Setting up the Cartesian Robot
Copied from Tony's blogpost at http://rapmanv3.blogspot.com/2009/05/printing.html and edited a little bit."
If you wish to print accurate parts then the machine must be put together accurately. This is stating the bleedin obvious but it can not be stressed enough. How many for instance have gone round the complete machine with the setting bars and ensured that they fit every position horizontal, vertical and diagonal? Did you tip the machine over and check all the bottom dimensions? The setting bar should slip on the rods easily, without bending or forcing in any way.
If you have taken care during the build and used the setting bars exclusively for every rod spacing and diagonal then the final test on the complete machine will be a relatively quick process, if not then the solution is to start on the bottom frame and get everything right from the ground up. There is no short cut for this. The best advice is use the setting bars for everything during the build, when you finish sub assemblies recheck when its been tightened up and get it perfect before you move on to the next stage.
Clean the 12mm bars! Polish the bars, remove any small rust spots, preservative, paint that may be adhering to the surface. Dress out any marks.
The X carriage
The main area to take care with on this assembly is to fit the bearing clamps correctly. Aim to get the clamp plates parallel with the top plate and then do all the nuts up finger tight only. When all three bearings are set in this way check the X carriage for movement, there should be zero to very slight play. If there is too much play tighten all the nuts a little by hand and retest. The end result is minimal play and the X carriage is very free to run on the bars. If it gets tight at either end then adjust the 12mm clamp plates on the Y Carriage.
The Y carriage
Follow the same guidelines for the Y carriage The belts should be adjusted to remove all slack but not be pulled over tight as this puts unnecessary strain on the motor and bearings. The Y belts should be fitted with the carriage at the front of the machine, ensure both ends are resting on the frame stops when the belts are tight.
The axis should run the full length of the track very easily with no tight spots. Tip: If you are getting holes on the print that are not perfectly round then the belts could be a little slack on that axis.
The Z axis
If a nut cannot be easily run top to bottom of the thread then it may be worth running a die down each rod. It is not uncommon to find debris from the plating process caught up in the thread profile.
Other tips for easy running, assemble the top anti-backlash nut at minimum engagement in the plastic retainer. This will reduce the spring pre load on the anti-backlash mechanism, you could even take a couple of coils off the springs. Check the captive nut at the bottom of the ant-backlash mechanism is fully seated in its recess. Push them fully home with a small set of pliers.
When you install the four rods on the machine, seat the bottom bearing in its housing then run the top nut up under the upper bearing and make sure it just locks the bearing in position, hold the top nut and tighten the bottom one against it. The threaded rod should be securely located between top and bottom plates without any vertical play. Check each rod turns freely and fit the belt. Do not over tighten the belt, light finger pressure on the long runs should deflect the belt 10 to 15mm.
Set the table height relative to the Y axis 12mm bars, use a vernier to ensure its as close as possible.
The sprung table can then be fitted and set using the extruder nozzle. To do this run the table up to below the nozzle, set so its just touching in the home corner, now push the extruder round the four corners and adjust the springs so its just touching at every point. You will have to run round a few times to get an accurate setting.
The extruder zero setting
Move the extruder over to the home position and adjust the table as described above, now run down the setting screw on the extruder until you just hear the switch click. Move the extruder away from the corner and give the screw another turn down. This sets the extruder safely above the table. Run the home command and check the height of the nozzle. Continue to make small adjustments to the setting screw until the nozzle is fractionally above the table. Between tests run the head over the table using the manual option on the machine menu.
next continue with Setting up the Extruder