YZ design idea.

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YZ design idea.

Postby MartyS » 2015-Oct-Wed-13-Oct

This idea popped into my head for using one threaded rod but still have a gantry with bearings on both sides, and avoid sagging on one side caused if you have the threaded rod off to the side.

Put the motor and threaded rod attached to the gantry in the middle, with the nut the rod screws into on a bar across the top.

Wouldn't want to put all the weight of the gantry on the stepper motor bearings so it will require a washer bolted to the threaded rod with a bearing to take the weight, and the motor attached below this.

Probably too complicated a setup just to avoid using 2 steppers + 2 threaded rods and keeping them in sync, but since the idea popped into my head I've been wondering how it would work?

Some quick and dirty CAD drawings to show the idea:

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Hay anyone seen this tried before?

If I get really bored this winter I might try it.
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YZ design idea.

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Re: YZ design idea.

Postby PxT » 2015-Oct-Wed-14-Oct

The Tantillus uses a similar Z-rod in the middle setup. The bed on that printer moves along Z so the setup is a little different but the idea is the same.
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Re: YZ design idea.

Postby MartyS » 2015-Oct-Wed-14-Oct

I know about those types, but the load (the bed) is not anywhere near the middle of the center of mass. It's between the smooth rods but off to the side of the bed.

Only way to have the Z rod truly in the middle and move the bed would be to have the motor in the middle of the bed and extend through the bottom of the printer, you would need a hole in any table you put the printer on... My other crazy idea was a scissor jack type setup that could lift the X axis and bed up (since my current DIY printer has the X axis built on an independent platform taken from a velleman 8200 kit), but it takes quite a bit of engineering to make one of those jacks and have no play or wobble. Other problem is too much moving mass up high, probably would lead to vibration issues.
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Re: YZ design idea.

Postby RetireeJay » 2015-Oct-Wed-19-Oct

To avoid the motor's screw going down through the middle of your print bed, maybe the motor could be mounted on top of the stationary gantry. But you'd also need to figure a way to make the threaded rod itself move up with the gantry rather than sticking down into the print zone. From your drawing, it looks like maybe you already thought of this. I know there are mechanical arrangements that make this possible, but I'm not sure if they are simple or inexpensive.

What if you used one motor, and Jon Lawrence's double-precision belt arrangement (160 steps per mm)? Then the gantry could be lifted either from the middle, or with two belts it could be lifted from each side, while still using just one motor. With belts, the motor could be almost anywhere: on the base, on the moving gantry, or on a crossbar above the gantry. The upper locations would lead to belt paths that are shorter and simpler.
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Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
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E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
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Re: YZ design idea.

Postby MartyS » 2015-Oct-Thu-11-Oct

RetireeJay wrote:To avoid the motor's screw going down through the middle of your print bed, maybe the motor could be mounted on top of the stationary gantry. But you'd also need to figure a way to make the threaded rod itself move up with the gantry rather than sticking down into the print zone. From your drawing, it looks like maybe you already thought of this. I know there are mechanical arrangements that make this possible, but I'm not sure if they are simple or inexpensive.



Only way to have the motor at the top would be to bolt the threaded rod to the gantry and build a system that would turn the nut, it would be hard to build something like that free of backlash...

Well, I suppose you could still use direct drive with the motor at the top of the threaded rod, but the motor would need to be attached to a second smaller gantry to stop it from rotating, when YZ was at the top the motor would be way up there....

What if you used one motor, and Jon Lawrence's double-precision belt arrangement (160 steps per mm)? Then the gantry could be lifted either from the middle, or with two belts it could be lifted from each side, while still using just one motor. With belts, the motor could be almost anywhere: on the base, on the moving gantry, or on a crossbar above the gantry. The upper locations would lead to belt paths that are shorter and simpler.


I thought about that a long time ago, had it all worked out, thought maybe steel wire under high tension would prevent play (would be bad to have Z bouncing on layer changes), 2 pulleys on the motor shaft and 2 wires, would require a lot of pulleys, and it seemed like it would be quite hard to maintain good tension and keep the gantry level...

So, doesn't seem like anyone has tried putting the Z motor in the middle of the Y gantry and screwing the Z threaded rod into a nut at the top... Might be all the more reason to try it someday, to have a unique design.
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Re: YZ design idea.

Postby orangefurball » 2015-Oct-Thu-17-Oct

This looks like an interesting idea. I was actually planning on making a "bridge" for my Jonbot Plus that would connect both vertical pairs of rods and also allow extruders mounting and filament spool holding, maybe I can add a quick Z Nut spot to this as well.

The only issue I see is the use of more material to connect the two Z carriages. But if it saves money on a motor, extra screw, extra Nut, and extra coupler it may be worth some extra plastic to find the mount point for the Z motor.
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Re: YZ design idea.

Postby MartyS » 2015-Oct-Fri-10-Oct

orangefurball wrote:The only issue I see is the use of more material to connect the two Z carriages.


I have a bunch of the extruded aluminum channel framing from the cheap velleman kit I got, that would be the backbone of the Y gantry if I do this someday. Of course I'd have to take apart my current setup using those parts, it's printing well so I'd have to get really bored to rebuild it again.

Still can't believe I got that kit for just over $200, it still see that old 8200 kit for sale for over $500 just about everywhere, Microcenter must have really got sick of having that last one sitting on their shelf.
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