overhang testing

[Bogdan Kecman]

ahoy fellow rapman owners ..

in the spirit of calibration of my machine I design a simple object to test how much overhang the machine can take. I'm skeinforge-ing it attm and will print using 0.35mm layer and 0.4mm layer to observe the difference as I noted while printing that there are some differences with overhang also when different layer thickness is used.

I will add the pic of the printed object when I print it but you might want to print it yourself so the STL and GTS is avalable:
http://www.thingiverse.com/thing:1169

With my limited printing experience, I noted that largest circular hole along XY plane (normal to the Z plane) that can be printed that will be usable is ~12mm diameter. Even that one is pretty "ugly" on the top and you have to do some cleaning, but you get usable object. The tear-drop shaped holes are "as big as you need them" as tear-drop shape keep the top angle's under problematic 60° limit. Now, with this overhang test, one can find where exactly the limit of his machine with his setting is - and this should save a lot of time experimenting with printing with support as now you know exactly on what degree you need your support (as experimenting show that my machine for e.g. can take much more then 60° but I really want to test it)

Post your results please, here or on thingiverse, and "do not worry if skeinforge takes long time to process the object as it has huge number of triangles"

[Bogdan Kecman]

not too happy with the result using .35mm thickness. 55 and 50 deg overhang can be cleaned up to look acceptable. 45 is ugly but "works" so if the visual effect is not important 45 deg will "work" even if there's something under it as long as you can access and clean it.

40, 35 and 30 also printed!!! but with lot of strings hanging. Going .4 will maybe improve it .. will try in a bit.

Here are some pic's of the top part only - directly from machine and cleaned up.

[unfold]

looks like a very good tool to test the overhangs. Thanks for sharing it bogdan

[Bogdan Kecman]

Yes, the good idea is to play with the outer shell thickness by adding "extra shell on *"

also, do set the infill solidity to the minimum (I use 0.1) to save the filament as you do not care how "strong" the object is

[Bogdan Kecman]

Did few prints, asked Tony to try it out also, and here are the results of the RapMan overhang votes.

All 3 tests shown are using following settings:

Code:

CARVE/Layer Thickness: 0.35
CLIP/clip over ..: 1.0
FILL/Grid Extra Overlap (ratio): 0.4
FILL/Infill Solidity (ratio): 0.1
INSET/Infill Perimeter Overlap (ratio): 0.4
INSET/Calculate Overlap from Perimeter and Infill: True
INSET/Remove Extrusion Overlap: True

The first print done on my RapMan using white (native) ABS filament (provided by BFB) at printing temperature of 243^o:

Still inside the machine:



And after some cleaning:


The overall strength of the object is very high. There is no way you can delaminate layers using bare hands on any of the regions. The print show that temperature is "bit too high" and this makes the strings drop pretty low on the overhang as seen on the "uncleared" object.


Second print is done by Tony using exactly the same BFB file with only difference, Tony is using BLACK ABS. As you all know, coloured abs need "slightly" higher temperature the white abs. As Tony is using exactly the same bfb code this print is also 243^o.

Picture of the object out of the machine:


As you can note, this print is "almost" ideal. There are some strings on the overhangs but almost no need to clean anything. Precision of the RapMan and proper temperature selection for the material used gives us usable overhang at 30^o - this is not what I expected at all...


After seeing the Tony's print I decided to try again with lower temp settings, I intentionally went way down to check what the other extreme will be and went for 237^o, so 6deg lower then initial print.

The object out of the machine:


and when some of the strings removed:


Lamination on the 90deg parts is great but lamination on overhangs is awful. You can easily break the object using bare hands on any overhang (ok, I do have bigger hands then most people but...)


To conclude, the 60^o limit for overhang without support is not that limiting as it first seemed to be. Setting the correct print temperature will give very good results with 45^o overhang and acceptable results even with 30^o.

[Bogdan Kecman]

I have cleaned the nozzle and designed another test - flat sides, not round and result is "wow"...

abs, white, 241C, 16mm/s, 0.4mm layer thickness .. and ... one side is 60, 55, 50, 45 degrees and another 40, 35, 30, 25, 20degrees ... yes, that top corner is 20 degrees overhang (or 160 degrees depends from what side you count) and it worked perfectly with 0.4mm .. I recon we could get 10 degrees with 0.3mm thickness

printing:


done, still in machine


done, out of the machine


more pictures on my rapman photo album