Save Time and Filament - Always Preview your Print!

All of the major slicing programs offer some sort of print preview feature, where you can examine the individual layers of the print.  This is a crucial functionality - I can't even count the number of catastrophic errors that I've caught by looking at that preview.  For example, today I downloaded some tree stumps off of thingiverse.  They looked great and would be super easy to print (nice big footprint, no meaningful overhangs, relatively short), so I loaded one up in Slic3r, sliced them, then transferred the gcode to my 3d printer to get things going.

While my printer was heating up, I decided to check out the preview... and a major problem pretty immediately jumped out at me.  Unbeknownst to me, these tree stumps had tiny little protrusions reaching a few fractions of a millimeter downwards.  I didn't notice them when I was looking at the model, but it caused Slic3r to "hover" the bulk of each stump about .2 mm above the printer bed.

So, I stopped the print before I could waste any filament, cut the bottoms off, then sliced it again and went on my merry way.  Here's a couple of screenshots, showing the original stump and my modified one in the preview window.  At the top layer, everything looks great:

Keep going down and everything's still looking good:

But get to the very first layer (which is a very important layer!), and a stark difference becomes apparent:

So, always check your print preview.  Besides doing a sanity check to make sure that I'm getting enough material printed onto the printing bed, I like to "watch the build" as I drag the bar up through the layers.  I'm watching out for material appearing in thin air or growing outwards at too dramatic a rate, or anything like that.  If the print passes this test, then I can be fairly confident that I'm going to have a fairly successful print!

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