1+2 Z axis bed levelling.

CNCModeller

Hi All,
I'm converting my Wanhao D4S to Duet 3 mini, and I'd like to add physical bed leveling as the parallelism of my upper and lower print surfaces is important to me.

My thoughts are to use the existing z axis for movement of the z platform with a tripod mount between the platform and the bed.

2 of those mounts would be driven by a small stepper or servo to do fine adjustment to physically level the bed on the platform using the probe.

Is this a realistic approach with RRF3? I get the feeling the multiple z axis approach in the wiki assumes all of the z axes move to cover the full range of motion.

If there is an existing thread on this, a point in the right direction would be great.

Any constructive thoughts would be much appreciated.

All the best
Barry M

dc42

I haven't tested it; but I think you could use M584 to switch the Z axis to the three levelling motors when you run G32 to do true bed levelling, and then switch back to the regular Z motor. See the recently-added note in the description of M584 in the GCodes wiki about disabling the motors concerned before you reassign an axis or extruder.

CNCModeller

Thanks @dc42, I'll have a good read up on the topic.

At least I can look at the hardware side with some confidence that it'll be usable.

Given that approach, would the +2 steppers remain energised to maintain the bed level during a print?

Many thanks for your input.

All the best
Barry M

o_lampe

@cncmodeller said in 1+2 Z axis bed levelling.:

Given that approach, would the +2 steppers remain energised to maintain the bed level during a print?

I'm afraid not...there is a workaround: if you set steps/mm for the big Z-motor to zero, while leveling. It is still energized (if it had moved before).
After leveling you do the same with the tripod motors...
Untested, so use at own risk

CNCModeller

@o_lampe said in 1+2 Z axis bed levelling.:

@cncmodeller said in 1+2 Z axis bed levelling.:

Given that approach, would the +2 steppers remain energised to maintain the bed level during a print?

I'm afraid not...there is a workaround: if you set steps/mm for the big Z-motor to zero, while leveling. It is still energized (if it had moved before).
After leveling you do the same with the tripod motors...
Untested, so use at own risk

I like that approach @o_lampe, so the machine thinks it has 3 full length Z lead screws and motors, but I control which moves when by the steps per mm.

Interesting... Will cogitate and digest.

I feel a cheep and cheerful physical mock-up coming on

CNCModeller

@o_lampe / @dc42 I also thought about just creating my own dedicated leveling macro assuming I can monitor the bed probe during each z axis move. That might open up the opportunity to use servos driven by pwm instead of steppers as I think I'll be out of stepper channels on my Duet 3 mini given what else I want to do.

o_lampe

@cncmodeller
That's a good idea, since the tripod (as I envision it) has it's own non-linear kinematics?
How often will you need these servos? Does your bed misalign so frequently, that it's worth the efford?
My bed rests on three ballscrews and I haven't had to touch their adjustment since day 1.

CNCModeller

@o_lampe said in 1+2 Z axis bed levelling.:

@cncmodeller
That's a good idea, since the tripod (as I envision it) has it's own non-linear kinematics?
How often will you need these servos? Does your bed misalign so frequently, that it's worth the efford?
My bed rests on three ballscrews and I haven't had to touch their adjustment since day 1.

Over time the bed does move as it's just cantilevered from the rails at the back of the printer. It's not much in terms of bed adhesion, it's more about ensuring part parallelism.

https://www.wanhao3dprinter.com/Unboxin/ShowArticle.asp?ArticleID=160

At times I stack and glue several prints to build model aircraft and it adds up.

I didn't want to print a raft as the glass smooth surface is great for gluing.

TBH it's all a mental experiment at the moment. As I rebuild it with my new Duet 3 mini I'm going to make some hardware changes and this is an option on the list.