Weird texture on underside of prints

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alackofcolor
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Weird texture on underside of prints

Post by alackofcolor » Sat May 14, 2016 5:13 am

I'm getting a strange, rough texture on the underside of prints that have a domed top (see attached picture). This seems to occur with and without support. Printing with Hatchbox filament, 220 C, with Simplify3D. Any idea what causes this and how I can get a smoother texture on the underside?
IMG_4217.JPG

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insta
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Re: Weird texture on underside of prints

Post by insta » Sat May 14, 2016 9:09 pm

Short answer is you can't print that shape with FDM printers and single support.
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Jules
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Re: Weird texture on underside of prints

Post by Jules » Sat May 14, 2016 9:42 pm

Slightly wordier +1.

Yep. Unfortunately, you've got gravity working against you. (Only option to make it better is a dual extruder system. You can print a different kind of filament that will not stick to the original in one of the nozzles, and use it as support that actually touches and supports the underside of the main print.)

Make sure the Outline Direction that you are selecting is Inside to Out.

alackofcolor
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Re: Weird texture on underside of prints

Post by alackofcolor » Sun May 15, 2016 1:07 pm

Well here's a pictures of the the same part (printed in two pieces) that I found, printed with a different printer. The underside of theirs is smooth after the support was removed.
11865006_10153614563111018_915493570516115280_o.jpg

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Jules
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Re: Weird texture on underside of prints

Post by Jules » Sun May 15, 2016 9:19 pm

alackofcolor wrote:Well here's a pictures of the the same part (printed in two pieces) that I found, printed with a different printer. The underside of theirs is smooth after the support was removed.
11865006_10153614563111018_915493570516115280_o.jpg
The pic you showed as an example is not perfectly smooth either....it only looks that way until you zoom in. (We generally analyze objects to see which printing direction is least objectionable from a "gravity" standpoint, and sometimes that means cutting the part into pieces and gluing them together after printing. On the other hand, if a face is hidden underneath a part, we might not bother with it. But the underlying problem, gravity, is not something that we have figured out how to circumvent yet with this kind of printer.) :lol:

The second print you posted is a lot smoother than your first result, which means the guy had his settings dialed in correctly for that filament.
(If that level is acceptable for your needs....read on.)

I would experiment with the following, one at a time, until I liked the result:

1. Make sure the Outline Direction for that print runs from Inside to Outside.

Absolutely Critical. Printing in that direction for overhang areas gives the filament something to hold on to, otherwise you're trying to print over empty space. (Needless to say - use multiple outlines.)

2. If you're printing PLA:

a. Remove the fan guard on the bed fan. This increases the cooling power to the print. PLA both warps up and slumps while it is hot, it stops when it cools completely.
b. Purchase a small desk fan and point it directly at the overhang areas that the bed fan does not reach.
c. Print at the lower-middle end of the print range - 220° is too hot for PLA with overhangs. (I print Hatchbox at 205°, with no fan guard, and don't need to use the desk fan very often.)
(i suspect that most of that slump problem in your print is from it printing too hot.)

3. Support

a. Horizontal Offset from part - 0.2 mm.
b. Use 2 dense support layers - 60%.
c. Extra inflation distance of 1.5 mm
d. Increase the support density to about 30%
e. Support angles of 45° and -45°

It's going to be a lot more tedious to remove the support, but it will give you a smoother bottom finish. (That's the trade-off.)

4. Outline Underspeed - 80%

Try those settings as a starting point and see if it works any better. If not, adjust one setting at a time and keep reprinting until you determine what works best for your shape.

(BIG Note: NOT the same when printing any other kind of filament. This is just for PLA. Other filaments have their own quirks, and can be read about in the Filaments section of the forum.) :D

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jimc
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Re: Weird texture on underside of prints

Post by jimc » Sun May 15, 2016 11:28 pm

if your trying to get the max angle out of printing with no support and want the cleanest undersides then lower the layer height as much as you can. .08-.1mm maybe. increase you extrusion width to as wide as you can for the nozzle you have installed and also be sure your perimeter order is set to inside first. on another note it does look like you might be printing a little hot. try dropping the temp by 5-10 deg.

alackofcolor
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Re: Weird texture on underside of prints

Post by alackofcolor » Sun May 15, 2016 11:46 pm

These are great suggestions everyone, thanks. I'm already printing at 0.1 mm, and my extrusion width is 0.40 with the newest nozzle installed. I never knew you could make that wider. I noticed that I was printing from the outside-in, which I'm definitely going to change now. I'm also going to decrease the temperature quite a bit.

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Matt_Sharkey
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Re: Weird texture on underside of prints

Post by Matt_Sharkey » Mon May 16, 2016 12:53 am

alackofcolor wrote:I noticed that I was printing from the outside-in, which I'm definitely going to change now. I'm also going to decrease the temperature quite a bit.
You probably just fixed 90% of your problems right there, temperature would be next.

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