View Full Version : Best way to harden 4140 Home shop
06-30-2007, 05:10 AM
I want to harden a splined shaft that i made for a republic lathe, 12"x1". can a okie do it with what A okie has. I bought a stainless bagg, Can I build a fire with the coals, with a pyrometer and thermocouplrer to check temp? Thank you hambone
06-30-2007, 10:25 AM
You can stack up some common firebricks to make a simple furnace using a propane torch(read large torch and lots of propane) for a heat source,it will work,but if the shaft is very long you can expect some warpage once you quench it.You can minimize some of the warping by dunking the shaft in the quench in a straight up and down vertical motion.It's possible you can pull it off without it warping,but don't be suprised if you have to straighten the shaft after heat treatmnet.
The other alternative would be to send the shaft out to a heat treating shop and have them do it.Heat treating is kind of an art form that takes years to master.
J. R. Williams
06-30-2007, 10:53 AM
Use the shaft as machined and forget any 'home brew' hardening. I will warp and cause more problems. Keeping shafts straight during hardening and final quenching is an art as previously noted.
06-30-2007, 12:16 PM
Thank you for the advice, I got alot of time in this thing, and I don't want to make a wrong move now.
I second the idea of either 1) use as-is or 2) send it out for hardening.
Personally, I'd use as-is. If it wears out in 20 years...make another one.
06-30-2007, 01:11 PM
If it positively has to be hardened, then if it was me I would send it out to get it nitrided.
This is a (relatively) lower temperature process which will give you a nice hard wearing surface, with far less likelyhood of distortion.
But as others have said, why not use it as it is? I replaced the EN8 (1040) unhardened leadscrew on my lathe 2 years ago, as it was a bit loose after 38 years and a lot of abuse, but still quite usable.
06-30-2007, 02:26 PM
if you had not already made the shaft I would recomened making the shaft with Q?&T 4140. It is already hardened and still machinable with h.s.s. tools.
Rather than use 4140 I use 1040 low alloy steel. It hardens nicely and is what I used for the pins on my bender as well as some of the dies. The main advantage is because it is a medium carbon low alloy steel it can be hardened just by heating to the critical temperature with a torch and quenched in water. It then may be drawn to the desired temper in a kitchen oven. It also machines very nicely and is commonly used for hydraulic cylinder shafting.
06-30-2007, 03:19 PM
1140 stressproof is good stuff too. It machines easy but is still tough stuff.