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Why does the Ender 3 only have 3 limit switches instead of 6?

How does it handle crashes on other sides? Is it worth adding them with a new mainboard?

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You only need 3 switches to determine/fix the position of the carriage (carrying the hotend) with respect to the printer frame (for X, Y and Z i.e. 3 dimensions). Firmware setup, by defining the offset and the traveling distance on each axis, determines the minimum and maximum displacement. By default the printer carriage will not go outside the boundaries and will not damage anything. That is sufficient for most printers, but, for those printers that have weak steppers and printers that produce prints that suffer from layer shifting, the coordinate system might be messed up, and the carriage may travel outside the initial boundaries, this can damage your printer, using maximum endstops will prevent the printer from destroying itself.

Why use only 3 switches? The reason for this could also be related to costs, you need half the amount of switches, cables and a less extended printer controller board.


I've had one printer setup with max limit switches, but they never got triggered (unless self triggered for testing), never had a layer shifting either.

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  • $\begingroup$ max-switches are pretty much overkill - unless your machine prints insane speeds, doesn't know its size before homing or re-homes to the "closest" endstop ever so often to ensure the print is true. $\endgroup$
    – Trish
    Dec 8 '20 at 23:09
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Because it knows the side of the build volume, all it needs to know is one physical location to home from. So knowing {x,y,z} (0,0,0), and knowing x(max) = 230, y(max) = 230, z(max) = 250, and knowing 1 step (x) = 0.001 mm, it can know when to stop before hitting the other side.

Because it knows where 0 is, and because it knows the maximum value, it knows where the other limit is through math.

2-sided limit switches are used on industrial equipment that have open-loop control mechanisms, like a lathe with a DRO, the DRO won't stop the lathe, so you need to hook up a limit switch on the other side to stop the lead screw... You could also have a maximum travel limit switch on a CNC router where if you send the spindle too far, you might break the equipment, or cause injury.

I hope this answered your question, and was also informative on how limit switches are used elsewhere... It's not perfect or exact, but I think it should give you a broad idea...

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