Keep PM-1236T or get back in line for PM-1340GT?

[mksj]

The model number listed and list price is that of the Bison combo, my old links go to that chuck. David, the travel of the independent is around 2.5", the scroll portion is a bit over 2". So by moving the jaw back plus the scroll you have close to 4.5" , but the jaw may hit the ways at that point. . I have spun the chuck up to around 2000 RPM, but usually I prefer my 5C or 6" 3J scroll for high speed work. The chuck is not any longer then a standard scroll 8" with back plate (4.5"), I do not see that as an issue vs, the pressure exerted when cutting which is further out. Below is the chuck on my 1340GT. The Gator back plate is an 8", use to be called the FLD-200D4, you would need to check with one of the chuck suppliers like Ajax Industries or Small Tools. You would need a back plate for most of these chucks except if you get a direct mount. Depending on the manufacturer, you may have to turn down the registration step slightly for the chuck to mount, but you do not need to do a face skim cut.

8" Bison 4 Jaw Combination Chuck

Nice reports guys. Mine is still in the box. I am still stuck on using the 6J set thru for barrel work when not using the front spider.

www.hobby-machinist.com

 

[davidpbest]

David, the travel of the independent is around 2.5", the scroll portion is a bit over 2".

Thanks Mark, that's about what I figured. Glad I didn't buy it.

 

[skcncx]

Thanks Mark, that's about what I figured. Glad I didn't buy it.

Regarding the combination chuck travel " travel of the independent is around 2.5", the scroll portion is a bit over 2"."

Is that a lot less than a standard 4 jaw independent? Seems like the total range of .16 - 7.87' is pretty big... though, that does assume you've reversed the jaw to get to the max.

I'm still thinking a 6" 3 jaw, as I do plan to do hex stock.... but I know a 4 jaw is likely needed at some point... and the concept of the combination chuck is pretty attractive, plus to sale.

 

[mksj]

Actually quite the opposite, the range is greater than a standard 4J, so your overall range is 4.5" for each jaw. You are limited by any type of chuck to maintain at least 4-5 teeth in the scroll/screw so they do not break. The jaw range on my PM/QMT 8" 4J independent is maybe 2.5" per jaw. Chucks have reversible jaws to fit large diameter work, but I have much more range on the combination chuck then any of my other chucks. As I mentioned, a number of other forum members have bought the combo and have been very happy with it. I use it less these days more because I am constantly swapping back and forth to my 5C, and for smaller work my PBA 6" is about 1/2 the weight.

 

[skcncx]

Actually quite the opposite, the range is greater than a standard 4J, so your overall range is 4.5" for each jaw. You are limited by any type of chuck to maintain at least 4-5 teeth in the scroll/screw so they do not break. The jaw range on my PM/QMT 8" 4J independent is maybe 2.5" per jaw. Chucks have reversible jaws to fit large diameter work, but I have much more range on the combination chuck then any of my other chucks. As I mentioned, a number of other forum members have bought the combo and have been very happy with it. I use it less these days more because I am constantly swapping back and forth to my 5C, and for smaller work my PBA 6" is about 1/2 the weight.

I think my only hesitation on the 8" combo chuck was it's size when turning at 1500-1800 RPM. That is where I've been when mostly when turning aluminum. Maybe that's not even needed for 1-2" round stock. The fact it is a primary chuck on a 1340 GT for some relieves some of those fears.

Aside from size, if you swap it frequently, the only downside I see is it's not good for hex stock. Though it appears you can turn hex stock with a 4 jaw.

Realistically, I don't see myself switching my chucks that often so I'm trying to land on the best style and quality chuck to start. If I can take advantage of this current sale on the bison combo chuck, I may not have a real need for a 6" 3 jaw set tru for a long time.

Turning hex stock and how much I do is speculation on my part... I have no specific projects in mind.

The scroll and independent feature makes it seem like a no brainer, why aren't they more common (or commonly talked about), etc at at least brought up when the topic of "if you only had one chuck question."

An ER40 or 5C for my line up will need to be out of a specific need. Though I start with common bar stock most of the time from .5" to 1.5" so I may end up finding I would use one more than I think. Pros and cons to both ER40 vs 5C.

 

[Ischgl99]

The downside to the combo chuck is expense, I can get a 4 jaw chuck for significantly less than that and do just about everything I need. After using it for a short period of time, dialing in stock is quick enough that I won’t switch to the three jaw chuck unless I have multiple parts that need to be done.

 

[davidpbest]

Actually quite the opposite, the range is greater than a standard 4J, so your overall range is 4.5" for each jaw. You are limited by any type of chuck to maintain at least 4-5 teeth in the scroll/screw so they do not break. The jaw range on my PM/QMT 8" 4J independent is maybe 2.5" per jaw. Chucks have reversible jaws to fit large diameter work, but I have much more range on the combination chuck then any of my other chucks. As I mentioned, a number of other forum members have bought the combo and have been very happy with it. I use it less these days more because I am constantly swapping back and forth to my 5C, and for smaller work my PBA 6" is about 1/2 the weight.

Mark I'm still not clear on the clamping range. If the part is (for example) 1" across in one direction, and 8" in the other (flat plate for instance), what are the limitations between minimum on one axis and maximum on the other? Sounds to me like it's a total of 5" maximum difference, right?

 

[mksj]

Best to show some pictures, as there is both a scroll and movable jaws, each which has a movement range. The scroll can only move to the center open section of the chuck otherwise the scroll plates will hit each other, the jaws are then advanced and can hold down to 0.2". I did some checking of repeatability of the scroll on clamping the same diameter rod and it stayed within +/-0.0003" TIR and then clamping a rod twice as large and it was +/-0.0005" TIR. I made dual chuck keys with magnets, so I can quickly center the stock, otherwise the standard chuck key has a smaller square on one of the arms for the independent adjustments.

The main downside is the weight and cost, and it all depends on the type of work one does. Most shops just use a 4J independent for larger stock because it often needs to be centered and they are not doing repeat work, or they just redial in the TIR. Smaller work, they may use a 3J or collet. I like that I can quickly get stock in/out of the chuck and do not need to waste my time redialing it in with my 4J independent, and I find that it holds work more securely then my 3J scroll in some circumstances. High RPM wise, it is less intimidating then my 3J which has two piece jaws that stick out much further from the chuck face.

Bison Combo Closed

Bison Combo Scroll Carriers Stop, and Must Advance the Jaws

Bison Combo Distance of Movable Jaw Travel

Bison Combo Maximum Internal Jaws Clamping, But Pushing the Limit.

Bison Combo TIR Zero 1

Bison Combo TIR Zero 2

 

[Janderso]

To alleviate that fear you should get a 1440GT. It is a great fear reducer.

Or a 15x50
Bigger is better imho

 

[Janderso]

I think a d1-4 direct mount 8" independent is listed on Ajax for $885. I don't know if the steel is the same but I've found that if I call and ask for a best price, they will quote a little less than the listing.

A combo 8" is pretty heavy and sticks out a long way from the spindle bearings so you want a stout spindle to handle it. Dave

I had the same experience with my Bison Four jaw. I called Ajax to verify I was buying the correct D1-6 adapter fir the 10” chuck.
They gave me a very good price for the pair.