How do I draw a gear to cut on my CNC? (Gear Maker gadget)

What it is

The software has no built-in gear drawing tool. Gear Maker, from the official gadget library, fills that gap. It draws the outline vectors for a spur gear from the number of teeth, the diametral pitch, the pressure angle and a center bore. The library notes it can also reopen a gear it made earlier so you can change the numbers partway through a job. It creates vectors only. You add the toolpaths.

Steps

1. Download the version 12 build from the gadget library and install it with Gadgets > Install New Gadget.
2. Open a job and choose Gadgets > Gear Maker.
3. Fill in the form:

• Anchor Point: where the gear is placed on the job.
• Number of Teeth.
• Diametral Pitch: teeth per unit of pitch diameter. The library describes it as teeth per inch or per centimeter of diameter.
• Pressure Angle: the angle used to shape the tooth flanks.
• Bore Diameter: the center hole the gear turns on.
• Line Resolution: how many line spans are used to build the curved tooth flanks.

4. Click OK, then cut the outline with a Profile toolpath and the bore with a pocket, profile or drilling toolpath.

Getting gears that mesh

• Diametral pitch equals the tooth count divided by the pitch diameter. So at one pitch, doubling the teeth doubles the pitch diameter.
• Use the same diametral pitch and the same pressure angle on both gears of a pair.
• A general gear reference gives the center distance as half the sum of the two pitch diameters. Lay out your axle holes from that.
• A standard gear reference notes that 20 degrees is the usual pressure angle today, with 14.5 degrees common on older gears.

Limits

• The tooth flanks are built from straight spans, so a low Line Resolution gives faceted teeth.
• The gadget does not check that your bit fits between the teeth. A round bit cannot cut a sharp inside corner, so preview the profile and pick a pitch coarse enough for your bit.

Pro tips

• Cut a test pair in scrap or MDF and check how freely they turn before using good stock.
• See the entry on the Profile toolpath for tabs so small gears do not come loose.