I've got a bar around 20mm square and 90mm long. I want it reasonably parallel along its length. I dont have a mill, so it need to be done in the 4-jaw of the lathe. Set it in the chuck, skim the first side. Turn it around, new 'flat' side against chuck jaws, skim to final size determined by how i've set my carriage stop. No problem.
So, now I have 2 reasonably parallel edges at the correct distance apart. I now need to get the third side skimmed and parallel. I can't just rely on putting side #4 against the chuck as this is unmachined yet. I don't have any true reference edge to put a DTI against, so how do I achieve true squareness? Once edge #3 is skimmed, the final side can be skimmed to the appropriate size via the stop.
How do I then avoid ending up with a 'traqezoid' form. This particular job is not super critical in itself, its just a thought that came to me when planning to do it? Have I missed the bl**ding obvious somewhere? Regards Mike