1340gt surface finish problem

[rherrell]

O.K. guys, and gals, I've tried every speed/feed combo, every carbide insert I have, every HSS tool I have, I've even put vibration isolation pads between the stand and the floor...nothing seems to work.

Here's what I get...

Please excuse my photography skills.

You can not only SEE the ripples, you can FEEL them.

I 've also tried changing the motor drive belt, I have a link belt on there now. The link belt helped a little(very little)

There doesn't seem to be any unusual vibration problem, a glass of water shows nothing.

Please don't tell me I need a VFD, a lathe of this caliber should not be doing this. However, if a VFD is the only cure then I guess I'll have to install one because I can't be sanding and polishing every part that comes off the lathe.

 

[Dan_S]

Can you show a close up shot?

That looks like your tool height is to high, or you had to much sickout, or maybe a little of both.

 

[rherrell]

Can you show a close up shot?

That looks like your tool height is to high, or you had to much sickout, or maybe a little of both.

Tool height is exactly right and the amount of stick out doesn't do anything. The photo is 5/8" round stock with 1.5" stick out, does the same thing with .5" stick out.

That shot is as close as I could get and still be in focus. I'll try and get a better photo if I can.

 

[jbolt]

Just a though, but the pattern suggests to me it is mechanical. I would try mounting a TDI on the carriage, put the tip on the ways (top & side) and run the carriage under power to see if you are getting any oscillation. If that is dead smooth I would then start looking at the spindle.

 

[JimDawson]

I has a similar problem with my lathe, snugged up the spindle bearings a bit and that fixed it. Your mileage may vary.

 

[firbikrhd1]

What is your feed rate? That almost looks like threads. If the radius of your tool is small and your rate of feed large you get a pattern like threads which is what that looks like in the picture.

How much is your work extended out of the chuck? Unsupported thin work can result in patterns like that.

Check gibs for proper adjustment, lead screw feed shaft possibly bent.

Tool on center without enough clearance.

 

[DrAsus]

Tagged for interest.

DrAsus

Sent from my XT1575 using Tapatalk

 

[mikey]

That looks like chatter to me. I would suggest reducing your tool lead angle first and see if that helps. If not, try reducing your cutting speed and increasing feed. Chatter is a resonance issue but that assumes everything is tight - gibs, tool holder, etc so check that everything is solid.

 

[JBowlin]

Looks like threads/chatter... stupid question but I have to ask, are you using half nuts for auto feed instead of power bar?

 

[rherrell]

I put a half thou DTI on the carriage and on the ways, it vibrates between two lines which means a little less than half a thou. When I do it by hand it's dead flat smooth.

The photos above are 770rpm and a .005" feed rate, I've tried them all and nothing helps.

These next photos are the same piece of aluminum with half of it turned at 475rpm with the slowest feed rate of .0027"

I'm not a camera guy so this is about as good as it's gonna get!

You can't really see it but the lines are still there but closer together due to the slower feed rate.