Mk. II 6" Craftsman 101.21200 lathe spindle

[matthewsx]

When I got my lathe the chuck was really stuck onto the spindle, like days and days of soaking and pounding on it to get it loose. As I've been tooling up I got a keyless drill chuck for the tailstock pretty early on and noticed it wouldn't drill on center in the 3 jaw.

I finally got around to buying a couple of centers so I could align the tailstock and noticed the tailstock was higher than the spindle. I got out a straightedge and confirmed this by clamping it between centers and watched it point towards the headstock. Then I rotated the spindle and it reversed come to find that when I put my tenths indicator on it I'm about 3 tenths out from being concentric.



Best I can figure is I somehow bent the spindle trying to get the chuck loose, or it was just that bad from the factory.



Well, back when I was trying to free up the chuck I purchased another spindle which I didn't end up using. I now have it soaking in Evaporust to clean up the taper bore and will install it tomorrow. Hopefully it's better because the error is too much to ignore.

John

 

[wa5cab]

Fortunately, a slight error in height is much less critical than the same error front to back. However, the smaller the part's finished diameter the more it affects the diameter of the part as you approach the tailstock.

 

[Nutfarmer]

Just looking at your set up to measure the run out of the spindle, three tens is great. You are also including the run out of the three jaw chuck. To measure the run out of the spindle remove the chuck and measure directly off the spindle. Three jaw chucks may have anywhere from one to three thous. run out in the chuck by its self. Good luck . Things may not be as far off as thought..

 

[markba633csi]

I have a MK2 also and I can tell you the overall accuracy and quality is not as good as it's predecessor the 618. The short spindle deflects more easily and the headstock drive has some high-wear points in the design of the drive coupling. The large step pulley is nearly always wobbly and non-concentric.
I think you are probably getting the best result already and there isn't much more you can do without a lot of re-engineering.
You might also find that the belt idler pulley bearing wears quickly- I bored mine out and fitted a needle bearing, with a new hardened steel shaft.
I do like the ease with which you can engage the backgears but I also have found they sometimes dis-engage under heavy cutting loads.
It is what it is- a variable speed motor makes it much nicer to use, and easier to overlook the flaws
-Mark

 

[matthewsx]

Thanks for all the feedback, I get the same error measured directly at the spindle so I'm pretty sure that's where the problem is.

So what I'm hearing here is this is normal for my lathe and it's best to just work around it rather than swapping out the spindle because the other one is unlikely to be any better. That's pretty much wanted to find out before going through the work of changing it so thanks again.

At least I'll have a nice clean replacement spindle if/when I need it


John

 

[wa5cab]

There are also two different MK 2 headstocks (not counting the few Zamak headstocks that were on the final few hundred machines that they sold). You haven't said what the model number of your machine is. The Atlas 3950 has ball bearings on the the spindle. Sears sold the same machine but called it the 101.21200. Around 1977, they went back to the Timken tapered roller bearing that were used in the Atlas 618 and Craftsman 101.21400. The model number of that machine was Atlas 10100 (inch thread cutting) and 10200 (Metric). AFAIK, Sears never sold either of those.

If you are really getting 3 tenths runout on the spindle, that is quite good for any lathe except some really high dollar ones. 3 tenths means 0.0003".

 

[matthewsx]

It's the ball bearing unit, 101.21200 that I wrote about in my other thread. My measuring might not be the best, I think I'll do a collar test to see what I get there.

John