how to draw (( internal involute spur gear )) in solidworks
How well do you want to model this? If your involute spur gear has a lot of teeth, flat edges on the teeth will look fine. Your drawing will be completely satisfactory when you send it to a gear cutter because the actual tooth form will be determined by the cutting tool. If there is a small number of teeth, you can fake the involute with a carefully chosen radius.
If you plan to rapid prototype this thing, or otherwise, generate an accurate part from the model, you must model an involute. Again, this is doable. Read up on involutes. You should be able to control a spline into something pretty close to an involutel
I don't think it is possible to perfectly sketch an involute curve in SW, even with an equation driven curve. I have seen add-ins that model gears and what they do is calculate the curve in excel or something and find a bunch of points along that curve, then put those points in SW and connect them with a spline or arcs or line segments.
The fabrication processes do not work perfectly either. The geometry will be better if you take the time to plot more data points.
A long time ago (check the feature property dates) I wanted to get a true involute for external teeth. Not having the math to use a spreadsheet, I just used sketches and equations to plot the end points of the "unwinding string". I recall that adding more points (at least for teeth this size) didn't really do much to refine the spline shape. Less is more in this case.
It's been so long since I played with gear geometry that I can't say how you would translate this method to an internal tooth, or if it's even possible. But you might find it interesting.
The problem here is that gear is an internal one.
As I note, I leave it to you to determine if this method of finding points to define a spline in the correct shape for an internal involute tooth profile is feasible, or not.
This might help, its done in AutoCad, but the principle should be the same: https://www.youtube.com/watch?v=JXYt2Qr789E
It's funny, I just came across that very video in my own quick Googleing of internal involute gears, and started to watch. Then I remembered that I'm not the one who needs an internal involute tooth profile just now, and that Mustafa must have access to Google (or Bing, or...) too.
The form is still an involute. You cannot use his gear. You can use his sketch.
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