A brief explanation of why corners of large 100% infill solids lift off the print bed during 3D printing, and my way of solving the problem.
I am printing a model that is essentially half of a box, meaning there is a bottom and 4 walls. The bottom and walls are thick (because it’s not actually a box) for strength and I printed it at 100% infill. When it was printed, the corners lifted during printing, causing the entire model to deform. Sometimes this can cause the entire print to fail.
Why does this happen? The bottom is touching the heated bed, it is hot. The temperature is lower further away from the bed. That means the colder plastic contracts.
The walls didn’t shrink nearly as much, that is because:
- We are printing layer by layer, the walls are not that warm to begin with
- Less material means less capacity for heat
- Less material means less material that can shrink. If the bottom was 100mm and shrunk to 99mm, then a 10mm wall would only shrink to 9.9 , so it is less noticable on a wall
To avoid this, you can simply not large print 100% infill objects. Also, use a brim on the bottom layer, which will hold down the bottom layer better. A funny looking trick is the “Micky Mouse Ears” technique, which puts down a pad on the corner of a model so the corner doesn’t lift.
However, my model was huge and thick and the even a full 20mm brim still couldn’t hold it down. My idea was, instead of using glue to keep the brim down, I make the brim super thick so that it’s stiffness is what is keeping it down. So I came up with this technique, the extra-thick-brim:
The stiffness keeps the first layer down on the bed. The extra-thick-brim is wide on the bottom and narrow on top, which gives it strength while preventing itself from curling. In fact, the triangular shape might even provide a force that is the exact opposite of lifting corners.
The downside is that this obviously uses more plastic and takes more time, plus takes up bed area, and you need to cut away the excess plastic after. But at least you are almost guaranteed a successful print on the first try, so when the situation is right, you are actually saving plastic and time by not having any failures.
To save some time and plastic while still using this method, put the extra-thick-brim around two models, so the weight of one model keeps the second model’s corners down. This saves two lengths worth of extra-thick-brim.
WHy 0.3mm for the bottom? That’s the default bottom layer thickness in the Cura slicer, which works pretty well. Why 0.8mm for the gap? It should be wide enough to avoid Z scarring from joining the outside and inside, and fit a thin knife blade into.
Through a view of the bottom, one can see that there’s still some force threatening the corner to lift, but now it is drastically reduced.