Why does the x&y use belts and the z uses the threadscrew?

These RepRap machines look amazing. I am investigating building a RepRap (MakerBot).

I have noticed that they all use belts and slide on bar for the X & Y axis but use belt or cog and threaded bar for the z axis. Could the X & Y axis use the same threaded technique or is there something I do not understand? Perhaps cost??

I do hope this was the correct place to post this. If not, please let me know where I should post.

Tks

X&Y have to change direction very quickly, so belt makes more since, Z has to lift a significant amount of weight, but not change direction, so threaded makes more since.

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repraplogphase.blogspot.com

The main reason against threaded rods on X&Y is because those drives are very slow.

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FiveD Firmware fork (supports Arduino Mega): [github.com]
reprapsource.com

Actually Threaded rod can be quite fast, the issue is going fast, then changing directions.

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repraplogphase.blogspot.com

Thanks guys. I wondered if this might be the case.

I see the Mendel uses the triangular frame and more plastic parts to make it sturdy whereas the MakerBot uses a box for it's sturdiness. It is interesting to see that the Mendel has it's X axis on the feeder rather than the platten (is that the correct term these days?). I realise the parts size is smaller on the MakerBot.

I am just getting a feel for this. I don't see the smaller size being a real issue. In fact I liked the micro-Mendel design. Did that design proceed?

It's not "official" but people are still working it. I am trying to convert it over to imperial, with 608 bearings, and nema 17 motors. Whosawhatsis? is doing a openscad conversion on it, and a several other people are going different directions.

The easiest route is BFB Rapman and MB Cupcake. I went the Cupcake route. The Fleming cnc Isaac Mendel & BotMil lLaser Mendel are both said to be workable, but there is VERY minimal in the wild confirmation of this. Profound Devices sells a kit also, but they have yet to even produce video internally of a viable kit.

$500 plus is a lot of money, and all RepRap printers have issues, the tech is new. Rapman breaks acrylic, Makebot wobbles, and the plastruder jams, Profound devices makes a good doorstop, BotMill is showing major customer service issues, and Isaac is in transition to new materials.

Check the RepRap and Makerbot Map, find a local (even if you have to drive 1-2 hours) and look at what they have, and get them to let you run it. There is no more generous community they the RepRap community.

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repraplogphase.blogspot.com

We are slowly developing a list of completed machines in the wild. One of the more recent machines is mhenson's. You can see video's of it running on youtube here.

BTW our new material is 100% black HDPE, instead of the previous wood/plastic composite. The parts are otherwise exactly the same, machined with the same toolpaths as the original kits.

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Isaac: a CNCed Mendel Derived RepStrap
FlemingCNC

If something breaks down on the z axis, the thread won't let the head descend onto the workpiece through force of gravity, which a direct-drive belt might allow. My adaptation uses a cable parallellogram to maintain z axis alignment with one z-screw, which only needs a single short belt from the stepper to the threaded rod - or a gearset, if there's one handy, say from a discarded printer - and does away with the long belt across the frame and the threaded rod and drive on the opposite side of the frame.

Edited 1 time(s). Last edit at 07/14/2010 07:17PM by murrayd.

> a cable parallellogram to maintain z axis alignment

Got a picture of that?

Interesting.