Gear reduction question

[dmellich]

If two gears/pulleys, different sizes say 60 teeth and 20 teeth are sitting on the same shaft next to each other, is there a reduction factor between them? If so, how is that factor used with other reductions being used? Are they multiplied or added? Thanks for any help.
David M. Ellich

[FotoPlasma]

There're more than a couple whitepapers about this topic.

You can find them here.

Also, How Stuff Works is a great resource for a great many things. They have an entire section devoted to gears and gear ratios.

Hope this helps.

[Specialagentjim]

Originally posted by dmellich
If two gears/pulleys, different sizes say 60 teeth and 20 teeth are sitting on the same shaft next to each other, is there a reduction factor between them? If so, how is that factor used with other reductions being used? Are they multiplied or added? Thanks for any help.
David M. Ellich

The way I figure these is I look at the rotations. If you have a 40 tooth gear interacting with a 20 tooth, which is on the same axis shaft as the 60, which is interacting wtih a 120, you would have:

40 teeth to 20 teeth = 1 turn of the first shaft results in 2 turns of the second.

Now your going from 2 turns from a 60 tooth shaft to 4 turns on the 120 tooth gear.

i think i did this right...although, i am doing this last minute at my grandfathers house...so if im not right id love to be corrected..If I get time when i get home, ill put some 3ds images up.

[dmellich]

I visited HSW some time ago and understand the basic concept of gear reduction. However, HSW does not address my question. Is there a reduction between 2 different size gears that are sitting on the same shaft, side by side and not meshed with anything else.

[Andy Baker]

If two dissimilar gears are mounted on the same shaft, then there is no reduction.

However, using this setup coupled with other gears is a good way to produce a reduction.

Here is an example:

A Fisher-Price motor has a 19 tooth gear.

This 19 tooth gear is mated with a 57 tooth gear, providing a 3:1 reduction translated to the shaft which the 57 tooth gear is mounted.

On that same shaft which the 57 tooth gear is mounted, there is another 19 tooth gear, attached to the same shaft.

Now, this second 19 tooth gear is meshed with a 4th gear, a 38 tooth gear, which provides an additional 2:1 reduction.

The total reduction of this system is a 6:1 speed reduction, done in a very small package.

Andy B.

[Gadget470]

In the attached picture, there is two ways for this to go.

I didn't count the teeth but i THINK the large are 48 Teeth, small are 16 teeth. This creates a 3:1 or 1:3 ratio depending on drive shaft.

Scenario A:
Brown is driven at 27 RPM
Brown spins Small Blue at 81 RPM [27 * 3]
Small Blue is attached to Large Blue therefore BOTH Blue spin at 81 RPM.
Large Blue spins Red at 243 RPM [81 * 3]

Final: 27:243 = 1:9
-=-=-=-=-=-=-=-=-=-=-
Scenario B:
Red is driven at 27 RPM
Red spins Large Blue at 9 RPM [27 / 3]
Large Blue is attached to Small Blue therefore BOTH Blue spin at 9 RPM
Small Blue spins Brown at 3 RPM [9 / 3]

Final: 27:3 = 9:1

[dmellich]

Thanks Andy and Gadget, your responses answer my question perfectly!