Assembly Assistance for the Printrbot Simple - 3D Printing: Build your Own 3D Printer and Print your own 3D Objects - page 49

Note
What are limit switches? Limit switches will cut power to a motor when
they are triggered, and they're used by the Printrbot Simple to stop the
motors spinning when certain limits are reached. For example, a lim-
it switch attached to the print bed can be used to stop the X-motor
when the print bed moves as far as possible to the right. Later you can
use limit switches to “talk” to the software (see Chapter 5 , “ First Print
with the Simple ”)—this lets the software know when the motors have
reached their maximum safe travel distance, as well as assist in defining
a starting point (called Home) for print jobs. Note that limit switches
were not available to me at the time I assembled my Printrbot, but in-
structions for installing limit switches are now available from Printrbot.
Limit switches are also shipped with all Printrbot kits, so there's really
no reason to not install them.
After you attach the bottom X-axis plate, it's time to add the fishing line used
to move the X-axis print bed left and right. The trick for the X-axis is to get the
line good and tight with three to four wraps around the vinyl tubing. It took me a
couple of tries, but I was able to get it tight enough that moving the plate by hand
would spin the tubing and the motor axle. Get a helper if you need someone to pull
tight on the fishing line while you tighten the bolts. I wish I'd had someone nearby
when I was at this step!
After you're satisfied that the bottom X-axis plate moves smoothly left and right
(and the fishing line stays secure on the vinyl tubing), attach the print bed using
the 3M bolts with the small springs between the top plate (print bed) and the bot-
tom plate. By tightening these four bolts, you'll be able to level the print bed when
you begin testing your printer.
It's critical that the print bed be completely level so that the tip of the hot end that
is extruding hot plastic doesn't scrape against any portion of the wood print bed.
When you're done with the X axis, it's time to tackle the Y axis. The Y-axis steps
are not complicated, but there are a lot of them! The Y-axis assembly starts when
you attach four bearings on one side of a laser-cut wood piece and four bearings
on the other side. (The step number may change, but this should help you know
when you've reached the Y-axis point in the assembly.)