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As mentioned in my previous question, I have some bed-levelling issues with my printer. Following the link in @tjb1's answer I figured they were all about to be solved - just follow the steps and bim, bam, flat printing aligned with the plane of the bed. I was wrong. Firmware is Marlin 1.1.0-RC8

From minow.blogspot.com:

For Marlin in Marlin.ino.Marlin.pde

DELTA_RADIUS is DELTA_SMOOTH_ROD_OFFSET - DELTA_EFFECTOR_OFFSET -DELTA_CARRIAGE_OFFSET To correct the problem, the best course is to change one of the variables set earlier to force the value of DELTA_RADIUS to increase(to lower the extruder nozzle) or to decrease (to raise the nozzle).

To lower the extruder nozzle increase DELTA_RADIUS by increasing DELTA_SMOOTH_ROD_OFFSET(Marlin) or PRINTER_RADIUS(Repetier).

To raise the extruder nozzle, decrease DELTA_RADIUS by decreasing DELTA_SMOOTH_ROD_OFFSET(Marlin) or PRINTER_RADIUS(Repetier). For your first cycle, if you are above the build surface, increase DELTA_RADIUS by (about) the same amount. If the extruder nozzle hits the build surface, decrease DELTA_RADIUS.

Next, repeat the ABC tower calibration process. Changing the DELTA_RADIUS changes the tower calibrations, so you must cycle through the process of adjusting the ABC buttons/scripts again. And when the ABC towers are set, test the center D button/script.

You may have to repeat this a few times with smaller changes to DELTA_RADIUS, but eventually, the drag on a piece of paper should be the same at all four locations. Now the printer knows how to print flat at a given Z height.

So I did that. It's about 5-6mm high in the center of the bed. On point in front of the 3 towers. And it stays pretty much there (less than one 'precision' business card movement, if any) when DELTA_SMOOTH_ROD_OFFSET is increased, increased more, or decreased, for that matter - we started wondering if there was a sign error issue and tried the other way.

There is mention on the page of "turning off EEPROM" lest values be over-ridden by those in EEPROM, but the text appears to suggest that it's a Repetier-firmware-specific problem. So I was not expecting to have it in Marlin. Does it also apply to Marlin, or:

TL;DR mode: why would changes that should affect the "DELTA_RADIUS" to get the printer on plane with the bed be ineffective?

delta printer]3

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OK, so a little more poking around finds that it does seem to be loading values from EEPROM and ignoring the configuration files. So that's not Repetier-firmware-specific.

...and I found M665 in G-code which lets me just set a value for it, then M500 saves it to said EEPROM. And it's making a difference (so much of one that I may need to reset Zmax before I can actually adjust it all out as the endpoints on the bed are now off, but they are all 4 much closer to being off by the same amount!)

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    $\begingroup$ I used this post to help me with my own printer, and this is what I found: Adjust the firmware to your needed values and hit M500 before you start moving around the bed. (M500 saves the firmware values to the EPPROM, so you always have the freshest values in there) it took me ~1 hour to calibrate my printer after discovering this. $\endgroup$ – Davik Mar 30 '18 at 17:51

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