Odd Patern on Turned Piece

[ddickey]

Checking HS alighnment DOC was .0015" I think. Took this pic during the spring pass. Material is 7075 I think 2-7/16" thick, 6" stickout.
I've noticed this before. Seems like it has started in the last year adn a half. Lathe is basically new.

 

[homebrewed]

I had a problem sort of like that which turned out to be a chipped insert. That likely isn't your problem since you're using HSS but maybe you have some swarf stuck to your cutter that's rubbing on the work.

Other possibilities include something that's loosened up (or is binding, like the LS). Another thought -- if it's a relatively new lathe maybe the HS bearings have bedded in some so the preload has decreased. Have you checked the spindle TIR?

 

[ddickey]

LS?
I thought about that also in regards to the bearings. When I first got it the the spindle seemed hard to turn. With the spindle in neutral I could spin the chuck by hand and it would spin for ~1.5 turns before stopping. It is more now probably 2.5-3. However, when you pull the chuck and spin the spindle it feels really tight. I don't remember doing that when new so I have no reference.
Probably < .00005" TIR.

 

[mmcmdl]

What was your feedrate and rpm ? I would add clearance to a tool and recut it not with the tangental bit being used .

 

[ddickey]

I think it was ~500rpm & .003" feed.

 

[homebrewed]

LS?
I thought about that also in regards to the bearings. When I first got it the the spindle seemed hard to turn. With the spindle in neutral I could spin the chuck by hand and it would spin for ~1.5 turns before stopping. It is more now probably 2.5-3. However, when you pull the chuck and spin the spindle it feels really tight. I don't remember doing that when new so I have no reference.
Probably < .00005" TIR.

After I added a handwheel to my LS I noticed that engaging the half nuts really increased the force necessary to turn the crank. Part (but not all) of the reason was that I had greased the bushings with heavy lithium grease. The drag greatly decreased after I cleaned off the grease and lubed them with way oil. I'm sure the change gears also now aren't working quite as hard to turn the LS.

Now that I'm thinking about it, I also noticed variations in the cut when I was using my LS handwheel to slowly advance the carriage. That turned out to be due to the saddle slide plates. They had worn enough that the saddle was wobbling slightly as I advanced it. I tightened them down and the problem disappeared. I'm pretty sure I would have had the same problem if I was using the power feed.

As usual, YMMV when it comes to these problems. Good luck on sorting it out!

 

[ddickey]

That was a suggestion by another member here. I did have my carriage/apron off the lather twice. Once to fix the lead screw lever interlock that had gone out of adjustment for some reason and the other was because I was curious how many oil ports the oiler was oiling, which by the way is completely inadequate imo. Anyway I thought I had the carriage gibs dialed in but maybe I need to tighten them a bit.

 

[Nutfarmer]

Change the tangent tool bits lead angle angle so that it is not under cutting when it’s feeding. At tool bit will cut better if there is an angle in the direction of travel. Hi

 

[ddickey]

I can't change the angle as I use a solid toolpost. The diamond tool has 5° negative lead angle.

 

[Illinoyance]

Improper engagement of the feed pinion with the rack can cause banding. That can be due to loose tolerances in manufacture, wear of the pinion and rack. Sufficient bed wear that lowers the saddle can create banding. The one thing they all have in common is cyclic variation n feed rate.