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Wrongway
05-25-2010, 11:28 AM
I have pretty much restored an Atlas/Craftsman 12" x 36" lathe and wonder what rpm at highest speed it should run? I can figure out the ratios ok, just need an idea so I can get the right pulley for the motor.

Tony Ennis
05-25-2010, 11:38 AM
If it has Babbitt bearings, I believe 1000 RPM is the max. I seem to recall about double that is the max for Timkin bearings.

If you don't get a definitive answer here ask on the Yahoo Atlas/Craftsman group. Supply your lathe's model number. Someone will know.

I think the pulley sizes change based upon the model/generation of lathe.

I believe the sizes of the dual motor pulley are 4.5" and 2.5" for 1937-ish Babbit models.

knudsen
05-25-2010, 02:06 PM
You may also find info here http://www.lathes.co.uk/craftsman/index.html or here http://www.lathes.co.uk/atlas/index.html

gzig5
05-25-2010, 03:46 PM
I think 2000-2200 is the top speed for the Timken bearing models with the factory pullies and motor.

I'd like to know how fast CAN they be run? I'm thinking of dedicating mine to small diameter collet work and would like to have 3000-4000 rpm. The 6" version will go up to 3200.

Tony Ennis
05-25-2010, 04:21 PM
I don't think running bearings at 2x their recommended max speed is going to work out.

Don Young
05-25-2010, 09:58 PM
I think 2000-2200 is the top speed for the Timken bearing models with the factory pullies and motor.

I'd like to know how fast CAN they be run? I'm thinking of dedicating mine to small diameter collet work and would like to have 3000-4000 rpm. The 6" version will go up to 3200.

I presume you are not planning on turning a regular 6" or so lathe chuck at that speed. Vibration gets to be a real problem when speeds are raised very much and I have read that chucks have been known to go from "together" to "apart" at high speeds. My lathes generally run about as fast as I feel comfortable running them.

gzig5
05-25-2010, 11:46 PM
I presume you are not planning on turning a regular 6" or so lathe chuck at that speed. Vibration gets to be a real problem when speeds are raised very much and I have read that chucks have been known to go from "together" to "apart" at high speeds. My lathes generally run about as fast as I feel comfortable running them.

Don,
Please note the words "collet work" in my statement. I'm talking about small pins and such, mounted in collet internal to the spindle. Anyway, I have a 6" steel Bison chuck that's mounted on my 14" Rockwell and it is rated for 4500 rpm so I could use that. Not all chucks are equal.

As for bearing ratings, I have no doubt that the bearings in a 12" Craftsman when properly set up can handle more than 2000 rpm without disintegrating. I just don't know what that max rpm is, but I plan on finding out. I think a better lubrication system than the original cups would be called for any increase in speeds though.

Wrongway, getting back to your original question, the top spindle speed from the factory was 2100 rpm with Timken bearings (which I believe all 12" Craftsman's had).

Black_Moons
05-26-2010, 12:33 AM
One thing you should keep in mind is the diamiter of these bearings.
Yes 2000rpm isent much, but if you have a 3" spindle (OD) thats some serious SFM those bearings are being exposed to. 1500SFM or so to be exact.
This is why they are limited to low speed when cheapo skateboard/die grinder/etc bearings are rated for 10,000rpm or whatever, at 1/2" thats only 1300SFM.

Also, lathe bearings are under 'preload'
Meaning just spining they have hundreds of pounds of force exerted on them to keep the spindle 'stiff'

skateboards and die grinders and such have little or no preload to deal with. Some you can even feel play in the shaft on! Vastly reduces the stress the bearings deal with.

gzig5
05-26-2010, 12:47 AM
One thing you should keep in mind is the diamiter of these bearings.
Yes 2000rpm isent much, but if you have a 3" spindle (OD) thats some serious SFM those bearings are being exposed to. 1500SFM or so to be exact.
This is why they are limited to low speed when cheapo skateboard/die grinder/etc bearings are rated for 10,000rpm or whatever, at 1/2" thats only 1300SFM.

Also, lathe bearings are under 'preload'
Meaning just spining they have hundreds of pounds of force exerted on them to keep the spindle 'stiff'

skateboards and die grinders and such have little or no preload to deal with. Some you can even feel play in the shaft on! Vastly reduces the stress the bearings deal with.

I am fully aware of how spindle bearings work and the forces involved. I think a few of your numbers are off (spindle is max 1.5"ish dia, no way there are hundreds of pounds preload) but thats not a big deal. So what is the max speed capability of the Timken bearings in a 12" Craftsman lathe?

ulav8r
05-27-2010, 09:42 AM
So what is the max speed capability of the Timken bearings in a 12" Craftsman lathe?

Find the bearing numbers, then search Timken's documentation to determine expected life at any given rpm
and load. It has been years since I have done anything like that so I will let you do your own research.

Wrongway
05-28-2010, 09:29 AM
My bad for not responding quicker. Thanks for the replies. I have 2 pulleys in the junk box and the fastest will yield around 1500 chuck rpm at its fastest. I will be using that for cost control and laziness. The headstock has roller type bearings in it and I won't be running it that fast for most operations, hss tool steel...Rex AAA...so I reckon it'll be fine. Great knowledge base here. Again, thanks for the replies.