Missing Drive Pulleys!

The kit of RepRapped parts that I ordered from Mendel-Parts didn't include the drive pulleys for the stepper motors for the X,Y & Z motors. This was pointed out on the site as they supplied commercial 3-D printed parts for these, but in my rush to order the parts I missed this important point. This left me in a bit of a hole during the build. I'd waited 6-weeks for the RepRapped parts and I wanted to get building and didn't want to wait for new drive pulleys. 


In the end I found a quick solution, I found a set of XL Series timing belt pulleys at McMaster that did the trick. I needed to drill out the central bore as it was about 0.1mm too small. I also ordered new belts in the XL Series just in case they pulleys didn't mesh with existing belts that I had (which they didn't!).


The pulleys fitted perfectly, however the pulleys have 10 teeth instead of 8, so my first prints ended up being 25% too big in every dimension. This required modifying the firmware on the Gen-6 electronics to calibrate for the bigger drive pulleys.


To do this I built a wooden fixture that fits on to the X-carriage in the extruder mounting holes and holds a pencil. This allowed me to draw directly on to the blue painters tape on the bed so that I could measure the X & Y distances. This test jig has also proven useful for several other calibrations so far. Once I get a chance, I'll probably convert this to a RepRapped version.


For the Z-axis calibration I just measured the distance between the bed and the carriage before and after a fixed move with my calipers, then calculated the delta.


I had to make the following modifications to the configuration.h file:



  #ifdef MCMASTER_10XL_PULLEYS
  // define XYZ parameter of McMaster 10-tooth XL-series pulleys
  // Added by JMB - 29-Oct-2010


    #define X_STEPS_PER_MM   31.484 //31.641   
    #define X_STEPS_PER_INCH (X_STEPS_PER_MM*INCHES_TO_MM) // *RO
    #define INVERT_X_DIR 1
    
    #define Y_STEPS_PER_MM   31.599 //31.394
    #define Y_STEPS_PER_INCH (Y_STEPS_PER_MM*INCHES_TO_MM) // *RO
    #define INVERT_Y_DIR 1
    
    #define Z_STEPS_PER_MM   2689.682
    #define Z_STEPS_PER_INCH (Z_STEPS_PER_MM*INCHES_TO_MM) // *RO
    #define INVERT_Z_DIR 0
    #endif



Test cubes are now printing perfectly square, although circles are slightly oval. I'm not sure if this is to do with belt tightness or if it is the minute difference in the X & Y calibration. Once I've worked out some of the other kinks I'll revisit this.