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Effects of gravity on FDM/FFF on overhangs, bridges and cantilevers

Posted by ErikDeBruijn 
Effects of gravity on FDM/FFF on overhangs, bridges and cantilevers
September 01, 2009 02:07AM
We all have our mental models of what would happen when you produce an object with overhangs without supports. If we explain it to people, we often say, material that's not supported, will fall down. This is not accurate. The effects of gravity are mostly insignificant. Some time ago, I'd tilted my RepRap less than 30 degrees, but I saw no real difference in the fabrication of a horizontal hole in a structure. I didn't want to put the entire machine on it's side or upside down. Luckily for us, NASA has done exactly that, and as a bonus also did many Zero-G tests!

We can probably learn a lot from this. It clearly illustrates that surface tension is a much stronger force when compared to gravity, at least at this small scale.

Of course, since we don't have a heated build chamber, it possible to let a thread of extrudate to solidify more quickly if we stretch it enough (high surface to volume ratio).

If at some point we would deviate from a layer-by-layer construction method, this would allow us to print on the side of an object after printing a main column. We can then have unlimited overhangs etc. The down side is that the complexity of the process increases a lot. Similar to CNC milling, design possibilities will start to depend on what the toolhead can reach.


Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]
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