Cartesian Concern ... Mendel Mania?

First off, the title is just a teaser to jiggle our brain cells to discuss what I believe is a serious question. So absolutely no "Mendelian offence" intended to anyone

I've been lurking in the Reprap and Ultimaker forums for nearly a year and am very impressed by both communities (I realise there is some overlap). I don't have a 3D printer yet, so I can't contribute anything particularly technical just now. But I am an engineer and I would like to contribute by triggering this discussion amongst the Reprap community. I am really interested to hear the response because I am genuinely concerned by this.

My basic question is this:

Why is there so little about moving-Z-platform designs in the Reprap Forums? (Moving-Y-platform Mendel designs seem to dominate.)

Darwin is of course an early example of moving-Z-platform design. Ultimaker is a more recent example which seems to be achieving good results (with the fantastic help of the Ultimaker community), so I presume there are no insurmountable technical blocks. I understand that Ultimaker grew out of Reprap and has a Creative Commons Licence ( [reprap.org] ), so I presume no licencing issues.

It seems that Ultimaker demonstrates that moving-z-platform concepts are alive and kicking. So why don't we see more about them on the Reprap Forums? Has there been a parting of the ways?

Edited 1 time(s). Last edit at 06/12/2012 08:27PM by SydneyDesigner.

I just released Tantillus which has a moving Z and I believe Printxel also uses a move Z.

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What the ultimaker design and several other newer designs do is make the X and Y steppers stationary, this makes a moving Z axis make a lot more sense. Even more when coupled with a Bowden style extruder.
I think a lot of the newer designs are likely to go the same way.
You're always going to see variations on existing designs, triangular frames don't lend themselves to moving Z and if your frame is largely threaded rod, triangular frames are a lot easier to assemble and get square that cubic frames.

SydneyDesigner Wrote:
> Why is there so little about moving-Z-platform
> designs in the Reprap Forums? (Moving-Y-platform
> Mendel designs seem to dominate.)

Because most of us have Mendel-style bots with a triangular frame, that doesn't lend itself well to a moving z-bed upgrade?

I'd also say with a moving y-bed you can make a smaller bot since you let the bed move outside of the bots initial footprint. Mendel does this, but Wallace much more.

And it's also simpler to ensure the bed is level at all times when it only moves in Y, especially when it's large.

Still, with the huge improvement in print quality we've had since the original Mendel design, there's no reason not to design a more complex bot with a moving z-bed, like Tantillus excellently demonstrates.

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-Nudel
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The Printrbot / Wallace style Y axis makes the printer smaller but the space it needs to run actually gets bigger. I.e. the space taken by the Y axis is normally the bed size plus the Y axis movement range. With a Printrbot the Y carriage is longer than the bed.

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On a Printxel with a 165mm printable Y distance the minimum Y footprint requirements are 255mm. The maximum Y footprint is 320mm. Not recommended, but if it was moved up to the common 200mm printable Y distance the maximum Y foot print would be 355mm. My printer sits next to my keyboard on my desk and is allocated nowhere near the maximum footprint requirements and it's very rarely a concern unless I am printing large objects. Usually I have parts and tools scattered all over the desk including under the printing platform and that's not been a concern either.

I don't undertstand how that can be. If the print area is 200mm then the minimum bed size is 200mm. It has to move 200mm so surely the minimum footprint is 400mm?

How can the footprint be less than twice the printable distance with a moving table?

Edited 1 time(s). Last edit at 06/13/2012 01:13PM by nophead.

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When the bearings are in the middle how is the footprint less than twice the build length plus the bit in the middle plus the bits at each end of the bed?

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[www.hydraraptor.blogspot.com]

You're right. I measured again. I was off by 100! It's 420 maximum not 320 for 165 build distance and 455 for 200 build distance.

So if it is 420mm for 165mm build, rather than 330 that implies the overhead is 90mm. If so why isn't the 200mm version 490mm footprint?

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[www.hydraraptor.blogspot.com]

Apparently I'm a bit slow today. Sheesh. The extra 35mm when going from 165mm to 200mm does needs to be added to both sides of the footprint. So yes the overhead is 90mm and a 200mm version would be 490mm.

I've not seen a Mendel anything in real life. Does the bed stay within the frame footprint when printing to the full extents?

No it overlaps a little. Mendel90 doesn't so it looks bigger but actually uses slightly less desk space. I run my machines inside boxes so I tend to notice these things.

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[www.hydraraptor.blogspot.com]

Thanks for your replies.

Yes, Tantillus is an exception, with a moving-Z-platform, like Ultimaker. (Printexl is in fact a moving-Y-platform like Mendel.)

I take your points @Polygonhell and @Nudel. Triangular Mendel-style frames don't lend themselves to a moving-Z-platform upgrade. So there may indeed be a bit of a legacy issue here due to what people have lying around to experiment with.

So, my main observation stands. There seems to be relatively little about moving-Z-platform designs in the Reprap Forums at the moment. Moving-Y-platform Mendel designs dominate. Even the home page is about moving-Y-platform Mendel designs with the only moving-Z-platform, Darwin, at the bottom as a legacy design. I do find this very strange, especially given the success of the moving-Z-platform Ultimaker over the last year or so.

I'd love to hear any more thoughts on this and how people think the Reprap forum might change from here.

The Ultimaker design use Bowden feed and a lot of us remain unconvinced it can be accurate and it needs more expensive 1.75mm filament. If you want to place 0.3mm filament with an accuracy of 0.1mm the input to the extruder needs placing to 0.1 * (0.3/1.75)^2 = 3um. How do you do that down a long flexible tube?

Having said that recent results look good but not so long ago they operated without retraction making complex shapes come out hairy. Most of the examples were single walled organic shapes where no retraction or slow down for corners is needed.

Also when the head moves in two directions the mechanism is more complicated. It needs fancy bearings and three times as many belts. Tantillus goes some way to solving that by using gears and wire, but how long do plastic gears remain free from backlash?

The traditional Mendel layout can produce excellent results and is simpler and cheaper and uses cheaper filament. If you prefer faster and smaller footprint then flying head might be better for you. There is now virtually every possible configuration out there.

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[www.hydraraptor.blogspot.com]

BTW - Ultimaker uses 3mm filament, not 1.75mm.

Sorry, thanks for correcting me, That requires even more feed precision, 1um for 0.1mm accuracy.

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[www.hydraraptor.blogspot.com]

Thanks again for your replies.

Yes, Ultimaker does use 3mm filament with its Bowden. And yes, it does seem to produce really good detail prints, fast - achieved through many software and hardware improvements over the last year or so. I think moving-Z-platform designs like this have a lot of promise.

Tantilus has already been mentioned. Who else is currently working on moving-Z-platform designs in the Reprap Forums? I'm particularly interested in larger printers - larger than Ultimaker if available.