Tips For Turning A36 Hot Rolled Steel

mrjbinok

mrjbinok

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Learning things every day as I start using my Craftsman 12x36 more and more.

I had purchased some 1 1/4" A36 Hot Rolled round bar for a drill jig project and soon found out that this isn't the easiest material to work with on the lathe. Problem being the hard outer surface of the stock plays hell with my cutting bits.

I am wanting to smooth the outer surface of the stock, and want to keep as much of the material as possible... not a critical diameter... more for esthetics. I mainly use the 3/8" indexable carbide tools but have tried 3/8" HSS ground to a little larger tip radius as well as the sharp tip. I've tried various lathe speeds and feed rates, using cutting fluid and not. What I end up with is dulling the cutter within 30 minutes and having to either re-grind the HSS or changing the carbide inserts. I have several pieces to make so it's getting frustrating to have so much down time

Last night I ordered some Cold Rolled TGP that should eliminate the problem, I hope... but I have enough of the hot rolled material that I would still like to use it up.

Can I get some tips and/or suggestions on machine setup and/or cutting techniques that will improve the life of my cutting tools?
 
Use a deep enough first cut to get under the scale, then turn up the speed until you get yellow to blue chips and you will get a better finish. A36 is not the best steel to machine, as I guess you have already discovered.
 
You said you bought some cold rolled T, G, & P.. T, G, & P is not really cold rolled. It's actually specially processed hot rolled that is rough turned, centerless ground to size, and polished. The most common one is La Salle 1144 which is sometimes referred to as "Stressproof" material. You will find it to cut like a dream. Unless you need the T, G, & P finish, go with one of the other material grades out there like 12L14, 1215 (which I prefer), 1144, for free machining grades. 1018, 1020, 1040/45, are not free machining grades, but are ok for certain needs. A36 grade is mainly for any welding project you may want to do in the future, but not for machining parts out of.
 
Yeah, the mill scale is a pain. As others have said, a deep first cut to get past it works, but that might be a problem for some of the smaller lathes to manage. I've taken to immersing any hot-rolled pieces in a bath of muriatic acid prior to turning. It throws the scale off right quick, leaving just the fresh steel surface. The vapours are not good for you, so I do it outside in a plastic tub and use full face shield/ gloves. I've heard vinegar works for this too, probably a bit slower, but I've not tried it myself.

-frank
 
Flood coolant, use negative rake carbide tooling meant for steel with a large nose radius and as mentioned above use a large depth of cut and spin as fast as you are comfortable with.

Cutting oil is not coolant as it doesn't remove the heat. Above all try not to use hot rolled bars whenever possible, also take note that 12L14 is mostly un-weldable due to the lead content, it was developed for automatic screw machine products but has been largely replaced by 1215 due to the toxicity of lead.
 
Thanks for the info. The parts I am making will end up as drill jigs to insert into a bushing and give a reproducible line up for drilling for a locking dowel pin through the shoulder. I will be heat treating to add some durability so my question (since I don't have time right now to research).... are the 2L14, 1215, 1144, and the 1018, 1020, 1040/45 grades heat treatable?
 
mrjbinok said:
Thanks for the info. The parts I am making will end up as drill jigs to insert into a bushing and give a reproducible line up for drilling for a locking dowel pin through the shoulder. I will be heat treating to add some durability so my question (since I don't have time right now to research).... are the 2L14, 1215, 1144, and the 1018, 1020, 1040/45 grades heat treatable?
Click to expand...

I believe that 1045 is heat treatable, however common practice is to buy thin walled drill bushings and press them into the jig, these are easily replaced when worn and are inexpensive.

As seen here http://www.mcmaster.com/#drill-bushings/=13t59i6
 
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