bjenk8100 Posted December 1, 2014 Share Posted December 1, 2014 Hello, I am not very good with 3D in autocad. However, I am able to draw 3D just very slowly compared with other programs. I am using autocad 2014 here. My problem is simple and might even be more of a math question. I cant figure this geometric calculation. I drew two boxes (10x10 and 5x5) separated by 10. Arch units. The smaller box is 10 in from center of bigger box. I then lofted the two boxes. After that I commanded volume and picked the loft. The volume is 583.333 cubic inches. I cannot figure out how that was calculated. The number makes sense when you think about it. It would definately be bigger than (5x5x10) but less then (10X10x10) There probably is a formula for volume between two objects on different planes. Some sort of integration I assume. I am looking that up now. I thought I would shoot this out. Maybe someone else knows off hand. Any help would be great. Tnx Brian Quote Link to comment Share on other sites More sharing options...
bjenk8100 Posted December 1, 2014 Author Share Posted December 1, 2014 Here is trapezoidal prism formula - H((A+B)/2)(L)/. It isnt working because A and B are extruded differently. Hmm I feel like a newb. H=Height of trapezoid L=extrusion or loft of trapezoid A+B=lengths of top and bottom of trapezoid and its all devided by 2 to take average of the top and bottom lengths ERRRRRRR!!!!!!!!!!!!! Quote Link to comment Share on other sites More sharing options...
SEANT Posted December 1, 2014 Share Posted December 1, 2014 Based on the description, it sounds like the volume formula for a pyramid would be more applicable. Quote Link to comment Share on other sites More sharing options...
bjenk8100 Posted December 3, 2014 Author Share Posted December 3, 2014 i attached the dwg. Two different size rectangles separated by 10" then lofted. If you open dwg and type volume command and select loft you will see that the volume is 583.333 in^3. I cant mathematically figure it out for some reason. It seems so simple. Give it a shot if your interested. Pyramid and Trapezoid prism are not working. rectangles-loft.dwg Quote Link to comment Share on other sites More sharing options...
gazza_au Posted December 4, 2014 Share Posted December 4, 2014 You can draw one of these with the 3D pyramid comand and specifiy the top radius. Massprop for volume. Quote Link to comment Share on other sites More sharing options...
SEANT Posted December 4, 2014 Share Posted December 4, 2014 The formula gazza_au posted applies to any manner of truncated pyramid. The more regular truncation of the pyramid in rectangle-loft.dwg could have it’s volume derived by two applications of the standard (Base to Point) pyramid equation: V = 1/3 * w * l * h One for the full pyramid 1/3 * 10 * 10 * 20 = 666.6667 One for truncated portion 1/3 * 5 * 5 * 10 = 83.3333 Actual volume of truncated pyramid = full pyramid – truncated portion. Quote Link to comment Share on other sites More sharing options...
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