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Has anyone seen a spec or recommendation?

Kelly McLaughlin

Kelly McLaughlin

Well-Known Member
Hi Folks, I'm redoing an Atlas 3986 12 x 36 lathe and it came to me with a 5" 3 jaw and an very heavy 8" 4 jaw Kitagawa that I feel is too much weight to hang off the 1 1/2 - 8 spindle, in research it looks like the 8" (or 4 jaw) chucks that were common on these lathes were hollowed or webbed for lack of a better term that would have reduced the weight considerably. Has anyone seen a recommendation or spec for a 1 1/2 spindle regarding how much weight is recommended?
 
That's a great question you've asked. Nobody really talks about that. Unfortunately I don't have an answer. I suspect its a function of the headstock bearings & spindle shaft section, but how to calculate? By comparative proportions - my 14x40 lathe has D1-4 spindle shaft has 2.5" diameter on the taper nose, 1.5" through hole hole. A typical 6" 3J chuck is maybe 20-25 pounds, +/- integrated or separate back plate, maybe another 5 pound for backplate? A typical 8" chuck might be 35-40 pounds +/- back plate. Plus the weight of machined part if unsupported. The 4J chuck I have is webbed out quite a bit, so I think there is design intent to minimize weight.

But I have never read a spec that the spindle should carry a max chuck weight of X. I think its kind of implied that chuck capacity somewhat matches lathe turning capacity but that's not very scientific. My swing over bed is 14". Swing over gap is 20" but I think that would be with facelplate which is much lighter. It could be your predecessor got a good deal on that chuck & mounted it. But it doesn't mean you aren't also prematurely wearing out your bearings.
 

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Hi Peter! My experience is similar to yours, In my opinion this chuck would be more at home on the 13-34 Standard Modern I sold to down size, on this machine the chuck dwarfs the spindle which, even though this lathe has the timken spindle I think it's too much rotating mass for the machine, kind of like the old tractors with flywheels the size of a cow : ). I haven't weighed it but I'd guess it at close to the 40 lb mark.My gut feeling is it's too much for this lathe at 3/4 hp and the small spindle.
 
Hi Kelly,

looks like you have another nice project on your hands. I’m sure it will be beautiful work as ever...

here is my take on large chucks:

* if balanced, they are great for increasing the surface finishes of your work as there is more mass in rotation
* you can safely clamp larger workpieces without the risk of the jaws being outside their safe engagement limit
* you can run the carriage into the chuck as it will no longer clear it
* they are harder on the gear train if there is no way to accelerate/decelerate them in a controlled manner (a VFD or a clutch helps, so do belts that slip a bit)
* in a screw—on spindle like the Atlas, it could come undone easier than a lighter version because of its mass together with a fast decel rate
* etc.....

i looked up the bearings that are most likely on your lathe:

they are probably Timken 16000 series for the front (16150 cone, 16284B cup) and 14000 series for the back (14125A cone, 14276B cup) of the spindle.

the basic ratings are as follows (here is the link for the front one https://cad.timken.com/item/tapered...gle-cones---imperial/16150#Basic Load Ratings )

C90 Dynamic Radial (90 million revs) 3300 lbf
C0 Static Radial 14800 lbf
Ca90 Dynamic Thrust (90 million revs). 2270 lbf

and for the rear: https://cad.timken.com/item/all-pro...rings-ts-tapered-single-imperi-2/14125a-14276

C90 Dynamic Radial (90 million revs) 3180 lbf
C0 Static Radial 13900 lbf
Ca90 Dynamic Thrust (90 million revs). 2080 lbf

from those numbers, running the larger chuck is no problem at all as you will never likely get close to the bearing limits.

as far a proportions of the chuck vs the lathe, that is a whole other story....

Cheers, Rudy
 
Hi Rudy! Yes I bought this Lathe to save it from the previous owner who had disassembled some of it to "restore" it so far I haven't found anything really wrong except for improper reassembly. They're no Standard Modern but it will make a nice serviceable little lathe for a hobbyist. (not to mention it was an excuse to put some of my Lathe bench Ideas into practice ) Thanks for taking the time to research the bearing info! from the diameter if the spindle I had no worries about the bearings but I share your thoughts on the rotating mass, I think this chuck is well beyond the diminishing return point with regard to surface finish : ) Next time I'm out at the shop where the lathe is I'll take a picture of it and the 5 inch 3 jaw side by side to show the difference. It's almost comical.
 
I finally remembered my camera when I was out working on the Lathe Here's a photo of my chucks just for fun. The small one is a 5" Bison the large is an 8" Kitagawa I disassembled them for service and inspection and the backing plate on the 8" Is over 3/4 of an inch thick so at lease a third of the weight, once the chuck was off the backing plate it didn't seem all that heavy so I'm on the fence, The assembly seems heavy but I with you Rudy on the smoother surface finish of the heavier chuck.
 

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Lathe.co.uk has reference to an 8" 4jaw at 21lbs "medium duty" for the 9/10 inch lathes and they have the same spindle thread as the 12". What is the weight of your chuck?
Lathe.co.uk also has a picture of a 12" with a 4jaw chuck. If you compare their picture of the mounted 4jaw to your machine with the 4jaw mounted, do they look like the same?
 
I had 8" inch chuck long time ago on the Chinese made BB 13 x 24 lathe. It looked a bit big and lathe's 1hp engine struggled to get it up speed especially when cold. Lathe came with 6" 4 jaw. On my smaller lathe with over 11" swing I went with 6" 4 jaw - through Chinese version 6" does not seem to be as much hollowed out as the 8" so weight difference may not be too extreme. RPM limit on 6" is 2500. Not sure about 8" but definitely less.

I doubt spindle will be hurt - remember you can place rather heavy stuff into a 6" chuck and spindle has to rotate the whole thing.
 
I don't have a lot of experience in this realm but I think your work would guide your choice. The only thing I'd consider is the chuck bore. I'd try and make sure the chuck doesn't reduce the diameter of stock you can put through the bore.
 
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