View Full Version : Another Question for Gwyn

03-18-2010, 12:07 AM
Hi Gwyn!

I wondered if you could tell me a little more about your gear software..? Does it allow you to input parameters to get gear ratios from simple params? What I mean is that I am wanting to cut gears for my throttle pots, using a large gear on the throttle lever and a smaller one to mount on my 3-turn pots. I would like to get as much rotation as possible out of the throttle lever throw so I was thinking 3 or 4 to 1 on a 3-turn, 100k pot. I wondered if the program you use will let you input say the drive ratio and the size of the larger gears root diameter, number of teeth, and outside diameter and then give you the output for that gear and the secondary smaller gear based on that input. I looked at a bunch of websites that allow you to design a gear or pair of gears to your own specs, but to be honest it seems over-blown for my simple needs.. I would send you a PM on this but I thought there may others that have input or wouold like to follow such a thread for future reference. I find myself bookmarking your posts all the time!

A320 Builder
Tampa, FL US

03-18-2010, 12:45 AM
Hi Buddy,
I bought my "Involute" gear cutting software here - http://www.realhamradio.com/gearhome.htm Well worth it!!!

Gear trains are quite simple really. Throttle set up - the average movement on a throttle lever is about 90 degrees, the average rotaion on a std pot is about 300 degrees. A 3:1 ratio gear train will turn the pot 270 degrees (3 x 90). This is what I use in my TQs. The "pitch circle" of a gear is a circle that is generally about half way up the height of the teeth. If you put two gears together, the point of contact is where the pitch circles of the two gears meet and where the teeth touch each other.
Simple example - If I cut 75 teeth on a gear blank with a pitch circle of 60mm, I would need 25 teeth on a gear blank with a pitch circle of 20mm.
75T driving 25T = 3:1 ratio. (Don't forget that the outside diameter of the gear is slightly larger than the pitch circle diameter when preparing a blank).
The cool bit, a simple equasion - add half the pitch circle diameters of each gear together and you have the centre to centre distance of each axle. Therefore the gears in this example would have a c/c distance of 40mm (60/2=30 added to 20/2=10)

The Involute gear software I am recommending for you allows you to determine - Pitch circle, No of teeth, type of tooth, number of spokes, thickness of spokes etc. It costs about $80 and produces .dxf files ready for the CNC machine.

Cheers Gwyn

03-18-2010, 03:32 PM

You could start with this freeware:


I've made a few gears with this simple program and it's quite OK.
Not in the same league as the one Gwyn is using, but anyway....

Happy milling!!