Home to Z max but also probe z min?

[CNCModeller]

Hi,
I'm currently homing to Z min with a bltouch, but want to setup power loss recovery, which will require homing to Z max, as the print will be in the way on restart.

My z min location / probed bed height changes slightly depending on which bed surface I'm using so I can't just use preset values.

Any thoughts on how to best achieve this?

Many thanks
Barry M

[jay_s_uk]

@cncmodeller probe the bed and then measure Z Max using G1 H3.
Then save it as part of the config-override using M500

[CNCModeller]

@jay_s_uk said in Home to Z max but also probe z min?:

@cncmodeller probe the bed and then measure Z Max using G1 H3.
Then save it as part of the config-override using M500

Thanks @jay_s_uk I'll give that a try.

[fcwilt]

@cncmodeller said in Home to Z max but also probe z min?:

@jay_s_uk said in Home to Z max but also probe z min?:

@cncmodeller probe the bed and then measure Z Max using G1 H3.
Then save it as part of the config-override using M500

Thanks @jay_s_uk I'll give that a try.

Do you have an endstop sensor positioned at Z max?

Thanks.

[jay_s_uk]

@fcwilt i do on my ender 3 although I don't use it much.

[CNCModeller]

@fcwilt said in Home to Z max but also probe z min?:

@cncmodeller said in Home to Z max but also probe z min?:

@jay_s_uk said in Home to Z max but also probe z min?:

@cncmodeller probe the bed and then measure Z Max using G1 H3.
Then save it as part of the config-override using M500

Thanks @jay_s_uk I'll give that a try.

Do you have an endstop sensor positioned at Z max?

Thanks.

@fcwilt

I have a movable z max endstop on a magnetic base that I can position just above my max print height. The z axis is 1200mm tall so a full height z zmax move takes a while. Z moves have to be slow to prevent the z axis lead screw from whipping.

Albeit now I have conditional gcode available I could schedule z move homing speed with height above the bed, will look into that

[fcwilt]

@cncmodeller said in Home to Z max but also probe z min?:

Z moves have to be slow to prevent the z axis lead screw from whipping.

I take it that the lead screw is not constrained at the free end?

I have found that constraining the free end works better which is contrary to common advice.

[CNCModeller]

@fcwilt said in Home to Z max but also probe z min?:

@cncmodeller said in Home to Z max but also probe z min?:

Z moves have to be slow to prevent the z axis lead screw from whipping.

I take it that the lead screw is not constrained at the free end?

I have found that constraining the free end works better which is contrary to common advice.

Unfortunately if you constrain the free end your going to get z wobble, especially on a long lead screw like this as they are never perfectly straight.

I had big issues with this on my Wanhao D5s.

[fcwilt]

@cncmodeller said in Home to Z max but also probe z min?:

Unfortunately if you constrain the free end your going to get z wobble, especially on a long lead screw like this as they are never perfectly straight.

As I said what I have found for my printers is that constraint works better but I have kinetic bed mounts which allow for some lateral motion from the lead screws so perhaps that is why it works in my case.

That said my most recent printer was recently converted to 3 Z steppers using belt drive and based on my experience with that printer I believe I will be using that approach for all new printers if applicable.