Making Gears

Well, I’m a bit novice to cad, so whats the easiest way to make gears?

If you actually want to make gears, the easiest way is to cut them from gear stock.

If you want to model them in Inventor, start with a disk-shaped blank, model a tooth shaped cut, and pattern it. To get the cut to look right, experiment with arc shaped edges by adjusting the radius of the arc. To get the cut to actually be right, learn about involute gear teeth by reading a good reference. You can find several good ones online by Googling “involute gear” or something similar.

www.firstcadlibrary.com

Here’s one of the best tutorials that I’ve found; it’s set up in Pro/E Wildfire 2, but as long as you can get Inventor to solve the equations, I think that it could work. It’s heavy on math, but you can scroll down to the solved equations, and implement those without necessarily working through the theory.

This will get you proper gear geometry, suitable for scaling to any size, and for cutting on a machine (such as an EDM, or a maybe even a waterjet or laser). Depending on your computer, and Inventor’s capabilities, it may also take a long time to regenerate that sketch, every time you load the model.

In practice, you don’t necessarily need that sort of precision for many jobs—it’s really up to you, depending on what you need it for, and what tolerances your equipment can hold. In the event that you can deal with slightly imperfect geometry, try GearGen (or here), which will output a gear with small arc segments, rather than a continuous curve, in .dxf format. This can be imported into Inventor, and extruded.

In any event, for simply drawing the gear, you can just pattern an approximately correct tooth (using an extruded cut) around the circumference. It’s also common to just model the gear as a cylinder with the pitch diameter.

in inventor 10
File>New…>Standard.iam>Dropdown on Assembly Panel and Click Design Accelerator>Spur Gears

You should be able to get it from there…if you don’t have inventor 10 talk with whomever is the main contact because they recieved the software.

(Someone beat me to it, but here are more details)

If you have Autodesk Inventor 10+, you can use the Design Accelerator. It’s a new tool in version 10 and in assembly files; it creates parts such as gears, sprockets, bolted connections (i.e. inserts a bolt and optional washers and nuts according to different parameters) and others. While in an assembly file, go to Tools > Design Accelerator. Select Gears (or something like that) and run through the wizard. I’m not too sure what the next steps exactly are. Play around with it and you’ll get the hang of it. You’ll probably want to stick to Designer mode instead of Engineer or Expert. Remember, you need to do this in an assembly file. After finishing the wizard, it’ll create the gear part files in the project folder. Alternatively, you can save the part as a new file once it is in the assembly. I hope you understand this, ask again if you don’t and I can get back to you with Inventor 10 equipped.

If you don’t have Autodesk Inventor 10+, which is my situation since my computer specs aren’t to its liking, you can download gear parts.

  1. Go to SDP/SI’s Online Catalogue
  2. Find the gear you’re looking for.
  3. Click on its part number.
  4. Click on 3D CAD Models in the bottom right corner of the popup.
  5. Click on Downoad CAD Model.
  6. Select STEP as your format (I believe STEP is better for Inventor than IGES and DXF, but I might be wrong) and download.

The gear part you download may not be exactly how you want it (wrong bore size or thickness) but you can always edit the file or copy the profile of the gear to a sketch in another part file.

I hope you are using gear models for presentation or manufacturing purposes, otherwise it’s pretty much unnecessary and will only slow your computer down by trying to display such a complicated CAD model. Circular discs with the diameter equal to the pitch diameter of the modelled gear will suffice for most designing purposes.

Yeh, thanks for your help. I guess I’ll stick with circles…they do the job. I’m using Alibre Design so I cant really use all those tools. Thats my fault, I should have stated it. Thanks again.

As far as I know, Alibre should be able to import STEP or IGES files such as those downloadable from FIRST CAD Library.

sanddrag beat me too it. I figured out how to import from the FirstCadLibrary. Well thanks for the help.

Im still reading the book on the design accelorator and cannot completely use it yet so for the time being this is what i do:

make a circle to the diameter of the gear and extrude it. I then draw two lines that are dimensioned at an angle of say 360/24/2/2. This would be for 24 teeth. draw a “V” and set the bottom to the depth of each tooth, and then extrude the cut. revolve by the number of teeth. Lastly, for constraint animations, i draw another circle SLIGHTLY smaller on top and extrude it to flatten the tips of the teeth to a similarly sized circle.

The math works itself out quite easily and your left with gear that may be easily constrained to an animation as the computer can find the gear ratio when assembling the product itself since the egdes of the teeth act resemble a similarly sized circle.

I just started the fisher price motor. Its shown below, and is only about halfway done and some resizing needs to be done, but it animates VERY well.

FisherPricemotorPIC.JPG


FisherPricemotorPIC.JPG