Turning Hot Rolled Mild Steel

[AllenH59]

I got a bunch of 1-1/2" hot rolled bar a while ago, and was playing with it in the lathe. It was horrible... It would tear and smear and chatter and no matter what I tried it would not turn smooth.. I have a blacksmith buddy around the corner, and we stuck a foot long piece in his propane forge, got it bright orange and quenched it in his rain barrel... I stuck it back in the lathe and it was very machinable. It cut clean and bright, and could cut .070/side without tool chatter.

[ERIE S-1 BERKSHIRES]

I use an Armstrong tool holder that was meant to be used with brazed carbide cutters, only I use quarter inch high speed Steel with a real nice curve radius I think the radius was 3/8 ? But you can take a pretty good cut and leave a good finish surface to my surprise

[armscor 1]

I have shied away from the stuff, warps and bends like a Banana when machined, too much internal stress.

[Steggy]

Heating and quenching HRS will modify the metal's microstructure and make it denser, producing better machining properties. Carbon will precipitate to the surface as well, although the common HRS grades don't have enough carbon for heating and quenching to significantly alter the material's properties.

[BadDog]

I haven't had the experience of hot roll bending and warping into a "banana". Cold roll, yes, but not hot roll. However, a lot of the stuff I do are for steel weldments/fabrications, so hot roll in its many forms is the normal go to. And yes, sometimes it can be really hard to get a good finish. Luckily, that's not usually a problem for my stuff. However, I have noted that miserable steel material for finish often surprisingly converts to a very nice finish with higher DOC using negative rake carbide tooling. I've been rather surprised on several occasions, but I don't know the full details on how much is needed to achieve such results.

[armscor 1]

I need new glasses, I miss read, my comment applies to cold rolled mild steel.
Tried turning with work piece mounted in chuck and other end supported in tailstock, machined about half the diameter and pulling back tailstock found it had severely warped.

[Harold_V]

Yep! It's generally a mistake to turn from a chuck with a center, and for that very reason*. If the piece you make is slender, you also risk making a part that is straight while in the machine, but is not when removed. To add to the insult, the center is most likely not going to be concentric with the part, because the part imparts an oscillation to the tailstock in an attempt to stay on center. The more rigid the part, the greater the oscillation. The degree of oscillation will be dependent on the amount of movement the part experiences as the stresses are changed, which is directly related to the diameter and length of the part. A rigid machine will display far less eccentricity than a light duty machine. Locking the quill on the tailstock will usually diminish the amount of oscillation as well.

If you must use a chuck and center, there's a little exercise you can use to enjoy success. It revolves around drilling the center only after roughing the part. It may sound crazy, but it works, and very well.

Grip your material in your chuck with no more than three times the diameter extended beyond the jaws. Rough turn to about .05" oversized, then extend the material again and repeat. Do this until you have the piece roughed to the desired length. At that point, and this is critical, using a center drill that is held by a short portion, so it can "hunt" for center, carefully start your centerdrill in the extended stock. Make sure the center drill picks up the true center, which most likely will NOT be the center of the material, as it will now be oscillating due to movement from stress relief, as well as the act of rechucking (rarely does a three jaw run true). You want the center you drill to run dead true, to NOT deflect the part.

When you have established the center hole, you can then begin the finishing operation, taking the part to size.

By following this procedure, you'll have effectively relieved the stress in the part, leaving enough material to correct any introduced errors.

*'As much as I dislike turning between centers, it has one feature that makes it quite acceptable, that being that the part is free to constantly correct itself, so in the end, it won't be crooked. The negative is that it is not generally a rigid setup, so cuts are a compromise of both feed and speed.

H

[liveaboard]

I use a lot of hot rolled steel; it's cheap and easy for me to get.
I usually cut slightly oversize, then polish with emery cloth. It only takes seconds.
Hot rolled steel is 80 eurocents a kilo, with tax and free delivery [if I buy more than a couple of hundred kilos].
I think that's 40-45 US cents per pound.
Of course it all depends on what you're doing.
Lately I've been trying out some better grades of steel, but I have to travel to obtain it and it costs 3x more.
I have some that I can temper and harden, which has been useful a few times already.