Turning eccentric

[BWS Arms]

I’m going to do some more test and measurements tonight and see if I can locate the problem

 

[stupoty]

I’m going to do some more test and measurements tonight and see if I can locate the problem

Is it not just the run out in the 3 jaw chuck ?

Even a new bison is probably only a couple of thousands repeatable.

Stu

 

[benmychree]

In the video, I see a continuous chip coming off the tool and a continuous line of cut; what makes you think it is cutting eccentric? I think that I do see ridges repeating as the cut goes along, that is likely something binding up in the feed train, like chips stuck in a feed gear root.

 

[BWS Arms]

I dont think so but I will confirm. I have a cheap 3 jaw on my smaller lathe that does have that much run out. If you watched the video, you can clearly see and hear it.

 

[BWS Arms]

Its more obvious in this clip. Its cutting heavier on one side. I had already made multiple passes and even blued it to be sure it was making a full cut.

 

[sdelivery]

Unless you have excessive play in the spindle, it would be nearly impossible to turn an eccentric. Even then, the symptom would be rough finish and chatter.

Play can easily be checked bu mounting a rigid shaft in the chuck and bringing a dial indicator into contact. If there is play, you will see the reading change as you push or pull on the chuck.

Three jaw chucks usually don't locate work concentric with the spindle axis, That is why we use four jaw chucks and dial in the work. Depending on the chuck and how much wear it has, you can see eccentricity of .010" or more. The lathe bearings should be preloaded so they will be slightly warm after use and there should be no axial play.

With a thermometer you should see between 120 f and 160 f

 

[sdelivery]

I am not going to make anyone happy with this comment but....
I steer clear of little cuts particularly if I want to see accuracy and Finnish.
Try a heavier cut that pushes the play out of the slide.

 

[stupoty]

Its more obvious in this clip. Its cutting heavier on one side. I had already made multiple passes and even blued it to be sure it was making a full cut.

Have you got end float ? you might need to adjust the pre-load on the bearings.

Stu

 

[BWS Arms]

I’ve tightened up the one bearing shown in the manual. I can spin the chuck 2-3 revolutions before it stops. 80-87 degrees temps at the front and back with IR thermometer. If I try to turn the chuck slowly, it feels sticky.

 

[sdelivery]

Depending on the machine, many cases there are two adjustments.
The first is inside the headstock and it is the one that controls the "preload" of the spindle.
The second is usually on the backside of the headstock where it controls whip or radial load.