I just did this today. I made a pot holder.
I clipped two 6" X 1" Omnigrid rulers together with small bull clips (if that didn't work for me I planned on using tape.).
My first attempt at using the darning foot wasn't very good so I tried it with a regular straight-stitch foot on my 403A but regardless of how light I set the presser foot pressure I continued to get distortion of the fabric (probably due to the bias grain on certain sides of the triangle). I didn't have a slant zipper foot in my arsenal so I returned to using a darning foot and just decided I'd have to learn how to move the fabric and ruler together to get a good free motion stitch lengths.
It was fun. I'll do it again but make my triangles bigger and use 1/2" rather than 1/4" increments. I found that the quilting was too dense even for a potholder by using 2" triangles and the 1/4" increments.
Thank you for the link yngldy.