Originally Posted by
John K Jordan
If the runout has always been there you may not have noticed it depending on how you used it. For example, gripping and turning square stock would result in a perfectly round turning regardless on the runout. I have several type and sets of pin and small spigot jaws and the Nova mini spigot jaws (which I like best and use often) and the runout is not unreasonable on any. The mini spigot jaws use 8 screws instead of 4 which seems like a better design.
Is the drill bit good, any burrs? Is the runout in the same place relative to the jaws and chuck if you rotate it some or use a different bit? (I used a hardened precision rod when checking for runout.)
I might be inclined to investigate further, maybe something like this: Remove the jaws and put them flat on the table in the right order and make sure they are a matched set. (someone somewhere could have mixed up some before you bought them which might be obvious.) Make sure the grooves and slides are clean, no burrs, and don’t have excessive play. (I use a small brass brush to clean, usually take the slides out and chuck apart and clean everything.) I bought some used SN chucks that had been abused and the mechanism on one was sloppy and the other was warped.
While the jaws are off, try gripping the drill with the slides themselves, no jaws, and check the runout. (I’ve turned small stock in Supernova II slides this way, I assume the G3 works the same way but I gave mine away so I can’t check.) If the runout is there with no jaws the chuck might be the problem. I checked a chuck like that and it was pretty good.
Reinstall the jaws in the same position and tighten the screws as described in the chuck manual and recheck the runout. Mark the high spot on the jaws and the chuck. Remove and reinstall the jaws in the next position and recheck. (The jaws don’t have to be mounted with jaw “1” on slide “1” - they can start on any slide as long as they stay in the right order.) See if the runout it’s the same and the high spot is in the same place relative to the jaws and the chuck. Based on what I found I might try other things.
JKJ