Z Bed setup with auto calibration, three leadscrew design

fcwilt

@nemesis said in Z Bed setup with auto calibration, three leadscrew design:

However a leadscrew is definitely not designed to be mounted on only one end and many printer design rely on that.

Two points define a line. So it works fine to have a lead screw setup that way when the bed is mounted using linear guides or the like.

Clearly if you are going to rely on the lead screws as guides then they will have to be mounted at both ends.

Frederick

antlestxp

i believe the m3d micro uses 4 lead screws in its corners as linear guides. im not sure if they are in any way used for bed leveling tho.

Nemesis

@fcwilt It would depend on the rigidity of the bed construction. However it is something that has crossed my mind.

Thnx for the insights. I won't be able to give a definet answer if it works or not until I get all the parts and that will be a couple of weeks at least. I will post back with the results.

From my tests with the short SFU1205 I have concluded it has little to no play so it should work fine. However I am working on a lot of assumptions.

Nemesis

@antlestxp 4 lead screws would be a option. However the issue with 4 points instead of 3 is that it can be a hassle to get it right and can even lead to torsion in the bed.

Also not sure if the duet wifi can do 4 point calibration.

Armatus

I would not try to build this without any other support rods at how large a Z chassis you want. The Z-chassis in my large printer is 34x22", it requires 3x 12mm lead screws and 5x 16mm smooth linear rods to keep the chassis perfectly level/rigid, anything less then this gave issues. You will absolutely run into vibration issues at the top end of your design without more support (I realize my example is much larger then what you're making, but will balance on the same principle). 2/3x 12mm smooth rods and 3x 12mm lead screws would do the job great, larger lead screws are just a waste of money unless you're building something giant. It can be difficult to find drive couplers for 12mm lead screws, I'm actually using nema 23's to drive them rather then standard 17's.

Nemesis

@armatus Thnx for the info. Yeah that is quite a bit larger indeed!

If I'm seeing it correctly you're using trapezoidal 12mm leadscrews. I couldn't find those anywhere. Also the T10 trapezoidal leadscrews I found where quite expensive when factoring in good nuts. The SFU1205 I found was only marginally cheaper then the SFU1605. But yeah it might be overkill.

Yeah the drive couples for 12mm to 5 mm are hard to find.

The machine looks awesome! A nice clean design!

I am still planning to test the 3 SFU1605 setup just to know how well that would work.

If it's good, it's good If not I want to use v slot wheels around all vertical beams in the frame. (so 4 guidance rails)

Another thing I'm pondering is whether to use 2020 or 3030 frame components.

Armatus

Yes 12mm trapezoidal leadscrews, Mcmaster has a great selection of all kinds of lead screws. https://www.mcmaster.com/7549k2
I strongly recommend the longer plastic flange nuts as apposed to the short brass ones.

V-slot wheels around the frame would help a lot, then you could likely get away with 3 lead screws. My experience with larger/longer leadscrews is at least one of the three will be slightly bent, meaning you'll have alignment issues each rotation without a stabilizer of some kind.

fcwilt

@armatus said in Z Bed setup with auto calibration, three leadscrew design:

I would not try to build this without any other support rods at how large a Z chassis you want. The Z-chassis in my large printer is 34x22", it requires 3x 12mm lead screws and 5x 16mm smooth linear rods to keep the chassis perfectly level/rigid, anything less then this gave issues.esized.jpg)

Given that rounds rods flex more than linear guides why did you choose to use them?

Thanks.

Frederick

Nemesis

@armatus To be honest with 16mm hardened steal lead screws I would be surprised if they're bent. But I could just be too much of an optimist

A lot of force is needed to bent 16mm stainless steal rods.

dc42

@nemesis said in Z Bed setup with auto calibration, three leadscrew design:

Also not sure if the duet wifi can do 4 point calibration.

It can, but I don't recommend using 4 leadscrews except for printers with very large beds.

Wyvern

I hate lead screws, if it was possible for my machine I would use belts.

I went through 4 lead screws to find two that were -almost- perfect, the instructions tell you that you attach the rods to the top and bottom using the supplied self-aligning bearings (this is an FT5 R-2 with dual lead screws with a single belt synchronized stepper) Having the lead screw attached in this way makes it almost impossible to remove binding, even then because you are restraining the Z screw from moving around to and fro- causes the bed to wobble- removing the top bearings helped with print quality.

lead screws are fine to be constrained in X-Y axis on say a CNC, this is because the axis only needs to be moderately accurate, but on 3D prints, especially decorative items, even the smallest amount of wobble is noticeable. Increasing the diameter of the lead is a double edged sword, on one hand, it will flex less under the weight of the bed, but on the other any variation of runout and out-of-round would force it's way onto the bed, rather than flex a little and allow the linear guides to resist the force from the leads.

I have almost no Z-wobble, but I have even considered going from dainty 8mm linear rods to 12mm rods to help mitigate this, in fact, I've toyed around with the idea to use 4 linear rails on 2020 extrusions as bed platform guides.

Ball screws are a possibility, but in order to get a quality part, you are paying an ungodly amount of money.

If I was to design a system it would have inverted lead screws, this way gravity pulls down on the bed instead of the lead screws fighting to keep the bed up, this would remove most all flex and would then only have to worry about the quality of the leads themselves.