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Lathe Weight Capacity?

B

Brian Albin

Plastic
Joined
Mar 9, 2018
I have a beginner's question.
I only see lathes measured in inches; inches of swing and length of bed. I have not seen a mention of pounds. Is it considered that the makers build lathes strong enough for any slug of steel that can be made to fit over the saddle and between the centers? If there is a weight limit, how does the operator determine it?
　
Thank you,
Brian
 
Pretty much, yes. I had a honkin' winch shaft in my little dinky 1760 tool room lathe that must have weighed 1100 lb. The biggest problem was inertia. The weight was no problem except loading and unloading. Good thing I had a good live center or the story might have been much different. Lathe spindle bearings are generally way over-designed for the weight they will likely see. Cutting forces exceed the work-piece weight many time over unless you are working in heavy industry.

I've seen big propulsion shaft lathes with 70 ton forgings being roughed out. There was barely clearance over the cross slide.
 
I have Turned some stuff that, at a glance anyone in their right mind would say :eek: (talking CNC)

But had to remove way covers, and mount a boring bar on the opposite side of the Turret from the Station that was called up in the program, just to Turn the OD. One off part, hopefully won't happen again!!

But since then I have always wondered if there was a general rule of thumb for stuff like that. Weight of Machine to weight of Part ratio or something?

R
 
Forrest Addy said:
..... Lathe spindle bearings are generally way over-designed for the weight they will likely see.......
Click to expand...

Yep.......The little 500 lb Logan 10" in my own shop has a spindle nose bearing rated for 4 tons. Just a fraction of that would purely flatten the lathe..... It was likely selected for size, not tons capacity, and derating that much will extend the expected bearing lifetime to way past the probable time of use.
 
Brian Albin said:
I have a beginner's question.
I only see lathes measured in inches; inches of swing and length of bed. I have not seen a mention of pounds. Is it considered that the makers build lathes strong enough for any slug of steel that can be made to fit over the saddle and between the centers? If there is a weight limit, how does the operator determine it?
　
Thank you,
Brian
Click to expand...

In general, yes. At least for lathes coming from reputable manufacturers and properly supported. Some lathes have a noticeable tendency to bend in the middle under the weight of the apron/tailstock + part and may need an extra support there. But the spindle bearings won't feel much a slug as large as you can fit between centers. They will however complain with large cutting forces - large thrust loads, like the ones generated with heavy drilling. It's always a good idea to drill a smaller diameter first and plow that 2" drill bit in, afterwards. With most non CNC lathes the lubrication of the spindle bearings may become marginal at low rpm and one might wish to alternate long periods of slow turning with with a couple of seconds of higher rpm's.
 
dian said:
1500 kg on a mt5 taper? interesting.
Click to expand...
Matches the load ratings on live centers. Mt5 skoda is rated for 3000lbs workpiece. MT5 skoda is not that small either, 70mm head diameter and weights couple of kilograms.
 
It actually is a very good question that no one talks about...

Bearing capacity won't tell you much as bearings in the radial direction can take an awful lot of load, usually.

I wish I had a photo...around 1989 the big* Niles lathe had a DC armature placed into it and the tailstock/dead center was affixed. Before the steady rest could be brought into play, the entire dead center - which was maybe 8" diameter at its biggest - schmeared down like a Hersey kiss and the armature fell on the ways.


*I think this lather swings around 12'
 
Most manufacturers have a load rating for each machine,doesnt account for abuse.
I remember calling the maker of a CNC asking how much weight can I hold unsupported in the chuck, they came back with a number wich included the weight of the chuck.
They also gave me a number for supported weight.
We also did the same for a Mill, it was surprising how much it was. But was told to slow rapids down below 50%.
 
dian said:
1500 kg on a mt5 taper? interesting.
Click to expand...

There were a couple of MT 5 DC with sheared-off tips in the chip tray of one old 'teens or twenties Niles I was often assigned to at Galis.

We didn't ordinarily turn anything all that heavy.

Mystery solved when I arrived early one second shift. Day Shift foreman and my shift foreman, obligatory USWA Union card-carrier just watching had a massive bottle jack on heavy timber across the ways of that old Niles Dreadnought.

They were trying to straighten a welded-up six inch-plus shaft about six feet long. Between centers.

All-hands KNEW better of course.

But those were hongry times, WEST, By God Virginia, where a Union-scale Machinist First Class, 20 years in and exalted to running a five-inch "bar" didn't make but about five US$ an hour.

"Management" folks did what they figured they had to do.

We bargaining-unit Chikn's surely weren't into no wildcat strikes to protect Old Iron "company" lathes. Best thing could happen is they'd trash an already fossilized War ONE lathe and we could hope their next buy from the scrappers got us a plumb wore-out War TWO lathe..... as an upgrade!

All our Foreman had come up through the ranks.

MY bet is they felt the same damned way...

Oy! Starving Companies living off OTHER starving Companies (coal mines, mostly..) in declining industries.

Grand as learning environments. Sore depressing otherwise.
 
I think the cross section of the center (the part buried into
the piece) placed in shear would be a limiting factor.

IIRC there is a chart posted around here somewhere....
 
Diameter seems to effect lathes more from a clutch and geartrain perspective with cutting torque transmission than just weight.
My elliot concorde 18x72 has a clutch pack of around 3.5" diameter and can slip as will my colchester mastiff with the same clutches
My old lang 21x78 clutches are about 8" in diameter, Ive never been able to make that thing sound like its under load!
 
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