Howard Winter wrote:

>> I believe he was using Archimedes screws (ie like the square-cut drive
>> screws on a lathe bed)
> 
> Ah, that would be Acme threads (cue the Roadrunner! :-)  

I had to look that up to know what you guys were talking about :)

Archimedes screw: http://en.wikipedia.org/wiki/Archimedes'_screw

Acme thread (different from square thread):
http://en.wikipedia.org/wiki/Acme_Thread_Form

> Presumably he didn't have the rods poking down from the ceiling all the
> time, which would mean he'd need their height above the ceiling for when
> they were retracted - fine if there isn't a room above! 

Yes, that's the problem with this, for what I want to use them at least.
It's also quite a bit more involved than a simple winch, and the friction
forces (which create a difference between up and down movement) are
probably considerable. 

Gerhard

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