Driven Dimensions...

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  Driven Dimensions...
  September 15, 2008, 08:57 AM Jay Tedeschi

  Really busy working on AU dataset(s) this week but I did not want to neglect all of my faithful readers… [grin]. In any case, as I was using a reference dimension to drive another in an equation it occurred to me that this technique that I use so often may not be evident to all of you.

  So, that being said lets jump right into it. If you have been using Inventor for any period of time longer than a week odds are you have seen this…

  

  Any time you try to dimension part of a sketch which is already “described” via some combination of dimensions and/or constraints you will see this warning. This is not a bad thing so relax… what you end up with on your sketch will be a driven dimension, but not in the classical sense of the word. No, this is more of a reference dimension. In any case, what you end up with is a dimension whose value is enclosed in parenthesis. It will look very similar to what you see below…

  

  Now, perhaps you are not aware that you can actually use this as a reference in an equation to drive another sketch dimension or feature size/position. In this case, I wanted to add a workplane with an angular offset equal to one half of the included angle of my part. Take a look at this last image…

  

  Here I have selected one of the two workplanes on either end of my part, then a work axis which is located at the intersection of these. I am prompted for an angular offset, so I select the driven dimension added in the previous step and then divide by two… and in my case, multiply the whole thing by negative 1 to get this new plane to offset to the correct side.
  Pretty cool huh?

  4 Comments | Add Comment The Gear Box > Inventor 2009, Inventor 2008, Tips

Comments

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  September 16, 2008 03:43 AM Stefaan Boel

  Ok Jay, this one is an easy one. What is more fun to me is to use a driven dimension to outline holes over an equal distance. If the total distance changes, the distance between all the holes will change also...maybe a worth a part 2 for this topic?

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  September 24, 2008 01:50 PM Jason Pealo

  Jay, That sketch is way too complicated. I hope the new users reading your blog don't look at that sketch and think it's a typical.

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  September 26, 2008 11:03 AM Jay Tedeschi

  Stefaan, Not sure I understand the example you are describing... can you send me an .ipt file that shows this? I'll write it up, post it and give you the credit if you do. jay.tedeschi@autodesk.com

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  September 26, 2008 11:12 AM Jay Tedeschi

  Jason, Good point... it definitely could have been made simpler by doing the two cutouts as separate sketches. However, this was a reverse engineering exercise and I was taking measurements off of the actual molded part... I did not have the overall profile dimensions without the cutouts.