BISON 6 jaw set tru backplate question

You might also want to check out Gator 'Tech-Tru' chuck + back plate combo. As someone else suggested, harvesting their back plate for a Bison chuck has high probability of fitting since (as I heard it) Gator was entirely based on Bisons dimensions to begin with. My 6" 3J and 8" 4J are both Bison & they are very nice. But the price has become completely stupid, at least here in Canada. Last year I bought a smaller Gator 5" for a rotary table & just because the price was reasonable, included their D1-4 backplate in the order. The back plate fit my lathe spindle nose perfectly. It was semi-machined so in-situ turning to fit the chuck recess gives about the best chance one can expect from the conventional type mount. That chuck repeats to within 0.001" on the lathe, which is about the same as my Bison integrated 3J. Opinions vary on Gator so I will leave you to research this forum & others. I've heard quality might vary based on when it purchased so factor that in. One story goes: great to spotty (as they/Asia converted production to cnc) then good again more recently (teething pains resolved). I would say in my case Gator was ~75-80% of the Bison quality where it counts, but for substantially less cost where I could buy 2 Gators for 1 Bison. Your prices may vary so its kind of situation specific.

I have not purchased Gators tech-tru system yet so cant comment on that. I would guess similar results. The set screws allow you to dial in the spindle/chuck axis very accurately whereas an integrated chuck you get what you get unless you are into jaw grinding. So even with set tru dialed in perfectly the question becomes how well the jaws repeat on stock and also repeat-ability as a function of diameter. Some folks don't factor this in or don't discuss much. Repeat of 0.0004" on a 1" dowel pin is nice, but if the same chuck yields 0.0015" on 2" pin, that's somewhat deflating. I can fiddle my repeat on the Bison 3J +/- 0.001" just by jaw tightening sequence/torque, changing D1 pin clock position, phase of the moon etc. Beyond this, its probably time to think about accurate collet chucks or 4J depending on the application, accuracy & if production time is an issue. Just my own personal views.

http://gatorchucksonline.com/Scroll-Chucks/Tech-Tru/PA-Series/Gator-PA-Series-Main.htm
 
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My 10in 6 jaw set true is very fast to center and once centered is off by less than 10/1000 over it's full range.

Interesting. Most of us find a set-tru accurate for the size we've adjusted it for but the adjustment doesn't necessarily hold true for other sized stock at the same setting, at least not less than a tenth.
 
10/1000 = "ten one-thousandths"
1/10,000 = "one ten-thousandth"

Not trying to be difficult and I'm pretty sure I understand what the OP meant, but there is a real difference in measurement between the two.

-frank
 
Okay, projected wrong but my point is that a set tru chuck is great for the work that it is dialed in for but will not usually hold tight tolerances for other work unless it is reset for that work. Well, at least that is true for my Yuasa set tru chuck.
 
If I'm chucking up something in the +/- .5" range from the original piece adjusted to, I'm good. Beyond that, I always check. I'm SO glad I bought my 8" PB before I was forced into retirement. It's the most accurate 3-jaw chuck I've owned.
 
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