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Can someone tell me how the Z axis limit switch works? Is it just attached to an i/o line or is there some sort of buffering or other circuitry. I want to replace it with an optical sensor which I think will be easier to adjust. Thank you for any information!

 

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google optical z axis ultimaker as I know other people have done it.

UM did some tests and found it to be accurate and repeatable to amazingly small amounts. I think maybe .00001 mm? That seems impossible but I think that was it.

I've never moved mine since the first day. I only move the screws. Besides my bed tends to shift over the course of a few days and it shifts in a strange direction - the front edge droops and the back edge tends to go *up* somehow. But mostly just the front edge droops. So I don't see how an adjustable or more accurate switch will help you.

 

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Thanks, GR5. I don't think it will be more accurate, but I do think I can make it a lot easier and faster to adjust. I want to use my UM for low volume production of a complex part that cannot be easily made by using conventional molds, so I'd like to be able to both level and adjust Z rapidly. I just finished my HB and added 3 position thumbscrew leveling with no springs. I also want to be able to level without mashing the nozzle into the build platform. I've got some ideas on how to do that, using conductive pieces so I can hear a beep when it's level.

 

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I can find several references via Google, but no one that has actually used an optical sensor, and no description of how to interface it. However, in doing the search I came across a thread in the UM forum that discusses commenting out the line referring to "moving Z to min endstops" in the Cura start/end gcode tab. This apparently sets the Z=0 to the current position, which is exactly what I want to do. The Z switch can then just be ignored. It would be nice to use it as a "safety", but if it is too low the machine won't go to 0 and if too high the nozzle would be mashed into the bed before reaching it.

One problem with removing the springs in the leveling mechanism is that there is no "give" if it tries to raise the platform above the nozzle. Perhaps detecting excess current draw in the Z stepper could be used as an emergency cutoff? Something to think about.

 

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Doesn't the lack of springs cause problems during printing if there's any variation in extrusion amount, resulting in possible blobs of plastic that can catch the print head (e.g., on a z-scar)?

 

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I took out my springs back in January and the screws come from below now. I've messed up a few times and scratched the blue tape a little but never anything serious.

I can't print with the UM sideways or upside-down anymore but I can live with that.

 

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Since I just finished the mod and haven't used it yet, I can't answer the question, but I must admit that I hadn't thought of that! The screws come from the bottom into blind pockets in the aluminum heatbed. The pockets are oversized to allow for thermal expansion. When I was printing with the stock plastic bed, blobs appeared from time to time and the nozzle "hopped over" them, so I guess that was the springs allowing it. If I have problems, I can always add some springs.

 

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Hi Mark

I have used an optical sensor previously and Birtho uses one now AFAIK. I stopped using mine due to inconsistent leveling though in hind sight it wasn't the sensor's fault.

A few people, me included are using heavier springs now which makes the platform steadier though you lose a bit of Z height.

As for adjusting your Z height in GCode, which I do, you use the M92 command which instructs the UM where any axis is at.

M92 Z0.1 ;Make Z more negative for a bigger gap

Using this takes out the need to have a Z adjusting screw and it's easy to make an exact adjustment.

 

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