# Cycloidal Gears Blanks

#### GregS

##### Registered User
I am hoping someone can provide me with a formula for determining the outer diameter of a gear blank given the module and number of teeth required.
This is for cycloidal teeth for which no existing wheels are available to measure.

Thank You,
Greg Schraiber

#### Wimberleytech

##### Registered User
I have constructed a few using an open-source tool called FreeCAD. You have to add the Gear module and then it is as simple as a few clicks. Then you can measure.
Here is the Wiki for the Cycloidal Gear calculations.
Hope this helps a little.

#### Allan Wolff

##### Moderator
NAWCC Member
There are calculators available online, but if you want the formula, it is:
Wheel diameter = Module X (number of teeth + allowance)
wheel diameter is in millimeters
allowance is 2.76 for 17 teeth or greater, 1.61 for 10 to 16 teeth, 1.71 for less than 10 teeth
More details can be found here.

#### rgmt79

NAWCC Member
All is explained in detail in Wheel and Pinion Cutting in Horology by J Malcolm Wild

Regards,

Richard

#### GregS

##### Registered User
I have constructed a few using an open-source tool called FreeCAD. You have to add the Gear module and then it is as simple as a few clicks. Then you can measure.
Here is the Wiki for the Cycloidal Gear calculations.
Hope this helps a little.
Thanks, Greg

#### GregS

##### Registered User
There are calculators available online, but if you want the formula, it is:
Wheel diameter = Module X (number of teeth + allowance)
wheel diameter is in millimeters
allowance is 2.76 for 17 teeth or greater, 1.61 for 10 to 16 teeth, 1.71 for less than 10 teeth
More details can be found here.
Allen, Thank you so much for the formula. Interestingly, this formula produces a diameter value that exacly matches the value derived from FreeCAD. Much Appreciated. Also, thank you for the PDF. Very informative.

I hope to post some photos and a write up for my "novel' gravity escapement and temperature compensated pendulum. I built the escapement and pendulum, before building the clock works because I wanted to make sure it would actually work before designing the wheels/pinions and all the other parts that will make it a real clock movement.

Thanks again,
Greg

#### GregS

##### Registered User
All is explained in detail in Wheel and Pinion Cutting in Horology by J Malcolm Wild

Regards,

Richard
Richard, Thanks for the book recommendation. I quick trip to amazon has that book on its way.
Cheers,
Greg

#### John MacArthur

NAWCC Member
I hope to post some photos and a write up for my "novel' gravity escapement and temperature compensated pendulum. I built the escapement and pendulum, before building the clock works because I wanted to make sure it would actually work before designing the wheels/pinions and all the other parts that will make it a real clock movement.

Thanks again,
Greg
Greg - Please do be sure to post photos and write-up of your escapement and pendulum. Those of us who are "precision nuts" are always interested.
John MacArthur

#### Wimberleytech

##### Registered User
Great...glad you took the plunge. I have used FreeCAD for about four years and have designed and printed countless useful tools and repair parts for stuff around here. Since my return to watchmaking, I have extended my designs to horological endeavors.

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