[Flat Six]

Originally Posted by Scott Douglas

When I ran into this problem making some picture frames it was a combination of things that caused it.
Chop saw I was using needed some 'fine' adjustment as I assumed it was good to go 'as is'. My son had used it to cut some angles that weren't standard and I assumed he had returned it to factory specs.

^^This

Originally Posted by Scott Douglas

I also found that I needed to be sure I was measuring things from the same edge every time. In machining speak, a datum edge. Wood isn't always parallel so the edges don't translate from side to side correctly, if you get my drift.
Hope this helps, it's my attempt to answer the question, but, I'm not a wood worker by any stretch and actually, uh, dislike working with wood because it's so hard to hold to a close tolerance. I used to be a machinist and could hold 0.0005" all day long once I got to know the machine I was using.
Good luck, I'm going out the garage to work on my RC truck now.

^^And this