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Modeling a globoidal cam


Modeling a globoidal cam

Hi all,

what I'm trying to do is the same cam you can see in this youtube video.

I have the motion law I want to assign to the rotation of the tower in function of the rotation of the cam.
In Mechanism environment, I've made the trace curves of some points of the roller that I've used to cut the cam with surfaces or variable section sweep.
For now, I've tried only one roller cut (three in total).
The cut was decent but there were points where I have interpenetration between cam and roller; especially at the start and the end of the cut.

So I've thinked that I had to rotate the plane of the roller where I've put the points for the trace curves. The situation was better but the motion law I've assigned to the roller was random: a sinusoidal law, as the main one, that at the half reverses the direction (otherwise the cut plane too on itself).

But, which is the right motion law to assign to the cut plane of the roller?

How would you have done?

Would you know tell me where can I find more detailed informations about this kind of 3D modeling?

I searched on the web, but I've not found nothing if not videos like what I've attached where, however, you can't see HOW to do it.



Accepted Solutions

Re: Modeling a globoidal cam

Remaining in PTC ambit, I am practical with MathCad 15 and Creo 2; but I don't understand this what has to do with the main argument.



Re: Modeling a globoidal cam

It is very problematic creating features such as this accurately. You can confirm this by patterning the revolved shape of the tool along the path. You will see that often, the profile is different.

This is much the same a gear hob. The helix on the hob are flat yet the result is an involute.

Try creating a centerline spline through the profile. Place a point along that curve. Now pattern that point along that curve. Then set the 1st point to along=0. Create a revolve cut the diameter of the groove width. Use the point pattern to pattern the cut. If all went well, the pattern will follow the normal of the spline which also follows the normal of how it was created.

Re: Modeling a globoidal cam

I have attached an example of why there is a difference.


This is a comparison with the cutting tool patterned through the groove.


You would have to shape your sweep to make sure you fully remove any interfering material in the cam.

Since this is often critical in the machining operation, you would have to specify the tool path and the cutter diameter to ensure conformance. You will require a small amount of clearance from your guide bearing so it can rotate. It is unfortunate that this is not easy to model correctly as it would be machined. I have been fighting this shortcoming for quite some time in Creo.

Typically we can define the requirements but not adequately represent this in CAD. Milling on a cylinder is just not as cut and dry as many believe. What's worse is that often the feature will fail in the way I have defined this due to accuracy issues. And with Creo 2.0 M040 or earlier, patterns like this fail at random intervals. I am fortunate that this one held up as good as it did.

Re: Modeling a globoidal cam

Hi Antonius,

in the file "cam_challenge_1_patterned", how can I cut off the material as you have shown us in you precedent picture?

I have to solidify (cut) each revolve feature of the pattern?


In this case some of these fails.


It is what you talked before?

Re: Modeling a globoidal cam

Just edit definition on the 1st instance of the revolve. Change it to "solid cut". All the patterned instances will follow.


Re: Modeling a globoidal cam

hello brother Giulio Fraulini how you take a trace curve....can u upload ur creo file where u make a trace curve,,,,i am facing problem regarding same thing...i want to make globoidal cam....but dont know how to model it,,,,can u please help me rrrregarding it.. please check image..this is what i want to make,,...IMG_20141226_175325_990.jpg



Re: Modeling a globoidal cam

These are great mechanisms. Thanks for posting the images.

If you know how to make trace curves, the trick is making the second motion object the "paper" (selection in the top of the trace curve dialog), and setting the output to 3D. Therefore, I pick a point on the roller bearing and I select the cam as the paper space. That will create the curve in the cam component.

Remember that you need the motion and the analysis complete so you can select it as the basis of the curve.

If you still cannot get it, I will upload the files later today as I am heading out the door right now.

Re: Modeling a globoidal cam

This is the video of how the 3D trace curve was generated.

Video Link : 5575

Re: Modeling a globoidal cam

Hi all,

Antonius has preceded me with the post of a video.

I found the manner to better draw this cam and I want to make a video tutorial.

Unfortunately, in this days I had not much free time, furthermore I'm not practical with software for screen video.

Just I'll be ready, I'll post what I've done with some references.

Re: Modeling a globoidal cam

Dear Antonius Dirriwachter...

thanks for this video.....and ur time....but if u see my model file...i am confouse that how much servo motor i have to attach with this assemble.....and how i control the motor to match the orignal working condition of this cam mechanism....i only just know that this is 8 ststion type dividing mechanism with some delay time during the neutral are of cam..i realy want to match the original working condition with my model...and after that i am able to make a trace curve for further modeling.....pleaseeee...if u still not check my file..please check it for better understanding of ervery person problem who want to make this type of camm...