I do a lot of my printing direct-on-base and am passionate about eliminating the flaring aka “elephant’s foot”. I wrote about the topic here (and if you click the first link in that post it takes you to a diagram illustrating the effect).
Tweaking the Z-tuning as Jennifer described (raising the build platform up until it’s “just low enough” for your print to stick) can definitely help. I’ve done extensive tuning on my Form 2 and substantially reduced (but not completely eliminated) the flaring.
Haven’t played with that knob yet on my Form 3. It was only introduced for that printer in a more recent firmware, but really glad to see it there.
If you want to get more exotic… one user applied a black coating onto the surface of his build platform and reported it completely eliminated the problem (presumably by reducing reflections):
There’s also a good suggestion in that thread which Formlabs could explore to improve the situation via software, eg:
Instead of applying the burn-in layer to the entire perimeter, PreForm could offset the perimeter of the first layer inside about 0.3 to 0.5 mm for the primary burn-in time … and then apply less laser power/time to the true perimeter
@Jennifer_K Has that suggestion ever been raised with your engineers?
@Terry_Miller I’d love to buy a coated build platform from you to play with if you ever decide to sell 'em!
Finally, I think I read somewhere the Form 3+ (note the “plus”) tweaked the laser power of the initial layers to also help reduce it. I’d love to hear from a Form 3+ user who’s printing directly on the build platform as to whether that’s true and they notice a difference compared to earlier models.