As an avid (read fanatic) wooden wheeled clock builder I have been on the lookout for some time for a nice program that will simply draw up gears that are useful in building clocks.

The clock shown here is 6" in diameter and uses a balance wheel escapement, it was all cut using the CNC I built with a lot of help from this forum. It lacks a case but that is next. Thanks everyone!!

Anyway I have found a good little program (out of the UK) for producing really good tooth forms for gears and its called "Involute and Cycloidal
Gear-Wheel GCode Generator" Its not perfect (need to do some work arounds for Mach 3) but worth working through to make it work. It found at:

http://www.realhamradio.com/gearhome.htm

Any other clock builders out there?

Hello John
I am trying to learn to build wooden geared clocks. I have the gear g code generator you mentioned and a trial version of mach3. The smallest router
bit I can find is 1/8 inch. Every gear I enter in involute ,the program tells me
the cutter is to big. I have not been able to figure out if the information I give
the program is wrong or if there is a work around some where. Can you tell me
how you would cut a gear with-# of teeth=10,Diametral Pitch=11,Pitch Circle=
23.09,Base Diameter=22.35,Outside Diameter=27.71,Root Diameter=17.55,Tooth
Thickness=3.2,Face Rad=5.0. Any help would be much appreciated.
Thanks Alonzo

Hi Alonzo,
Glad to hear that someone else is as crazy as I am.

I put the data you posted into the program and you are absolutely right. It says that 1/8" bit is too big for that gear/pinion. In fact you could cut the gear and just ignore the warning and all that would happen is that the gullet would be under cut and a slightly weaker tooth would result. (The contact surface would have the proper shape.) If the undercut is too much then the gear won't be strong enough, and a tooth will break off.

I am cutting pinions of the size you specify and I am using a 1/16" bit or 0.062".
These are available at the site given below. They have a huge selection and the address I'm giving here is where I get my 1/16" bits and I get 10 at a time. I run them at 4 - 8 inches per minute and take cuts of about 0.08" per pass. They have a pretty good life and over time (3 or 4 gears) they will start to scorch, but that doesn't produce a bad surface for me and I continue to use them until I manage to do something stupid and break them.

http://drillcity.stores.yahoo.net/10fracpac.html

I notice that you put in a press angle of 14.5º in the involute program - do you have a reason for this? The default is 20º.

Hi John
I am crazy, according to my wife. I'm a bricklayer, out of work for about two weeks, so I stay up all night on the web searching for information on gear proportion,cnc config,software and on and on and on. I really appreciate your reply and information and you are right,the 14.5 was a mistake. I have some free plans for wooden geared clocks that
look like they will cut ok with a 1/8" bit, but I do plan to get the bits you recommended. I would still like to know how to size my own gears. Do you know how to do this?
Thanks Alonzo

Hi Alonzo,
I'm not sure exactly what you mean by "Size the gears" for a clock. The process I ususally follow it this:
1. I play with the arithmetic of gear ratios until I get something that appeals to me. For example I like a 1 sec pendulum and so I usually go for a 30 tooth escape, because I can then put a second hand on the escape and it will turn once per minute. Working up the ratios for the next gears I will aim for one that turns once per hour - this will then be the time train driver. The next gear will depend on how often you want to wind the clock - 12hr, 24hr, weekly. I don't recommend longer than once a week because the weights get just too big, in the order of 20 pounds or more, and thats generally too much for wooden teeth.
2. When I know the various teeth and leaves in the pinions I will go on the involute design program and play with the module until I get a gear I can cut on my CNC which has a maximum of 8 inches. Each gear and pinion must have the same module but successive gears and matching pinions can have their own distinct module.
3. The only part that requires CAD or careful drafting is the pallets and that is a little involved. If you don't know how to design pallets I'd be glad to send you some information.

John

Hi John
When I thought my only option was a 1/8" bit, I was wondering if I increased the scale of all the gears in a set of plans by the same amount, would the gears still work properly. Then I was playing with the gear template generator at http://woodgears.ca/gear_cutting/template.html and noticed that by increasing
the tooth spacing, it seemed to increase the size. As I said I was just playing around with it while searching for something else. I will have to go back to see if increasing the tooth spacing recalculated the number of teeth or increased the pitch diameter. I saw a picture of the worlds largest wooden clock, and if I remember right, the gear the maker was standing by looked to be 8' tall,and could have been cut with a chain saw. I haven't made anything yet. Just recently got Mach3 to Ref all, and motors tuned and calibrated. I physically started this hobby about 6 months ago,after being in masonry for 42 years, so I am not even close to designing any thing yet. Thanks for the info. offer, and your design process description compartmentalized a lot of the things swirling in my head.
Thanks Alonzo

Hi Alonzo,
Your're on the right track. The module, if your working in mm or the Diametric Pitch, if your working in inches do and are exactly the same thing. They indicate the number of teeth per distance or in other words the tooth size. The number of teeth per gear or pinion is choosen by the designer and then the size of the gear will be controlled by the module or diametric pitch. So as a designer you can control the physical size of the gears simply by controlling the module, this in turn will control your bit size on the CNC table, while maintaining the gear ratios unchanged.

Just as a matter of interest the error that your table works within is fixed and if that error is say 1/100" then a gear that is 0.25" in diameter will look pretty bad while that same 1/100" in a 12" diameter gear will look and run fine.

Very small gears can be successfully cut using the Involute Gear Generator - "Involute and Cycloidal Gear-Wheel GCode Generator" The attached photo shows a tiny pinion sitting on my little finger. It was cut using 1/32" end mill. It is driving a 60 tooth wheel giving me a one step reduction from minutes to hours in the time train of a clock.

The programing people have put out version 3.001 and changed the program name to "Gear Wheel Designer" it has some really nice improvements that eliminate most of the editing in the gCode. Its now pretty much plug and play.

http://www.realhamradio.com/gearhome.htm