Fixing the elephant's foot (first layer bulge)

I have been adjusting first layer height, z offset, and first layer extrusion width, but I just can't get a first layer that doesn't stick out on the sides.

This is annoying when printing a very large number of small things that are supposed to easily fit together. I would strongly prefer to not have to fix each of potentially thousands of small pieces by hand with a razor blade. (especially considering the whole point of 3d printing is to make things with a computer, not by hand!)

I did the following tests, printing a 50x50x2 test plate. The actual plate measures 49.97 mm wide with calipers, while the foot part is 50.60 mm. Small, but enough to prevent blocks from fitting together nicely.

first layer height / z offset / first layer extrusion width

Test #1: uneven, lumpy elephants foot edge
0.3 / 0.0 / 150%

Test #2: parts didn't stick resulting in defects on the bottom
0.3 / 0.05 / 150%

Test #3: Seems like correct z height now, large noticeable elephant's foot though
0.3 / 0.025 / 150%

Test #4: still noticeable elephants foot
0.3 / 0.025 / 130%

Test #5: Didn't stick to bed
0.3 / 0.025 / 110%

Test #6: Seems closer to desired result, less noticeable foot but still there
0.2 / 0.025 / 150%

Test #7: Looks really good but still has elephant's foot
0.2 / 0.025 / 200%

Test #8: Seems pretty good also but still has elephant's foot
0.2 / 0.05 / 200%

Test #9: Probably the best result, so far I think, with the least amount of elephant's foot, but still noticeable. Unfortunately, after running this test a few more times, it only sticks 1 out of 5 times.
0.2 / 0.025 / 130%

Tests 6, 7, and 9 seem pretty damn close, with test 9 probably being the closest of all. (but has the sticking issue)

What do I do now?

I really wish I could just keep a large first layer extrusion width, but simply shrink the entire dimension of the first layer by a small percentage. (I'm using slic3r)

How do I fix this?

Edited 1 time(s). Last edit at 01/20/2020 06:49PM by foul_owl.

This is a Slicer setting in some slicers...

in PrusaSlicer: Advanced -> elephant foot correction (put something like 0.15->0.35)

I would upgrade to PrusaSlicer....

Hard to make sense of those test results.
Your bed Z offset should be negative. I just mention this as we all assume it is and just write the number. But it would go some way to explaining your issues.
An offset of 0.025 seems very low. The paper test is usually some where between - 0.15 and - 0.25. Don't know how you are measuring 0.025 but that doesn't give much margin for variability with temperature, vibration etc.
If you run more than 100% extrusion its going to flow side ways and print over size. So you want to be at 100% and ensure you have the correct heights set. There is still a risk it wont stick though.

Often i accept an oversize 1 st layer, in fact I use a brim which helps it stick. Then run a file around the print to clean up.