View Full Version : 4340 induction hardened steel shaft ?

12-27-2012, 09:14 PM
So, last question I hope. I turned my shaft for my hydraulic motor.
The shaft rides on the needle bearings. The original was Induction hardened.

I read in the "hand book" the shaft should be rc 56 or greater.

I made mine out of 4340, I think it is around RC 35-40.
So, should I heat it at home to make it harder or just use it as is.
If I heat it at home what process should I use and will that deform the shaft at all ?


Rich Carlstedt
12-28-2012, 12:15 AM
You are correct, the 4340 will be at RC 38 .
The bearing will not last if you do not have a RC 56 +
Do you have an extra piece ? If you do, you can practice on it.

You need to heat the shaft upto 1550 degrees F for a few minutes and then quench in Oil
Make sure you enter the oil vertically to minimise warp and make small circle 8's in the oil
After it cools, temper it at 400 degrees. You can do that by marking it with a felt tip pen, and heating the shaft evenly
with a propane torch. As soon as the ink mark fades, set the piece aside and it will be drawn down OK
You will have a RC 58

Dr Stan
12-28-2012, 12:46 AM
Another option is to turn the shaft down and press on hardened sleeves if the design will allow for this.

12-28-2012, 01:10 AM
Might bend like a banana once you apply heat, that is why they are heat treated, then ground afterwards.. Not to mention there will be a surface finish requirement if you want to expect any life out of the needle rollers...

As mentioned the press on hardened inner ring if possible might be the go... Otherwise leave it soft... Depending on how much use it is going to get, might last a long long time... If it has minimal side load, it probably will last a long long time...