Dan Pihlaja

Warning: Dangerous use of "Make Equal" for lines in 2D sketches

Discussion created by Dan Pihlaja on May 13, 2020
Latest reply on May 13, 2020 by Frederick Law

This may have been discussed somewhere else, but in a 2 minute search, I couldn't find it.


I am using SW 2018 SP5


OK, I use "Make equal" for lines all the time.  I prefer to use it instead of adding two dimensions and linking one to the other.


However, I just ran into a situation where it confuddled me.  And created something that, if I hadn't caught it, would have cost us some money in rework.


The situation:

I have two lines in 2 different revolve sketches that I want to be equal length.

These two lines are NOT on parallel planes.  The planes are 35 degrees from each other.  I thought that it was impossible to make lines equal length if they were not on parallel planes.  However, when I selected it, I wasn't even thinking about that and it worked!


Here are the two lines:



The length of the line on the right is 0.12475" long (creating a diameter of 0.2495" once revolved).


The line that I matched it to after "Make Equal" has been applied, is 0.1022" long.  Which the projected length of the first line, when you project it onto a plane at 35 degrees. Example:




So, when I asked it to "make equal" it not only let me do it, but then proceeded to make the line the incorrect length and instead made it the projected length.


I am glad that I noticed it.  However, I may not have if the 2 planes were 1 or 2 degrees from each other.


Here is a test:

The 2 planes are 45 degrees to each other.  The 1st line drawn is 2" long.



Drawing a line on the angled plane and making it "equal length", makes the line 1.414" long:



Simply changing the angle of the angled plane to 10 degrees changes the length of the line to 1.97":



In the case that I originally used, it was an easy catch, and now that I know that this happens (it only happens to 2D sketches and NOT 3D sketches), I can prevent it.


However, if I could imagine a scenario in which I have an imported model and I am sketching on 2 different surfaces and they are off by half a degree or so, this could be dangerous.


Things to watch out for in the future.