Overhang test for RepRap/RapMan/RepStrap

by BogdanKecman, published

Overhang test for RepRap/RapMan/RepStrap by BogdanKecman Oct 24, 2009
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The simple object to test the maximum overhang 3D printer can deal with. The angles are, top to bottom:




In short, the bottom part is 80,70,60 that should work on every machine and the top part is 55-30 in 5° steps so you can then find what overhead angles you can "live with", what the "good" ones are and what angles are unprintable.

I have now added also a test_overhang_flat.stl after imho valid comment that overhang on the round and flat surface is not same, so here's the one to test the flat overhang.

One side (right) is 60, 55, 50, 45° (with 90° in between) and other side (left) is 40,35,30,25,20° (with 90° in between).


Print the object - without support

There is also stl with only "TOP" part that is problematic so with overhang below 60° if you do not want to print the whole object as you know machine will work ok with up to 60°.

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Objects that are round in the XY-plane allow for higher overhang angles because you're also wrapping filament around the already printed perimeter. I would not be amazed at all of you could print completely horizontal overhangs or even slightly negative angles, as long as you're fusing the newly extruded material with the material that's there. I would be positively happy to find out that this is possible, though! As discussed in the RepRap in space objects ( http://blog.reprap.org/2009/10/printing-in-space.htmlhttp://blog.reprap.org/2009/10... ) and this thread ( http://dev.forums.reprap.org/read.php?14,27036http://dev.forums.reprap.org/r... ).

This seems feasible if you've printed with layer height .20 mm. For round items you end up extruding as much to the outside of the object as you are extruding on top of it. Gravity is not affecting the process much, the material is too light and too viscous and sticky for that.

Still, this is a great benchmark item to test this possibility with. I think that, without very strict tolerance requirements you could print horizontally with non-circular objects as well. You cannot wrap filament around it, but you can extrude it to the side of a perimeter, very close to it, and
while doing this, push down this outer perimeter by making it soft because of the heat that's in the newly extruded filament. You essentially mechanically massage the perimeter flat with the extruder hovering at a constant height (or perhaps even actively pushing filament down a bit).

So, we're ju
st starting to find out how to make support material and now we're reducing the need for it ;)

Well, since the horizontal unsupported layers would not resist warping, it will get really complicated if you're going to compensate for that to get the object how you like it. Rigid support structures ar
e probably essential to consistently get reliable objects across a range of slightly different additive digital fabricators.

What do you guys think?

The flat test image is uploaded, the object is perfect, scared me when the print was done - all surfaces are perfect, the 20 degree overhang is strong and good !!! ... I did not expect that from round, especially not from flat test.

The object was printed using 0.4mm layer thickness, 241C and 16mm/sec. My nozzle is now ~0.6mm (I was not gentle cleaning it so it is bit bigger then it used to be, clean spurt of abs get;s out to be 0.8mm dia).

Anyhow, I think the test_overhang_top and test_overhang_flat are good tests for your
settings. The object itself is fairly big. The base is 35x25mm, height is bit over 7cm and top width is bit under 12cm. You can notice warping forces trough the object, on every start of the overhang you see it trying to delaminate...

Very good thing having this object is, visual guide to how big e
ach overhang angle actually is in real life :D

More pictures: http://picasaweb.google.com/bogdan.kecman/RapManhttp://picasaweb.google.com/bo...


You can c more about the test here: http://www.bitsfrombytes.com/fora/user/index.php?topic=292.0http://www.bitsfrombytes.com/f... .. it has some details about different printer settings etc.

The point about wrapping filament around is IMHO valid so I made another object ( test_overhang_flat.stl ) that is same thing only with flat surfaces. Starting the print now :) and will add more comments both on bfb forum and will put new pictures here

With regards to printing with support, the b
itsfrombytes is now working on twin extruder machine that can print both support and main material. They are still testing it with ABS in both extruders (different color) and have astonishing results, check it here: http://rapmanv3.blogspot.com/2009/10/colour-printing-next-step.htmlhttp://rapmanv3.blogspot.com/2...

I normally use
skeinforge to generate support and print support with lower temperature and get super cool objects. The only issue with printing support from skeinforge is the amount of filament skeinfoge uses for support (and I cannot get ABS locally and have to import from UK, thanks to BFB that's not that hard t
o do but again .. not easy either; so wasting too much filament printing support is not fun).

Anyhow, I'd like to c some results of other machines printing the both overhang test objects.


Yes, saw Tony's results. Great developments! I just finished my blog post a minute ago:
It starts out as a general introduction towards a larger audience, but I end up talking about your object and tricks to reduce support. I will see if I can find the time to print your object. With a smaller layer height, you might be able to do bigger overhangs as well. Making the inner shells first and then the outer perimeters might also help.

That object is printed with "too high temperature" and "clogged nozzle" ... Cleaned nozzle print's that object "almost perfect" ... I noticed that my nozzle is messed up when I tried printing at lower temp, cleaned it and ... wruuuuuuum .. works like a charm .. That print is btw 0.35mm layer thickness but is not really representative... The one Tony printed is "almost perfect".

I'm just finishing the print of the test_overhang_flat at the moment and (almost done). The print is currently at the middle of the 25
° overhang and it is printing it "perfectly" ... I'm completely amazed by the results - and I'm printing using 0.4mm 241°C white ABS.