What causes this pattern?

[BWS Arms]

I have noticed a weird looking pattern after taking a test cut on this piece of 2.5” 6061. It kind of looks like a cross hatch pattern. I suspect worn spindle bearings are the cause but would like opinions from others. I purchased this lathe thinking it was gear noise but now I’m not so sure.

 

[akjeff]

I have noticed a weird looking pattern after taking a test cut on this piece of 2.5” 6061. It kind of looks like a cross hatch pattern. I suspect worn spindle bearings are the cause but would like opinions from others. I purchased this lathe thinking it was gear noise but now I’m not so sure.

Try varying the speed/feed. What RPM, nose radius? Positive or negative rake?

 

[BWS Arms]

That was 540 RPM. Only a .006” cut. Feed was .004. I was using a 7 degree positive DCGT insert and I will have to check on the radius

 

[twhite]

If you can put a center in it. It looks like slight vibration. Kick the speed up once you do that.


Cutting oil is my blood.

 

[mattthemuppet2]

could also be a slight harmonic with the lead screw and cutting pressure. Try hand feeding at about the same rate and same rpm/DOC, that will give you a good clue if it's the power feed. If it is, try changing the feed speed up or down and see if it goes away.

 

[BWS Arms]

I will try that after I finish the alignment.

 

[akjeff]

That was 540 RPM. Only a .006” cut. Feed was .004. I was using a 7 degree positive DCGT insert and I will have to check on the radius

You could easily double ( or even triple ) your RPM. You're running really slow for aluminum, especially while taking a light cut. Adjust the feed per rev based on the nose radius of the insert. Many times the insert manufacture will list the suggested speed/feed on the box label. If it's a 32.51 insert, I'd try at least 1000 RPM and .006" per rev. If it's a 32.52 feed it even faster.

 

[BWS Arms]

I have 12" sticking out past the chuck jaws. Thats why I was at 540 RPM. I wanted to turn it faster but was concerned about the stickout.

 

[BWS Arms]

I am taking light cuts to limit deflection. I am aligning the headstock.

 

[DavidR8]

I have 12" sticking out past the chuck jaws. Thats why I was at 540 RPM. I wanted to turn it faster but was concerned about the stickout.

At 12" of stickout you definitely need tailstock support regardless of how light the cuts are.
The rule for stickout is 2x diameter so at 2.5" diameter, 12" is over twice the amount of stickout.