> > Threaded rod isn't all that efficient, but there's different grades.
> > Ballswcrews work the best, but are expensive by comparison.
> 
> Yes, that's true. I've read that ballscrews are more 
> sensitive WRT lubrification than normal screws. Is this true?
> 
> > Another method to get linear movement is to have the cable 
> in a loop, 
> > with one end wound around the threaded rod, the other 
> around a pulley.  
> > Cable is tensioned by a spring.  Rod turns, cable winds 
> 'on' one end, 
> > and 'off' the other.  Old timers would say "just like old radio 
> > tuners!" but I've seen the same setup in photocopiers.
> 
> But probably not pushing/pulling 800...1000 N?
> 
> Gerhard


Ballscrews don't like getting dirty.  On machinery they are usually placed
out of harms way, and have wipers fitted to keep them clean.  Grit still
manages to get into everything.

You'd be surprised at how well the cable setup works.  If you get slippage,
you just wind the cable around the rod a couple more times.  Not sure of the
efficiency or mechanical advantages, but the force is really only limited by
the strength of the cable.  You don't really need a spring to keep tension,
you can attach the ends of the cable to whatever it is you're moving.

As a complete aside on simple ideas, I recently discovered how the tracks
are kept taut on bulldozers, not that I'd ever wondered.  On most
motorcycles, to remove slack in the chain you loosen the rear axle, slide
the wheel back, and re-tighten.  On a bulldozer, it's hydraulic.  Rather
than pressure being applied by air or springs, it's by grease.  When the
track becomes loose, you just pump in more grease.  The grease can't be
compressed, so the tension is maintained.  Rather neat, I thought.  I've
contemplated making this work on a bike.

Tony

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