Hello Guys,
I was wondering, when there is a specification for backlash in planetary gearboxes, they always say:
Backlash 5 arc-min for example.

Is it 5 arc-min at the input or at the output? anyone knows?

THanks!
Fernando

If it wasn't for the output I'd be upset.   But, if your thinking of buying one, better to ask the seller and be safe.

Brett

Bret,
I was thinking it was the other way around, i´d rather have 5 arcmin backlash in the input, and if the ratio is 5:1 then you'd have 1 arcmin at the output, which would translate into les linear backlash.

I might be wrong!
Regards
Fernando

No Fernando, your exactly right. I have my head up my butt.  I was thinking of overdriveing. I have a 3000 RPM motor I would like to turn a spindle 10,000 with if I can get the right bearings and balanceing.

You got any good links to multi speed (2 or 3 ranges), high tolerance gear boxes a man can afford? For the spindle they wouldn't have to be very high tolerance really.

Brett

Hey Brett,
Not really, i have never come to use any gearboxes for stepping up, and certainly not to 10,000 rpm!

at 10,000 rpm, bearings alone might cost a lot. (just guessing)

I might suggest using a motorized high frequency spindle with a VFD,
or trying to do it with a pulley system and a vfd on an induction motor.
If you get a 3000 rpm motor you might get away with runing it at 120Hz which will get you 6,000 rpm, then a 2:1 pulley system might do the job, just check belt ratings to see if they can take your HP at those rpm.
Fernando

No Fernando, your exactly right. I have my head up my butt. 
Brett

So just another normal day then

Hood

So just another normal day then

Hood

Better than average. 

Brett

I'd say it would be measured at the input of the gear train....IE: the motor shaft. Assuming the load (or ball screw) were held stationary, the measurement would be the angle of rotation of the input device.
RC

Gearbox backlash is the angular rotation in degrees, minutes, and seconds of the amount of play in a shaft.  What that means is;  if you were rotating a shaft in one direction, pushing a load forward, then you reversed the rotation, the amount of free play before the load starts to move in the opposite direction is the backlash.  It is measured in degrees, or parts of a degree (there are 60 minutes in a degree, and 60 seconds in a minute).   The best explanation I ever heard for arc-minutes, or arc-seconds, is this....  If an airplane left New York City heading in a straight line for Los Angeles and was off by ONE-ARC-SECOND, it would miss the center of the runway in L.A. by 12 feet.  So over a distance of 3000 miles, you would be off by 12 feet.   If you were off by 1 ARC-MINUTE, you would miss the runway by 60 times 12, or 720 feet. (about 2 football fields).     

Ok then, a 5 arc minute 10:1 planetary gearbox, would have .5 arc minute backlash on the output shaft... 

If you add a 1" diameter pinion on that shaft... then...

S=r*angle .......... S=.5*0.000145...........angle in radians... that translates to 0.000072" of linear backlash??
That seems too low... i guess i'll ask some manufacturer.

Best regards
Fernando

Ok, read a little before going to bed.

According to Neugart, the backlash stated in all catalogs is measured on the low speed side, so on a common application of reducing the rpm output of a servo, the backlash is measured in the output.

So there you go

Regards
Fernando