Modeling an Equation Driven Involute Spur Gear in Solidworks 

Can you explain why you made the diametrical pitch dependent on the pitch diameter? What does this solve?

Matthew Miller I'm using SDW 2014, not sure if it will work on older versions. I simply put "N" (without quotes) into the field "Number of Instances" when I did the circular pattern. This way I can make a bunch of different size gears without having to update the number of teeth in the equations AND the circular pattern. As for the pitch diameter, I just made another variable (named pitchdia I think) and changed the value for "P" to an equation based on "pitchdia." This really doesn't solve anything for most practical uses, but when you're making a bunch of different sized gears, it shaves a minute or two off each one.

Damn it. I just lost an hour erasing and redoing everything step by step. I was going crazy until I figured it out on my own.... I was going nuts! Now that I'm reading your comment I feel trolled xD BTW great tutorial Yang Cao, but you should have used an equation in the circular pattern, that's pretty obvious. So you don't have to manually adjust it every time. Number of patterns must be equal to "N". Same thing for the fillets, you could have used an equation like "fillet radius equals 0.5*clearance" or sth like that.

You are a gentleman and a scholar. Thank you so much for this comment.

I had an issue with that, but I changed my fillet so that it was included in the sketch, and then set it to an equation.

Thank you sir. True legend lol

thanks alot for this

Im so happy I can make gears now!!!!

If you're referring to the *180/pi, this is the conversion from radians to degrees. This is here because the equation calls for radians, (notice "phi rad"), however our pressure angle is in degrees

Circular pattern when linked revert back to same value any idea

Why pattern 20 when he got 18 teeth? it happened to me when i designed my gear (different characteristics)

That is just a value for "t" I randomly selected after a few trial.

he chose 0.68 so he can put bounds on the curve of that first involute line, otherwise it would keep plotting for all infinite points of t (reference for anyone else wondering)

this determines the length of the curve from the start . it is the end point of the curve. it just needs to be long enough to go past the outer edge of the gear body so you can trim it later. type 2.00 in that field and you will see what happens.

+Jeff Biss Have you, by any chance, figured out yet why it fails at 39 teeth? I'm experiencing the same problem.

+tobyteddy222, nope, I have not figured out why. I have contacted my reseller and they said that they are looking into it, I sent them my part file. I think that it has something to do with base circle being a smaller diameter than the dedendum circle. If you look at the results of 39 teeth, you'll see that the tooth base produces "notches" with the involutes. Trimming the dedendum circle and each involute turns one of the involutes red and the "The sketch has not been undated..." message is displayed. I will post any resolution when I get it.

+tobyteddy222, I still haven't received a reason why this fails but have developed a work around: 1. Open an new sketch on the same plane as that which holds the equation driven involutes. 2. Select the involutes and the base (dedendum) circle. 3. Click Convert Entities. Those features are now copied onto the new sketch with no equation driven relations between them. They can now be trimmed as required so that you can use the new sketch to Extrude Cut the disc. After you extrude cut, simply create a Circular Pattern using that Cut-Extrude feature and you're done! You can now create spur gears of any number of teeth up to 105. There is a problem with this method because 360/(4*N)-alpha equals zero when N = 105.3916. So, gears with 106 and more teeth will fail.