My printer is based on the original Rostock design with 8mm rods and linear bearing for the vertical towers. I use belts and pulleys, not spectra line to control the tower carriages. I am using TRAXXAS joints, not magnetic balls or even DuBro joints. And I am not using auto-bed-leveling code. And I REALLY like the way my machine prints.
Auto Bed Leveling
I appreciate the work done to add automatic bed leveling to firmware. As clever as it is, it is not a substitute for good build quality or sloppy fine tuning. A Delta will print best when accurately built and tuned (see my earlier posts). Auto bed leveling should keep a tuned delta printing accurately over time, hopefully isolating the printer from minor misalignment that can happen as it is moved or bumped on the workbench. Auto bed leveling should not, however, be used to compensate for initial firmware tuning. Turn off auto bed leveling when tuning a newly built (or re-built) delta printer, tune, and then turn it on.
I am totally impressed by the visual impact and general rigidity of extrusion based printer. But I haven't had a need to change from my Rostock / 8mm rod based configuration...my printer makes beautiful prints. I carefully chose my linear bearings and rods, and keep after cleaning and lubrication. And because I use belts and pulleys (which have become more available lately!) I have no steps per mm calculation headaches. It seems to me that the original Rostock concept was most in keeping with the Maker ethic and the RepRap focus on minimizing the use of speciality items to keep the result accessible and low cost.
The smoothest, most slop-free delta effector I have made actually used the original Rostock printed U-joints with CF rods. My current printer uses TRAXXAS joints with CF rods, but if I find myself with another opportunity to build or rebuild, I'll seriously consider going back to the original design. Why buy when you can make something as good or better? I appreciate seizing opportunities to create a better mousetrap. But is it really a better mousetrap?
Measurement and tuning
On a delta...here is what matters
- Build it right! Accurate dimensions are far less important than symmetry. The towers must be parallel and equidistant. The six diagonal rods must all be equal in length.
- Turn off EEPROM and auto bed leveling when tuning.
- The only firmware tweaks that are important are steps per mm (which controls general X and Y movement, and Z height), DELTA_RADIUS (which controls "flatness" ) and DELTA_DIAGONAL_ROD (which controls X and Y dimensional accuracy). Set and tune these values in this order.
- I see a lot of conversation about carefully measuring DELTA_SMOOTH_ROD_OFFSET, DELTA_EFFECTOR_OFFSET, and DELTA_CARRIAGE_OFFSET. These only matter when starting to dial in DELTA_RADIUS. Use them as starting information. See #3 above. After all, what matters is that the printer is printing flat and accurately in X,Y, and Z dimensions.
- Tune the firmware so that the printer prints correctly. Tuning firmware to match the (presumed) "as built"measurements of the printer is not the fast-path to a smooth and accurate printer.
- Only turn on EEPROM and auto bed leveling when tuning is complete.