Inventor General Discussion

Inventor General Discussion

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JDMather
Posts: 28,246
Registered: ‎04-20-2006
Message 21 of 48 (783 Views)

Re: Sweep Cut a solid

12-12-2011 01:29 PM in reply to: kakaboo

All you need for the CNC is the path - not the geometry.  (in fact, the geometry confuses the issue as far as creating CNC path)
Considering manufacturing tolerance and clerance between conveyed part - why need perfect (can't manufacture perfect parts anyhow).

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whunter
Posts: 206
Registered: ‎06-25-2009
Message 22 of 48 (765 Views)

Re: Sweep Cut a solid

12-12-2011 10:05 PM in reply to: dnewman
Do you model all your bolt threads? No. Is a sheet metal part a perfect representation of the real thing? No. It's called a digital prototype for a reason. What does it matter how you've accomplished the digital prototype, as long as it is an accurate representation of the real part. Plus, you know how you're going to machine the part anyhow, so weather your digital prototype is 100% correct or 99.917%, what difference does it make?
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JDMather
Posts: 28,246
Registered: ‎04-20-2006
Message 23 of 48 (754 Views)

Re: Sweep Cut a solid

12-13-2011 04:07 AM in reply to: kakaboo

Apparently the solid sweep cut in SolidWorks is severly limited

http://www.eng-tips.com/viewthread.cfm?qid=312336

 

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sbixler
Posts: 1,968
Registered: ‎09-15-2003
Message 24 of 48 (749 Views)

Re: Sweep Cut a solid

12-13-2011 04:46 AM in reply to: kakaboo

I beg to disagree, at least for the case of a fixed-pitch helix.  Sweeping a 3D solid will leave a helical cut with a perfectly consistent 2D profile.  The challenge for Inventor users is to work out what that 2D profile looks like.  But I agree, too, that perfection in the model is not necessary in the case of feed screws.  Nobody would dream of trying to produce one by NC directly from the model!


kakaboo wrote:

I'm afraid sweeping of 2D profile - no matter how shaped and positioned in relation to 3D path curvature - will not produce results identical to sweeping 3D solid.

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cwhetten
Posts: 1,090
Registered: ‎09-03-2008
Message 25 of 48 (721 Views)

Re: Sweep Cut a solid

12-13-2011 01:29 PM in reply to: sbixler

This is definitely not a simple problem.  Here is one cross-section, cut on a plane parallel to the helical axis.

 

Scroller Cut.png

 

This shape was created with the patterned cylindrical cut feature mentioned above.  The shape appears to be approximated by a series of elliptical arcs, each with a slightly longer major axis (vertical in this image) and a constant minor axis (equal to the diameter of the small cylinder--the dashed circle in the image).  The center mark of each elliptical section is shown, and they appear to be laid out in a parabolic shape, or maybe elliptical, or even sinusoidal.

 

Not an easy shape to sketch in Inventor, anyway.

 

 

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whunter
Posts: 206
Registered: ‎06-25-2009
Message 26 of 48 (699 Views)

Re: Sweep Cut a solid

12-14-2011 04:59 AM in reply to: cwhetten

Very nice!

 

I think you're on to something here: the locus (of the points) is probably sinusoidal (projection of the helix's path?). If you draw a circle at each locus, and construct a spline that's tangent to those circles' outer boundary, I think you'll have a very good approximation.

 

I'll try it and see what transpires.

 

In the mean time, here's an improved version of the IPT I posted originally. Now fully parametric (you can change the cutting depth, diameter, pitch, etc). See the parameters in the file.

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cwhetten
Posts: 1,090
Registered: ‎09-03-2008
Message 27 of 48 (683 Views)

Re: Sweep Cut a solid

12-14-2011 10:09 AM in reply to: whunter

The latest part you posted is quite interesting.  How did you come up with that approach?  The logical progression isn't quite clear to me, although the approximation is impressively good.

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whunter
Posts: 206
Registered: ‎06-25-2009
Message 28 of 48 (677 Views)

Re: Sweep Cut a solid

12-14-2011 10:35 AM in reply to: cwhetten

Thanks.

 

I figured you have to take the 3D path into account somehow, and the easiest is just a silhouette of that 3D path/volume.

 

There's a 3rd, more terse approach, see attached.

 

Sadly, I'm working on a 4th method...

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whunter
Posts: 206
Registered: ‎06-25-2009
Message 29 of 48 (646 Views)

Re: Sweep Cut a solid

01-20-2012 03:21 AM in reply to: whunter

3rd method is the best I can do, the 4th method I had in mind doesn't give good results. Whom can I invoice for this :smileywink:?

Contributor
kakaboo
Posts: 15
Registered: ‎12-06-2011
Message 30 of 48 (614 Views)

Re: Sweep Cut a solid

01-24-2012 07:22 PM in reply to: whunter

Dear whunter, let's talk about invoice later :smileyvery-happy:. For now please make sure the attachment contains readable data - I can't see a thing!

cheers.

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