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Elninio
04-18-2011, 03:57 PM
http://prius.ecrostech.com/original/Understanding/Animations/Normal.gif
http://img.directindustry.com/images_di/photo-g/planetary-gearbox-473207.jpg

Has anyone used planetary gears to improve the accuracy of their dials? For example, with one a 1:2 ratio planetary gear reduction, you could turn your gear twice as much before you advanced one thou. One thou is fine with your current dial (probably), but imagine you wanted to advance 1/2 thou or 1/4 thou, without having to guess it - it is now harder.

Edit; found this page, "Vernier drives": http://jlkolb.cts.com/site/vernier.htm
Edit; found this page, "Tex's Inch-Metric Conversion Dial for a South Bend Lathe." http://www.cams-club.org/meeting-history/2008-11-25/index.html
http://www.cams-club.org/meeting-history/2008-11-25/Tex's%20Conversion%20Dial%202.JPG

vernier alternative:
http://technology.niagarac.on.ca/sop/images/Vernier.jpg

willmac
04-18-2011, 04:06 PM
Elninio-

Nice graphics! the answer to your exact question is no, however a related but different arrangement is used for geared Metric/Imperial dials on some machines. My mill has these and it is a very nice feature.

drmico60
04-18-2011, 04:08 PM
http://prius.ecrostech.com/original/Understanding/Animations/Normal.gif

Has anyone used planetary gears to improve the accuracy of their dials? For example, with one a 1:2 ratio planetary gear reduction, you could turn your gear twice as much before you advanced one thou. One thou is fine with your current dial (probably), but imagine you wanted to advance 1/2 thou or 1/4 thou, without having to guess it - it is now harder.

Such reducers were frequently used in the past, back in the days of valve (tube) sets, for the tuning knob of short wave radios.
Mike

The Artful Bodger
04-18-2011, 04:10 PM
No I havent but they were once very common on radio and other electronic equipment and I am sure there are still plenty of those bits to be found. They are still available although in a reduced range. Unfortunately the shaft size is pretty much restricted to just 1/4".
Google "vernier drive"

Something to note about radio reduction knobs is that most are friction reduction so although they have a nice 'feel' they are not a positive connection so a dial on the knob itself may not show reliable repeatability.

BTW, one of the easiest ways of getting an improvement is to increase the diameter of the scale and the handle.

Black_Moons
04-18-2011, 04:15 PM
I would assume it would add backlash and error. Its much easyer just to use a finer pitch screw or a larger dial :)

The Artful Bodger
04-18-2011, 04:19 PM
I would assume it would add backlash and error. Its much easyer just to use a finer pitch screw or a larger dial :)

There is no perceptible backlash in a friction reduction drive and in those radio controls that used gear reduction they often used a split gear to eliminate backlash.

Yes, large dial and fine pitch screw!

Elninio
04-18-2011, 04:20 PM
It doesn't matter if it adds backlash, since your machine will have some anyway. If your slides are sufficiently tight, you can feel the different between backlash and tightness.

Elninio
04-18-2011, 04:27 PM
willmac, I think I know what you're talking about, like this?
http://technology.niagarac.on.ca/sop/images/Vernier.jpg

Mcgyver
04-18-2011, 04:31 PM
for that matter, why does it have to be planetary? On my big lathe the compound is geared between dial and screw....would accomplish the same would it not?

Elninio
04-18-2011, 04:40 PM
for that matter, why does it have to be planetary? On my big lathe the compound is geared between dial and screw....would accomplish the same would it not?

Most lathes aren't like that, so the planteray gear is compac tand gets added between the hand-wheel and compound. It will only stick out a bit more, maybe an inch at most. I've added a pic to my original post.