New Bison lathe chuck not holding work from slipping
About six months ago I purchase a new Bison 8" 3 jaw chuck for my 12CK Monarch. The instructions said to not over torque the jaws. The T-handle furnished is smaller than the ones I use on the 10" SB. Problem is that even with a new chuck key with more leverage, I cannot keep work from slipping unless I use a 16" "helper" on the key, which I really don't like doing. Light work is ok, but one reason for the Monarch is the muscle which I cannot use with this chuck.
Any thoughts or suggestions?
My understanding of a 3 jaw scroll chuck is that if you torque them down to much, the scroll becomes deformed and at that place you have defeated the self centering useage. I can relate this to an overtorqued screw thread that becomes distorted and if you were to check the lead, it would vary at the place where the event took place. I have always tried to use a 4 jaw when I had a problem with the slick jaws of a 3 jaw slipping. This slippage was usually caused by a deep cut with a heavy feed.
Make sure the chuck is lubed internally.
Make sure the workpiece is clean and oil free.
Put a strip of emery cloth between the work and each jaw, grit side towards the work.
Tighten up evenly on all three pinions, assuming there are more than one.
Wedge type chucks allow/give considerably more holding force than a scroll chuck:
Manual chucks Fplus, F+, F - wedge block chucks, independent chucks PSA - characteristics
I believe Bison also make a similar design. They are not cheap though.
I have a 5" Forkhardt F type that came with my lathe.
What material and what kind of cuts are we talking about and what tool is being use?
There is such a thing as pushing a tool outside of its limits.
Hard to beat a 4-jaw for any sort of hogging, 3-jaws aren't really meant for it, whatever the make. With that said I've taken some pretty good cuts with them and never had work spin, I did have work push back before though, so its usually good to have a spider in the back when that possibility arises.
That is the first I've seen of the wedge type. Will they go full range by turning the tightening screw? Or is there a limited throw of the jaws via the screw?
Originally Posted by Phil Burman
Is the Forkhardt F type a self centering chuck?
When we got a new bison chuck for the Mazak we found the same problem.
We put in the old chuck and the die head 1"-8TPI threaded parts in it and it held fine.
Now the Bison is old and has some use it bites like crazy and wont mar the parts. I guess when the jaws get some wear and the chuck has had oil on it for years it grabs much better.
Dont give up on the old chucks, they will do what the new one will not in some aplictions..
Now days I buy chucks with 2 peice jaws so its nothing to make soft ones for lots of grip surface.
My bet its not the chuck but the new sharp jaws of the chuck causing the problem. I do think the old chucks had a finer pitch scrool thus making them bite harder but I doubt it make too much diffrence. We are meat heads anyway.
I wish you the best of luck.
Put some moly grease on the scroll and on the teeth of the master jaws, then look at the tips of the hard jaws. If they are too narrow, reface them to have a small concave radius so there are 2 lines that contact the work. I bet your old jaws look like that. Might have some diametrical grooves too. Or get some hard jaws that look like 4 jaw jaws, with the waffle faces.
Originally Posted by SND
Yes, I have a Bison 12" chuck (actually 3) that seems to hold GREAT, except on ONE, I get the bar "pushing back" when turning bar stock at what most machinists would barely consider "hogging". Even more strange, only with the HARD JAWS! NOT with soft jaws! Gotta love it when things don't make sense!
One other thing! The first bison I got, had an oil "zerk" (as opposed to a GREASE "zerk"/fitting).
Trouble is...that hole led to NOWHERE! It wasn't drilled all the way to the scroll!
I drilled my own grease fitting hole TO the scroll, where the lube NEEDS to get to!
Part of the problem with a 3 jaw is also the squirm effect: when one of the jaws opposes the tool, the workpiece is stiffer in that plane, than when the work rotates another 60°, where nothing is opposing the tool. So you've got a cyclic 3 lobed vibration induced in the workpiece every revolution. Combine this with the end thrust of the tool, and you create a definite squirm effect. If the jaws are smooth, it takes enormous squeeze to positively stop the piece from moving axially.
Most likely, you will damage the scroll if the chuck is small for the task and you try to really crank it up. Better to use an endstop, or a roughing jaw of some sort.
On our Summit lathes, with 4.125" spindle bore, we've always had this slippage problem, because we don't want to change 12" chucks back and forth on a whim. But because we can put large diameter heavy bars through the spindle, we mounted another 12" chuck on the outboard end of the spindles. If the work is long enough to be held in both chucks, it doesn't slip through, but for shorter pieces, we mount a stop bar held in the rear chuck, to butt the workpiece against, while only the front chuck does all the driving. That also eliminates the work pushing through.
Edit: if you know anybody who has a Rocklinizer, you might get them to rocklinize the jaw grip surfaces. This amounts to a very fine grit roughing up of the jaws that may last a while. However, the carbide particles that get embedded in the process will raise likely raise hell on polished surfaces such as chromed rods.
If one of us apprentices (1964) was busted using a cheater on a chuck wrench we'd get what ever was in the instructor's hand upside the head - sandwich or broom handle. Before we graduated from 4 jaw chucks and were allowed to use a three jaw chuck or collet we had to chuck up a workpiece selected from the job table and dial it in - in two minutes or less.
