8" Bison 4 Jaw Combination Chuck

Darkzero, the combo has several factors that can influence the clamping error. You have the cumulative error/movement of both a scroll and the independent jaws (with a separate screw mechanism in the each jaw carrier). There is also the method of torquing each jaw, that it is hard to be symmetrical between the jaws without a torque wrench. I would say that most of the time once set, I can repeat to around 0.001", but you can essentially get this down to nil very quickly. The other aspect that surprises me on this chuck, is that at least mine, has the least angular skew of any of my chucks. It holds stock much better than my 3J scroll.
 
I received my Bison chuck and back plate today.Looks really great. I bought the back plate from MSC. They have a 30% off promo going on that made the price very competitive and it shipped immediately. All in all a real good deal. I am still working on getting the lather set up so I can't try it just yet.

Paul
 
I took a couple of shots of the piece of plywood that protects the ways when changing chucks. Its a simple design that holds securely and still slides easily back and forth. As I mentioned earlier, It also doubles as a platform for tooling etc.
IMG_1566.JPG IMG_1564.JPG
The bottom is simple wood strips that ride on the inside of the ways with no play.
No fancy sealer, just a soaking with WD-40 and wiped dry.
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Jeez, the lathe is dirty...:bawling:
 
mksj said:
Mikey is correct, just like a Set-Tru chuck but adjusting each jaw on a scroll mechanism instead of the chuck relative to the backing plate. Also a lot quicker then a Set-Tru to adjust. Still, a Set-Tru repeats very well, but there can be some variation depending on the size of the piece and also if the jaws are reversed, it usually requires readjusting the chuck TIR. In my experience, the sequence of tightening the Set-Tru bolts and chuck to the back plate is more critical to setting up the chuck. The combo is a piece of cake, relative to a Set-Tru, but a Set-Tru once set has better repeatability of the scroll.

So with a combination chuck each independent jaw moves on a scroll mechanism carrier which it is attached to a screw mechanism that then adjusts the jaw. Each jaw can be adjusted independently, the scroll moves all 4 jaws simultaneous in whatever position they are set. It makes it easy to remove your work quickly and then reinserting and maintaining the same concentricity. So I usually will use the scroll and tighten down on stock, and then tweak the independent jaws to 0 the TIR. I usually can do this in under a minute, since you are using two keys you can torque bot down, and then turn the chuck 90 degrees and do the other two. Once set, you can just use the scroll and maintain better than 0.002" TIR on repeat parts, but if I need to be spot on I will tweak one of the independent jaws as needed. One aspect that I do like about the 4J with twin keys, is you can get a good feel on the torque/tension that is applied to the jaws. The twin keys have plenty of torque for their size, remember that when using the scroll it is setting the pressure for all four jaws.
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Thanks for confirming that, Mark. You guys have some cool toys, that's for sure. I don't do multiple like parts often enough to justify having one of these things but I can see how it can be handy. I'll make do with my 4 jaw chucks and my adjust-tru for now. Christ, I already have seven lathe chucks; have to draw a line somewhere. :(
 
Darkzero THIS IS MIND CONTROL YOU NEED THIS CHUCK AND A SECOND ONE FOR A GIFT TO A POOR GUY IN A WHEELCHAIR this is a recording . You know it's a great one to have for that square stock job coming up. If I had any odd shaped lathe jobs it would be on its way. Never know what kind of things will come up in a job shop.
 
Mark and Paco, what is the rule of thumb for scroll plate engagement with the jaw carriers? You can roll the chuck jaws out using the scroll key until you are seeing the scroll plate grooves. Is there some rule of thumb on how many grooves one should expose? Of course you can also move the independent jaws out on their carries and the same question also applies to how many threads of the carrier operating screws one should expose .

The manual that came with the chuck is a tiny little booklet and it does show clamping ranges. Perhaps that is what one should focus on vs. fussing over the scroll plate groove engagement on the jaws.
 
Hi Alan,
There are several factors to consider, but my understanding is that the load capacity is based on all the scroll teeth being engaged, and this would also apply to the independent jaw on the scroll carrier. You can see the scroll plate when it becomes exposed and no longer engages the jaw carrier. Yo might try to scroll the chuck to get a good feel of the range, and also that of the independent jaw (I would want at least 4 turns of engagement). I have seen the jaw teeth break when too few teeth have been engaged, so something like 4 teeth is what is what you would want. These chucks also specify working diameters and loads as follows:
CLAMPING RANGES FOR 4-JAW CHUCKS.jpg
 

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I received mine last week. First impression was wow, this thing is big and heavy. Hoisting it up for the first time left me wishing I was wearing some steel toe boots!

The chuck has a very nice finish and looks very well machined. I also bought the back plate from MSC. I mounted it bare on the spindle and it seemed to have no detectable run-out. I then installed the plate on the chuck. The fit seemed perfect, again very well machined.

I used the chuck to make the keys that Mark and Paco have.

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I quickly found that they are a necessity to work with this chuck. The stock key is a PITA to adjust the chuck, at least on a 1340GT. There is just not much room to spare with the length of the key. The design of Marks keys was excellent and greatly enhanced the dialing in process.

My take on this chuck is that it gives you the accuracy of a standard 4-jaw, but much easier to dial in and re-tru if you have to remove the work piece. While I rarely use my regular 4-jaw because of the time it takes to dial in, I would be more inclined to use this one due to the ease of adjustment.

My only issue is the size and weight. I tend to use my collet chuck and a 5” 3-jaw the most as it is so easy to handle them and switch out when necessary. For me, this chuck is so substantial, it leaves me less inclined to switch it out for one of the other chucks that could work better for the application at hand. With that said the size issue is subjective and more reflective of the personal preferences of the user. I think a 6” version of this chuck (if they make one) would be a little better suited for me and the PM1340. Maybe I just need to go to the gym some more. It is a very nice chuck, and for the bargain price paid, I am happy to have it as part of the growing inventory of attachments.
 
I gather that this chuck was on-sale and that sale has ended. With that said, would someone please post what they paid for one of these combo chucks?
I am not really in the market because the pricing that I see is about 3/4ths the price that I paid for the entire lathe but would like to have a price to compare future offerings too.

thanks

Mike
 
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