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CAD software limitations/work arounds

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I recently was drawing my 74 gun ship full size in Solidworks (SW2004) and ran into a limitation when I went to lay off the gun deck. It's an arc running through 3 points, set at the aft perpendicular (294in above rabbet of keel), dead-flat (270in above rabbet keel) and forward perpendicular (294in) across a span of (2112in; 176ft between perpendiculars).


I researched it a little and found that SW has a 500m (1640ft) envelope, the radius I needed to draw exceeds this. I tried splitting up the radius into 2 segments but the aft arc still exceeds this envelope.  I  can add a spline but the spline dips below the horizontal by a small margin aft of the dead-flat, so I think I need to calculate a few more points. Anyway. I wanted to mention this as a possible work around and wondered if anyone has run into other limitations in there CAD programs.



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Does not change the radius point by breaking the arc up into segments. You might try plotting 9 or more points along the curve and forcing the spline through 3 at a time. May not end up tangent, spine to spine, but at model scale it should be undetectable.


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Try this site to calculate three points segments on a arc of a given radius.




Then if you like draw a scaled down version and scale it up and see if it matches.

I would hope they do.


I am using SW2007 and do not yet know if I will have the same problem some time in the near (I hope) future.



Edited by AON
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Don, I'm using CorelCAD and ran into similar issues with my body plan station curves. I lifted a lot more points and used splines for the stations and that seemed to work (still have do proof diagonals). So I think your approach is a good solution--will be curious to read how your scaling up works out for you.




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Were I going to scale up part of a smaller circle, I would drop a vertical line down from the radius point. that would act as a reference line to center the expanded segment, you can always get a circle to intersect two points if the circle is large enough but that alone will not result in symmetrical appearance between two fixed points on your plans, That vertical line may be handy to have available to fine tune the horizontal position of your enlarged curve.


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So, I have been experimenting with SW2004 and tried to scale my sketch. I started with a scale of 1:48. SW gives me two ways the scale up. One is to scale the sketch itself. This method caused SW to through a hissy fit with a nasty little note:


  gun deck: Warning: The sketch has not been updated because solving it would result in invalid geometry (such as a zero-length line).  Consider :
     o Deleting the invalid geometry.
     o Changing relations or dimensions to eliminate the invalid geometry.


Despite this, SW actually produced an arc that measures 21793.59906027 inches. My experience though has taught me that when SW is unhappy it's best to find another solution.


The other method involves scaling the part, I went back to my original sketch and did a mid-plane surface extrude of 1/16 inch, then I went to the Feature Manager and did a Scale. SW didn't complain about this method. So it would seem I am home free - not.


Both methods have draw backs, as the scaled entity or part can't be used for anything other than for reference; in other words you can't build upon it or set up any relations to it. I think this is because even though the radius was scaled up it is still larger than the 1640ft envelope.


I think drawing a arc at 1:48 or even 1/2 scale would allow me to go in and get some very accurate measurements at different stations that I can then carry over to my full size and lay off a spline.

Edited by Don9of11
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