Quote Originally Posted by simonl View Post
If you turn between centres and it shows a taper, how would you know if it's from a twisted bed (or other issues) or from a mis aligned tailstock? Adjusting the tailstock would remove the taper but you could still have other alignment issues.

I could be wrong, just a thought?

Simon

The idea is to turn the ends of the bar so that both ends have the same diameter, by adjusting the tailstock.
The longer the bar the better the results.
This means the bar is running true to the line between the end of the spindle to the tailstock.
If the spindle is true to that line it is true to the bed.
In order tot find out you replace the cutting tool by an indicator.
Set the indicator to zero touching the end of the bar near the tailstock in the horizontal centre.(measurement1)
Mark the position of the carriage.
Then take out the bar and replace headstok center by a 4 jaw.
Leave the indicator in the toolholder as is.
Indicate the bar in the 4 jaw so it runs deadtrue close to the 4 jaw and at the end of the bar.

The bar will now be running true to the axis of the spindle.

Repeat measurement 1 on the bar held in the 4 jaw.
If the spindle is out of alignment the indicator in the toolholder will now show the amount of misalignment of the spindle.

correct misalignment of the headstock and repeat the procedure