hi check the tapered seating on the spindle which the chucks locate on,if damaged or worn the chucks will not run true,tailstocks can be very worn on the bottom sliding face if they have been used too much for drilling,put centres in the headstock and tailstock and bring the tailstock up to see if the tapers align,if the tailstock is worn the tail stock centre will be lower and nearly impossible to correct and will produce crap work. Dont forget most round heads are around fifty years old.
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