You are right Sage, leans side to side by about 1/32”. As you can see from the attached pic. your idea was my 1st try but for some reason didn’t work well and I had to remove it. Adding one more angle to make an X with two angles is my next step if I see no improvement but so far she feels solid.

Gerry the sides of the gantry are not MDF but rather 3/4" plywood. I don’t know which one is more resistant to bending but thought that plywood would be better. You idea about the steel angles down the side was one of my 1st thoughts but after careful observation I noticed that its not the sides that are bending but rather the whole gantry assembly leans from side to side and therefore an X bracing looks like to be the answer.

As I mentioned, the machine works very well and the only problem so far is when I cut circles less then 1.5” diameter the circles are not perfect circles. Cutting larger circles, curves and lines there is no problem

Thank you both for your help