Strange finish on turned aluminum

ChrisAttebery

Rocket Nerd
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Jan 11, 2018
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308
Hello,

I'm still getting used to the Yangzhou 13x40 Gear Head Lathe I bought a few months ago. I turned a 2.125 - 16 thread gauge over the weekend and it has a weird finish. I did a finish pass on the center section of the gauge from right to left, but the finish has a pattern that goes from left to right. I turned it at 400 rpm, .003" IPR feed rate, .010" DOC. What would cause this? It seems counter-intuitive to me.

I'd appreciate any input you could give me.


Chris

IMG_5862.jpg
 
Were you getting a lot of chatter. The bevel on left side of threads looks chattered. Could be reflection. Even the far left looks bad. Like bob asked is your tool a sharp point? Did you back out when movin the carriage? Is that the spring pass on return?
 
I'm using a TCGT 32.51 insert. This pass was at the low end of the recommended feed and DOC. I'm not sure where to start on the feed setup that's why I was asking.

Double check your complete setup for the feed. Also looks like you are using a pointy tool.
 
I wasn't getting excessive chatter. It was a light finish pass. I backed the tool off before I returned the carriage.

The far left end was cut at a high feed and DOC. I can understand why the finish is poor at that end.

Were you getting a lot of chatter. The bevel on left side of threads looks chattered. Could be reflection. Even the far left looks bad. Like bob asked is your tool a sharp point? Did you back out when movin the carriage? Is that the spring pass on return?
 
Do you have the manual for the machine? Is there a threading chart on the lathe? Is the lead screw metric or imperial?
 
This machine appears to be the same as the Grizzly G4016. I've been using their manual as a reference. There are charts for feed and threading on the lathe. It was in feed mode when I did the finish pass.
 
Those reverse thread patterns are a form of resonant chatter. 400 rpm is way slow for carbide (210 fpm) , and the cut is shallow. Try burying the end radius of the insert in the work and running at 2000 RPM. With a 32.51 insert, you want depth of cut to be at least 0.016.

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