Constraint Confusion

[Gandalf_Sr]

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6704 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: 0c449d7e8f9b2b1fb93e3f8d1865e2f59d7ed253
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17

I am an EE trying to learn FreeCAD. I watched a few tutorial videos and started my first design which is a '+' shaped object with 4 counterbored holes. I padded my first sketch and then drew a second sketch of 4 circles on the top surface to create the counterbores which I was able to do (see picture) but FreeCAD is telling me that I have still 2 degrees of freedom. I can take each pair of opposite circles and move them in the x or y axis but how do I constrain them? Is there a way to lock to an axis?

You may note from the purple circles in the picture that I have created an edge linked to an external geometry for 2 of the original holes but I can't see how to constrain the new circles to be concentric to the original ones.

Please help.

[Gandalf_Sr]

I figured it out, I needed to set constraints for zero distance between my circle centers and the origin. That got rid of the last 2 constraints.

[r-frank]

Hello.

Please don't use zero length constraints.
They will make the solver slow and maybe lead to a crash ...

The better idea is to set a coincident (or PointonPoint) constraint between the center points of your circles.

Roland

[quick61]

Yes, r-frank is correct, one should not use 0.0 mm distance constraints. Following the general rule that geometrical constraints should be used whenever possible, there is no instance where a 0.0 mm constraint can not be replaced by a geometrical constraint. While in a simple Sketch like you have in your example, using such a constraint would be no big deal, it is just a very bad practice to get into and can lead to real troubles on down the line when your sketches get more complexity to them.

Mark

[Gandalf_Sr]

Thanks guys