Rack and pinion in Fusion 360

[BelgiqueB]

Hi,

what is the trick to correctly meshing/spacing a rack and pinion in Fusion 360, what point on the pinion do you align with what point on the rack? See the screen shot below, is there an easy way?

 

[Agroshield]

The term used for where gears mesh is called 'pitch line'. On a gear, you have 'pitch circle diameter', which is given by a simple formula (PCD = Number of teeth x Module). Clearly, this formula breaks down for a rack, which is a gear with an infinite number of teeth. On a rack, the pitch line is where the tooth and the space are of equal thickness.

 

[Hopefuldave]

The term used for where gears mesh is called 'pitch line'. On a gear, you have 'pitch circle diameter', which is given by a simple formula (PCD = Number of teeth x Module). Clearly, this formula breaks down for a rack, which is a gear with an infinite number of teeth. On a rack, the pitch line is where the tooth and the space are of equal thickness.

Or for Imperial gears, pitch diameter's number of teeth divided by Diametral Pitch, e.g. a 32 tooth 8 DP has a pitch diameter of 4"
If you're drawing the rack from scratch, the tooth faces are straight lines at the pressure angle from normal to the axis, for module form that's usually 20*, imperial can be 14.5* or 20*. The rack tooth "gullets" are deeper than theoretical too to give working clearance.

Dave H. (the other one)

 

[BelgiqueB]

Thanks for the info, I'm a little familiar with all this. I was hoping I could just download manufacturer step files of rack an pinion and then have Fusion 360 position them meshed correctly, but it seems Fusion does not have this function. I'll have to do it manually I guess.

 

[Agroshield]

...I was hoping I could just download manufacturer step files of rack an pinion and then have Fusion 360 position them meshed correctly...

I think you are expecting too much. STEP files are the geometry of the part. The pitch circles of gears are derived properties. Would you expect to download a solid model and for it to indicate the centre of gravity of the part? Would you expect to download a 3D CAD file of a metric bolt and for it to show the pitch diameter of the thread?

 

[BelgiqueB]

I think you are expecting too much. STEP files are the geometry of the part. The pitch circles of gears are derived properties. Would you expect to download a solid model and for it to indicate the centre of gravity of the part? Would you expect to download a 3D CAD file of a metric bolt and for it to show the pitch diameter of the thread?

Very true, Fusion 360 has been the first real cad program I've used, before it I was always messing around in Sketchup. I am very impressed by it's possibilities but guess there are (logical) limits to what it can do.

Using the pitch diameter and pitch line for the rack you explained it's easy enough to mesh them, after thinking about it I'll design some adjustability in the mounting plates for small construction errors.

 

[mike os]

Ime if you know what you are going to use then the manufacturer's will probably have a better model for you than a generic

 

[Hopefuldave]

Ime if you know what you are going to use then the manufacturer's will probably have a better model for you than a generic

I've found plenty for TurboCAD (which I've been using for decades), the online community's good for hints and tips, too, but they sometimes get a bit long-winded in their explanations or assume you've got a week to draw e.g. an internal gear profile...

Dave H. (the other one)

 

[mike os]

With fusion do you get access to part studio etc?