Lathe bed flatness

[Canadium]

I finally got around to checking the accuracy of the bed on my small 9 inch South Bend lathe. I took advantage of the fact I currently have the lathe all in pieces to take the entire bed and put it upside down on my 3' surface plate so that I could check deviation in the bed with feeler gauges. To my surprise I found the only significant deviation was a uniform 1.5 thou depression under the head stock. Since there would be no wear under the head stock I assume it was manufactured this way and that there is actually no appreciable wear on this bed. Any thoughts/opinions?

 

[skippyelwell]

I went through a South bend restoration kick for a while and I'm sure everyone of those lathes had some very thin shims under the head when it was torn down, maybe it's deliberate?

 

[mickeyf]

Cheaper/easier to shim it up than grind it down?

 

[Canadium]

I went through a South bend restoration kick for a while and I'm sure everyone of those lathes had some very thin shims under the head when it was torn down, maybe it's deliberate?

Thats interesting! I've only ever had one other South Bend 9A and it had pretty thick shims under the head stock but this one didn't have any?!

 

[trlvn]

You might want to check the height of the tailstock v. the headstock. I would speculate that in the manufacturing process, a late-stage check would be to compare the height of the two. It would probably be easier to intentionally make the headstock a smidge low and then shim it up rather than either shim or re-machine the tailstock. (Just my guess.) Perhaps yours is close enough to not require a shim?

Also, I believe that the heights are not even all that critical. They need to be close but if one is high or low by a couple of thous, the amount of taper that would result would be miniscule. It is much more important that the centres be parallel to the travel of the cutting tool.

Craig
(And props for picking out an old lathe with minimal wear!)

 

[Clipper]

I went through an 820 Logan years ago and found shims under the back left hand side of the head stock. The lathe came from a machinists estate sale and was in pristine condition except for spindle bearings. I got lots of not very nice comments about that on the Logan forum; "it's junk, sell it, etc"
I reassembled it with new bearings and the same shims and it turned beautiful parts!