What are the pros/cons of the various Z-Bed solutions?

Hey there,

I'm working on designing a new 3D printer. I've settled on an XY print head and a Z bed, but I'm not sure how I should go about raising and lowering the bed.

I've seen a couple solutions:
MakerBot Replicator - Single Leadscrew with two supporting linear rods
Mendel90, i3 etc - Two Leadscrews each with a supporting linear rod with individual motors (I think I've seen one z-bed implemented this way)
Reprap Darwin - Four Leadscrews with a single motor and pulley

The machine I'm developing is intended to be compact, so I'm looking at the Replicator style z-bed currently because it's cheaper than the other methods I've heard of and it looks a little more appealing. However, I'm sure that it's not such a simple design, supporting the platform so that it remains flat thought the print could be an issue I'd assume.

I've currently got a mendel90, so I get the general gist of the dual leadscrew style's pros and cons.

I'd be interested to hear of any other z-bed solutions out there and what the pros and cons of each method are. Ideally I'm looking for something mechanically simple but accurate and reliable.

One idea I've thought of is similar to the replicator's style but would look like this:

+---------+
|    x    |
|         |
|         |
| o      o|
+---------+

Where the X is the leadscrew and the Os are smooth rods with a printed support to clamp the board. I feel like this might be a good solution but I'm far form certain, would the z-screw's wobble have a more pronounced effect with the smooth rods further away? I don't think it would given they're forming a triangle, but I couldn't be certain.

Thanks for your time.

Edited 2 time(s). Last edit at 01/03/2016 11:06AM by Draghi.

You want the lifting force to be applied close to the bearings, otherwise, the mechanism is liable to bind.

Cantilevering the bed with one screw and two bearings/guide rails all along one side of the bed can be made to work if you're willing to use some high precision/heavy duty hardware.
I think two screws, each with a guide rail/bearing on opposite sides of the bed, probably works fine, without any extraordinary hardware/design effort.
3 screws with 2 or 3 bearings/rails should work.
4 screws are unnecessary and the system will bind very easily.

Whenever you use multiple screws, they should be synchronized at all times, or the bed will tilt or worse, the mechanism will bind. The only way to ensure that multiple screws remain synchronized is to connect them to a single motor with a belt.

I've seen some designs that use 3 screws without any bearings- they rely on the straightness of the screws and precision fit of the nuts to keep the bed fixed laterally. I think this could work if your screws and nuts are high enough quality (precision ground ball screws, maybe), but unless you have them laying around, it is probably too expensive an option.

When cantilevering, I'd avoid end-supported rails in favor of fully supported rails. I'd also use linear guides instead of round rails wherever possible. If using end-supported rails, I'd use the largest diameter rails I could find/afford.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
Cantilevering the bed with one screw and two bearings/guide rails all along one side of the bed can be made to work if you're willing to use some high precision/heavy duty hardware

Ultimaker and other printers are build on this formular. 12mm rods. LMK12UU square flanged bearings and an 8mm lead screw.
Preferebly using an anti-backlash nut as Well.

E3D has a similar design.

I've recently build a fem um2 Clones ans it works fine.
Some sort of rods or guides on the opposite site of the rods and screw would be usefull for a smoother ride in fast moves, which isnt important for printning, but I also suspects it would help with longlevity of the beds' rigidity.

Edited 1 time(s). Last edit at 01/17/2016 04:40PM by dintid.

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Go with a three point setup, using two smooth rods and one lead screw in the middle. The lead screw won't need to be thicker than 8mm, but depending on your bed size you might want up to 16mm smooth rods and bearings. Whatever you do, don't go less than 10mm unless your bed size is less than 200mm x 200mm.

Put all three points in the back, perhaps with the lead screw farther forward.

I'm working on a similar design right now:
[forums.reprap.org]

Im working on a CoreXY 12"x24" printer
with a fixed Build plate and moving Gantry using the Quad Lead Screw setup. and using Vslot to help keep it aligned.
still designing.

this thread is helpful. kinda worried about binding.

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With two motors driving four screws I'd be worried about binding, too. Take an example from all the printers that have two motors lifting the X axis- it isn't reliable. If the motors lose sync, your platform tilts. If it tilts it binds. With microstepping you can't guarantee that the both ends of your platform are going to end up at the same level when you power the machine down. After a couple on-off cycles there's no telling where the thing will end up. Autoleveling can't/won't fix this.

You figured out that at each end of the platform it would be better to have one motor driving two screws. Why does the reasoning that got you there not extend to having one motor drive all 4 screws?

Why four screws?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

1 Motor driving 4 screws, seems ok. but finding a long Gt2 Loop that is over 2000mm is a challenge

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Makerparts.ca
Your Canadian source for V-Slot Extrusion, CNC and 3D Printing Parts and Accessories.
we are proud to be an official Openbuilds distributor.

You could use more than one belt.

Quote
makerparts
1 Motor driving 4 screws, seems ok. but finding a long Gt2 Loop that is over 2000mm is a challenge

RobotDigg deliver belts up to 50m length

---

My Instructables - both total newbie instructables and some for intermediate users.
My Designs on Thingiverse
YouTube channel containing a few 3D printing videos - they are videos for my Instructables, and mostly not standalone.
Ultius / Tantillus Thingiverse Group

Quote
dintid

Quote
makerparts
1 Motor driving 4 screws, seems ok. but finding a long Gt2 Loop that is over 2000mm is a challenge

RobotDigg deliver belts up to 50m length

Yes but they have a min qty of like 100 belts I believe.

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Makerparts.ca
Your Canadian source for V-Slot Extrusion, CNC and 3D Printing Parts and Accessories.
we are proud to be an official Openbuilds distributor.

Quote
stephenrc
You could use more than one belt.

Does that just introduce more slack / tension issues

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Makerparts.ca
Your Canadian source for V-Slot Extrusion, CNC and 3D Printing Parts and Accessories.
we are proud to be an official Openbuilds distributor.

If tension or slack is a problem, consider using a chain drive. Since the Z doesn't move fast, the extra weight of the chain won't affect it.

Quote
makerparts

Quote
dintid

Quote
makerparts
1 Motor driving 4 screws, seems ok. but finding a long Gt2 Loop that is over 2000mm is a challenge

RobotDigg deliver belts up to 50m length

Yes but they have a min qty of like 100 belts I believe.

I often buy single parts as private person. You think about Alibaba

---

My Instructables - both total newbie instructables and some for intermediate users.
My Designs on Thingiverse
YouTube channel containing a few 3D printing videos - they are videos for my Instructables, and mostly not standalone.
Ultius / Tantillus Thingiverse Group

Quote
makerparts
1 Motor driving 4 screws, seems ok. but finding a long Gt2 Loop that is over 2000mm is a challenge

You don't have to use GT2 belt. It isn't critical. I have a 5mm pitch belt (I don't recall the designation) in my printer's Z axis. I bought it from Stock Drive Products (SDP/SI). In fact, if you use a larger pitch belt you may be able to print the pulleys for it.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]