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So I need to design a cylindrical cam (aka barrel cam I think). I'm an aerospace engineer so I've never had a course on cams/gear design (wish I had though). Is there a general equation for the curve (path) on a cylindrical cam of known radius?

Here's a picture of my application; it's basically like a fishing reel. I need to use it to wind thread from a bigger spool to a smaller spool that will work on my sewing machine. The top rod with the purple thing is the input and the black thing is a rubber belt that turns the green drum. The green drum is the part I need to have a cam path on so that it moves the red arm. Any help or pointing to references is greatly appreciated!

enter image description here

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  • $\begingroup$ Well the only thing you really need to know about cam design is that the function of the cam profile needs to be continious to the fourth derivate or you will get issues with vibrations. $\endgroup$ – joojaa Feb 18 '19 at 15:00
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    $\begingroup$ Btw the names of the derivates of position are velocity, acceleration, jerk, snap, (crackle and pop) $\endgroup$ – joojaa Feb 18 '19 at 15:03
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You have half the answer in your question. The device is known as a level wind mechanism and is a groove cut into the drum for the follower/rod in your drawing. A segment of video on the YouTube will show you a general shape for this mechanism.

It's effectively a helix that reaches from end to end with a gentle curve to reverse direction (and cross the previous groove).

More information can be found at Google Patents including a hard-to-find diagram of the rod:

cam winder rod

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  • $\begingroup$ awesome I'll have to look into that then. I found a design book for cams but it doesnt really talk at all about this sort of mechanism; just mentioned that it exists. I've considered a "plate" cam (i think?) and changing the orientation of the guide rod but that would require bevel gears... $\endgroup$ – als0052 Feb 20 '19 at 18:44
  • $\begingroup$ So I've done some looking and I'm still not able to really find the equations I need to design the follower path. Is there just a general equation? I mean there has to be right? Also, text books or any other suggestions on learning this would be great $\endgroup$ – als0052 Feb 20 '19 at 20:10
  • $\begingroup$ Consider to unwrap the cylinder into a rectangle, draw a sloped line from one corner to the opposite diagonal. Factor in the rpm, but translate it to mm per second or feet per minute or miles per hour to determine how it fits with your objective. Once you have one slope, invert it, join it with a smooth transition. If 3D printing is an option for you, Fusion 360 model it, or OpenSCAD model it to create a testable prototype? $\endgroup$ – fred_dot_u Feb 21 '19 at 1:14

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