Gear design --some remarks.

[FixitMike]

In previous posts, I have mentioned a deficiency in most gear design programs in that they draw a gear tooth profile with a sharp inside corner at the bottom of the tooth. This, of course, cannot be cut with a router, you will always have the radius of the cutter present. As a result, the sharp corners of the mating teeth may interfere and cause binding.

Well, there are two easy solutions to this. Either one will work.
1. Mount the gears farther apart. Increase the center distance by the amount of the cuter radius. That way the tips of the mating gear(s) will not reach the area of the radius. This also increases the backlash between the gears which allows them to run more smoothly.

2: Add fillet radii to the corners of the ends of the mating gear(s), equal to the cutter radius. In this case, you should first also offset the gear contour inward slightly to provide backlash.

Offset for backlash not shown.

[kp91]

I used the Mathias Wandel gear generator from woodgears.ca and imported them into aspire with success. My gears were from 6 inches to 20 inches in diameter.

[naijin]

Just to satisfy my quriosity, why are the teeth of the gear that funny shape, I have never seen a gear with such teeth most of them are triangular with a curved top and botthom, no straight lines or angles, I seet it having a problem meshing
and turning without a jerky motion?
Nick

[tomgardiner]

This profile is a refinement of early peg gears but allow for smooth engagement of the teeth through their rotation. (I incorrectly called them hypoid earlier)

[tomgardiner]

Check out involute gear on wikipedia. It has a nifty animation.

[LittleGreyMan]

As Tom answered, the involute function is the answer.

Najin, I hope most of gears around you are involute gears, including the ones in your car or you'll probably have some mechanical issues soon

[naijin]

Hi there littleGreyMan, yes they probably are involute gears, I wouldn't know the difference between involute or outvolute but I do know that they sure as hell don't look anything like the gears in the diagram,
my car is an auto anyway, (just pulling your leg..... it's been a long day and the beer is getting hot!!! Cheers)
Nick

[LittleGreyMan]

I do know that they sure as hell don't look anything like the gears in the diagram

They probably do, except for small low cost gears without power transmission requirement. Increase the number of teeth on woodgears.ca and you'll see the teeth look more triangular. But they are not. If you can have a closer look to a "big" gear, you'll see the shape is not a simple line, but a curve.

[LittleGreyMan]

Note the involute shape, easier to see on a big gear.



Not sure the shape makes any difference for the operator in this case

[FixitMike]

Just to satisfy my quriosity, why are the teeth of the gear that funny shape, I have never seen a gear with such teeth most of them are triangular with a curved top and bottom, no straight lines or angles, I see it having a problem meshing and turning without a jerky motion?
Nick

The gear teeth were generated using the Vectric Gear gadget. I didn't pay much attention to the shapes other than using them to illustrate my point. They will work for wood, but are not the pure involute shape that most of are used to. If the contour above the pitch line is involute, they will work fine, as long as the shape below the pitch line does not cause interference.

More than you may want to know about gears:
Industrial gears use the involute shape. Two advantages that they have are: 1. They can be cut (generated) on a hobbing machine. Only one cutter is needed regardless of the number of teeth. 2. Two involute gears will run together with conjugate action even if the center distance is incorrect. (Conjugate action means that if one gear turns at a constant velocity, the mate will also turn at a constant velocity.) These are important advantages for industrial power transmission use. They are not so important for wood gears.

[kp91]

Add a helical aspect to the gear and you'll get smoother power transmission through all speed ranges.

This was the output side of a 3 Megawatt gas turbine that led to the alternator. Ran 33 years without a problem.