Hi Tom. Welcome. Good to see you here. I greatly enjoy your entertaining
and informative posts to GlowBugs. :-)
To your question. I'm no expert on the matter but I think the unidirectional
backlash is due to a spring being compressed when you turn the tuning
knob CCW. That spring pressure is pushing back against the "pistol" and
trying to turn the Acme screw thread. This is a case where you want a little
more friction in the system. Try loosening the main tuning knob and see if
there is a felt washer or two between the knob and the 0-100 dial plate. If
not you need one or two, can't recall what TT uses. Hold slight pressure on
the knob, compressing the felt washer slightly, as you tighten the setscrew.
That will provide some friction between the knob and dial plate which turn at
different rates. Play with that and see what you get.
There is a plastic bearing on the back end of the PTO enclosure which is
spaced from the enclusre by one or more flat washers under the two fixing
screws. That spacing adjusts spring pressure on the screw thread which in
turn adjusts the pressure on the ball drive. I sometimes play with that
spacing as well but I think it has more to do with eliminating slippage in the
ball drive than in minimizing backlash.
Good luck. The Century 21 is an interesting rig. Sort of solid state HW-16,
but not quite. :-)
73,
-Lee-
WA3FIY
On 29 May 2009 at 20:05, Tom NØJMY wrote:
>
> Hello. New member here. I have some Century 21's here which seem to
> all exhibit dial backlash (maybe I should call it knob backlash) when
> turning the tuning knob counter-clockwise. The closer you get to the
> CCW end of the dial travel the worse the backlash becomes. There is no
> backlash when turning the knob clockwise.
>
> I've read quite a bit about dial slippage and rebuilding the PTO in the
> C-21, but these units have all been cleaned and lubricated, turn freely,
> and there is no dial slippage.
>
> Have any of you fellows run into this problem? Is this an inherent
> characteristic of the C-21 PTO, or is it a problem that can be fixed?
>
> Thanks in advance,
>
> Tom, NØJMY . .
>
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>
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