Three jaw chuck gripping faces are hard steel ground smooth and concentric; they are slippery. Over-tightening doesn't really help much. Avoid cheaters on chuck wrenches. NEVER use a cheater on a new three jaw. You cannot tighten them enough to drive them into the metal as you can with jaws having serrated gripping faces like on a typical four jaw chuck. Naturally, slipping work may be a problem if you attempt to drill larger holes from the solid, heavy feeds with a form tool, etc.
How is the work slipping? If you're drilling on continuous diameter work, it's not uncommon for the drill to push the work deeper in the chuck. Without a shoulder to keep the work from drifting into the chuck there's no real cure short of severaly over-torquing the jaws. The best solution is a "chuck stop" a hunk of slightly smaller material or pipe inserted in the jaws. The chuck stop is intended to bear against the chuck face to prevent the work's axial movement. If the work is smaller than the chuck bore use a short piece of solid stock machined to suit so it bridges the bore.
If the work is slipping because you have to use a short grip then again a chuck stop may help.
If boils down to this: a GP three jaw chuck is not a heavy duty work holder. The chuck wrench has a handle whose length is calculated to limit the torque an operator can exert. For all its mass and apparent beef a three jaw chuck is pretty delicate. If you have a little wreck like break a parting tool and you may discover the chuck's run-out has increased for that particular gripping diameter. Have a major wreck and there is a real possibility that one or more of the jaws have been sprung slightly. It will no longer grip cylindrical work straight - the work may nutate slightly, that is, naturally assume a slight angle to the spindle axis: the runout will increase with distance from the jaws.
The solution is to use a four jaw chuck for items that have to be strongly gripped, require best concentricity, hold work that's odd-shaped, or whose grippng surfaces are not quite concentric with the portion you wish to reference for machining.
Devotes of three jaw chucks will stoutly defend their use in all practical situations but if you wish to keep the three jaw chuck's major advantage - quick accurate concentric grip - pristine you have to protect it from the risks of casual use. There are two kinds of three jaw chucks: accurate and those wrecked one or more times.
So to return to the original topic, I suggest a chuck stop if indicated or a use as a default work holder - a four jaw you can afford to abuse.
Last edited by Forrest Addy; 02-24-2012 at 10:34 PM.
Well, I see I am not the only one with this problem. I tried Ferrous Antiquos suggestion of the emery cloth. That didn't work at all. Not even close. The problem I had this afternoon was with 4140 Rc 32, 1 1/2 OD, 120 rpm, .10 depth of cut, .008"/rev HSS tool bit. Should have been a walk in the park for the 12CK, but not for the chuck. Wound up backing down to .03 depth. I've had problems with this chuck both spinning and drifting inward. Next to try is soft jaws and if that doesn't work, hard jaws with diamond waffle pattern on the faces.
Cheat! Turn a couple of inches back on the end you will chuck on and bank against the shoulder you produced. It won't take much of a shoulder to put an end to this problem.
If you have the interior all lubed/anti-seized up, then.....
I got nothing, besides using the key in each of the three sockets.
That's the technique for drill chucks; to get max grip, successively torque the chuck in each of the three locations. (I can't find any internet citations, but I'm convinced I read it.....somewhere)
And perhaps a soft mallet to tap each jaw as you torque the chuck key.
On edit: Okay, here's a citation:
Is there a correct way to tighten a drill chuck?
On edit: Ferrous Antiquos mentioned using all three "pinions", but I'm not going to delete my post.
Nobody ever said anything to me about using all three holes to tighten a drill chuck, and I've never done it.
Unlike a 3 jaw scroll chuck where which hole you use to tighten WILL make a difference...
I was originally taught to use all three holes on a lathe chuck, but when my boss at work saw me doing it, he said "What are you doing? Just use one." So I just use one now at work, especially since I'm usually in a hurry.
At home (my good friend's home/shop, actually) I also just use one, but for a different reason. The adjust-tru 3 jaw chuck on the 15" Clausing Colchester only has one hole! And I find it kind of funny that this lathe belongs to that guy that originally taught me to always snug up all three.
I'm going to throw a different philosophy out there.........
It's not your Bison.........it's the nature of the beast with a 8" 3-jaw chuck. I don't feel they have much grip at all. Plenty good enough for light to medium cuts, but nothing requiring serious grip. I have a 8" Buck (actually 7 of them) and none of them will hold for any hogging, unless I use soft jaws and a positive step in the jaw to keep them from pushing back.
Now, a 10" or 12" chuck has serious grip, in my opinion.
Your mileage may vary.
If you are really frustrated by the chuck, and I would be too, I think I'd set up a small nose radius boring bar, and lightly bore the jaws at a feedrate of about .03"/rev, with barely any depth of cut. The idea is to impart a light duty serration.
Do this operation with a negative rake triangular 331 insert or even a D or V insert with the top corner of the insert ground a little on a diamond wheel so as to remove the edge hone, leaving the corner of the insert very sharp.
If you set the chuck to bore at about 1.5" diameter, you should preload the jaws. You can often accomplish this with a thin disk of material set in behind the jaws, in the area where the scroll teeth on each jaw will catch the disk and you can snug them down. Indicate the jaws first to check the concentricity you get from this setup.....you don't want to bore them out of round.
Alternatively, maybe you could get the jaw grip surfaces sandblasted? It doesn't take much to enhance the grip tremendously.