both the spindle and drive unit run free. I am thinking the motor might be the problem. In the past, the lathe has functioned properly.
That definitely sounds like the motor is the problem... One other possibility is amount of power getting to the lathe. Lathes ar notoriously power hungry when starting up before they reach operating speed due to the mass and momentum of the cone pullies, spindle, chuck and weight of the object being turned. When you say this is a 110 Sears motor, I assume its wired with a standard plug and plugged into an outlet? This may be a weak point in the system, you should measure the voltage at the motor when it is under starting load and be sure its over 110 VAC. If not, this may be part of the problem...
My recommendation would be to use a 220 VAC single phase motor and direct wire it to a master switch/with its own fuses or circuit breakers in a circuit similar to what an electric drier or range would use...
An even nicer solution, if you have to replace the motor, get a 1 hp, 3ph, 220 VAC and use a VFD device to run it off the single phase power if that is all you have available. This will allow you variable speeds at each belt setting...
As to the belt slipping off the pully, that can be for two reasons, one, usually the belt is too loose and slipping. Adjust the belt tension and when not running the lathe, the belt tension lever should always be in the relaxed position to allow the belt to recover from the heat and tension stretching that occurs when in operation.
The second cause is that the belt is the wrong material...
Southbend recommends a two layer belt, outer layer being a plastic polymer bonded to an inner layer of leather. The polymer, probably nylon from the looks and feel of it, is the strength of the belt and the leather is what grips the pully...
Before Southbend was bought up by Le Blond, you used to be able to purchase an endless loop belt kit direct from Southbend for these lathes. The belt, as described above, comes with the ends skived and a small can of some type of what I assume is a flexible epoxy resin used to glue the belt into one continuous loop in place around the pulleys.
When I overhauled and rebuilt my 16" Southbend toolrom lathe, I bought one of these belt kits from Southbend and installed it when I put the lathe back together. Once adjusted initially and again after a week or so of use, I've never had to adjust the belt again in over 20 years of intermittent use... Its a fantastic drive belt, smooth and quiet and no slip... When I bought my 1978 Southbend 13" toolroom lathe, it came with this type belt and again. results are the same, no need for adjusting, no slipping and plenty of power, and smooth and quiet...
Seems to me I read recently that Southbend Lathe Co. has been either bought again, or has become independent and is no longer part of Le Blond.
Parts are still available however Grizzly is now the parts distributor:
http://www.grizzly.com/products/brands/southbend/parts.aspx
Happy Shooting,
Mitch & Shadow...
