Small scale flying gantry?

Is there any particular reason a flying style gantry is not used on small scale printers (<300 mm^3)? It seems like it could be possible and would give you a large build area to machine size ratio.

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greghoge.com

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The biggest problems I can see with it are moving mass and the fact that everything is cantilevered. The massive top of the gantry is cantilevered off its base, and the Z axis is cantilevered off the top of the gantry. Every time the gantry reverses direction, it will flex, as will the Z-axis with the extruder hanging down from it, and the extruder will swing like a pendulum. If you make it massive enough to be rigid, then you have problems moving it because of all that mass. You'll have a tough time getting decent layer registration, especially when the extruder is at very low Z coordinates.

This a common layout for CNC routers because it provides a large cutting area with a small footprint and because they typically operate much slower than 3D printers so they can build them heavy enough to be rigid. I suspect CNC routed items are generally not subjected to the same quality expectations as 3D prints.

Edited 2 time(s). Last edit at 10/21/2015 03:14PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Well, the Dentist got everything right about why the setup doesn't work for 3D printers, but the reason it is used for CNC routing is that the tool on the router must maneuver around features of the object it is working on that can be up to the full build height. Therefore, a CNC must pursue a minimum "tool footprint" even at a sacrifice of stability.

But the pictured machine is neither one, it's a gardening robot designed by someone who thinks that "Wealthy and lazy crop farmer unwilling to employ low-wage labor" is a market segment somehow. It was compared to 3D printing to make it more effective at it's primary job of securing research grant money.

Yea I understand the cantilever effects, but it seems like an odd reason NOT to try that gantry style at a smaller scale when it is the main style used in large format printers which use larger cantilevers and heavier structural components.

As for the picture, I just grabbed the first one off google that looked close to what I was thinking of. Guess I should have looked a little more closely... Anyway, i think this is a better representation of what I'm working on:

[partsolutions.com]

The z axis won't go down past the print bed, but I'm using carbon fiber rod for lightweight, and d shaped drive shafts to remotely drive a coreXZ mechanism. I also figured out I can add some triangular supports to the XZ axis assembly. I'll post a screen shot when I'm finished the CAD, hopefully after this weekend.

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greghoge.com

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