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

[davidpbest]

Best to show some pictures, as there is both a scroll and movable jaws, each which has a movement range.

Bison Combo Maximum Internal Jaws Clamping, But Pushing the Limit.
View attachment 426647

So my suspicion is correct - 5" is the max difference possible between one pair versus the other. Hence you could chuck up a 1x6" plate, but not a 1x7".

I had the opportunity to buy that 8" Bison combination several years ago. I ordered it when it was on sale for a smoking hot deal, then they emailed me an said they oversold their inventory position and offered me the "Semi-Steel" version at the same price as the forged steel version that was on sale. I wasn't comfortable running an 8" Semi-Steel on the 1340GT at speeds above 1200 RPM so I turned down that offer. Glad I did not since I routinely need wider than 5" difference between the two axis of the jaw pairs.

In addition, I wouldn't want my principal chuck to have single piece jaws either - too many times I've needed to make my own jaws for clamping thin-walled tubing material and have needed jaws with a profile that matched the ID or OD of the part being turned.

 

[mksj]

The jaws are reversible on the combo and could hold a 1x9, possibly a 1x10. In comparison to the PM/QMT direct mount which I have, it holds a smaller diameter and it also has one piece reversible jaws. When you get into a Bison direct mount 8" independent 4J chuck with one piece jaws they run close to 1K in semi-steel and the two piece jaws are over 1.4K in forged steel, and neither of those can hold small stock. At that price you could get the combo and a 6" 3J scroll.

The combo is more versatile, for a 4J, and if I need soft jaws, they would go on my 3J 6" scroll chuck. So it comes down to preference and cost. I find the combo much more functional as a 4J chuck and getting it at a lower price makes it attractive. But a good 3J scroll with two piece jaws adds to the versatility if you need soft jaws. So far I have not used soft jaws, and if I need a soft interface I make caps out of aluminum.

Each person develops their own preference based on their experiences and what they do, there is no right answer for everybody.

 

[skcncx]

For what it's worth, I have found that the 8" combo chuck listed in this thread has 2 variants, at least 2 common variants, there appear to be 2 more as well. The one that has been linked to, and that's on sale for a big discount at grizzly is the semi-steel one, rated at 2,000 RPM.

8" Bison 4 jaw combo chuck

• Semi Steel : 4605-8" / Part # 7-848-0800 / 2,000 RPM
• Forged Steel : 4805-8" / Part # 7-849-0800 / 2,500 RPM

Not sure when, but many pictures of the semi steel one, grizzly and photos from @mksj shows it rating at 2,500 RPM marked on the chuck itself... though that is not the case anymore and pictures are just outdated. Supposedly the same semi-steel chuck as always, they've just changed the rating. That's essentially straight from bison-america's response via email.

The forged one goes for about $500 more than the semi steel. Typically, $1500 for semi steel and $2,000 for forged.

I've had a little extra free time at work today .

Apples to oranges... but PM's 3 jaw, adjustable (set tru style), balanced and rated at 4,000 RPM is one great deal!

 

[mksj]

Mine is forged steel, but all moot since the maximum speed of the lathe is in the 1800-2000 RPM range. You will find that for a given diameter chuck, that they will have similar maximum speeds for semi-steel vs. forged steel which has to do with the centrifugal force applied and the structural strength of the material. The maximum speed on my 6.3" PBA 3J scroll is 4900 RPM. Below is the Bison specs for their combos. If I had to pay the full list price of the chuck in today's market, I would think twice about buying the chuck, different story if you can snag it for close to 1/2 price.

 

[skcncx]

Mine is forged steel, but all moot since the maximum speed of the lathe is in the 1800-2000 RPM range.

Yea, I shouldn't get hung up on semi-steel vs forged.

Out of curiosity, can you visibly (or easily) tell the difference between cast iron and forged steel if you are seeing it in person?

Sounds like they did change the one you have then. That model number is labeled as cast iron in their docs. It looks like the 4 digit specifies the material 4605 - semi steel / cast iron, 4805 - forged steel, etcs... Not sure what 4505 or 4705 would be.

 

[mksj]

I purchased mine probably 14 years ago, so do not recall the part numbers from back then. Since I have not had a forged and semi-steel side by side I would not know the visual difference. Although my forged chucks usually appear a bit cleaner in the castings and finish. Usually forged is around 30% more expensive, but only necessary if you need the additional speed rating.

Lathe Chucks Technical Information | MSC Industrial Supply Co.

To determine which type of spindle nose mounting your lathe requires, consult the diagrams below, then read the chart beneath the appropriate diagram.

www.mscdirect.com

 

[maticulus]

In case someone here currently on the backorder waiting list, or is looking for a deal is interested and is in driving distance of PM, they have these up for bid;

(2) Damaged PM-1440E-LB METAL LATHES SOLD AS IS FOR PARTS TO MAKE 1 MACHINE | eBay

Machine 2 had fallen on its end cover (Where the belts are, this cover is not there because it was smashed) - The carriage did not take a hit and all with with that end of the machine looks good. So use one for parts, combine them to make a good machine.

www.ebay.com

 

[Wvlarry]

In case someone here currently on the backorder waiting list, or is looking for a deal is interested and is in driving distance of PM, they have these up for bid;

(2) Damaged PM-1440E-LB METAL LATHES SOLD AS IS FOR PARTS TO MAKE 1 MACHINE | eBay

Machine 2 had fallen on its end cover (Where the belts are, this cover is not there because it was smashed) - The carriage did not take a hit and all with with that end of the machine looks good. So use one for parts, combine them to make a good machine.

www.ebay.com

They also have 2 PM-1440BV, same deal, damaged in shipping. Not sure how to post link for them.

 

[maticulus]

They also have 2 PM-1440BV, same deal, damaged in shipping. Not sure how to post link for them.

Just copy the browser address and paste. Pretty concerning coincidence of "injuries" for this many of the same lathe in transit. Hope I don't run into any problems when my order arrives.

(2) Damaged PM-1440BV METAL LATHES SOLD AS IS FOR PARTS TO MAKE 1 MACHINE | eBay

Machines are being sold as is, for parts. Machine 2 is to be used for parts ONLY, it is not being sold with the ability to turn it in to a working machine. (The casting on the carriage is broken so its not salvageable).

www.ebay.com