Finish problems on my lathe

seanb

seanb

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I am having some problems when turning on the lathe. I get this irregular bumpy finish not matter what the speed feed or tool used.

It doesnt matter how close I am to the headstock either.

hss produces a different pattern vs carbide but the pattern is still there.

The picture show part of the barrel where I polished out the marks.

Could the motor cause these marks? My lathe is a grizzly 12x36 belt drive


barrel.jpg


barrel.jpg

barrel.jpg
 
Have you set your tool on the center? It looks like the tool is to high and dragging on the bottom of the tool bit. You also look like your feeding to fast. Some of the import lathes use the feed screw for moving the saddle.. Does yours or does it also have a feed shaft? Take a picture of your tool bit. Before you put your shaft in move the tail-stock with a dead center in it up and lock it and move your bit to the center to check the height. When your cutting look at the compound and cross slide and see if anything is moving or rocking. take some pic's and do those tests and let us know what happens.
 
I was getting the same look on the Atlas, matched up perfectly with the leadscrew. I could see the difference of the finish visually but it was not measurable. I changed to a larger radius tool and slower feed to get rid of that finish.
A bent or not properly supported leadscrew has been suggested before.
Pierre
 
I'm assuming you're referring to the finish on the right of your picture. That looks as though the feed is far too aggressive, almost like you're using the half-nut for turning. I'm not familiar with your machine, it may be set up that way. If not use the regular saddle feed and try a feed rate of about .015" and see how that looks.

Doug
 
Re: Finish problems on my lathe. Update

Thanks to everyone who replied.

It looks like my feed shaft is bent.

I have a leadscrew on my lathe and a feed shaft.

Last night I used the leadscrew to turn some stock and the problem went away.

Hopefully it is just misaligned and not bent.

Any ideas on how to test it?

Heres a link to my lathe

http://www.grizzly.com/outlet/12-x-37-Belt-Drive-Gap-Bed-Lathe/G9249
 
Re: Finish problems on my lathe. Update

With an imprint so pronounced, you should be able to see the bend! That's one of the most pronounced symptoms I've ever seen!

Did you check all your carriage gib screws? Is everthing snugged-up properly (not too tight or loose)? I've learned through the school of hard knocks that drive-screws AND/OR carriage problems can cause these problems. One time, a guy here found it to be the bearings at the end of one of the driverods. -Pretty sure it was Tony who finally pointed the guy in the right direction. We tried a million things before that finally was over...

Point being, don't get hung up looking at the bark and make sure you look at the trees too. I've now learned to say these problems are usually due to driverod assembly and carriage adjustment issues. -And I suppose that if a lathe were not properly bolted down and "leveled" properly, it could make the carriage more susceptible to unwanted movement.

Ray

seanb said:
Thanks to everyone who replied.

It looks like my feed shaft is bent.

I have a leadscrew on my lathe and a feed shaft.

Last night I used the leadscrew to turn some stock and the problem went away.

Hopefully it is just misaligned and not bent.

Any ideas on how to test it?

Heres a link to my lathe

http://www.grizzly.com/outlet/12-x-37-Belt-Drive-Gap-Bed-Lathe/G9249
Click to expand...
 
The carriage could be riding 'high' on the top of the vee's instead of on the vee's. Had this problem with my 9" SBL last year. Corrected it and been doing fine since!
 
I just came in from my shop, I have a clone of the Jet. I took a good look and I agree with Ray, I would look at the carriage. There is no way the feed rod could cause this directly. Likely the gibs are too loose or the ways are too dry and there is a lot of stiction.
Pierre
 
Re: Finish problems on my lathe FIXED!!!

I pulled the sadle apart, after I took the feed shaft out. The bolt the holds the worm gear had almost fallen out allowing the worm gear to move back and forth. The gib was also loose on the carriage, but im not sure that was the issue

I fixed both of those things and took a test cut. Problem fixed.

Thanks everbody
 
Good the see that you were able to solve the problem. I vote for the loose worm gear.
Pierre
 
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