Which lathe chuck?

[CNC Pro]

I just acquired a Chevalier model FCL-1840 CNC lathe with a 8-station turret. I need to invest in a 10” 3-jaw chuck (D1-6). I’ve been looking at Bison’s offerings. Should I go for the Bison “SET-TRU” series? Or for less $$ go for Bison’s standard 3-jaw scroll chuck? Or other brands? Any suggestions?

[HuFlungDung]

I think it would be well worth having the set-tru feature. There could be plenty of opportunity to turn a part end for end and try to make it run concentric in the second setup.

The set tru feature does not affect the accuracy of the scroll itself, so you should have a chuck at least as good as a plain one, if they take care in the manufacture of it. Examine and compare their accuracy specs just to be sure.

[CNC Pro]

But is the “set-tru” worth the extra $500.00? What does it really offer?

[BobWarfield]

As Hu mentions, settru lets you dial in concentricity just like on a 4-jaw. So, the scenario he gives, where you need to flip a part in the chuck to machine the portion held in the jaws is a good example where it might be helpful to you.

If you never have to be able to use the chuck to track concentricity with a part put into the chuck, i.e. you only machine raw stock or don't care, it probably isn't worth the extra cost.

Best,

BW

[Mcgyver]

don't understand the Q - are you asking was the set-tru means? the jaws are individually adjustable, you set it to run true (for a particular dia). each time you use it at that dia, it runs as true as you set it. like HuFlung said though, you haven't changed the accuracy of the scroll and it will perform as any other three jaw of you change dia's. imo Bison chucks are ok, not Pratt Burndrd or Rohm, but nice to work with and better value than the aforementioned...eastern European iirc and much better than the junk you see coming from China/India/etc

[CNC Pro]

Thank you, now I understand benefit of the set-tru. Is this a feature on the Pratt Burndrd or Rohm brands as well?

[Geof]

Originally Posted by Mcgyver don't understand the Q - are you asking was the set-tru means? the jaws are individually adjustable, you set it to run true (for a particular dia). each time you use it at that dia, it runs as true as you set it. like HuFlung said though, you haven't changed the accuracy of the scroll and it will perform as any other three jaw of you change dia's. imo Bison chucks are ok, not Pratt Burndrd or Rohm, but nice to work with and better value than the aforementioned...eastern European iirc and much better than the junk you see coming from China/India/etc

The Bison set tru trues up the entire chuck body not the individual jaws; or at least that is how the ones I have work. It is correct that you can true the chuck up on something a particular diameter and it will not be as true at other diameters but it is pretty darn close as in less than 0.001 tir. Also if you want to be really picky it is not difficult to re-true it gripping the diameter you are working with. If ALL you ever do is hold rough stock that always has the OD turned it is not worth the extra money. The first time you have a job that has to be flipped end for end and run true, not nearly true, you will curse the day you decided to save money. Spend the money now!

[Mcgyver]

Originally Posted by CNC Pro Thank you, now I understand benefit of the set-tru. Is this a feature on the Pratt Burndrd or Rohm brands as well?

not on the ones I have but Pratt does offer it, not sure of Rohm... I mentioned them because you asked for other brand suggestions. Those are two top quality chucks. I've also owned bison chucks and they are good, somehow didn't strike me as being as nice as the PB or Rohm, but that may be my prejudice. i think they are probably better value, haven't priced the PB or Rohms in awhile, but I remember them being mucho $$$$.

Geof is right that the chuck body is adjusted relative to the backplate, its was the Pratt Burnerd "griptrue" i was thinking of that as three adjustment screws, and I mistakenly said they adjust the jaws, they to just make fine adjustments to the eccentricity of the body to backplate.

Geof's comment that once adjusted they hold very close over a range raises a point as to what exactly is the error in a 3 jaw. I'd thought that matching scrolls and jaws were bloody tough manufacture better than a few thou error over their range of movement, in other words once you've adjusted the chuck for one dia, the error in the scroll would cause it to hold parts a couple of thou eccentric at a different dia. My Pratt Burnerd gives a couple of thou runout and the body is concentric within a tenth or two of the mounting and the scroll is a tight fit in the body - that couple of thou that its out has to be from scroll error doesn't it? if it gets you less than a thou tir over the range of the chuck, that's impressive.

[CNC Pro]

Can you guys comment on the mounting method of these chucks? I’ve seen D1-6 back plates, for use on flat back chucks. But, while surfing the web for Bison dealers, I’ve seen what appears to be the (6) cam lock pins already on the backside of some chucks. Are these chucks available as only “flat back”, and what I’m seeing on web sites is with a back plate already installed? Or are these chucks available with the cam locks already machined into the chuck, thus eliminating the back plate?
Thanks for the feedback!

[Geof]

Originally Posted by CNC Pro ....... Are these chucks available as only “flat back”, and what I’m seeing on web sites is with a back plate already installed? Or are these chucks available with the cam locks already machined into the chuck, thus eliminating the back plate? Thanks for the feedback!

I have only seen flat back Bison chucks and the camlock is a back plate. Camlocks are very handy if you need to change chucks frequently. I have seen manual lathes with cam lock designed into the spindle nose but when you need an adpater on the spindle and on the chuck this pushes the chuck quite a distance out.

[DareBee]

The Bison chucks are available in 3 or 4 "machined in" mount types camlock being one of them.

[RICHARD ZASTROW]

Why not try the original? Buck Adjustru (now Kitigawa?)