Gear Design Problem

[freerangequark]

Hi,

I spend my days designing modular buildings so this gear problem is a bit out of my realm of experience. I am looking for some help designing a gear set for an invention of mine. I know gear design basics, but this is beyond what I know. Any help would be greatly appreciated. The needed gears (to be made from plastic) are part of a kids toy that I am developing on my own time and with my own money.

For my prototype, I will need to make a 3D solid model in AutoCAD and will export it for fabrication perhaps via stereo lithography.

I need two identical gears which combine to create a beveled helical gear set. As far as I can tell, the relationship of these two gears will not permit a straight spline design.

Here are a couple of drawings (top view and front view) that will better describe what I need for this project.... (NOTE: The gears in the pics will not mesh and are only shown to describe the geometrical relationship of the two gears.

http://www.gsg.microminutes.com/images/gear

1 of 2.jpg

http://www.gsg.microminutes.com/images/gear

2 of 2.jpg

The angular dimension on the first drawing is 48 degrees.
The angular dimension on the second drawing is 12 degrees.

I found the equations for designing "Helical Gears for a given shaft angle with equal center distances", and I found equations for designing Bevel Gears. I couldn't find equations that covered a combination of the two.

I have found several programs that will help to create gear models, however none of them will handle this type of design.

So my question is how do I go about designing beveled helical gears?

Thanks for your help.


-Glenn

 

[Windward]

insideman, just curious, what does the Hootnanny gear toy look like?

 

[insideman]

Windward: The hootnanny consists of a formed metal plate 6 7/8 x 8 with a six inch gear mounted on it. A one inch gear with a crank serves to drive it. Two other one inch gears are also mounted on the plate. One of these can be manually moved to different locations, remaining in mesh with the big gear. The two one inch gears have eccentric pins on them to drive a pair of bars. The bars are joined at one end, with provisions to hold a pencil or pen. The bars have rows of holes so different effective bar lengths can be had. A paper disc can be mounted on the large gear. Turning the crank rotates everything, making fanciful marks on the paper.

This was a successful toy from about 1922 to perhaps 1955, with gap or the war years. I thought a redesign to overcome some of its shortcomings would be viable, but I seem to be the only one who is interested in such a project. I could make it to work with any size paper, not just six inch disks. Plastic ould be used instead of metal stampings and screw machine parts. Assembly could be greatly simplified.

Does this help?

 

[Windward]

insideman, I have never seen anything like it, but I wish I had. I wasn't born too late either.

 

[unclesyd]

Is this the something like you are trying to build.

http://www.math.dartmouth.edu/~dlittle/java/SpiroGraph/

The toy. There is another one that uses just round gears “ ?travel doodles? ”

http://www.hasbro.com/pl/page.viewproduct/product_id.12927/dn/default.cfm

 

[insideman]

Windward: Not trochoids. Much more like the Spirograph. Spirographs are a bit difficult for some kids to operate.