Auto Bed Leveling Questions

Hi, first of all, I'm unsure where to post this topic in firmware or safety or general sections because I concerned about the nozzle and bed safety as well.

I have Geeetech Prusa I3B with sanguino 1.3a board, upgraded the hot end to e3d v6, somewhat 'low-profile' extruder mount design to maximize z height. When all axis are homed the nozzle sits outside of the bed and probably lower or higher than the bed surface.

I am going to upgrade to aluminum bed paired with inductive sensor so I don't have to use bulldog clips anymore (hopefully). However, since my probe will be sitting way past of x min, should be negative position (to the left of nozzle by about 30-50mm I think), there's a risk of my z axis or motor will continue to spin for eternity crashing to the coupler.

My question is, can I use 2 endstop switches, one is the mechanical which is supplied/stock/default z axis and another one is the probe for auto bed leveling sequence wired into single z min port?

Reason being having a default z endstop is to avoid the z axis crashing to the coupler due z probe sits outside of x axis when x axis are homed.

Another question would be, is there any auto bed leveling sequence that I might able to modify, for example, default home sequence, then add another few extra steps?

Thank you in advance
-sarf

Here's how I did this - hope it helps.

[forums.reprap.org]
[forums.reprap.org]

Richard

Not much info I can get, but may I request your prusa i3 setups especially your z axis endstops, your bed leveling and your wired up z axis? I'm assuming you succeeded in wiring them in parallel (both into z-min pins)

Your topic 'endstop question' by far I only know you are attempting to let the printer correct itself when max are hit but no such feature, so you chose to force stop the printer when they're hit instead

Your 'opto leveling with mechanical', I don't really understand how you set up your printer's z axis endstop/probe, so I'm requesting picture for it

I am still wondering though because my probe going to sit outside of the print area when all are homed . So far I haven't get the correct information for this exact scenario yet

By the way, I'm not an electronic kinda guy, that's why I'm asking around for my safety especially

Basically, what happened if the probe and endstops are wired together into a single z-min port, and during the bed leveling procedure, the endstop would be triggered?

From what I have in mind is 2,

1. set the bed higher or the endstop trigger screw lower so that either one of the end stops giving a triggered signal/value
2. put the mechanical endstops to max but this contradicts with auto bed leveling probe

Anyone done this before?

It is exactly what I have done. I used the diagram in the posts above. I set the bed levelling gap larger than the true height. I use the endstop (mechanical) to protect the bed and hotend and the bed-levelling sensor to sense the bed levels and compensate for it. I can still adjust (fine tune) first layer height using the endstop adjustment using a 3mm screw on one of the X-axis ends. Even after adjusting that the height will follow the bed levels as it prints - adjusting the endstop just adjusts the baseline height. It took quite a bit of experimentation (about a day, actually) but it works.

I use the Z-min endstop wired as per my post in the thread above timed at July 13, 2015 02:59PM. My i3 settings are exactly the same as they were prior to doing this - nothing has changed although I did rewire the mechanical endstop switch. I have since changed to Repetier firmware and it, too, worked just fine.

Richard

Edited 1 time(s). Last edit at 07/28/2015 02:41PM by RGN01.

I'm sorry, sometimes I have a hard time understanding . So, basically when all homed your nozzle would sit at outside of the print bed, and much more lower than the bed?

Hi RGN01, are you interested to test this out for me? [forums.reprap.org]

Sorry, I'm not able to test this - I have one printer and it is in almost full time use (when I'm not upgrading it!)

When I home with the Z-home (on Repetier Host) then my nozzle is at the 0.1mm height above the bed. After I have set that I do the 'auto-level' using a script in Repetier and this then measures the bed in three places while the nozzle is about 12mm above the bed. When I print nozzle moves in a plane defined by the 'auto-level' with the Z-home as a baseline (in other words the nozzle moves up and down to compensate for any out of level but uses the Z-home as a starting point).

If, for any reason, I wish to adjust the nozzle gap then I simply adjust the Z-home position as you would on any printer without a 'auto-level' system.

This is all on my Prusa i3 Steel using my own design Z-carriage and auto-level system.

Richard

What if during the bed probing process triggers the mechanical endstop, wouldn't that be the same like not having probe as well?

From your post above, as what I understand probes at 12mm height off the bed to avoid mechanical endstop being triggered rather than by about 2-5mm off the bed?

Seeing your post above, its seems like marlin/repetier firmware uses the parameter defined in the auto bed leveling setting, but contradicts with my first question since after auto bed leveling are done, endstops will be triggered during print, marlin might use it as another new z home value

confused

That is why I have set it up like this. When it Z-probes it is 10 - 12 mm above the mechanical endstop.

The mechanical endstop is not triggered in print - the Z-probe corrections are too small for this. I guess it could happen if your bed had a very low spot that Z-probe tries to compensate for but suspect that you'd be seeing other problems in that case.

Richard

I see, what I had in mind though based on your setup, gonna set the z homed lower than the bed by about 1mm as long as the mechanical switch are not triggered but only sensor does. Somehow this kind of setup can be dangerous though as the head might crash/break the bed if x and y are not homed first to get the bed out of the way of the nozzle during z axis homed.

What a risky way to do it, I wonder if using z-home offset would be helpful though eg z axis sits 5mm lower than the bed, set z offset to -5 to let the z axis sits above the surface at 0mm (endstop not triggered) when auto bed leveling procedure called, it will probe like normal but unsure if the firmware can do something like this though but I got hunch it can since bed leveling is almost similar to z axis homing?