Four Axis Mendel

I've just watched the video of Mendel printing upside down. http://vimeo.com/7141942

I have had a search on the forums and not come up with this point, appologies if it has allready been pointed out, but if the machine had a fourth axis (rotation) to turn the whole machine over, it would be possible to print hollow objects / overhangs that are not currently possible. The whole machine could be rotated to make any overhang vertical.

I need to think a bit more about it, but I wonder if there would be much advantage going to 6 axis.

Any thoughts?

... there were some related discussions, don't know where ... you need only 5 axes, as you can replace any 6th by rotating one of the others ... snd yes, a 5-axis-RepRap would be a big advantage, but the software is a really big venture too

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Yup, Daniel Lipsker figured it out:
[reprap.org]

I really need to get email working, then you can talk to him.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

I didn't know that there was a Wiki page for Dany Lipsker. I've talked with him a fair amount, and I'll try to fill that out more thoroughly.

But I don't think he mentioned an extra axis in the way that titcombj is suggesting (at least, now how I envision it).

I think Dany's tool moves the extruder head in 5 or 6 degrees of freedom. I was proposing adding degrees of freedom to the whole machine so that the problem of sag due to gravity can be mitigated by turning the machine so that overhangs are now vertical rather than horizontal.

Imagine creating a thin walled hollow cube. The machine starts in the normal orientation laying down a flat square then builds up the walls. Currently there is no way that a Mendel could close the top of the box, but by rotating the whole machine 90degrees the overhanging top is now a vertical wall that can be built up without sagging.

The mechanics of adding two rotation axis to the Mendel would be relatively straight forward, but as VDX says, the software to detect overhangs and decide weather to rotate the machine would be at least as big a challenge.

It would only work for a small subset of cases. Imagine your box now has a hole in the middle of the lid.

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[www.hydraraptor.blogspot.com]

Yes, I think the better solution that is considerably easier to implement in HW and SW is to have a second extruder head for support material. AFAIK this is still on the RepRap TODO list.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

A Hole in the middle of the lid would still work fine.
First, build half the lid.

oo      oo
oooo  oooo
oooooooooo

Then turn it on it's side, and build the other half:

ooo999
ooo888
oo  77
oo  66
o    5
o    4   
oo  33 
oo  33
ooo222
ooo111

Of course, this solution only highlights the complexity of the software needed. But at least software complexity is easily replicatable.

What this technique WOULDN'T work for is an overhang that goes over and down and is suspended, like the arms hanging at the side of a humanoid figurine.

Edited 2 time(s). Last edit at 04/30/2010 09:29AM by jgilmore.

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I'm building it with Baling Wire

What Adrian's experiment shows is that gravity is largely irrelevant. Support material is not to support the filament against gravity, it is something for the plastic to stick to so that the extruder can turn a corner and the filament follows its path.

It also needs to stick well enough to hold the filament down against the warping force. You can't simply extrude into mid air no matter which way up the machine is.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> What Adrian's experiment shows is that gravity is
> largely irrelevant. Support material is not to
> support the filament against gravity, it is
> something for the plastic to stick to so that the
> extruder can turn a corner and the filament
> follows its path.
>
> It also needs to stick well enough to hold the
> filament down against the warping force. You can't
> simply extrude into mid air no matter which way up
> the machine is.

This would imply that the overhangs problem should be solvable in software. I.E. if the filament is extruded next to an existing filament it will stick to it (sideways) and that will be enough, at least until warping becomes an issue. The only rule that would need to be enforced is that filament should be extruded next to the oldest (coldest) filament that you can. No extruding a filament out into space, telling the extruder to do a 180, and expecting a 2-filament wide "tongue" sticking out into space! Such things would have to be treated the same way we'd treat a very tall skinny part, with a little added, and then a wait for the "layer" to cure.

The failed hollow naked lady that forrest produced clearly demonstrates that gravity does play a part. There is such a thing as sag. What I don't know is if that part has a steep enough tilt that the extruded filament simply wasn't close enough to the old filament to stick? If so the problem might have been solvable by making the shell two strands thick at that point, printing the outward side (close to existing material) first.

Hrm, maybe there's more to this software approach than I thought.

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I'm building it with Baling Wire

The filament has to be squished onto the layer below to bond well. If you were building sideways into free space you would need the extruder to turn on its side. Then you need a five axis machine and have all the tool / workpiece collision problems.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> The filament has to be squished onto the layer
> below to bond well.

well, or well enough? I wish I had a machine to test with. I recall an incident where somebody was printing the raft, and had a setting wrong where one entire side wasn't attached to the table - was "floating" - and the filament still bonded well enough (side-to-side) to float the whole edge of the raft. Can't remember enough keywords to really try a search though.

The question is: would it bond well enough to support the filament? Even for a little bit? If so, they the next layer above that would be squished into it and provide the real anti-delamination strength.

It's more usual to speak about delamination horizontaly.

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I'm building it with Baling Wire