I need to replace the old Union Mfg Co. chuck on my SB 13. I have another 6" chuck on hand. It would attach to the old backing plate after I drill three thru holes in the backing plate on what I believe to be a 5.592" bolt circle. I have not measured it yet. This Chinese chuck has a recessed step in it about 3/16" deep. Do I need to adapt the backing plate so that it has a step in it to accurately locate the chuck and to provide rigidity or will the three M8 bolts have enough strength to hold it securely?
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