Using the Spur Gears featurescript

andy_grove

I need to create my own spur gears for a project and I saw the new spur gear generator featurescript and it looks like what I need but I am having trouble understanding where to start. When I "use" this featurescript it gives me a sketch with multiple gears but I just want two. Am I supposed to start with a new sketch and add the gears I need or am I just supposed to edit the provided sketch?

bradley_sauln

take a look at the pdf of the public document tied to that FeatureScript: https://cad.onshape.com/documents/5742c8cde4b06c68b362d748/v/c65839fc6078faeb4d2aece1/e/5e653835ca09dd3451bd9e3b

Essentially, in a sketch you create a point where you want the center of the gear to go. From there you exit the sketch and use the spur gear FeatureScript to generate the spur gear based on the input you give it. 

https://cad.onshape.com/help/#customfeature.htm?Highlight=featurescript

bradley_sauln

take a look at the pdf of the public document tied to that FeatureScript: https://cad.onshape.com/documents/5742c8cde4b06c68b362d748/v/c65839fc6078faeb4d2aece1/e/5e653835ca09dd3451bd9e3b

Essentially, in a sketch you create a point where you want the center of the gear to go. From there you exit the sketch and use the spur gear FeatureScript to generate the spur gear based on the input you give it. 

https://cad.onshape.com/help/#customfeature.htm?Highlight=featurescript

Thomas_Homes

I am would like to make a helical gear using the helical gear feature in this feature script. Is the module which I must input for a helical gear the transverse module, just like it is when making a regular spur gear, or should I be inputing the normal module instead? 

NeilCooke

Normal module.

dbaarda

The term "normal module" and "transverse module" can be a bit confusing, and I think NeilCooke is actually wrong above.

The problem is with straight spur gears "normal module" and "transverse module" are the same, and are often called just "module" or "normal module".

But in a helical gear, "transverse module" is technically defined as the module as measured in the plane of gear rotation, and "normal module" is measured in the plane perpendicular to the tooth angle.

I think "normal" refers to the gear-cutting hardware size/shape, and you would use a "normal" 1.0mm module cutter to make a helix gear as you would use to make a straight gear, because you always cut in the direction of the tooth angle. But this does mean the "transverse module" depends on the helix angle for helical gears. You can (and you can get) helical gears with a transverse module of 1.0mm, but these have to be cut with a custom tool that depends on the helix angle, because the "normal module" is not actually that "normal" for those gears.

The Spur Gear featurescript works by first creating the transverse (in the plane of rotation) profile for the gear, and then extruding (for straight gears) or sweeping (for helical gears) that profile. It does not adjust the module of the transverse profile to account for the helix angle, so technically the module setting you enter in the inputs is the transverse module.

Note that the general use of "normal module" for specifying helical gears instead of "transverse module" is an artefact of how they are machined. IMHO you normally want to specify the transverse module. CAD and 3DPrinting don't have the normal machine manufacturing limitations so being able to specify the transverse module is nicer. However, if you intend to get these gears machined somewhere, you probably want to specify the normal module or you'll end up paying more.

dbaarda

Oh yeah, the reason why specifying the transverse module is nicer is the pitch circle diameter is traverse module * number of teeth. When you specify the gear profile using the normal module, the gear diameter changes when you change the helix angle.