Manual bed level before or after setting z height?

Hi,

I’ve been following the user manual for installing a bltouch/firmware update which has worked fine (testing) so far but I have a couple of questions before setting the z height :

  1. The tip of the bltouch is 1.75mm above (away from the bed) the nozzle tip … I would have put this as a custom mount setting but you state in the instructions this should be zero (as we set the z height later) … Just checking this is correct and that I should set z as zero in the custom mount settings.

  2. Post the BLTouch installation I would like to Manually level the bed (the instructions are not clear to me) - do I set the z height BEFORE attempting the manually level the bed ?. I’m a little nervous if the bed is way out of level that manually levelling in one higher corner (after setting the z height in the centre) will crash the nozzle in the bed

Thanks

Ian

Yes. Contrary to X and Y offsets, exact Z height is not only dependent of the mount but also of the exact model of the BLTouch (they do not have the same size and they do not trigger at the same height). So it is better to start with 0 and set the height with the Z height screen.

This is not really important as the two are not directly related. Usually, you set the offsets of the BLTouch, them do a manual leveling (and redo it from time to time in case the bed moves), then set the Z-height and then an automatic leveling (I recommend to do this before each print as part of the starting g-code sequence).

I do not understand that.

Thanks … “my logic” (not understanding the technical operation of the bltouch levelling) is that if the centre of the bed (where I assume the Bltouch Z height setting is done) is 0.1mm away from the nozzle (once z height adjustment is finished) then if any corner is 0.1mm higher than at centre then I was worried the bed would crash in to this corner of the bed when manually bed levelling. (i.e. the bltouch not be smart enough to realise that the corner was 0.1mm higher than the centre of the bed)

That’s why I was asking if you should manually bed level BEFORE setting the z offset (it does this at the centre of the bed I take it)

As I’ve got a nice New PEI spring steel bed Fitted I don’t want to damage this In the corners by doing something silly.

Thanks

Ian

Yes, it can.

BLTouch is not used during manual leveling (except to home at the center), so even if it is smart, it can’t know where the corners are. With manual leveling, it does not probe corners.

Well as I’ve taken off the z end stop how does it know when to stop when manually levelling if it doesn’t use the bltouch sensor during manual levelling ?

I was thinking of setting the z height in the centre as normal post bltouch and then unlocking the motors and just moving manually the nozzle ( hopefully still 0.1mm above centre) to each corner just to hopefully make sure it wouldn’t slam in to the bed on manually levelling in the corners.

I haven’t used the firmware yet (still got to hot glue in the connectors now it’s tested) so maybe this is possible ?

This does not change anything. The BLTouch when homing has the same role than the Z endstop. Previously, without the BLTouch, you have exactly the same problem: if the endstop is not at the right height or if the bed is not level, you will touch the bed somewhere and scratch it potentially.

Yes, you can.

Thanks a lot I’ll give this a punt later

Hi, some feedback on the process I ended up adopting :

  1. I set the z height at the centre of the bed with no problem.

  2. I threw caution to the wind and went for auto bed levelling and to my pleasant surprise just as when setting the z height the nozzle remains the circa 2-3mm or so above the bed at each levelling point. (My bed was pretty level to start with)

It would be quite useful to note this in your manual as it takes the anxiety (nozzle crashing in to the bed) out of going straight for autobed levelling after setting the z height.

Although it wasn’t a problem for me it’s probably worth advising to check before that the x gantry is parallel to the bed (using a mini spirit level) because then you could easily see a bed so far out of level it would cause nozzle crash problems on autobed levelling.

Very impressed with the speed of autobed levelling

Thanks for a great effort (a couple of small questions I’ll post separately)