Re: [ATM] Worm mounting

["Don Clement" <clement.focuser@verizon.net>]

>  Would you consider -
> having built this type of drive that the performance would be worth me
going
> the extra step here? I would appreciate your comments on your mounts
> performance in actual use....



Using a cable drive as the final reduction is definitely worth going the
extra step. With a cable final drive there can be an improvement in drive
performance over a precision worm without needing high precision machine
tools or high precision techniques such as grinding or lapping of precision
hardened surfaces. With a properly made cable drive, there is negligible
wear and soft materials such as MDF or aluminum can be used. The cables in
fact roll on these surfaces and roll on each other similar to the rolling
action of involute spur gears, with even less friction than spur gears.
There is zero backlash in the final stage reduction. Stiffness approaches a
solid using small diameter multi-strand aircraft cable. Some have had good
success with polymer (Kevlar) or Nylon fishing line for the cables. There is
no need for lubrication with cable drive and there is immunity from grit and
dirt contamination. The cable drive surfaces do not have to be enclosed like
the worm-worm gear set should be. The pinion and final drive surface are
straight and smooth, easily turned on an ordinary lathe or machined with a
router. Unlike the band drive there are no extreme tensions required for
high stiffness. In fact, there is almost no tension between driven disc and
drive pinion. The cable drive is more tolerant of runnout and alignment than
worm or band drive. Multiple cables allow for averaging. The overall system
precision of a cable drive using ordinary turned machined or routed surfaces
can exceed that of highly ground and lapped surfaces through averaging of
multiple cables.  The only negatives are limited rotation and the drive
pinion and driven disc must be wide enough to accommodate the axial travel
of the cables as they traverse a helical path up and down. A common
misconception is that the drive pinion and driven disc have grooves or need
some type of end stop for the cables. There are no end stops or grooves in a
properly constructed cable drive. The cables roll freely, unconstrained. The
drive pinion and driven disc are straight and smooth.

Yes, the extraordinary precision and high performance of a cable drive is
worth going the extra steps. An amateur can make a high precision cable
drive without high precision tools.



Don Clement

Running Springs, California


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