Scaling on X axis changes XY axis angles

Change basic cube to a board shape, Z=.1, X=8, Y=.4. Edit mode; grab back left 2 vertices along X axis for a 60 degree angle on the left side of the board. Select all vertices, and do Mesh - Symmetrize - -X to +X. Now the other side looks great, too. Duplicate object. Scale smaller only on the X axis. Results is the 60 degree angle is now less than 60 degrees.

Why? Why didn't it make a shorter board with 60 degree angles on each end? Why did it not scale the back vertices the same distance as the front vertices? Is there a way to make it scale both the back and front vertices at the same time the same distance along the X, (or any), axis?

I tried "Delta Scaling" and got the same results. It seems to apply a percentage of distance, instead of the exact distances I provide it, thus distorting the shape.In other words, (and using different figures ... not the ones above), a 1 meter box with the front left at 1 meter, but the back changed to .8 meters, when scaled from 1 meter to .8 meters will take 20% off the length of the front, and 20% off the length of the back, instead of taking .2 meters off of both, as expected.

These angles don't change when the entire object is scaled, (vs. just one axis), using the Scale command, but it does when entering the exact values into the Transform tab, where one axis at a time has to be entered. Why would it do it differently for a single axis?

EDIT

It was wrong of me to expect someone to build this to see what I mean, so I made some screen shots:

• Scale will change the angle of angled edges when scaling by 1 axis, that's what scale is. If you scale by all axes at once obviously object won't be changed but not if by only 1. It's the same as if you select one of those angled edges and scale it by X axis. Oct 18, 2019 at 22:49
• Seems to state what I showed. I guess the question I meant to ask is more about how to get around this "feature" without having to take each object into edit mode after scaling. Oct 23, 2019 at 0:48
• Workaround is to use Hook modifier and hook each face to new empty, then scale empties. blender.stackexchange.com/questions/63906/…. If working with geometry grabbing those faces is the tool to work with, not scale. Another one could be Edge Slide with limits turned off (select face, press G twice and hold Alt, at least those were shortcuts in 2.79) Oct 25, 2019 at 20:16
• Thank you. I will try that. I noticed one comment on that link about it being a tedious process. What I've had to do instead is a tedious process. This one you point me to looks smoother and more accurate, so, tedious or not, that alone is worth it. Um, but it'll be awhile before I can try it. Halloween stuff is tying up my Blender right now. Oct 29, 2019 at 22:56