Dennis Dohogne

Nice Trick for Design Tables to Show Driven Dimensions

Discussion created by Dennis Dohogne on Apr 14, 2017
Latest reply on Jun 21, 2018 by Matt Peneguy

I've been a fan of Design Tables since they came out with the initial release of SolidWorks in 1995.  In most cases I prefer them over just using Equations.  For one thing I can more readily create the configurations than by using equations.  But the bigger two reasons are that we can 1) leverage the strength of the spreadsheets with its vast array of functions, even referencing other tabs within the worksheet, and 2) we can collect extra information from the model and show it in the Design Table.  This post is about collecting that extra information.


I have evolved a really nice parametric gear file over the years and in SWX2016 it became vastly easier.  An involute curve defines the shape of the gear tooth, but it is a complicated shape.  I did not like the equation driven curve using the Involute function for a variety of reasons so I worked with the geometric definition of an involute.  In SWX2016 they introduced the ability to make a straight line segment and an arc segment equal in length.  This allowed me to make a much simpler sketch with a whole lot less math.


Now here is the cool thing about the Design Tables, you CAN have DRIVEN values in them.  Normally, if you would go to add a driven dimension to a DT it would tell you that that is not allowed.  BUT if you select the driven dimension name in the sketch and paste it to Notepad to collect the terms you want to add to the DT you can then go to the DT and paste them there.

This DT was created with just a few parameters that are the green and yellow ones on the left of the gray blank column.  I added the other stuff to the right of the blank column and color coded things with green for input values to define the configurations and yellow for calculated values that control dimensions.  I have these configuration names to be a string automatically created from the green input parameters.  At this point everything is great.  Then I added the columns colored blue and pasted in their headers from  the driven dimension names that had been copied to Notepad.  These are values I want to know for various reasons.  These blue cells are blank at this point of creation and there is no problem with that.  Exit the DT and let it create any new configurations.  If you were to then go back to the DT you would see some or all of these blue cells populated.  Voila!  You can now show driven values in the DT!!   ==> A note of caution:  These driven values are only updated if the configuration has been regenerated.  It is possible to have changes to a configuration that would affect your list of driven values, but those values aren't updated unless the configuration is regenerated.  This drove me nuts until I figured that little trick out.  So now when I want to see these extra pieces of information I just make sure the configurations have been regenerated (showing the green check mark next to the configuration name) before I go to the Design Table.


By the way, when I first did this gear model there were only about six segments to define the spline.  I thought that was enough as everything looked right, but when I did a measurement of the pressure angle I saw there was an error in the neighborhood of 0.5 degrees.  This was way too much for the purposes of this file (wire EDM prototypes from the CAD file).  The base circle is defined by the Pitch Diameter * cos(Pressure Angle) and the sketch works from there.  However, a line tangent to the spline at the pitch diameter should also have an angle with a ray that matches the pressure angle.  That is why I created the driven dimension PressAngle_Measured@Sketch2.  The comparison of this angle to the prescribed pressure angle is in the two rightmost columns.  This gear sketch uses about 19 or 20 segments to define the involute curve and the results are pretty good, less than 1/1000th of a degree in all but the very last row on this list.


Since this is an observation on how to get driven data into a Design Table it applies to all DT's, whether in a part file or an assembly file.  I'm tickled pink about this!!