It depends on how comfortable you are hacking the firmware (to enable dual extruders & thermistors, but without setting the Z_HOME_DIR to downwards). You can make the spider home upwards still -- and it works well for the v4. You get it close enough with the bumpscrew then release & re-clamp the hotends to set them level. Do this after the bed itself is leveled.
Here's some commands I'd use in your case to manually level the bed. If you think of the 4 levelling screws as 1->4 clockwise from 0,0 (so front-left is 1, back-left is 2, etc), loosen the lockscrews and all the leveling screws as far as they go except #1. This should put an obvious tilt on the bed. Without the second hotend installed, do a manual bed leveling:
Repeat the "G28 Z0" command while adjusting the endstop screw until the hotend is good enough, then slide a piece of printer paper under it and loosen the clamp to let it drop to the bed. It should not be a big change -- 1mm or so at the most. Tighten the clamp and don't loosen it again for the remainder of the process. Screw #1 is now set.
Tighten screw #2 until the hotend passes the paper-drag test.
Tighten screw #3 until the hotend passes the paper-drag test.
Tighten screw #4 until the hotend passes the paper-drag test.
Code: Select all
G28 X0 Y0
G1 X103 Y125
This code will lower the bed most of the way down, kill all motors, home X & Y, move them to the middle of the bed, disable the motors again, then pull Z to the top. From here, you can push the bed and X carriage around by hand to hit the 4 corners again and tweak the final distance on the screws. Never change screw #1 or loosen the hotend while doing this. After you pass the paper test on all 4 corners, tighten the lockscrews.
Install the second hotend, push it up into the holder, clamp it down.
Slide a piece of paper under the hotends, loosen both screws so they drop onto the paper, tighten both screws up. Done! The process will take like ... 4 minutes.