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Pen Holder with BullDog XL Foot Print
A pen holder that fits in the same foot print as the BullDog XL extruder. Calibrate your printer or use it as a drawbot.3D printer parts and enhancements
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This is a pen holder that has the same foot print as the BullDog XL extruder. It allows you to mount a pen on your printer to use it as a drawbot or to calibrate your printer's X and Y axes. The pen, up to 12mm diameter, is secured in the hinged mount by a 6-32 screw. An optional rubber band can help apply downward pressure if the weight of the pen is insufficient. The hinge uses a 6-32 screw also.
This pen holder be used to calibrate your printer's X and Y axes very accurately. First, tape a piece of paper to the print bed. Next, you're going to have the printer draw a square with sides parallel to the X and Y axes. Use as large a square as you can on your printbed- the bigger it is, the better your calibration will be. You can do that by manually moving the extruder carriage via pronterface or other host software, via the encoder/LCD panel if your printer has one, or via a simple gcode file that will do it automatically. Mark the X and Y directions on the paper so you don't get mixed up later. Now measure the length of the lines in the X and Y directions. Use the measured values to correct the steps/mm settings in your firmware. The formula is: new steps/mm = target size / measured size X old steps/mm. After a couple iterations of that process, you should have accurate calibration of the steps/mm in both axes.
Next, check the orthogonality of the X and Y axes. Draw a square using the freshly calibrated steps/mm. Measure the square from diagonal corner to diagonal corner. Did you get the same number? If not, your printer's X and Y axes are not perpendicular to each other. You'll have to figure out how to make the necessary adjustments on your printer depending upon how it is built.
I made a spreadsheet that will calculate the error/offset in the printer axis end positions based on the measurement of the long diagonal of the printed square/rectangle and the length of the sides. You can grab it here: http://mark.rehorst.com/misc/XY_square_error_calculator.ods The spreadsheet tells you how far you have to move one end of either axis to correct the error in X/Y orthogonality.
I printed with Coex3D green ABS, 0.2mm layers, 30% infill, no support material. I used a brim to help keep the corners on the print bed. When assembled, the hinge should move easily, but should not allow the pen to wobble. It will print tight- you may need to use a file or a little sand paper to open it just enough for easy motion without it wobbling.
Materials and methods
- Your favorite filament
- two 6-32 screws, one for the hinge and the other to lock the pen in place.
- a rubber band
- a pen up to 12 mm diameter
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