I¡¯ve not come across the Unimat 4 before but it looks very much like a red U3!
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Two dead centres, one in each of the holes in the headstock and tailstock spindles would check whether these shafts are aligned at the point of exit¡
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What was holding your centre drill? Presumably a drill chuck or collet. Have you checked that for eccentricity?
Is the bed bent or twisted - or being twisted by being fastened down to a base board? (I use some birch ply under each end of the bed to avoid the middle support grounding on the wooden baseboard and potentially bending the bed).
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Just some ideas to check¡ I can¡¯t imagine how you would true up the tailstock casting. Would a U3 one fit? I have no idea. The bed looks to have the same profile from photos.
