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How to sweep a profile along a curve and maintain its orientation with respect to one plane?

james_aguilar160james_aguilar160 Member Posts: 50

Hi, I'm working on building a marble auger for my son. It involves a spiral/helix path for a marble to ride up, and at the top, a hole for the marble to come out and go down a ramp.

Near the top of the auger, I need to open a hole in the side of the column, and blend the path of the marble from the spiral onto the ramp.

I'm running into a problem with this. I have a projected curve that blends the curve of the marble and the desired output angle. However, when I sweep profiles along this curve, they have a tendency to roll about the path of the curve. This leads to undesired cuts in the sidewall of the auger, and final geometry that has a different tilt than desired.

Here's a simple demonstration of the problem. In this part studio, you can see a simplified representation of the marble path on the spiral.

https://cad.onshape.com/documents/6613cffc2b455a05194a3f23/w/4c78ec5d45a1b38c8a1e81b8/e/fbdffdb669dcf6c031ee0d16?renderMode=0&uiState=6762d122ea1bb7208a332c98

Notice how the swept profile retains its upright orientation.

Here's a simplified version of the projected curve and the result of sweeping the profile along that.

https://cad.onshape.com/documents/6613cffc2b455a05194a3f23/w/4c78ec5d45a1b38c8a1e81b8/e/bb7a37ed6f2c852bba2e6e52?renderMode=0&uiState=6762d15aea1bb7208a332e41

Notice how the profile is tilted to the left by the end of the sweep. I want it to stay vertical the way it does in the helix case.

Does anyone know how to accomplish this? If not, what's my best alternative?

Comments

  • james_aguilar160james_aguilar160 Member Posts: 50

    Looks like this was literally just asked and answered by another person. The answer is to lock the profile direction to the top plane.

    I need to read more about this option to understand how it works but for now I'm very happy that it works.

  • james_aguilar160james_aguilar160 Member Posts: 50

    Okay, I have worked a little more on it. For anyone else trying to create a marble works it seems like the actual best approach is to do two sweeps, one after the other.

    The first sweep will create a surface along which the track can run. This sweep uses lock profile direction with the top plane as the direction. This ensures that at each point the line on the surface perpendicular to the curve is also parallel to the top plane.

    The second sweep creates the solid. This is created using the desired marble carrier profile. With this sweep, you lock the profile face to the surface you just created.

    The benefit of this approach is that at each point along the curve, in the plane perpendicular to the curve, the cross section of the sweep has the same profile as it does in the original sketch. (If we were to do this step first with lock profile direction, then the cross section of the vertical plane that is perpendicular to the curve in xy would have this property, which in the case of extreme curvature could distort the actual cross section along the direction of marble travel).

    Now, I don't know how well this would work for really sharp curves — but I'm not sure Onshape could really help with that because the calculating where the marble will be on the track is a physics question, not a shape question. I think for reasonable shapes the approach described here will be adequate.

    https://cad.onshape.com/documents/6613cffc2b455a05194a3f23/w/4c78ec5d45a1b38c8a1e81b8/e/bb7a37ed6f2c852bba2e6e52?renderMode=0&uiState=67634abf683b973ce71d9878

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