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Author Topic: Advantage of Those Double Gears With Springs  (Read 1060 times)
K0OD
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Posts: 2591




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« on: February 14, 2012, 10:07:49 AM »

I often see this arrangement in older radios including the clockwork-like VFO drive on the 1977-vintage TS-820 I'm restoring: Two gears, side by side, with one or two springs set into the gears. What does that arrangement accomplish?

http://tinyurl.com/7ve5avq
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KG6AF
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« Reply #1 on: February 14, 2012, 10:16:27 AM »


They're anti-backlash gears.  The idea is to eliminate the mechanical hysteresis that you sometimes get between conventional gears.  If you've ever tuned an old radio in one direction, then tuned it in the other direction and noticed a slight delay before the gears remeshed, that's what these gears are meant to address.
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N9DG
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« Reply #2 on: February 14, 2012, 10:17:19 AM »

Removes the "slop" so that there is no backlash when you stop turning one way and then start turning the other direction. Cheap stamped gears like that are not precise, so using two of them spring loaded against each other makes up for that lack of precision.
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K0OD
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« Reply #3 on: February 14, 2012, 11:10:28 AM »

KG6AF said:
Quote
They're anti-backlash gears.

Thanks guys. Both posts are excellent. Not an easy thing to research in Google unless one knows the correct name which, as it turns out, is "anti-backlash gears."
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AA4HA
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« Reply #4 on: February 14, 2012, 11:45:49 AM »

With anti-backlash gears be careful how much you "load" them. Usually it only takes one or two teeth of offset from a relaxed backlash gear setup to put sufficient tension on them. If you really try to wind down the "loading" to the max you will make it tougher to tune as the gears are constantly trying to clash together.

You will find anti-backlash gears in some very high end equipment like the R-390A receiver. Those of us who work on those types of radios are used to the feel of a properly set-up anti-backlash gear-train. Too tight and you get "R-390A wrist" from tuning across 1 MHz chunks of the band. Many of us take pride in how smooth we can make that gear setup to work as it is coupled to an excellent PTO and an odometer type frequency display. We go to extremes like the use of specific synthetic lubricants for gearshafts and adjusting the swash-plate like compensator on the PTO for frequency linearity.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
AC5UP
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« Reply #5 on: February 14, 2012, 12:53:02 PM »

...in the 23rd Century they're using Dilithium Lubrinite on R-390A's and it works quite well.

Unfortunately all amplitude modulated signals were outlawed from over the air transmission in the 22nd Century, but aside from that the old rigs still have a following... Listening to bootleg CB'ers, signal generators, old MP3's of Alex Jones, Brother Stair, Dr. euGene Scott, thunderstorms in the Gulf of Mexico.......... You know, obsolete radio stuff you can't find in the cloud.

There are retired people living in nursing homes who have never heard static in their entire life, yet they somehow know they're missing something.... If they could only figure out what it is.   Roll Eyes
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Never change a password on a Friday                
G3RZP
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« Reply #6 on: February 15, 2012, 12:44:06 AM »

Even perfectly formed gears on their own will have some backlash because of the clearances necessary. If there is no clearance to begin with, there soon will be because of wear.

I haven't seen anti-backlash helical gears, but I can't see any reason why they couldn't be done if wanted.
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