Advice Please

eric.grulke.79

eric.grulke.79

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I would like some advice from all you learned folks. I want to replace the chuck on my lathe.

History. It is a Magnum-Cut 16-60, made by Frejoth in PRC. I purchased it used from a plumbing shop and never actually got to talk to the original purchaser. It has a 10" 3 jaw, D-1 6 with a back plate and a 14"(300mm) 4 jaw, direct mount D1-6. The 3 jaw is showing .020" TIR, that is a little too much for me. The 4 jaw has a pin that doesn't lock well, has unlocked on me twice.

I am looking at the mid-grade Bison 3 jaw Direct mount D1-6 to replace the current 3 jaw. There is $600.00 difference between the 10" and the 8".

Question: Is there any reason I shouldn't go for the 8" vice the 10".

Thanks

Eric
 
I am not a huge fan of direct mount 3jaw chucks, though it will probably be fine if you get a Bison. A universal mount with a back plate gives you the chance to center the chuck properly (leave a few though on the spigot and knock the chuck around till it is centered), direct mount is only as good as the manufacturer. I would not waste money on a set-tru unless you are a pro. The set-tru makes centering the chuck faster - a concern for pros when time is money. The set-tru also has less chance of getting knocked off center if doing very heavy cuts.

As for what size? Unless you are cutting big things often, no reason not to go with the 8" and use the 4jaw for big stuff. The cost different is because of rated RPM, big chucks are under boatloads of force at high speed.

Are you really set on a new chuck? Unless the jaws themselves are bellmouthed or damaged, you can easily re-center the 3jaw on it's backing plate. Also a good idea to make sure the backing plate is properly fitted to the spindle, if it falls loose when you release the cams, it is not properly fitted. It should require a light tap with a mallet to get it free. When the backing plate is put onto the spindle, there should be 0.001" - 0.002" gap that the cams will pull tight. I made a plug that matches my spindle with a shoulder about 0.020" above proper fit so I can measure the gap with a feeler gage or gage block. Just skim the mounting face of the backing plate (another reason not to buy a direct mount -both the chuck and the spindle must be within spec) until it is right. Needless to say you want to carefully stone the plate and the spindle first.
once the plate is properly mounted, mount it and skim it, cut the spigot slightly undersized and mount the chuck lightly. Clamp a dowel pin and center the chuck with a mallet, then torque the screws down. Mark the chuck and the spindle so it goes back the same way every time. A decent chuck will repeat to under 0.002", and often under a thou.
 
The chuck (or back plate) can also be tight on the mounting taper, having no contact with the spindle face. The back plate (or unitized tooling) must be snug against the spindle taper while also having zero gap against the flat spindle face. Put a good light behind the spindle to chuck interface and look carefully for any light coming through that will show gaps. Gaps cause misalignment between spindle and chuck. It is quite common to find this on D1 tooling, but is fairly easily fixed (ask if you find that.) As to your pin mountings, they are adjustable one full turn at a time by removing the socket head screws that fit in the pin slots and prevent rotation. There should be marks on the spindle that show the allowable range where the cam locks should end up when tightened. Many camlock pins have a groove around them that should be flush with the back plate for initial fitting. Sometimes the pins will need be be readjusted to fit correctly, one full turn at a time. Another gotcha is that the socket screw heads cannot protrude above the back plate surface! Found that once helping a friend.
 
This Cushman 10" 4jaw with reversible jaws is up for auction on Tuesday of this week.
http://www.hoffonlineauctions.net/cgi-bin/mnlist.cgi?hoff8/278/showall
I'm guessing she will go cheap. Additionally, a 3jaw or other might pop up at local auction before my bride and I leave Minnesota enroute to Dabblers' shop near Banf at the end of July.
Minnedosa Manitoba doesn't look that far out of the way. However, warning it'd cost you a cup of coffee and a sandwich!

It appears to me as thought the existing threaded mount would come off. I've got an extra D1-6 backplate I'd sell cheap (you'd need D1-6 pins). You'd also need to bolt her to the D1-6 plate in order to connect the two.

Meanwhile let me know if you'd be interested in me watching for a 3jaw or adjust-tru type.
I wouldn't buy a 3jaw unless it had adjust-tru centering. But, that's on me.

Daryl
MN
 
I would size the chuck to at least the spindle bore.
 
jbolt said:
I would size the chuck to at least the spindle bore.
Click to expand...

I've found that that is critical if you are doing larger and longer stock which you want to fit through the spindle.

However, having smaller than spindle bore is helpful when needing to hold small parts, as at least on my 4jaw the larger hole means the jaws don't close as small.
I've chucked a smaller chuck inside the larger and/or held a 5c collet block and run very slow rpm. Slow rpm required that that the job takes longer. And I don't know that a chuck inside a chuck is best practice.

Daryl
MN
 
Thanks for the replies guys, I'll work on the suggestions before throwing money at something that won't fix the issue. The 3 jaw is on a backing plate and fights tight to the spindle, requires more than a little tap to get it free. The 4 jaw is a direct mount, I'll check the pins on it !!


Sent from my iPhone using Tapatalk
 
A little more info I should have stated at the beginning, I sometimes have gaps from my brain to the outside world.

I have run a dial indicator on the 3 jaw chuck and on stock in the chuck, the chuck run true, it when I indicate the stock that I am getting the run out. The conclusion I drew from that was that the chuck body is running fine, it's the jaws and the scroll plate that are out. ( I was going to say out of tolerance but I don't know what the manufactures tolerances are).

Thoughts please
 
Uglydog said:
This Cushman 10" 4jaw with reversible jaws is up for auction on Tuesday of this week.
http://www.hoffonlineauctions.net/cgi-bin/mnlist.cgi?hoff8/278/showall
I'm guessing she will go cheap. Additionally, a 3jaw or other might pop up at local auction before my bride and I leave Minnesota enroute to Dabblers' shop near Banf at the end of July.
Minnedosa Manitoba doesn't look that far out of the way. However, warning it'd cost you a cup of coffee and a sandwich!

It appears to me as thought the existing threaded mount would come off. I've got an extra D1-6 backplate I'd sell cheap (you'd need D1-6 pins). You'd also need to bolt her to the D1-6 plate in order to connect the two.

Meanwhile let me know if you'd be interested in me watching for a 3jaw or adjust-tru type.
I wouldn't buy a 3jaw unless it had adjust-tru centering. But, that's on me.

Daryl
MN
Click to expand...
 
Uglydog said:
It appears to me as thought the existing threaded mount would come off. I've got an extra D1-6 backplate I'd sell cheap (you'd need D1-6 pins). You'd also need to bolt her to the D1-6 plate in order to connect the two.
Click to expand...
I have eight like new D1-6 pins (a set plus 2 spares) in good condition that I have no use for...
 
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