What Would Make This Pattern On The Lathe?

Looks normal to me for under the conditions mentioned. If you have a curling chip and then it stops currying and falls off the work and a new chip curl starts. That will cause a surface finish disorder. 1018 is kinda gummy to machine. It will tear off instead of being cut off. Also a cause for an irregular surface finish. Try a lubricant and a very sharp tool bit. If you want a nice looking tooled finish, try using 12L14. If you still get a bad finish. Then you would have something wrong with your set-up, but I doubt it.
 
Sometimes rotating your toolpost (thus, the edge relief angle) can help.
 
Thanks for all the great advice everyone! I didn't get a chance to work in the shop today but I will experiment with some of the suggestions some evening this week and I will report back what I find. Thanks again!
 
Lynrob said:
Thanks for all the great advice everyone! I didn't get a chance to work in the shop today but I will experiment with some of the suggestions some evening this week and I will report back what I find. Thanks again!
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On the last pass,slow the feed rate down considerably,remove .005 or less with a cutting fluid like cutting oil.You probably won't have to file or sand.Not even polish. I turn 1018 once in a while,prefer the leaded steels though.As long as the finish looks like your pics,which is not bad,then the slow feed and slight cut with oil will do the rest on the last pass.
mike
 
Look up the optimal speed and the optimal feed for the tool and the material. Try again and report back. Best to go with what is best for speed and feed. Just telling you to go slower or faster is not the best way to go. Check the numbers and use them.
 
Cadillac STS said:
Look up the optimal speed and the optimal feed for the tool and the material. Try again and report back. Best to go with what is best for speed and feed. Just telling you to go slower or faster is not the best way to go. Check the numbers and use them.
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Very good advice.
 
Wreck™Wreck said:
That material is not likely produce a nice surface finish ever, it tears leaving the artifacts that you are seeing. Either use another material which will be more expensive and less easily purchased or live with the finish and polish it with abrasives afterwards.
Using flood coolant and turning up the speed and feeds will also help.
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Agree here. 1018 is a tough material to get a good finish on from just cutting. If you ran it dry, most likely there is a bit of build up on the cutting tool intermittently and that will cause the grooving. The 'numbers' would suggest 2,000 RPM +. I would run at least around 1200 RPM and a feed rate of at least .007 with a .015-ish tool nose radius, and cutting fluid.
 
I get improved finish with the tangential by feeding from left to right, while taking a shallow cut - less than 5 thou.

When the goal is a good finish then the vertical shear tool is my weapon of choice, see: http://www.gadgetbuilder.com/VerticalShearBit.html
It may take a couple shallow passes to get below the rings shown in your picture.

Use cutting oil with either tool .
 
I'd agree with Gadget, if you are going to use hss/cobalt you will most likely get a better finish with a vertical shear tool.

If you use carbide and run close to the maximum sfpm, with feed & doc both over 0.010" you can get an almost polished finish, but the chips will be coming off blue/purple and the carriage will be moving fast enough to make you uncomfortable.
 
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