Pick-up / drag lines turning mild steel

Try a bit of solid lube or oil on it, and also honing the end of the cutting tool helps to eliminate BUE (Built up Edge) which is whats happening. Minor imperfections, can make stock build up on the cutting tool edge which then scares or drags the turned surface. Are you useing HSS or carbide? Carbide likes a higher speed and feed than HSS does.

Some hot rolled steels are horrible to g et a decent f>>Hi guys,

Got Carbide?

Coolant/Lubrcant?

Had a recent experience with one of he apprentices in our shop. He was trying to get a decent finish on some hot rolled stock with HSS. Couldn't.

A carbide insert and a heavy cut at high rpm left a mirror finish.

Pretty unnerving with all the hot chips rattling around, esp. for the guy that was not all that comfortable in front of the lathe yet.

We ended up making the part od 12l14 and all went well.

Cheers Trevor Jones

As Roy said it can be hard to get a good finish on hot rolled steel. I've found the same as you - try finding some "free-machining" steel it turns well with a nice finish. I don't know exactly what "free-machining" means, perhaps some one else will enlighten us. I guess the alloy composition gives it nice machining properties.

rob

Cold rolled (1018) causes the same problem I have had much better results turning 4140. It seems to be a good general purpose steel that can also be tempered a bit.

Jack

Wow, great response! I was fairly vague in my post, so I'll fill in a bit of detail:

I tried a few types of tooling, mostly negative rake carbide-insert type of various shapes, with no real difference in the finish between tools. I had the best luck with a cheap-and-cheerful standard carbide tool (not an insert) with a positive rake, but it was still hit and miss

I checked the height of the tool, and tried from dead center to slightly above. Speed didn't seem to make much difference, although the finest feed availiable on the lathe (0.003" / rev) seemed best. I tried both with flood coolant, cutting oil, and dry.

Still the tool would seemingly pick-up a burr and drag a groove for about one rev and release it. I'm concerned because the grooves would be a bit deep for a good polish with emery, and the dimensional tolerances would be out.

The toolpost and all other parts of the system seem very rigid. I put a dial indicator right on the tool while it was cutting and didn't see more that 1/10 thou movement in the tool (up and down).

The suggestions I've seen from your replies have included the following: type of lube, grinding for a steeper front rake to prevent burring, higher speeds with the carbide inserts, etc. Hot-rolled mild steel is probably the most common stock for a lathe. Has anyone got a suggestion based on the additional info above?

Thanks in advance, and for the earlier replies. Great suggestions - maybe the additional info will help.

Damian

Free machining steel has, pardon the word, "Lead" in it. 12L14, leaded steel, cuts real easy with that addition of lead. Sulfur in the matal will make the metal cut easier too. The smaller the tool nose radius the easier it is to get a good finish. HSS bits will give you a decent finish at lower speeds. Carbide needs to run at a surface speed of about

John

Which may or may not improve things, depending on other factors.

Which should to an excellent job of improving things, given a good sharp tool, properly set.

Which is a lovely metal to work on, but which typed as you have it is likely to confuse someone who is not accustomed to it. Try "12L14", where the 'L' is upper case, so less likely to be confused with another '1' (one).

And the 'L' here usually means that there is lead in the alloy, which does significantly improve machinability. (Though on some alloys, it can mean other things.)

Enjoy, DoN.

I would probbaly go with positive rake inserts as its a lot eaier to g et a better finish.......even though your lathe should be plenty ridgid to use negative, I get a better finish with positives. Run the brazed carbides at higher pseeds and feeds as well, and carbides do not like to take whisker cuts, so pl;an your cut accordingly.

As for lube I Use automatic transmission fluid, and it works fantastic and is about as cheap as you can get.....doe snot rust, works fine with anything I mill or turn, and it does not staiun metal.

Any steel with a L in the alloy will be free machining or leaded steel, 14L10 is one in particular. I think the lead in the steel acts as a lube of sorts, but not entirely sure on that, but most leaded steels IIRC can not be adequately heat treated, so thats a draw back..

I always run my cutting tools cutting edge dead on centerline.

Regards

Indeed, DoN.

My Bad! Thanks for pointing that out. I understood what is written when I read through it, but I knew what I was trying to say!

Cheers Trevor Jones

Funny! I wondered where that tap went!

Thanks for the insight.

Is doe snot rust worse than buck snot rust? 8-} Bob