The Beall Clock Forum

General => Wheels and pinions => Topic started by: bobledoux on April 19, 2007, 04:20:36 PM

Title: Question about Cycloidal Wheel Design
Post by: bobledoux on April 19, 2007, 04:20:36 PM
I’m laying out wheels with cycloidal teeth using TurboCad.  Among my references is Fine Woodworking, Spring 1978.

On page 49 is a discussion about shaping wheel teeth to match pinions.  The shape of the wheel teeth depends on the number of teeth in the pinion.

In simple terms,

Set a compass and draw the wheel pitch diameter circle.

Set the compass to create a circle half the pitch diameter of the pinion.

With this compass setting draw a circle at any point on the wheel pitch diameter circle.

The circle will create the shape of the addenda on two adjoining teeth.

Question: Is this a reasonable way to create cycloidal wheel patterns?

The article also suggests that the shape of pinion teeth depends on the pinion material.  In wood the teeth should have parallel faces.  In brass the faces should taper toward the bottom of the tooth.

Does this make sense?
Title: cycloidal gears
Post by: SCAR on April 24, 2007, 02:43:05 PM
That is only an approximation to a true cycloidal form.  A true cycloidal form cannot be made using arc segments alone.  For clocks, any approximation will probably give good service since gear motion is start-stop.  My company uses a form called PRESCOTT for some molded gears (no, we don't make clocks), and it is made with circular arc segments.

True cycloidal teeth are formed by "generating circles" -- one above the pitch circle (addenda circle) and one below (dedenda circle).  The curves for add and ded are traced out as a point on the generating circles roll without slipping along the pitch circle (in opposite directions).  For gears in mesh, the size of the addenda circle of the pinion is equal to the size of the gear's dedenda circle, and vice versa.  For pinions of few teeth, the diameter of the addenda circle of the gear is made equal to half the pinion pitch circle diameter.  This has an interesting property of making the pinion dedenda straight radial lines.  The do "taper" to the center of the pinion.

The parallel flanks for wooden gears is probably just a strength consideration.

I'll try to scan a sketch to clarify.
Title: Gears & TurboCad
Post by: bobbytbird on April 24, 2007, 03:51:05 PM
If you are using TurboCad Pro, is there a reason why you are not using the Cycloidal gear functionality built into the product. Goto AddOns/Special Tools/Insert/Gear Contour.
Title: Turbocad
Post by: millerdlca on April 24, 2007, 07:39:09 PM
The gear tool in TurboCAD creates involute gears, not cycloidal.  That's one reason I'm creating a program to generate a cycloidal gear profile.

Title: Cycloidal Calculator
Post by: bobbytbird on April 24, 2007, 08:03:35 PM
Does the calculator at provide anything useful respecting what is required to draft the gear?
Title: Thanks, Everyone
Post by: bobledoux on April 25, 2007, 06:15:28 AM
I think I've got this figured out.

I have the low cost TurboCAD version that I'm just starting to learn.  It doesn't appear to have the "Addons" menu option so I'm designing the gears from scratch.

The Sparks site is nice.  My learning curve has been based on the classic English system and not the metric module system.  I'll  start studying the module system.
Title: Cycloidal Gear Generation
Post by: bobbytbird on April 25, 2007, 10:51:51 AM
I assume you are as much interested in building the gear yourself as you are in the final solution given you are not looking at the several programs available, one of which is at for $49
Title: Question about Cycloidal Wheel Design
Post by: Dave on April 25, 2007, 01:04:13 PM
I wish they did a program for chordal pitch gears as used by Harrison, i have some of the info and it is doing my head in. Bobledoux, the module system is very easy to understand, once you have done a few calculations to familiarise yourself with the process. I use the mod system all the time but convert to imperial to fall in with my workshop measuring gear, regards Dave
Title: Question about Cycloidal Wheel Design
Post by: D.Tholf on December 02, 2009, 06:50:17 PM
follow the same guidelines.

after seeing about 10 threads in one week about what 15" wheel can i use, i made this.

the bolt pattern is 5 x 4.75"
Title: Question about Cycloidal Wheel Design
Post by: peraborsera on December 19, 2009, 03:20:42 PM
i emaled greg weld wheels and they told me that they are coming out with a 15X10 with a 7.5 back space just for f bodys. not out yet but coming leate this summer and that they will be the star not the lights