gear reduction units cost? where to get? benefits?

[douglasco]

Where do i find zero-backlash gear reduction for servos and steppers? The ones i see don't indicate zero-backlash. Whats the benefit of using them that over a good belt drive like the ones at cncpartskit.com: http://www.cncpartskit.com/belt_reduction.html
Their 10:1 is $379, can't imagine a gear reduction unit being much more then that.

[RICHARD ZASTROW]

There really is no "zero backlash" gear reduction. There are low backlash reducers. The reason is gears would bind up if there were no clearance "backlash". It's like trying to put a 1.0000" shaft in a 1.0000" hole, interference fit.

There are anti-backlash gears and worms that are usually spring loaded to take up the clearance. The spring load complies with the irregularities and clearance of the gears.

The more accurate the gear, the less clearance or irregularity. Unfortunately, the more accurate the gear the higher the cost.

It's that old line again, "Speed costs money, how fast do you want to go?" Reads "Accuracy and precision are expensive. How fussy are you?"

Cone Drive makes a worm-wormwheel unit with a belville spring loaded anti-backlash worm. Not cheap and it is possible to overpower the spring load and cause backlash by exceeding the design load.

There are also spring loaded split gears available to take up backlash.

All will have a certain amount of reversal error.

As far as belts, you might want to investigate Gates carbon fiber synchronous belts. They have near zero stretch after initial tension set.

I have no interest in either Cone Drive or Gates other than as a "specifier" when I deign machines.

Dick Z

[Al_The_Man]

I generally use the likes of Bayside Planetary, they are fairly low B.L. and come up on ebay regularly.
The advantage over belts comes in when you are looking at the need for higher ratio's, belt reduction is usually only practical to a certain degree, but usually a lot cheaper.
Al.

[douglasco]

So what is "fairly low"?
How much Back Lash is acceptable. Is there like a Best, good, minumum rule of thumb to go by? Its usually measured in arc minutes correct? I see Dynatorch's planetary drives are "less than 5 arc minutes backlash" I believe they are apex brand, judging from their website, just the gear box runs about $700 a piece. What about 10-20 arc minutes range- that seems to be fairly cheap. All that happens is i loose resolution in my machine correct? If most tables have .001" resolution and my plasma cutter only has .015, then i would imagine doubling or quadrupling the backlash wouldn't add too much onto my .015", maybe what, .020?

[douglasco]

Had another thought. Backlash isn't proportional to gear ratio is it? a 5:1 box with 8 arc minutes of backlash will have the same backlash effects on a machine as a 10:1 box with 8 arc minutes would?

[douglasco]

"I generally use the likes of Bayside Planetary"

So I bought some of those Bayside planetaries, only to find out the backlash is 15 arc mins. And these are the low backlash option models. That doesn't sound to good to me. Thats about the same as worm gear units and they are MUCH cheaper. Somebody tell me some good news.

[Al_The_Man]

Originally Posted by douglasco So I bought some of those Bayside planetaries, only to find out the backlash is 15 arc mins. .

The ones I got were 10 arc-min standard, the optional low BL were 5 arc-min.
Al.

[douglasco]

Yep, yours must be the new more expensive helical cut ones, thats the specs i was reading when i bought these. Mine are the NE series, <15 arc mins backlash. Oh well, i'm going to run them i guess. Easy plug and play solution for now. About $140 a piece after its all said and done. I just hate to drop $400 a piece on a belt drive solution and am looking for something i don't have to build from scratch.

[Mariss Freimanis]

The benefits of reduction are matching motor power to the load (having the motor turning at its best power RPM) and inertial load matching (optimum power transfer for best acceleration of a load).

Mariss

[jcc3inc]

Sir,

Please note that last stage gear backlash results in lost motion; the size of your drive pinion enters here as well. If you have a given backlash AND a large drive pinion (4", for example), you will have twice as much lost motion as when using a 2" diameter pinion. In order to have a good operating system, one would like to have several pinion/rack teeth in contact at a time, so smaller diameter pinions -> finer gear pitch.

If you take a careful look at your entire machine, you will likely have several places where there is springiness/lost motion, so the very low gearbox backlash may well not be as significant in terms of the overall machine performance.

Rergards,
Jack C.