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Old 26th September 2011, 10:43 AM   #1
Terry Capps
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Default Modeling a Sheet Metal Screw?

I sometimes model mechanical assemblies that are quite small so that I can see how all the pieces will fit together before I actually build it. I know how to model a "machine" screw, but I am having trouble modeling a "sheet metal" screw. For most of the screw, the thread modeling is basically the same as it is for a "machine screw", but at the end of the screw the diameter of the shaft and threads decreases down to a point (see attached pictures). I can imagine doing it if there was a "revolve_with_scaling" function, but there isn't. The "Extrude_with_scaling" won't work because the profile of the thread needs to revolve around the shaft, not just move around it.

Does anyone have any idea how to do this?
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Last edited by Terry Capps; 27th September 2011 at 10:54 AM.
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Old 27th September 2011, 02:33 PM   #2
luuckyy
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Default Re: Modeling a Sheet Metal Screw

Maybe the beginning of an answer here :
http://www.supercoldmilk.com/ac3dplug/wave3d.html
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Old 27th September 2011, 06:40 PM   #3
captainpeter
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Default Re: Modeling a Sheet Metal Screw

If anyone is interested, I have compiled a Mac version from the posted source code.

cheers
peter
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Old 27th September 2011, 08:18 PM   #4
Terry Capps
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Default Re: Modeling a Sheet Metal Screw

Thanks for replying to my post.

Unfortunately, it doesn't look as though the wave3D function will help. I have attached a couple of images that illustrate why. In the first image, I have created a segment of screw thread similar to what you would use to create a "machine screw". It contains the profile of the thread and the portion of screw inner post between the threads. I have also used the wave3D function to create a spiral path. However, the only function that we have to make the thread & screw wall pattern follow the spiral path is the "Extrude along Path" which is what I have done in the second image. The problem is that the thread pattern is simply moved along the spiral path. To get the thread to always face the outside of the spiral, the thread pattern would have to revolve as it followed the path.

Can anyone suggest a way to use the wave3D function in this way?
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Last edited by Terry Capps; 28th September 2011 at 07:48 AM.
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Old 1st October 2011, 04:41 PM   #5
luuckyy
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Default Re: Modeling a Sheet Metal Screw

The idea I have is to use the wave3D plugin to built a canvas, then extrude edges as needed to model the screw face by face ... needless to say that it is time consuming, but I don't see any other way for now ...

What I've done in the pictures above :
- use the wave3D plugin as usual
- duplicate the spline and move it a little bit on the Y axis
- merge both splines
- extrude edges, and move extruded vertices on their target using the canvas
- and so on and so on ...

- extrude by normal each faces corresponding to the outer part of the screw
- remove extruded faces except top and bottom
- snap vertices together ...
- and so on ...

Not too sure it will help but good luck anyway.
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Old 1st October 2011, 07:48 PM   #6
Terry Capps
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Default Re: Modeling a Sheet Metal Screw

Thanks, luuckyy

I'll see what I can do with this.

I wish that we had a revolve_with_scaling kind of feature.
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Old 1st December 2011, 10:01 AM   #7
Terry Capps
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Default Re: Modeling a Sheet Metal Screw

If anyone is interested, I created a PowerBasic program to create a *.ac file with the surfaces of the screw thread that fit over the Sheet Metal (aka Self-Tapping) Screw's pointed tip as illustrated in the attached image.
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