Z lead screw bottom support for new build

Hi,

I'm designing a new printer, and trying to figure out how to mount my z axis. Using a motor on top and an 8mm lead screw secured with an 8mm coupler, so the bottom end will be dangling down. I do plan to install a bearing mount, but I'm wondering if there's a need to actually support the screw from the bottom, since all that's holding it in place is that coupler grub screw? If so, are there any good designs for such a support? Seems like it would need to rotate with the screw, so perhaps something based on a bearing, like a bearing with the hole blocked off?

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anvoice
Hi,

I'm designing a new printer, and trying to figure out how to mount my z axis. Using a motor on top and an 8mm lead screw secured with an 8mm coupler, so the bottom end will be dangling down. I do plan to install a bearing mount, but I'm wondering if there's a need to actually support the screw from the bottom, since all that's holding it in place is that coupler grub screw? If so, are there any good designs for such a support? Seems like it would need to rotate with the screw, so perhaps something based on a bearing, like a bearing with the hole blocked off?

You could try something like Flanged self centering bearing They also have 2 grub screws to secure the rod and you could always put a piece of metal under it as well.

HTH Doug

Thanks, that seems very usable.

As far as the piece of metal goes, wouldn't it impede rotation if the metal can't rotate with the screw? That's why I thought about something like a piece of metal actually attached to the center portion of a bearing, so that it could spin, but I doubt I could make something like that unless premade ones are sold.

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anvoice
Thanks, that seems very usable.

As far as the piece of metal goes, wouldn't it impede rotation if the metal can't rotate with the screw? That's why I thought about something like a piece of metal actually attached to the center portion of a bearing, so that it could spin, but I doubt I could make something like that unless premade ones are sold.

You could put that pieces of metal on a thrust bearing Something like this that would work in fact you wouldn't need the piece of metal just make sur the end of your rod is flat or maybe even have the end turned down to fit the centre of the bearing (or put a cone point on the end of it).

Doug

Having a free end on your Z-axis lead screw is OK,
anything else may constrain it too much.

The lead nut -- attached to the table or Z-lift
should be a zero-backlash nut

The SolidDoodle, DaVinci, Ordbot 3D printers use un-constrained z-axis leadscrew

[tinyworkshop.org]

Will there be guides on Z-Axis to provide for precision non -rotating lift?

A flexible coupling should be used between stepper motor and leadscrew

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dougal1957
You could put that pieces of metal on a thrust bearing Something like this that would work in fact you wouldn't need the piece of metal just make sur the end of your rod is flat or maybe even have the end turned down to fit the centre of the bearing (or put a cone point on the end of it).
Doug

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cozmicray
Having a free end on your Z-axis lead screw is OK,
anything else may constrain it too much.

I'm thinking of placing the z motors on top of my frame: I hoped that would minimize possible bending of the screws. However that would leave the entire weight of the screws and the bed supported by entirely by the coupler's grub screws, so I thought of a support on the bottom. If there are significant flaws to this design decision, please feel free to critique.

Having the ends turned to fit a 6mm bearing sounds like a good idea, but I'd have to search for a metal shop that's willing to do this small a job and doesn't overcharge for it.

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cozmicray
The lead nut -- attached to the table or Z-lift
should be a zero-backlash nut

So basically an anti-backlash nut for the z axis? I thought those weren't necessary there since gravity would help eliminate backlash, normally anti-backlash is recommended for X and Y axis...

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cozmicray
The SolidDoodle, DaVinci, Ordbot 3D printers use un-constrained z-axis leadscrew

Yep, from what I can see they have motors on the bottom.

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cozmicray
Will there be guides on Z-Axis to provide for precision non -rotating lift?

I plan to have wheels on the stage that will travel up on the V-slot frame, which people claim provides an excellent linear guide.

Edited 2 time(s). Last edit at 11/15/2014 08:59PM by anvoice.

Here's a rough design of the core version of the printer. As you can see the Z-motors are on top so I'm worried about supporting their weight and that of the print bed with just the coupler grub screws. Seems like there needs to be a support at the bottom.



Edited 1 time(s). Last edit at 11/17/2014 06:05PM by anvoice.

Two Z- drives on one side Why?
Screw has large mechanical advantage
one will easily lift table

Your design
Huge cantalevered bed

Why not put Z-screws on opposite sides of bed?
Where are guides going to be?

Look at Core XY !

[www.corexy.com]

The one in the corner is a Y-axis motor. I do have 2 total Z-axis motors though as that seems standard even for smaller sized printers. As I mentioned my worry is that the couplers alone won't hold the weight of the bed.

It's a rough design, so I don't have all parts shown. I plan to have wheels on the side of the bed opposite the Z-screws: these will prevent the bed from putting torque on the nuts, and also serve as linear guides. They will ride up the V-slot extrusion. That's the reason the bed extends all the way to the opposite corners.

I do have screws on opposite sides of the bed, at least I'd call those opposite sides (2 corners on the same edge) unless you mean diagonally across which I've never seen before. The V-slot frame will be the guide for all axes.

I do like the core XY design, but I'm not sure it's directly applicable to my Cartesian lead screw machine. May try core XY in the future, but I'd like to try out the screws to see if they offer any advantage.

Jo Prusa is right with it's i3 Z conception. You don't need to maintain the leadscrew ont it's end until you don't reach the critical speed, start point when the screw stars to wobble.

---

Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

A printer like the Ordbot Hadron and others
[www.buildlog.net]

have two leadscrews on Z axis for even lift of gantry

RAMPS easily runs two motors on one driver

Coupler anchored into motor shaft by two screws
perhaps with cones into shaft
and two screws into leadscrew flats
Should support a ton without coming apart?

Constraining the leadscrew will give you problems

Constrained at coupler, drive nut, and bottom support,
without precise alignment -- binding

Float the bottom support (allow it to move around in X, Y)

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Zavashier
Jo Prusa is right with it's i3 Z conception. You don't need to maintain the leadscrew ont it's end until you don't reach the critical speed, start point when the screw stars to wobble.

ca_7802_127169943588174200_norm.jpg

I know about the theory behind the critical speed. I'm saying my motors are on top of the printer, so the only thing supporting the Z screws and the bed from falling down are the couplers. Thus, I thought I may need some kind of support on the bottom of the screws, since the weight of the bed, especially with large amounts of plastic on it, may be too much for the couplers.

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cozmicray
A printer like the Ordbot Hadron and others
[www.buildlog.net]

Coupler anchored into motor shaft by two screws
perhaps with cones into shaft
and two screws into leadscrew flats
Should support a ton without coming apart?

Constraining the leadscrew will give you problems

Constrained at coupler, drive nut, and bottom support,
without precise alignment -- binding

Float the bottom support (allow it to move around in X, Y)

That's a good suggestion. The biggest problem is I don't have extensive machining capabilities, so I can't easily modify the screw: even giving it flats will likely be a challenge.

I think I'll see I can drill some small holes into the screw for the coupler grubs, and perhaps glue a piece of metal to a bearing and use that as a bottom support. It'd basically be a rotating support that doesn't constrain the screw while taking some of the stress of the grub screws on top.