It looks like there are a lot of reasonably inexpensive DROs out there. X and Y are mass-sensitive, have to move fast, and don't generally need to be super-repeatable when it comes to homing, so limit switches make lots of sense and DROs wouldn't. Z is typically not so mass-sensitive, moves slow, but should be very repeatable for homing, especially with non-sprung beds where a head crash is extra bad. Many DROs preserve absolute position across a power-off, and many of them speak known protocols. I did google and site searches, but I don't see any instances of using a DRO for closed-loop Z absolute position. I would still want a limit switch as a backup, but setting an absolute origin in a DRO and then going straight to the first-layer Z height without dancing on a limit switch feels like it could be a win on a sufficiently stable machine. Just pondering here... Am I missing something obvious? https://reprap.org/forum/read.php?152,835659,835659#msg-835659 Mon, 20 Jul 2026 20:53:33 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?152,835659,835662#msg-835662 https://reprap.org/forum/read.php?152,835659,835662#msg-835662
Springs on bed leveling screws aren't there to protect against head crashes. If they could do that the bed would be bouncing around all the time.

Head crashes aren't a matter of getting a more accurate position sensor. It's about firmware reliability. If the firmware is set up incorrectly or ignores the switch/sensor input, the nozzle is going to crash into the bed whether you use a switch, a hall effect sensor, an opto interruptor, or a DRO.

Better documentation on properly configuring the Z axis would help prevent user errors.]]> the_digital_dentist General New Machines Topics Sat, 06 Oct 2018 14:35:22 -0400 https://reprap.org/forum/read.php?152,835659,835659#msg-835659 https://reprap.org/forum/read.php?152,835659,835659#msg-835659
X and Y are mass-sensitive, have to move fast, and don't generally need to be super-repeatable when it comes to homing, so limit switches make lots of sense and DROs wouldn't.

Z is typically not so mass-sensitive, moves slow, but should be very repeatable for homing, especially with non-sprung beds where a head crash is extra bad.

Many DROs preserve absolute position across a power-off, and many of them speak known protocols.

I did google and site searches, but I don't see any instances of using a DRO for closed-loop Z absolute position. I would still want a limit switch as a backup, but setting an absolute origin in a DRO and then going straight to the first-layer Z height without dancing on a limit switch feels like it could be a win on a sufficiently stable machine.

Just pondering here...

Am I missing something obvious?]]> mcdanlj General New Machines Topics Sat, 06 Oct 2018 13:27:43 -0400