Hello all,

I recently graduated from a tech school and I am working as my company's only automation guy, and i'm new. My question regards transfer of energy through either a timing belt and pulleys or using gears. The application requires high(er) speeds. two shafts rotating at 14-15k and one shaft rotating at 28-30k.

I have already built a prototype using a timing belt with pulleys, but i'm not seeing that good of results. The shafts are .2505 +- .0005 O.D. and 7.176 in length and made from steel, not sure what type(may be drill rod). I have a motor that will reach "8000" rpm, and geared accordingly to achieve the desired RPM range on each of the 3 shafts. The first thing i want to change is the length of the shafts, if i could i would like to bring them down to 2-4" and still remain the .2505 in O.D. and instead of using pulleys and a timing belt i would like to use three separate smaller DC motors and use metal gears to achieve the desired RPMs.

Because i am new to this, and not very smart i would like to receive some opinions. I am not sure on where to start for calculating motor size. And i don't work with anyone that would know how to either. Is there a way to estimate the amount of friction from a timing belt and pulleys? or using metal gears, like a spur gear and worm gear? the load on the end of each shaft is a felt wheel used for buffing, they are 1 1/2" dia. and .25-.5 thick. these "buffing wheels" will touch off on a very small surface for only a few seconds.


So to summarize my rambling, gears or Pulley & timing belt? or maybe another suggestion? hope i provided enough of the right info, I am new to the industry and fresh out of tech school so please cut me some slack!

 

Gears would put less overhung or side load on the shaft. Any deflection will cause major issues at those speeds (as you may have already noticed) Usually there are efficiency ratings for gearing, not friction ratings. If you gears are 90% efficient, then you need to multiply your torque requirements by 1/.90. Noise may be an issue also. I wonder if nylon gears would work? If you stay with a belt, I would suggest a flat belt, or maybe a V-belt. I would not suggest a synchronous (timing) belt. It will be noisier and you probably do not need synchronized position. I would highly recommend investing in the Machinery Handbook.

Bill Sturm

 

Thanks Bill,

Say if I went with gears, being nylon or not, and the shaft cams (that would be the correct way to say it right?) by no more then .005 would I still be able to use gears? Or would this question be dependent on the type of gears I would use? The lathe we have in our machine shop isn't the greatest, so any in house shafts over 3.5" aren't concentric (like the ones I have now)

Ideally I would like to run the shafts using one small(er) DC motor per shaft mounted at 90 degrees and use helical gears. Would I see any benefits from using a worm gear and a spur gear over the helical gears? The motors don't need to be mounted at 90 degrees from the shaft(s).

Jake H.

 

Since you are gearing up, if you used a worm gear you would be using the spur to drive the worm. That generally doesn't work too well because the friction is usually too high. I think you would want normal spur or helical gears.

 

Thanks for the input!