Andrija Posted November 12, 2014 Share Posted November 12, 2014 Hi guys! Recently I tackled a problem modeling a coffee table I designed during my high school. I'm having a problem lofting a solid leg through 5 cross sections using guidelines. Weird thing is, I managed to do this once, but I wasn't quite happy with shape of side view curve. I slightly changed the spline shape and now loft doesn't work. The drawing is in the attachment. Cross sections and guidelines are in separate layers for better visibility. On the "finished" green table model you can see highlighted corrections I made to the previous version. Thanks! novi3d.dwg Quote Link to comment Share on other sites More sharing options...
nestly Posted November 12, 2014 Share Posted November 12, 2014 I believe the profile vertices are not exactly coincident with the spline path. You may need to turn up the precision (UNITS command) to detect the very small inaccuracies (0.00000361) Quote Link to comment Share on other sites More sharing options...
Andrija Posted November 12, 2014 Author Share Posted November 12, 2014 Turning up the precision to more decimal places will increase or decrease inaccuracy tolerance? I believe I read about that somewhere, but not completely sure In fact, when selecting the spline and activating display fit points it shows the fit point on a cross section vertex -> see picture. I don't think that is actual problem with loft because I had the same anomalia with previous loft and it worked fine. Now, selecting guidelines just makes loft disappear. Here are pics before and after selecting a guideline. I don't know where I'm wrong... Quote Link to comment Share on other sites More sharing options...
ReMark Posted November 12, 2014 Share Posted November 12, 2014 I agree with nestly. I did a quick test using your profiles but redrawing all the splines making sure they were snapped to the intersections of each profile. The result? The Loft command worked with no problem. I'd suggest you do the same. Quote Link to comment Share on other sites More sharing options...
nestly Posted November 12, 2014 Share Posted November 12, 2014 Turning up the precision to more decimal places will increase or decrease inaccuracy tolerance? Neither. AutoCAD always uses the same precision (I believe it calculates 16 digits), but the user can decide how much of that precision they want AutoCAD to display to them. It's basically rounding. According to my measurements, the distance between the profile vertex and the spline fit points is 0.00000646, but since your drawing is setup to display a precision of 0.0000, AutoCAD is only going to show you 0.0000 Quote Link to comment Share on other sites More sharing options...
Andrija Posted November 15, 2014 Author Share Posted November 15, 2014 Ok. Did the thing ReMark suggested and lofted the thing. Interestigly, the problem wasn't in the cross section-guideline snap points but rather in the guideline spline shape at the top profile. See pic -> Green guideline is the "ideal one" (Ideal - meaning it gives the perfect shape) on which the loft didn't work. This line ends as a tangent on the last fit point on spline (near cursor). Golden guideline is the default spline without end tangent adjustment. This one lofts with no problem but gives awkward shape when completing model. Red line is kind of a compromise between green and golden. It gives acceptable shape and works as a loft guideline. Cad acted pretty weird with this one, because I managed to loft it only after several tries. It seemed to me like guideline selecting sequence determines whether you can pull of the loft of not Could it be a general "problem" with Cad that it won't loft alongside guideline that is tangent to profile/cross section? Quote Link to comment Share on other sites More sharing options...
Andrija Posted November 15, 2014 Author Share Posted November 15, 2014 Neither. AutoCAD always uses the same precision (I believe it calculates 16 digits), but the user can decide how much of that precision they want AutoCAD to display to them. It's basically rounding. According to my measurements, the distance between the profile vertex and the spline fit points is 0.00000646, but since your drawing is setup to display a precision of 0.0000, AutoCAD is only going to show you 0.0000 But is there such thing as inaccuracy tollerance? This information is somewhere in the back of my head and I'm not completely sure where I got it from... Like, there is some kind of variable set which determines how precise is CAD when working with objects, ignoring minor junctions and object overlapping... Quote Link to comment Share on other sites More sharing options...
nestly Posted November 15, 2014 Share Posted November 15, 2014 With a few exceptions, my experience is that misalignment as small as 0.00000001 will cause 3D modeling operations to fail. On the other hand, commands such as Hatch and Region seem to ignore the actual tolerance values and will either succeed or fail based on the screen zoom level. How it's supposed to work --> http://www.ellenfinkelstein.com/acadblog/dealing-with-gaps/ How it actually works --> Quote Link to comment Share on other sites More sharing options...
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