Help creating a gear?

[Drew]

I am trying to create a gear that I have in my hand. I tried using the FCGear workbench I got from the addon macro.

But I really do not know my stuff, apart from the number of teeth I am not sure what the other parameters mean, so I am trying to get the gear to be the right radius.

I attached the gear I made thus far:

Servo_Gear.fcstd

(468.42 KiB) Downloaded 74 times

My measurements are:

• Outer Diameter: 30mm

• Tooth height (from tip of tooth, to base of tooth): 2mm

• Number of teeth: 55

OS: "Manjaro Linux"
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.Unknown
Build type: Release
Python version: 2.7.13
Qt version: 4.8.7
Coin version: 3.1.3
OCC version: 6.9.1

[jmaustpc]

I am on my phone just now so I can't check, but from memory the diameter of the gear is defined by the PCD, I think it is called that, Pitch Circle Diameter, it's the diameter at the average of the meshed teeth, so roughly about the diameter of the gear at about half way along its teeth.

[chrisb]

Perhaps that forum discussion which includes some images might help: https://forum.freecadweb.org/viewtopic. ... 20#p103834

[mrdic]

Pitch circle is the diameter of the gear pair's contact point. If PCDs overlap or don't contact, the gears' teeth slide and wear against each other instead of rolling.

[looo]

I think measuring the pitch circle is quite difficult. And without the pitch-circle-diameter it will be quite difficult to obtain the other parameters. So maybe you have to assume some things...
For example: you can simple create the gear by a given axis distance and the number of teeth. calculate the module by:
module = 2 * axis_distance / (num_teeth_1 + num_teeth_2)

[mrdic]

If you've got the axle mounting of the gear pair to work from, it's easier to work out the PCDs from the distance between their axles' centres (which is easier to physically measure) and the gearset's ratio than from the gears themselves. The PCDs touch at the ratio distance between the axle centres.

[Drew]

I really do not know my terminology in this, I am doing this for a hobby in constructing a design for an XY plotter.

And to design a certain portion of the project I need to get this gear that I have into a CAD file to properly make.

Here is an image of the gear (which I should have included from the start...):

IMG_20170528_153030.jpg (698.13 KiB) Viewed 2915 times

So the axis distance is the radius to the base of the teeth?

Which is 13.5mm, times 2 so 27mm over the number of teeth 27 / 55. So the module needs to be 5.4? correct?

[looo]

With axis-distance I meant the distance of the centers of the pair of gears.
here it is called "centre distance":


I have added your image to the freecad file, and modified the parameters of the gear slightly (number of teeth should be 56). If you can achieve to make a better picture (or scan) of the gear, I think this will be the most accurate way to reproduce it.
As the file is too big for the forum, I have uploaded it to github:
https://github.com/looooo/FCGear/blob/m ... ture.fcstd