move z axis using driveshaft & printed worm gears

would there be any disadvantage to using a driveshaft, driven by a stepper, with worm gears on the ends that would mesh with the gears on the end of the z threaded rods? Any advantage?

it's just a concept i'm thinking of.
advantages:
no z belt, yet only one motor
threaded rod is cheap
no belt skipping
printable worm gears
possibility to use high gear ratios for more torque/accuracy

disadvantages:
would need a couple more 608 bearings, at least
possibly harder to adjust each rod independently
no belt skipping BUT if there is binding and not enough power, the stepper will skip steps
more, possibly difficult, gears to print

You don't want to gear it down more because the threaded rod is slow enough already. A better idea would be some 1:1 printed bevel gears to turn the drive through 90 degrees without changing the ratio.

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[www.hydraraptor.blogspot.com]

That's fine too, as long as there's room in under the machine.

I was thinking that the driveshaft could be to the side of the z gear if using worm gears, but i'm imagining that a bevel gear system would have to have the driveshaft run under the z threaded rod.

bevel gears would certainly be easier to print than a worm gear, though.

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Why is the z axis so slow? is it because if it goes too fast the belt slips and grinds?

It's because it's a threaded rod driving it, instead of a belt. It moves 1/20" for each rotation of the stepper (if you're using 1/4-20 threaded rod) as compared to belt drive, which for a 8 toothed pulley moves the bed eight teeth worth. Since the belt is 5mm per tooth, that's 40mm.

That's just off the top of my head, and I disclaim any responsibility for the correctness of any numbers in the post. The idea is right though.

I saw Bill20R3's version of this, he had the bevel gears printed out no problem, and was trying to mount them at the top of the axis so the axel ran above the top of the machine. It wasn't working when I looked at it, but I don't recall why. Maybe something about mounting the axel to properly mesh the gears? That may have been it.

You can probably ignore any backlash introduced by the gears, as the error shouldn't be enough to make a difference in printing.

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I'm building it with Baling Wire