Sizing a stepper motor for Z and three drive shafts.

Simspeed

I see that you have the motors under the screws and it looks like the motors will be taking the full weight of the bed? Difficult to tell from the pics. If so, then my concern is that steppers don't generally have thrust bearings and aren't usually designed with the spindles to be loaded in that manner. If you have some sort of thrust bearing under the screws or if the motors you plan on using have thrust bearings (which is unusual) then it's not an issue.
Ian

Thanks for your comments Ian. The bottom plate for each C-Beam upright has a bearing pocket that supports the shaft assembly. The shaft itself has a locking collar that bears the weight of the assembly (XY carriage proportionally) on the bearing housing. The bearings are not radial thrust bearings; just std. shaft bearing Openbuilds offers. The motor shafts and bearings bear no weight so we're comfortable with that part of the design. The top of the shafts are free floating inside the top plate which has an oversize hole surrounding the shaft penetration. If the OB bearings prove to be a problem I'll have to replace them with some form of thrust or tapered bearing to support the XY carriage weight.

I believe I am really going to like the flexibility of independent motors for the four Z screws when dc42 finalizes firmware to control them. It is an added cost, but in my application being able to level the carriage to the fixed bed is more desirable than the alternative. I don't like to spend unnecessarily, because like most of us my resources are limited, but at the beginning of the project (its gone through several iterations now), I decided the design would take precedence using least expensive components where available. For example the OB acme lead screws over more expensive ball screws, and nylon wheels over linear guides. I did splurged on C-beam extrusions but they offer a much more rigid structure and enclosed routing of the drive components. The polycarbonate enclosure is another expense but I believe the long term benefits outweigh the costs.

I am experimenting with a less expensive linear guide approach. I test printed nylon guide supports for the Z and Y axis that are encouraging. I ordered IGUS Tribo filament to test in comparison to the nylon sliders and OB wheels. That should be arriving any day now, so I'm excited to see what the outcome of those test will be.

BTW….I very much enjoyed your blog presentations on multi-color printing. Show us some more on your current printer when you get the chance. Thanks...Terry

Simspeed

@dc42:

I would be concerned about that too. You could mount the leadscrews on thrust bearings, then it would be convenient to use 1:2 gearing to drive them from the motors. Or revert to using belt drive. Or perhaps it is possible to find a thrust bearing/leadscrew combo that lets the leadscrew shaft protrude below the bearing, then you could use a flexible coupler to connect it to the stepper motor.

Thanks dc42….see my comments above concerning support of the Z screws. I am looking forward to your finished work on the 4 Z motor firmware. Thanks to you and all the DuetWifi team.