Making undersides of overhangs smoother

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SHoutzager
 
Posts: 66
Joined: Sun Jan 03, 2016 4:02 pm

Making undersides of overhangs smoother

Tue Feb 14, 2017 9:34 am

Are there ways to make undersides of overhangs any smoother? I have tried really dense supports. If my undersides are at an angle or curved then they are going to be rough. :|

greybeard
 
Posts: 48
Joined: Mon Mar 02, 2015 1:23 pm

Re: Making undersides of overhangs smoother

Tue Feb 14, 2017 2:38 pm

80% of my engineering parts have overhangs… Many prints were required to dial-in the process parameters. I no longer need or use supports except on flat overhangs (which I avoid).

Here are some tips for better prints on overhanging and curved surfaces

Part Design:
Overhangs below 45 deg from horizontal are a pain. Suggest increasing the angle. However, good print parameters will give good results (45 deg example photo)

Curved overhangs: Depending on the part, some parts of the surface will be lower than 45deg

Print Parameters:
Don’t use Auto flow multiplier
For PLA, use a flow multiplier of 1.02 to 1.05
Increase internal infill to 35%
Try different infills and infill angles
Don’t use the fan until past the zone of print difficulty
Increase the temperature - a lot. If the filament box recommends 220deg max, use 230 to to 235 (why? You want the suspended threads to bond and not be cold.
Increase outline overlap to at least 25% or more
Use print height of 0.1 (or 0.2 max)

Use a good brand of filament (I used all of them and you couldn’t pay me to use Hatchbox again). I prefer eSun

The attached small stl file part for testing your parameters - whatever part you use for testing, build a test/sample board…
Attachments
DroopTest1.stl
DroopTest
(55.75 KiB) Downloaded 11 times
sampleboard.jpg
Sampleboard
45deg.png
view from down under

SHoutzager
 
Posts: 66
Joined: Sun Jan 03, 2016 4:02 pm

Re: Making undersides of overhangs smoother

Wed Feb 15, 2017 11:13 am

Nice Work! thanks. So you don't use supports if the overhang is 20 degrees from horizontal?

greybeard
 
Posts: 48
Joined: Mon Mar 02, 2015 1:23 pm

Re: Making undersides of overhangs smoother

Wed Feb 15, 2017 12:15 pm

Perhaps I wasn't clear... I avoid overhangs less than 45deg. Bottom edge radius and chamfer's can be printed well considering the print parameters mentioned.

Though seldom needed, when I use supports, I use dense supports and ensure a gap of at least 0.2mm and ensure the infill pattern does not have fill angle running parallel with the outer shell length runs. Also adjust the infill density and part density...

Also, ensure infill pattern does not produce telegraphing into the shell. This may, and often does happen - changing the part orientation about the z-axis and infill style can address this...

You can get perfect prints with effort, trial and error.

Attached photos :
The Lid has a 20deg hemisphere radius, printed withOut any supports (not even dense spts). For this part, my Harley gas tank lid, I did not care about the inside (and did not want to waste ff for supports). No loose filaments though a bit ugly but nothing hanging down, droopy/stringy - all ff is firmly bonded..

The Gear bottom is totally horizontal without supports. This is a bearing surface that rides on a small hemisphere - none of the ff is loose (though they look loose in photo but all are solidly bonded to upper infill (printed at 230 deg)
Attachments
Lid.jpg
Tank Lid
N20_BtmView.jpg
Gear btm view
DroopFF.png
gear print

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