Before you start make sure that the floor stand is level and fully and equally supported upon its feet. This procedure will ensure that you are not introducing twist into the bed by bolting the lathe down. Now, without moving the saddle, start tightening the bolts at the tailstock end and add shims as required until tightening the bolts causes no movement on the dial gauge. It is unlikely that tightening the headstock end bolts will cause any twist, but if so, add shims until the bolts can be tightened fully without any twisting taking place. Start tightening the hold-down bolts at the headstock end and watch the dial gauge, any change in reading will indicate twist being introduced into the bed. Mount a dial gauge on the cross slide and position this at the tailstock end of the bar and wind in to give a reading of about 15 thou. Then chuck a length of bar at least two thirds the length of the bed. In my experience shimming is needed mostly at the tailstock end.Ī quick method of checking for bed twist, not as good as the spirit level method I described in my last post, because it does not take into account any "built-in"twist, but useful anyway is as follows: First slacken all four hold-down bolts and slacken the drive belt off completely. I have set up several lathes in my time and have never had to use shims anywhere near this amount. You say you have tried Rollie's Dad's method and have used shim as much as 36 thou under the headstock. Re- reading that I am wondering, is it important that once the dial gauge is set it remains in that position, ie, since it is in the toolpost the cross slide is not moved? I have been re-positioning for each new pair of measurements after changing shims. I am inserting shims under the headstock, between its foot and the tray and whilst I can move the point at which these readings occur they remain the same, or very similar, with shims from 3 thou up to 36 thou under either the front or the back of the headstock. Originally I get a tir of 2 thou at the chuck and 7 thou 11 " out so the RDM "near end average distance" and far end version would be half those measurements. I am using a 13" length of 1/2" silver steel which is of uniform diameter over it's complete length, at least whithin my abilty to measure it. I've sussed Rollie's Dad's method, I think, and applied it today. The bolts holding the headstock to the bed are not obvious, presumably under all that sheet steel somewhere and I am afraid a precision level is not in my armoury so it's brute force and ignorance as usual here. Thanks for all the pointers chaps, reporting back.
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