cast iron or steel chuck?

[dixdance]

I want to mount an 8" 3 jaw chuck w/ 2pc jaws on a big (24") patternmakers lathe. I'm on a budget, and don't need super accuracy, so I'm thinking of finding a used one on eBay but I've been cautioned that cast iron chucks can't handle faster rpms. How can I tell whether a chuck is cast iron, semi steel, or steel if it isn't marked?

Or should I just go with a cheap import? Are the cheap chucks on ebay pretty much the same, or can anyone recommend any one particular source? Will they hold a reasonable tolerance?

Thanks,
Richard Newman

[pcarpenter]

I suppose a spark test would help identify the material. Cast iron tends to make small granular sparks when ground. I don't know enough about spark tests to help separate semi-steel (malleable iron if I understand correctly) from grey iron, and I always found the drawings of spark types a little hard to relate to real sparks. Pictures would be nice.

I would think that a lathe that large likely doesn't have the sort of high spindle speeds that would be problematic anyway (say 1200 rpm and up). You are also going way down in diameter which dramatically reduces the centrifugal forces that might want to take a lesser chuck apart.

Paul

[sch]

I would be surprised if a 24" lathe would have a max rpm higher than even a low end CI 8" chuck could handle. 8" chucks should handle 2000-2500 rpm. Forrest had an article on this and other matters a year or so back. High end purpose rated 8" chucks can go into the 4-5k rpm range and for prices in the $5k or so range you can get chucks rated at twice that rpm.

[dixdance]

This is an Oliver woodworking lathe with a top speed of 1800 rpm, but I wouldn't be going high than 1200, most likely 900.

[Swarf&Sparks]

hit it with a medium hammer, if it cracks, it's cast

[dixdance]

I like that method Swarf... think I could get an eBay seller to do that before bidding?

Richard

[Swarf&Sparks]

either you ask him/her if it's cast, or you ask him/her to perform the test before shipping.
Poisonally, I wouldn't put cast on ANY lathe unless a faceplate; and that at low speed.
Having said that, I've faced plates for a couple of local woodturners, but I knew it was cast iron and took appropriate precautions (and someone else cleaned up)

[wierdscience]

Your most common 8" lathe chucks with 2pc jaws will be semi-steel and will take 1200 rpm no problem,1800 rpm however it starts to get iffy.

If there is any chance you or anyone else will ever run it 1800 then by all means buy a rated steel bodied chuck.Bison makes several styles.

[sch]

Bison rates their semisteel scroll chucks at 2500rpm, steel chucks at 4000rpm. Both are for 'balanced' loads in 8" chucks.