I've got a matrix and have done several 80% frames with it.
The big thing for me was to match the width of the carbide
cutters to the slide rail width. NEXT thing was having a large
new file to deck the frame with. (Waiting for Vinegar to etch
file teeth to re-sharpen them is hard for me.)
Lastly be generous with lubing the carriage. I wasn't and galled
it a little bit. Didn't really stop anything but made it harder to
crank the lead screw.
And finally, you can cut one rail channel at a time to reduce the
load on the carriage. I did that with a couple builds and even
though it took longer, it made me happier due to less things
for me to watch.