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Lathe test bar

skippyelwell

skippyelwell

Ultra Member
I've purchased a 3ft piece of 3/4" tool steel/drill rod and am getting ready to make my own test bar to align the new lathe.
I've watched a couple of vids but I thought I would ask you guys before I start cutting if there is anything I should watch out for, tricks, tips?
 
skippyelwell said:
I've purchased a 3ft piece of 3/4" tool steel/drill rod and am getting ready to make my own test bar to align the new lathe.
I've watched a couple of vids but I thought I would ask you guys before I start cutting if there is anything I should watch out for, tricks, tips?
Click to expand...
Why cut ? Run an indicator instead.
 
The straightest rods I have found are hydraulic cylinder rods. They are also chromed and dead hard. Drill rod is nowhere near straight enough IMHO.

I scrounged some from a local equipment place that services farm machinery. Cutting to length was a job though.
 
We have had this debate on here before.

My short summary of those discussions are that running an indicator on a known good bar isn't good enough. It's too difficult to separate out the runout from the concentricity. Rolly's dad's method works but only for rough alignment. Similarly, using a ground test bar in the spindle taper isn't repeatable - even if you can find a quality test bar (which most test bars are not).

It is better to cut your own bar because done properly, that bar left in the jaws as originally cut, will be true to the axis of the spindle. The alignment of the head and bed becomes mostly a matter of eliminating taper and indicator differences.

Of course, the bed must be aligned first.
 
Oh yes, and as I recall, beyond about 8 inches, a schedule 80 pipe is better than a bar because gravity makes the solid bar bend too much from its own weight.

I'll see if I can find those discussions and link them here.
 
Here is another thread on the same subject. It isn't the one I was thinking of, but still lots of good discussion here.

Test bar
 
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