Control rods. Riveted U.C.

[Andrew Rowe]

Probably was 4140 -medium tensile , you can also get '' free cutting '' steels which cuts and forms threads better than mild steel grades.

[Lynn Eades]

I was only ever talking about the finished length of the rod, including the threads and nothing extra. I'm sure I have already covered this. (see line 5 first post)

The rod is a medium tensile, which is what you would require. You have to be able to put a thread on it, but you want it strong.
Free cutting mild steel has a lower tensile strength than mild steel (mild steel doesn't have a spec) It is higher in lead content to make the thread cutting easier. It is not suitable for this job.

On the thread cutting;
It is easy to screw it up! (start it crooked)
When you buy your steel for your long rods, and you have cut them to length, you have only one shot at it.
The best way to do it (unless you have access to special thread rolling gear) is to put the rod in a lathe (chuck) and your die holder against the spindle of the tail stock.
This helps you to keep it all square for the thread cutting
You can then "feed' the die with the tail stock, while turning the chuck by hand (maybe easier swinging it with the chuck key)
It the case of the long rods, careful planning to support the rod is required (maybe put it in a pipe that fits in the hole through the headstock and supporting the other end with a stand or timber frame or what have you) Make sure the lathe is isolated (switched off at the main) or serious damage is likely.

[tankbarrell]

If anybody needs these, I can do them as required. I would suggest EN8 and I would thread them in a capstan using a Coventry diehead, this would give perfect threads.

[Lynn Eades]

Adrian, can you explain the EN system? I remember (as a young fella) the steel crank to have for a Lotus twin cam was made from EN40B.
If I was over there, I'd be taking up your offer.

[tankbarrell]

Lynn, it's the old British system BS970, superseded some years ago by a newer version with different codes.

Freecutting MS that you mentioned was EN1A and is now 230M07 where the 07 indicates carbon content, i.e 0.07 %. EN8 is now 080M40 so 0.4%. Carbon content is a good indicator of a steels ability to be hardened.

EN40B is now 722M24 and is a 3% chromium molydenum nitriding steel that when nitrogen hardened (nitriding) has a very hard wear resistant case and a tough (60tons) core. Ideal for a crank!

[RichardT10829]

Just thinking out loud, how much load can you put on the brake rod in reality? Do you think the small lever that is the brake pedal has sufficient length to pull a set of threads ?

I am only asking as I have access to a load of mild rod I understand the need for a greater tensile if the rod worked in compression

It's a shame that I need to go order some EN8

[Lew Skelton]

I don't want to come in late and blow it to bits but I used shiny mild steel rod for my long brake rods, I didn't think that the threads would ever pull off or the mild steel rod to be inferior, the clevis's are screwed on about an inch and a bit with a locknut so its not like they are compromised by being held by 3-4 turns. I cut my own thread using hand tools and the rods are working fine. Also made the engine to rear plate and clutch rods with mild as well as the accelerator rod. When cutting the old rods I replaced (as parts were excessively rusty, I cut them with a hacksaw) then re used sections I did not notice any increase in hardness. My carrier has been getting around fine. Im not saying take my advice as im just a mechanic, but if you have a supply of mild it would poss do.

[tankbarrell]

Originally Posted by RichardT10829

I am only asking as I have access to a load of mild rod I understand the need for a greater tensile if the rod worked in compression

That's a contradiction!

I'm sure mild steel would be fine though, normal bright mild steel is EN3B, it has a tensile strength of about 80% that of EN8.