I have already mentioned the fact that my frame went together
in such a way that the bottom cross rods (front and rear) are not quite parallel
to each other and perpendicular to the longitudinal bottom rods http://julianh72.blogspot.com/2011/08/main-frame-build-and-alignment.html
. Nevertheless, I carried on with the installation of the Z-Axis (in accordance
with Part 8 of the Visual Guide http://garyhodgson.com/reprap/prusa-mendel-visual-instructions/
), hoping everything would sort itself out.
First step is to align the bottom cross rod with the top
cross rods (the X-Axis), and mount the Z-Axis round bars in the Z-Axis Motor Mounts
– no problems here. As recommended in the Visual Guide, I spent a bit of time making sure the round
rods were truly vertical and parallel with each other, and all seemed to go OK.
I then snapped two PLA Bushings onto each Z-Axis round rod.
As I found with the Y-Axis, at first they were quite stiff, but a little bit of
light oil, and moving them up and down the rods 20 or 30 times soon had them
sliding quite freely.
Next step was to glue the pre-assembled X-Axis assembly onto
the PLA bushings. The Visual Guide doesn’t specify the type of glue; I went
with Super Glue, and it seems to be holding fine so far. After making sure everything
seemed to be well and truly aligned, I left the machine overnight to let the
glue dry properly. The next night, I removed the temporary support from the
X-Axis, and tried moving the assembly up and down the Z-Rods (being careful to
keep the X-Axis assembly horizontal, to avoid “binding” of the PLA bushes
against the smooth rods) – it slides quite smoothly – great!
I found that I had to ream the Z-Screw Rod Couplers to get them
to fit easily on the motor shafts and the M8 threaded rods. I don’t know if
this is typical or not, but a quick pass with a 5 mm drill bit on the motor end
and an 8 mm drill bit on the threaded rod end got them clean enough to fit
snugly onto both shafts.
Next step was to install M8 nuts into the bottom of the
X-Axis Idler Mount and Motor Mount, as well as the “optional” spring and second
M8 nut in the top of the two mounts. I very soon found that the springs that were
supplied with my kit are too small in diameter to fit over M8 threaded rods, so
in my case, the “optional” springs had no option but to be omitted.
I installed
the upper M8 nuts anyway – not sure yet whether this was a good move or not.
This was all a bit fiddly until I managed to get the M8 threaded Z-Rods into place,
so that the M8 nuts could all be held in place by the threaded rods.
Next came the installation of the two Z-Axis motors. The
Visual Guide says it is optional to install locating screws for these two
motors, citing issues with “binding” of the Z-Axis motion if the whole system
is not perfectly aligned. Quite frankly, the whole idea of NOT fixing the
motors in place appals my engineering instincts, but the motors are a very snug
fit in their RP’ed mounts, and I figure I can always install the screws later,
so for now, I have left the Z-Axis Motor mounting screws out.
The motor /
screw-rod couplers go on next – no problems here because of my earlier job of
reaming them out a bit to fit nicely.
I then wind the two threaded rods up until they engage fully
in the couplers (leaving a gap of a few mm between the bottom end of the motor
shaft and the top end of the threaded rods, to allow the couplers to “flex” to
absorb any misalignment), and tighten all of the screws on the couplers.
After checking that everything seems to be straight and
true, I put a spirit level on the X-Axis assembly, and wind one of the Z-Axis threaded
rods to level the assembly. I then very carefully wind BOTH Z-Axis rods together
to see how the whole Z-Axis motion travels. To my delight (and I must admit, some
surprise!), the X-Axis assembly moves smoothly (but slowly) from top to bottom
of the Z-Axis.
I don’t want to sound over-confident, but this is all beginning
to look like it might just work!
So … off to bed before the next stage of the assembly – assembling
and installing the X-Carriage.
I left the top nuts out of my X ends completely- this way, if I do something stupid and my printer tries to ram the nozzle through the bed, it ends up just winding the Z nuts out the bottom of the X ends - inconvenient, but a far preferable failure mode to the alternatives.
ReplyDeleteGravity is mostly sufficient to bring my X axis down. When I get rid of my Z belt arrangement it should be ample. On the odd occasion where it gets stuck, I can push it manually back onto the nut, and this never happens during printing because Z only moves up!
Triffid Hunter,
ReplyDeleteThanks for the comments - until I get the electronics sorted out and connected (still waiting for my RAMPS kit), I won't know if / how my machine will work, but I'll bear your comments in mind. Without the springs installed, I don't think the top nuts actually do anything at all, other than perhaps provide a bit more control / restraint to the Z-Axis motion.
(Nice work on the Wooden Mendel, by the way!)