William, get out your dail indicator and set it up behind your mandrel in the center, with the blanks on use the center bushing. Turn the lathe by hand for all of the tests, set the mandrel up before without the blank and make sure it is true, then put your blanks on the mandrel and lighty tighten the nut while you are turning the lathe by hand, as you are tighteng the nut at any time it gets out of true, rotate the blanks until it it true and then you can tighten the nut tight and it will stay ture. I have tried this many times and most of the time I put the blanks on the mandrel they needed a bit of turning the blanks to get them true. When they are true I have taken 6 inch channel locks and tighten them down and they will stay true unless they are a soft wood like pine and the bushinge will crush into the wood. Other things that I have found is to make sure the bushings are on past the threads or it may let the bushing throw the mandrel out of round.
Some bushings fit lost on the mandrel with up to 4 thousand play.
As I have said if every thing is true and square then you can tighten the nut and it will stay ture.
I put the blanks on and tighten the nut and bring the tail stock up but not tuching the mandrel
and turn the lathe by hand to make sure it turns true, If it dosen't then rotate the blanks or find out why it is not true, glue on the ends of the bushings or a burr on the tube can do this. This works the best for
me.
This is my opinion on this and I do not recommend to use pliers.
Bob