Pierce and coincident, aren’t they the same thing?
They are the same in that they are both sketch relationships, but that’s about as far as that goes.
SolidWorks defines a Pierce Relation as a relation that makes a sketch point coincident to the location at which an axis, edge, line, or spline pierces the sketch plane.
Okay…so what does that mean?
Let’s take a look.
I’ve created a spline on my top plane and a circle on my front plane. If I choose to make the circle and the spline coincident the center of the circle will move on the sketch plane to be coincident with the spline but not touch the spline.
Let’s look at this from a few different angles.
From a view normal to the sketch plane we can see the coincident relationship.
I can move the circle on the sketch plane and it continues to maintain a coincident relationship to the spline.
But if we look from a different angle (let’s say the top), we see a much different picture. The circle may be coincident with the spline when looking at the sketch plane, but it doesn’t actually touch the spline. The spline does not pierce the circle at any point.
However, when I add a pierce relationship, which is a 3-dimensional relationship, the circle is now moved to a location where the spline pierces or passes through the Front plane, our sketch plane.
Okay, but if we look at our spline we can see it pierces or passes through our sketch plane at a number of places. How do we select the exact location where we want our circle to have a pierce relationship?
It’s easier than you may think –
By selecting the spline closest to where it passes through the sketch plane, the circle will move to a place where the spline pierces closest to that location.
Super neat, huh?
Okay, so why does all this matter?
Well having a pierce relationship is nearly critical when creating a sweep. Here’s rule of thumb, when you create a sweep, create your path first and your profile second. If you create them in the opposite order you will not be able to create a pierce relationship between the two sketches.
Take a look below. I’ve created a profile, a path, and two guide curves. I’ve set up my profile using coincident relationships with the path and guide curves. Notice the profile also has vertical and horizontal relations.
Whoa! Not good folks, not good. Let’s see if we can fix this a bit and get better results.
Using the same set of sketches, I’ve updated the relationships on the vertices of the profile to pierce the path and guide curves. I also changed the horizontal and vertical relations to perpendicular and parallel.
Why did I do this? Look at the result, much better. Phew!
By using relations that don’t restrict the profile (horizontal and vertical are restrictive) it allows the profile to rotate independently along the sweep. By using a pierce relationship at the vertices, it also allows the profile to move along the path and maintain a pierce relationship yielding a much better result.
Pierce and Coincident, the same thing? They are the same as much as apples and oranges are the same. They may both be fruit but that’s where the similarities end.