4 jaw chucks

srfallsallot

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What is the difference between optional PM 8" High Precision 4 Jaw lathe chuck and the stock 8" 4 jaw chuck? Does it justify the $399?
 
The high precision one is made in Taiwan. The standard on is China made. It was worth it to me.
 
On an independent 4 jaw, other then having a balance problem I would say it's not worth a premium price. Now if you are talking about a 4 jaw scroll chuck then thats a different story altogether!
 
I would be concerned about the quality of cast iron in the chuck body. Especially if working on out of balance items or larger items that may only use half the threads on the chuck jaws.
 
FWIW, the four jaw chuck that came with my Grizzly G0602 had jaws that tapered in at the rear, providing an insecure mounting for parts and resulting in an unstable condition at extended distances from the chuck. Properly ground jaws should have a slight outward taper at the rear of the chuck.

I reground my jaws but you shouldn't have to do that with a new chuck.
 
I initially had a Chinese version 4J independent, was so crude and out of balance I could not get it past 400 RPM. It was replaced with the QMT 8" 4J independent and the difference was significant. Much better casting, even has balance weights on the inside, no vibration spinning it over 1000 RPM. Grind of jaws and movement was much better. It is worth the upgrade if you plan to use the 4J. Price is $380, I do not know if they give any credit if it is a substitution for the Chinese 4J. I guess you could always use the Chinese one on a rotary table.
 
I initially had a Chinese version 4J independent, was so crude and out of balance I could not get it past 400 RPM. It was replaced with the QMT 8" 4J independent and the difference was significant. Much better casting, even has balance weights on the inside, no vibration spinning it over 1000 RPM. Grind of jaws and movement was much better. It is worth the upgrade if you plan to use the 4J. Price is $380, I do not know if they give any credit if it is a substitution for the Chinese 4J. I guess you could always use the Chinese one on a rotary table.

Agree with this assessment. :)

For the OP: I got tired of trying to use the Chinese 4-jaw my 1340GT originally came with and got one of Matt's Taiwan made ones. Difference is night and day. I primarily use mine to offset bore compensators for 1911s and appreciate the increase in accuracy and quality of the Taiwan made one. YMMV of course. :)
 
The standard 4 jaw on my budget lathe had poorly ground jaws similar to what RJ had on his. The jaws had to be ground to get them to hold properly (ie. straight).
Since the 4 jaw has turned out to be the workhorse for me I would tend to get the better one even if it is $399 extra.
 
If it was me, I would take the free one and use that while I saved the money for a good used Rohm or Pratt Burnerd 4JC on ebay.
 
I had no idea there would be so many things wrong with a cheap chuck I would have thought maybe the jaws weren't as hard , I'm learning so much on this site thank you all . Of course I wish I would have known this before I bought a 8" Grizzly 4 jaw for $100 , never been mounted so I guess I'm in for a surprise
 
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