Cartesian Robot Build
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Build
Set-up
If you wish to print accurate parts then the machine must be put together accurately. I know this is stating the bleedin obvious but it can not be stressed enough. How many of you 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 I am afraid 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 axis
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 axis
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 circular features on the print that are not perfectly round then the belts could be a little slack on that axis.
The Z axis
A few people have reported difficulty in assembly of the z drive. The following notes will hopefully give a few hints and tips to achieving a nice free running axis.
Threaded rod.
The threaded rods are easily damaged if care is not taken. To ensure each rod is perfect, take each in turn and check to see if a nut will run easily from top to bottom. If you find the nut snags in a few places then the rod will benefit from running a die down the full length, this will restore the thread form and clean out any debris left over from the plating process. The easiest way to do this is to set the die in the vice and fit each rod in turn into the chuck of a battery powered drill. Use the drill to run the rod through the die and back out again.
The anti backlash assembly relies on the fact that the bottom nut is locked to its holder and is not able to move, the rest of the assembly is designed to push down on the bottom nut to ensure the nut is always running on the top flank of the threadform, thus preventing any backlash.
Misalignment of the bottom nut is one of the primary causes of tightness in the drive. The laser cut for the bottom nut is a tight tolerance and needs to be so in order to stop any rotation of the nut with respect to the table support bracket. Check that the laser cut through the material is perfectly square with the top and bottom surface. It is not uncommon to have to file a little out of the acrylic so the nut is perfectly square. Test the nut is square by running the thread rod through the nut when assembled in the bottom bracket, use a set square and test the thread rod is square to the bottom bracket.
Example of this can be seen here and here
After adjustment if the bottom nut has any rotational movement in the bracket then it will need to be glued in place.
The next stage is to test the fit of the top nut in the top bracket, this can be as free as you like, it only acts as a spring retainer. If it is at all tight then file the hexagonal hole and give it a little room to move about.
Next I am going to deviate from the manual a little and recommend you cut off the top two coils of the anti-backlash spring to reduce its tension when assembled.
Place the spring on the rod and follow it with the top nut, the final assembly should have the top anti-backlash nut at minimum engagement in the plastic retainer.
The last two tips reduce the tension applied to the bottom nut. Even with the modifications detailed here the resulting tension on the bottom nut is more than enough.
Assembly to the machine:
Install the four rods in each corner of the frame, 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.
If you follow these guidelines the drive will run easily
The Table
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.
Setup
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.
