allowable weight on a lathe spindle?

[Arquibaldo]

Dear machinists:

I own a 9" South Bend clone, with a 1.5" spindle, threaded 8 TPI, bored MT-3
and running on tapered roller bearings. Could an experienced lathe machinist
give me an educated guess on the allowable weight (chuck+work) on this spindle?
I realise that leverage also plays a role, so the longer the (unsupported) work,
the smaller the weight should be, right?

I ask because I bought a new 160mm (about 6") 4-jaw chuck, which seems quite
heavy: 10.6Kg (about 23 lb), including the mounting plate. Overall length
is 100mm (4") from the end of the spindle thread to the tip of the jaws.
Will I be able to use this chuck, with something like say a 10 Kg (20 lb) work,
without bending the spindle or damaging the bearings?

Nelson

[Geof]

No problem. The spindle and bearings will be capable of carrying a load in the hundreds of kg.

If you want to get an idea of the load carrying capacity of bearings the size of the ones in a lathe spindle just consider they are about the same size as those the wheels of motor vehicles. They can carry a load far bigger than you will ever put in the machine.