Set up square bar in a lathe

You need a four jaw chuck to hold a square bar, but the jaws are not self-cen­tring…

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The jaws all move in­de­pen­dently – con­cen­tric lines are pro­vided as a guide to help set each jaw to ap­prox­i­mately the same depth. Use these to get the bar roughly cen­tral. 2

Round bar can be set with a clock gauge, but us­ing the cut­ting tool works well here. Move the tool for­ward un­til it touches and then move the lathe saddle up the bed, out of the way. 3

Ro­tate the chuck half a turn and bring the saddle back across, ad­just jaws un­til the gap is equal ei­ther side. Once done, ro­tate 90° to set the other plane – it’ll take a few goes... 4

... and don’t fully tighten the first jaw pair till the end, as the bar needs to slide in them to ad­just the other plane. If you can get an even score from the tool on each face, it’s about right.

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