Thread: Help South Bend 13 cutting woes

I have my lathe up and running but I can not get a smooth cut, have tried different cutters HSS, Carbide, have also tried different material. I don't have any chatter or vibrations, chuck has about .005 run out what do I need to look for to fix the problem. Also I have used the medium speed and the slowest feed and still has a terrible finish.

I'd look at two things to start: First, if you're using a sharp pointed tool with an "as ground" finish, you'll have a very difficult time getting a smooth finish. Most "factory made" carbide tools that I've seen come with a sharp corner at the cutting edge. Even if you're grinding your own, the finish left by standard wheels on HSS bits or by silicon carbide wheels on carbide bits will not lead to a smooth finish. You need to very slightly round the sharp point as seen in the "plan view" by using a fine oil or water stone if it's HSS or with a diamond file if it's carbide. Also, doing a finishing dress on the the cutting edges with a diamond file will do wonders for the quality of the finish.

Second, look at the feed rate you're using. A smooth finish will require a relatively low feed rate regardless of how well you've dressed up the cutting tool.

But start by making sure that the tool does not have a sharp point and that the cutting edges have been lightly dressed after grinding. I use a combination diamond file with 600 grit on one side and 1200 on the other. The diamond file works well on HSS as well. I think there's a statement in HTRAL to the effect that a good machinist always dresses his tool bits with a fine stone after grinding. (Diamond files were not in wide use back in 1936 when my copy was printed. ) Not to say that you're not a good machinist but I've been amazed at how much difference that final touch can make in the finish on the workpiece.

Then, after all that is taken care of, look at the material. In particular, hot-rolled structural steel products are very difficult to machine with a smooth finish. Some stainless materials are also difficult to machine smoothly if the tool is not freshly sharpened and dressed. If I'm making rubber molds out of 316, for example, I'll usually dress the carbide tool twice during the machining process--once to start and once just before the final dimension cuts are made and I can obtain a very nice finish. HSS tools would require much more frequent attention.

If there's nothing loose on your lathe there's no reason you can't produce a smooth finish.

That wobbling chuck might be introducing some vibration. I'd also address that. Another thing with grinding bits: get yourself a nice stone and hone the edge (after grinding). Grinding a wheel leaves it only (so) sharp. Honing it will make it REALLY sharp.

adjust your tool like has been said, and hand feed a cut{slow} on center of work and see if finish is any better..

"Also I have used the medium speed and the slowest feed"
Ah. For finishing, you want fast RPM, light cuts, tool grinds discussed above, and I assume you are using cutting oil? The dark pipe thread cutting oil from the big box hardware store will do nicely. If you don't like oil smoke, get a small fan.
Also, what sort of material are you cutting? If it's steel from that same big box store, you are NOT going to get a decent finish. No one is. it's crap steel. Same with A-36 material. Go to speedymetals.com, look at the materials, they have quite a bit of info. Look at the machinability index number. If you are just starting out, get some 12L14 and work with that. Not the strongest stuff in the world, rusts if you look at it wrong, but cuts beautifully.
Pitch the carbide until you understand HSS grinds. Get an aluminum oxide wheel to grind it with. Try Rockler Hardware if you have a 6" grinder. There are nice diagrams of how to grid a tool if you search, good ones are in "How to Run a Lathe" which you can get for free I think in the yahoo southbend groups.
(I have no connection to speedy or rockler other than being a long time satisfied customer)

I really appreciate the input guys it has been a lot of years since I sharpened a tool bit but after your advice and a little tweaking I have a nice finish just like I remember the way we did in my dads job shop over 30 years ago. Kinda like ridding a bike the more you do the more it comes back, I now have a SB just like the one he had in his shop and I have his old Gerstner and Sons Tool box on the bench pretty cool I think I may need a mill next !!!!!

Dconrad:
You have been bitten! Enjoy your new passion.

Not to discount any of the early replies, but the number one problem in machining is chip removal. Adequate nose radius and sharp edges are of course very important, but adequate chip clearance is often overlooked. Fine cuts and light feeds create small chips that often get trapped behind the tool and drag on the work spoiling the finish. Watch the tool closely and make certain your setup allows the chips to exit the tool area.