How to Reduce Height Shrinkage?

[eric-lester 1]

I was wondering if someone could give some advice on how to decrease what I call "height shrinkage," that is, where the base of the print ends up being larger than the top of it. For example, I was printing a short ring with no buildplate adhesion out of PLA with a heated bed. The piece was about two inches across and a quarter of an inch high and is basically just a cylinder with letters across it. When I took it off the plate, I noticed that the top was clearly smaller around than the bottom! (In this case, only by about 1/16'' so it probably won't matter all that much.)

I looked the issue up and saw it called "elephant foot," but the reasons offered seemed weak. I can only guess that this occurs because the heated plate results in uneven cooling for the rest of the print. Regardless, any tips? Thanks!

[geert_2 557]

In my experience, there are two main causes:

1) For good bed adhesion, the first layer needs to be squished hard agains the glass plate. This tends to spread that layer out a bit, thus widening it. Solution: calibrate the build plate for a higher gap between nozzle and first layer, so that the first layer isn't squished so hard.

2) The heated build plate makes the bottom layers melt and sag a little bit, since the optimal build plate temp is around the glass transition temp of the material (= the temp at which it begins to get weak). Solution: use a lower build plate temp.

Both solutions give a far worse adhesion of the model to the build plate. So I usually prefer a little bit of elephant feet, rather than bad adhesion, especially for difficult to print models.