How to create a point at the center of a sketch pattern

neobobkrause

I have a sketch that contains a linear sketch pattern. Now I need to position two additional copies of this sketch so that the 3 are offset 120 degrees around the center of the pattern entities. I'm as yet not able to find this center point in order to define this relationship between each copy of the sketch.

Here's another catch... The dimensions, spacing and count of the entities in the linear sketch pattern are defined using variable expressions. Changing a variable value could therefore affect the location of the center point around which each copy of the sketch rotates.

Is this possible in OnShape? 

- Bob

jakeramsley

I guess it depends on what you mean by the center of the pattern.  You can add a point and set a mid-point constraint between 3 points (select middle, then the ends in that order to apply).

_Ðave_

@bob_krause how did you get variables to work for the entity count? If I knew how to do that I think I can get a solution to your issue.

neobobkrause

Dave, I didn't get a variable to work for entity counts yet. I've punted on that issue for the moment by hardcoding a number in. But let's assume that a variable would fit there. How would that lend itself to a solution for rotating around the center of a sketch pattern? Please also consider that the spacing between entities, which I am controlling via a variable, may also change. Thanks for all the thought you're putting in. It's an interesting problem for me too.

_Ðave_

Bob, once you can put a point at the center of a pattern the rest is simple. Your problem is that the center changes as the count changes. What doesn't change is the starting point at the lower left of the pattern. Therefore knowing the spacing and count in both the x and y direction a formula could be inserted in the into the dimensions from that starting point to the center point.

neobobkrause

I see. You're saying to calculate the center point of the pattern using the same variables used to define the pattern? If count, which is hard coded now, were to be based on a variable later, I just need to change the expression for the pattern and at the same time change the expression for the center point. Have I got that right?

Sorry, I'm obviously still getting my arms around OnShape.

_Ðave_

the idea is that all you would change is the variable. The expression would include the variable therefore changing the variable would auto update the expression and keep the point at the center of the pattern.