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

mksj said:
Think off a scroll chuck and then add a screw type adjustment on top of that that acts the same as an independent chuck. Look at the previous picture and you will see the carrier that is operated by the scroll and then the jaw position with a scroll adjuster between them,

You use the scroll to get the work in/out of the chuck and for repeat work that you do not need sub 0.001" accuracy on the repeat. You can tweak opposing jaws to null out any TIR if needed. As there are slight difference in jaw torquing, this accounts for a slight variation with repeat use of the scroll. The other plus of this chuck is three-fold, first it can hold work down to 0.2" because the jaws are narrow at the tips, second is it can hold work more securely because of the opposing jaws, and third you can compensate for holding power if the work is not perfectly cylindrical.
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Thanks for the explanation! So I get all the benefits of a 4 jaw independent and the speed of a scroll chuck.

Round, square , odd shaped stuff it works for… then the only thing I’d likely need a 3 jaw for is if I plan to turn hex stock… i think that profile needs a 3 or 6 jaw.

I assume plain back means it’s flat and then any 6” d1-4 it’ll adapt to for mounting to lathe. I assume there’s a standard for mating plain back chucks to d1-4 backing plates. Thanks for the tip on saving $ with the more cost effective backing plate, that doesn’t have to be a bison brand.

So I assume for most work on the 1340gt an 8” chuck is a good size though jaws could get close to interfering with ways.. but I’ll turn most diameters 2” and less. Can reverse the jaws as well.
 
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
 
That is a good deal on that Bison combination chuck. Mark, do you know the adjustment range limit at each jaw?
 
davidpbest said:
That is a good deal on that Bison combination chuck. Mark, do you know the adjustment range limit at each jaw?
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This is from the spec sheet... they don't seem to list the range of travel for each jaw, I assume you mean the independent travel portion.

Looks like they just give you the min to max clamping range.

The grizzly site indicates it's a forged steel body, but according to bison, the 7-848-0800 is cast iron/semi steel. The 4805-8" 7-849-0800 is the forged steel version. Cast iron is rated at 2000 RPM, forged steel at 2,500... PM's adjustable 3 jaw is rated for 4,000 RPM and listed as Tempered Steel body.... just noticing all the spec differences.

I'm wondering if 8" for turning aluminum at high speeds on the 1340GT... I'd be better using a 6" chuck with less mass. But this combo chuck and sale will be hard to pass up.

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Beckerkumm said:
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
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That's a concern I have and don't have a good sense if I do a lot of aluminum turning in the higher speeds... 1-2" diameter stock mostly, a 6" maybe better fit. There's a lot of dynamics and different aspect to ordering and sizing all these accessories to the late and type of work. I have no sense of how stout the PM-1340GT to handle a heavier 8" chuck for daily use and turning in the 1000 to 2000 rpm range.
 
skcncx said:
This is from the spec sheet... they don't seem to list the range of travel for each jaw, I assume you mean the independent travel portion.
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Yes, that’s why I asked Mark. I passed on a Bison combination sweet deal a few years ago because I couldn’t get to the bottom of this spec. I often chuck up very oddd sized parts, including flat plate ~5” x 1” and couldn’t get comfortable that a combination is a full functional substitute for a conventional 4-Jaw. Neither is it a replacement for a Set-true 3-Jaw if you do a lot of work with hex bar stock (which I do).
 
I'm not sure the Grizzly link is really a combo chuck. The picture is but the description is just of an independent chuck. Dave
 
Beckerkumm said:
I'm not sure the Grizzly link is really a combo chuck. The picture is but the description is just of an independent chuck. Dave
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They also say it's forged, but it's cast-iron/semi steel. Makes you wonder what they'll send you. Drives me nuts when pictures, descriptions and part numbers don't line up.

Based on the model number shown, it does map to Bison's combination chuck on their site.

Model# 7-848-0800

GrizzlyBison-america.com
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I only ran steel 8" to 700-900 RPM with zero issues, I did not switch the pullies around, and change the belt, so all you did for RPM was twist the dial. That would need a tachometer, so I kept the low range, and upped the RPM in low range
 
Probably worth the chance on the Grizzly sale for those who can handle that chuck. Worst case is Grizzly would give you your money back. Bast case is really good. Dave
 
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