Correcting this finish

L

Livnpaintball

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So after a few months I finally get to play with my lathe, put in some 1.5" 1040 and made some chips. Played with speed and feed, HSS and ceramic. Speed was set at 1200rpm with .002 feed gave me the best finish but this took place. What causes this type of finish? Starts out nice then gets a little rough..

IMG_1266.JPG
 
Chip build up at the tip? I have seen this on Aluminum where a build up of the metal sticks right at the cutting edge. A chip formed at the cutting edge and the tool is now a little duller than before. No lube can cause both problems.
Pierre
 
I'd be turning 1 1/2" 1040 steel at about 280 RPM with HSS tooling. I haven't tried ceramic.
 
I agree with Pierre - a BUE or perhaps a chipped insert is suggested by a smooth cut that transitions into a bad cut. It is also possible that you have developed some hard spots and if your depth of cut is too shallow the insert may be skating over the surface. Try taking a bigger depth of cut and see what happens.

With carbide, you might want to up your speed to about 1800-2000 rpm and use cutting fluid.
 
check your depth of cut a .002 cut doesn't give as good a finish as a 0010 cut.If you have to cut say .0030 take it in 2 cuts .0015 . 6 cuts at 005 won't give as nice a finish.
 
Livnpaintball said:
So after a few months I finally get to play with my lathe, put in some 1.5" 1040 and made some chips. Played with speed and feed, HSS and ceramic. Speed was set at 1200rpm with .002 feed gave me the best finish but this took place. What causes this type of finish? Starts out nice then gets a little rough..
Click to expand...
Which one gave you the finish in the photo, HSS or ceramic?

Tom
 
Ceramic, ordered some carbide and going to turn the speed up with the depth of cut and see what happens!
 
I’m just spit balling here, so ignore me if you see fit. Won’t hurt my feeling. (I only have one left.)

Can’t tell from the pic, but is the work piece supported by a live center or steady rest? If so, could the work piece be “unseating” itself as the cut proceeds? Tailstock slipping? Dead center with insufficient lube? Does the transition in the finish always happen at the same location in carriage travel?

I don’t understand the “too shallow of a cut” theory. My bench lathe isn’t all that rigid and I have to creep up on precision diameters due to flex in the system. I have shaved the last few 10ths off with spring passes and had a great finish. I do mostly aluminum, though, so that may be the difference. I use HSS tools exclusively. Just throwing that out there FWIW.

Tom
 
From what I've experienced aluminum doesn't suffer from the "too shallow" problem, usually it's the hard steels and stainless
M
 
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