A critical operation in terms of getting good work out of the machine is leveling the Visible Robot’s working platform (also called its workbed, or “bed” for short). This should be leveled not in terms of level with the earth (although that might be nice), but with respect to the tools it will use. If the robot is being used as a 3D-printer, for example, the tool we care about is the extruder. In particular, we want the tip of the extruder nozzle to represent the ‘Z-Home’ position. We achieve this by setting the Z-min microswitch to “click” when we are almost touching the bed on all four corners. The distance between the tip of the nozzle and the bed surface is the working height for the first layer of plastic—a height at which the extruder can lay down filament that’s both close enough to widen the first layer so that it easily sticks to the surface during the print, but not so close that it causes the plastic to bulge out parallel to the trace being laid, where it may well then be pulled up off the bed when the extruder comes by for a parallel trace. I use a height of .004” (0.1mm) for work with PLA plastic.
Here’s how to do it.
BTW: This technique should work for any cartesian-style (box-like) 3D-printer having a Z-minimum sensor setting and levelers for each of the four corners. Though the measurements will likely differ.
- Set all leveling dial nuts such that they can be turned to elevate or reduce the height of the platform equally. This means that a nut that is 1/4” (6.35mm) tall will be able to elevate a corner of the platform about 1/8” (3.175mm). Likewise, it will be able to reduce the height 1/8”. Taller nuts—double size—may be easier to achive leveling with.
- Move the extruder tip up and away from the platform using the Manual Control of your control software (e.g., Repetier Host, Cura, etc.). This is so that it won’t crash into the bed if the bed isn’t level along the extruder’s travel.
- Test that your Z-min microswitch is working by raising the extruder, say 40mm above the bed.
a) Press the ‘Home Z” control on your software, while keeping one finger on your power supply switch in order to turn it off should this be needed.
b) With your other hand, manually toggle the microswitch as it descends before it comes close to the bed.
c) On toggling the microswitch, the downward motion should stop. If it doesn’t, and continues to descend, switch off the power supply to stop it. If you had to switch off the power supply, fix what’s wrong with the microswitch circuit. This is usually a bad connection either at the microswitch itself (bad solder joint?) or at the Visible Robot’s control board (e.g., RAMPS, Megatronics, Printrboard, etc.), but could also simply be a bad microswitch.
- If you haven’t tested each of the axes previously, use this same technique to ensure all the microswitches are working. Toggling any microswitch should cause the robot to stop moving in that direction.
- Home the ‘X’ axis. (This control is the little “Home” icon with an “X” in it).
- Home the ‘Y’ axis.
- These last two steps will put the robot at [0, 0, ?] [Xposition, Yposition, Zposition] (if you’ve set the “Home” position to Xminimum and Yminimum).
- Raise or lower the Z axis so that the nozzle tip is about 10mm (0.4”) above the surface of the bed.
- Using the Manual Control of your control software, jog the Z-axis downward in 1mm increments until you can see just a tiny bit of space between the tip and the surface or until it is stopped because the microswitch was triggered.
- If the tip would touch the bed before the Z-readout of the controlling software indicates 0.00, you’ll need to lower the microswitch in order to raise the nozzle. One complete turn (360deg.) will move the microswitch 0.5mm. (This is the pitch measurement of the M3—3mm—screw that’s used for the Zmin adjustment).
a) First, raise the Z-axis so that the microswitch is completely open (Normally Open, or ‘NO’). 10mm should do it.
b) Turn the Zmin adjustment screw (it sits beside the Z-axis motor) counter-clockwise (CCW). This allows the spring to push the Zmin microswitch downward.
- On the other hand, if the microswitch was triggered before the nozzle came close to the bed as you performed Step #9:
a) Raise the Z-axis to allow the microswitch to come to its open position. As noted in Step #10a above, about 10mm is good.
b) Turn the Zmin adjustment screw clockwise (CW) to raise the microswitch—thereby allowing the Z-axis to descend lower before the switch is triggered.
- Use a .1mm or .004” feeler gauge or a piece of printer paper to judge the height of the nozzle above the workbed. If you can just barely feel the gauge or the piece of paper touching both nozzle and bed as you move your gauge back and forth, you’ve set a good working height. (It happens that 20# printer paper is .1mm (.004”) thick). Of course, if you’re planning to set your nozzle to work at a different height, substitute gauge dimensions as needed.
- If the distance between the nozzle tip and bed isn’t quite right yet, go back to Steps #8 to #12 until it’s correct. Remember that proper leveling is a real key to getting good prints. Take the time to get it right and you’ll save a lot of frustration that comes with botched prints.
- From here on, you won’t touch the Zmin adjustment screw unless you exceed the limits of what the leveling dial nuts allow. Instead, you’ll be using the Visible Robot’s leveling dials. These rotate a nut around a ¼-20 bolt (¼ inch diameter, with 20 threads-per-inch (TPI)) to change the height at each corner. Twenty threads per inch yields a thread pitch—the linear distance gained in one revolution—of 0.05”. So, for every revolution of the leveling dial the height will change by 0.05”, or 1.27mm.
If you think of the leveling dial as a clock, moving the dial from twelve o’clock to one o’clock will change the height of the bed -0.1mm. Moving it from twelve o’clock to eleven o’clock will raise it 0.1mm.
- Raise the Z-axis by 10mm. Then move it to one of the other corners.
- Repeat the steps #9 to #13, but instead of using the Zmin adjustment screw, change the height of the bed with the leveling dial for that corner.
- Raise the Z-axis by 10mm. Go to a third corner that’s not been leveled.
- Repeat Steps #9 to #13, again using the leveling dials. Then go to Step #19
- Raise the Z-axis by 10mm. Go to the last corner.
- Repeat Steps #9 to #13, as before, using the leveling dials to set the height.
You’re DONE. Treat yourself to an ice cream sundae—or a banana split if you’re really hungry.