rod of 5/16" diameter and 2.7m long. One end with the adjusting thread has become S shaped and horribly mangled. The other end is a crude 90 degree bend with a split pin into the compensator. The whole piece is ravaged by 40 years of tin worm, so I want to replace it.

First problem is that I am determined not to go mail order. I lecture everyone else about buying local, so that's what I want to do.

I am coming across "Computer says no" and other nonsense from local steel stockholders. The only one that was helpful can offer me 5/16 stainless 316 or 303 in 8mm for £20. I need to cut a thread in one end of about 6" and the other end about an inch, to go into a clevis. I have a set of Machine Mart dies and I am concerned about how difficult it will be to cut a thread in the bar.

The 303 is softer, but slightly larger diameter, so I wonder if the hardness difference will be negated? I could cut M8 but don't really want to metricate an imperial built van.

 

[piman]

Hello AJL,

there is not really a problem threading stainless steel, especially if you use a cutting compound e.g. Trufolex. Do check the diameter of the bar, it will probably be a shade under 5/16" which is fine. If it is over it will make cutting the thread difficult, this makes the 8mm bar a non starter (Staying with imperial thread) as that is 5 thou over 5/16", unless you get it turned down?

Alec

 

[mike 109444]

Are the MM dies "proper" split dies? Most of the cheaper ones don't seam to be (aka Aldi etc) Reason a proper split die would work better is you can use the small screw that goes into the split to open up the die by several thou and thus do a rough cut of thread then adjust down and do finish cut. Use cutting grease/Rocol etc. Is the thread 5/16 BSF, UNF, UNC, Whitworth? ok keeping it imperial but which one!

 

[Lawnmowerboy]

Stainless will cut better with a proper split die you set in a proper die holder. I'm not a fan of die nuts. Use a good quality die with plenty of cutting compound. Either ROCOL RTD or dormer supercut. The difference between the decent stuff and the cheap stuff is huge.

Be careful not to work harden the stainless as it can happen very easily if you let it get hot.

 

[Pete.]

I could cut M8 but don't really want to metricate an imperial built van.

You already did

I have a vintage caravan which has a brake pull rod of 5/16" diameter and 2.7m long.

 

[madkayaker]

I used 8mm threaded rod to replace the well warn brake pull rod on my trailer

 

[ajlelectronics]

Thankyou for all your help guys. I finally found a supplier who wanted to be helpful. Cotswold Steels of Babdown Aerodrome, Tetbury, Gloucestershire.

As I was going to a job 3 miles north, I went there after he told me that he had 6m of 5/16" mild that he could cut into two pieces for transport. Wouldn't take more than a fiver for the lot. So that's me sorted, I just have to cut the threads.

The MM dies are proper ones, I wouldn't bother with die nuts apart from thread cleaning. I have never used thread cutting lubricants and never had an issue with mild, maybe I should order some and start making use of it. Perhaps a smear of grease for now will be helpful?

If I had to, I was going to use three pieces of studding with couplers, but I know how I would view a job like that if I came across it!

 

[Lawnmowerboy]

If you've never used a cutting compound for threading you don't realise how much easier it makes a job. Some of the better cutting compounds claim to double tool life.