[Arm-netbook] lian dong san wei 3d printer

[Luke Kenneth Casson Leighton]

http://rhombus-tech.net/3d_printers/lian_dong_san_wei/

starting some build instructions and also noting which parts are
missing, what improvements can be made.  so far i have the entire
frame done and it's reaasonably stable but not as rigid as i was
expecting: that's going to be down to the use of "interior" L-shaped
brackets that go *inside* the 20x20 runners, as opposed to the use of
triangular corner-braces which i know would make the entire thing as
stiff as a... stiff thing.

i've only made one assembly mistake, which is on the x-axis: the
hot-end holder with the linear bearings in it is upside-down, which
results in the belt being subtly shifted upwards by about 4mm.. out of
true.  that means that the belt is pointing at weird angles, being
slackest when the print head is in the centre and under high tension
*and a different length* at the edges.  arse.  it means a full
disassembly of the z-axes *and* the x-asis sub-assemblies, and
recalibration.  arse.

also... *sigh*... there are certain design decisions made by chris
palmer (creator of the mendel90) which, when you look at other
reprap-style 3d printers you just... smack your head in dismay.

josef prusa, who is unfortunately worshipped for being one of the
first to actually sell 3d printers, is not someone who can be said to
actually be capable of sound engineering judgement, and this printer
is unfortunately "inspired" by his efforts... and therefore has
*vertical* x-axis rods (supporting the print-head).  what that means
is that the weight of the print-head *twists* the rods.  i'm holding
the end of the nozzle and moving it _gently_ around... and it's
wobbling by about TWO millimetres.

soo.... yeah.  this is undergoing a redesign before committing to 10
more.  also i can take the opportunity to reduce the "lever" effect
(the printhead being a long way away from the middle point of the 2
x-axis rods).

l.

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crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68