Rigidbot Z Wobble Solution

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The Rigidbot is a bit of an older printer by now, but I'm sure there are still a few of them out there. Mine suffered from z axis wobble for a long time, many years, but decided to address it recently. The source of the problem is the manufacturing tolerances and assembly tolerances... hard to get everything perfectly square when you have no adjustment. My X gantry guide rods and lead screw were fighting each other down at the bottom of Z travel. The alignment was off and the aluminum misalignment couplers were having to bend to account for the misalignment and it was pushing the X gantry around in weird ways leading to wobble. You will need to print these parts before hand (I suggest something stronger than PLA), and you will need a rafter's square to check squareness. So here is how to address this. 1. Make sure your frame is square. It might mean disassembly, but do your best to square your frame, this is going to help a lot and give you a good baseline to start and only having to make minimal adjustments later. 2. Next, remove the 3 M3 screws on each of the brass nuts holding the X gantry to your lead screw. 3. Slide the X gantry to the top of the machine and lightly clamp it to the top rails. If your frame is square this is going to give you a good place to start. If it's not, we can make more adjustments later. 4. Loosen the set screws on your aluminum couplers (if you don't have the z axis upgrade motors with built in lead screws). Remove the lead screws. Check for straightness on a flat surface (important!). I used a piece of glass. If you don't have couplers, skip this step but still check for rod straightness! If your lead screws are bent you will not be able to get it right! 5. Remove the four M3 screws holding each Z axis motor to the plastic mount. Then, remove the four M4 screws holding each plastic mount to the frame. 6. Throw away crappy non-adjustable Z motor mount and attach fancy new adjustable z motor mount using the four M4 screws. Do not tighten. Screws should be snug but loose enough to slide the new z mount along the frame rails in the Y direction. 7. Use the four M3 screws to attach each Z motor to the new adjustable mounts. Tighten, but keep loose enough that the motor can slide in the x direction. 8. Install new solid coupler onto z motor shaft, do not tighten. Install lead screw into coupler. Make sure your brass lead screw nut is on the rod and under the X gantry. Once it the lead screw is seated in the new coupler and is poking through the X gantry hole, install M3 screws and lock nuts into the solid coupler and tighten. If you do not have couplers, your rod should already be poking through the X gantry as it is already coupled to the motor inherently. 9. With your hand, run the brass lead screw nut up to the bottom of the X gantry. Don't put it in the place where it seats, leave it ~0.5" from the bottom of the gantry so that it doesn't pull the lead screw into alignment with the gantry hole. 10. Use your hand to slowly spin the z axis lead screw. Use a light touch and spin at the coupler, don't grab the rod. Try not to impart any load on the screw, just spin it and watch the small portion of screw sticking out from the top of the X gantry. If it spins freely and doesn't wobble, great! If its wobbly, sticking in some places, and you feel resistance in some spots and not others then play around a bit with the adjustment in your new mount. Use your rafters square to check the squareness of your lead screw against your X gantry guide rods, and against the X gantry steel bar. This gives you two perpendicular planes of reference on your X gantry. This is what we are trying to align our lead screws to. Once the lead screw is square in both planes to the X gantry, you can spin the rod again and it should be nicely aligned. If it is off a tiny bit, don't worry, it should still be a big improvement. 11. Run the brass lead screw nut up to the seated position of your X gantry. Do not crank on it. It should be seated snug, but don't torque it into place. Your X gantry is already at its max height and you are only going to be imparting a bending load on your lead screw and messing up your measurements on the other axis you are working on. Install the 3 M3 screws that hold the brass nut to the X gantry and tighten. 12.Turn on your printer and use the motors to lower your X gantry about half way. Pay attention to the lead screws, z motor mounts, and your print head. Are they wobbling on the way down? You may have to move it up and down several times to get a good look at everything. If nothing is binding, the loose screws holding the Z steppers and the adjustable mounts to the frame may allow everything to self align. They probably won't though, so if things are wobbling around when the Z height is about half way, then keep moving the gantry up and down and use your hands to move each stepper and adjustable mount to a position where the wobble is eliminated or minimal. With the X gantry at half the z travel, check your lead screw squareness in both planes against your X gantry again. If it is square in both planes you should see very little wobble. 13. Home the Z axis and repeat the above. I find this is the most important area to make sure everything is square because this is the usable area on your printer. Run the x gantry up and down and spend some time making sure the lead screws are square to your x gantry in both planes. 14. Once you are satisfied with the result, tighten down the screws holding the z mounts to the frame, and steppers to the z mounts. 15. Run the X gantry up and down from min to max travel and pay attention to your print head... is it wobbling? Run a test print such as the calibration cube and check your walls... there should be a huge improvement! Additional thoughts: - If your printer is really out of whack and you need to compensate even more, put the aluminum couplers back on. I didn't want to use them as I saw them as a crutch to getting my alignment right. They can compensate a bit for angular and parallelism alignment issues, but I'd rather try and actually have it aligned than to rely on something trying to bend into alignment. - If those fail, look into old ham couplers. I think they would put less stress on the X gantry and slide about nicely to compensate for some misalignment. - I also toyed with the idea of mounting my Z axis upside down... You would have to disassemble the frame and swap your frame rails at the top for the ones with the z mounts. Or just drill and tap new holes for the z mounts into the top bars, but you may not be able to do it with enough precision. The idea behind this is that the design of the printer mounts the lead screw with one end fixed and one end free... When the lead screw nut is at the free end, the coupler only has to deflect a small amount to account for angular misalignment and the X gantry won't have to fight with it which creates minimal wobble. Unfortunately, the free end is at the top of the z travel where you rarely use the printer. By flipping the z motors upside down, now your free ends are near the print bed where you typically spend most of your print time. I didn't try this, but in my head it makes sense ¯\_(ツ)_/¯ Hope this helps!

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