100 Microns

100 microns ( A.K.A 100 micrometers ) is interesting, it is roughly the length of 100 bacterium sitting next to each other in a line. 100 microns is 0.1mm, think of one millimetre cut into 10 equal pieces. When I first saw this advertised figure as ‘print accuracy’ on a number of different printer sites, my first thought was, I can model using voxels, especially since I have my own voxel engine, who doesn’t nowadays? Now the workable print volume on my particular printer is 210x190x140 cubic millimetres, or 210x10x190x10x140x10 = 5,586,000,000 100 micron cubes , roughly 5.5 billion voxels. My engine can and does cope with this number, I had to optimise my vertex buffers a little and make my shaders take up the slack, but it was ‘doable’.

After a period of feeling rather pleased with myself, I noticed a pulley was slipping on my printer and I realised I needed a replacement. I’d caused this problem by being a bit rubbish at building, I’d filed them too aggressively, to make them easier for me to fit ( live and learn! ) Anyway, when you look into this world of pulleys ( they connect a  stepper motor to a timing belt ) , you soon realise ( or it gets pointed out by someone ) that a substitute ( different configuration – more or less teeth, different diameter etc ) pulley will change the timing of your machine and that an adjustment of the machine’s firmware will be required, i.e Printers need to know how to map actual steps ( rotations ) taken by a stepper motor to mm travelled in the real world. As it turns out, that advertised 100 microns is an upper bound, in reality the figure is much lower  … in my case it was something very tiny like 6 microns of travel per step ( 6 bacterium ) … Nice to know, but it rendered my voxel idea untenable, just think of how much memory would now be required to model this! Be lazy about it and round the 6 microns up to 10 microns, its implies 1000 times more voxels! The 5.5 billion voxels turns into 5.5 trillion! Ouch!

Incidentally, here’s a small trick, since we’re playing with length and volume. Assume your printer software tells you that you need x meters of plastic to print your model, now assume you want to print your model at half its original scale … how much plastic? Think of your unscaled model wrapped in a cube, now imagine that cube cut into 8 equal sizes cubes, each is 1/8th of the original volume and your scaled model fits perfectly into one of them, therefore, to print the smaller version should require roughly, only 1/8th the amount of plastic!

On a closing note, you are more bacteria than you are human cells! That is, we have 10 times more bacteria living on us and in us, than we have actual human cells, sobering thought.

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