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uma

How to improve the print quality

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Folks,

 

Here is the problem i am facing. I am trying to print this intricate cell phone cover design using UM2. I am using slic3r for this design. the top layer finish and the intricate designs are not finished properly. I can see small blobs wherever the head starts and retracts. Moreover, the surface finish of the infill is not smooth. I am afraid this piece can be used with my cell phone.

 

Following are the important settings

Layer height = first layer height = .3

Speed = 30-50 mm/s (50mm/s on internal perimeter, 30mm on solid infill, external perimeter and all other areas where surface finish is important)

Temperature for PLA: tried it from 220 to 235 in steps of 5. No difference

Used lift Z feature in Slic3r so that the design is not spoiled during travel or retraction.

The retraction settings used: 4.5mm @ 35 and 40 mm/sec

 

Let me know what can be done to improve the surface finish.

 

photo 5

photo 4

photo 3

photo 2

photo 1

 

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Reduce your layer height. 0.3mm is marginal for a 0.4mm nozzle to begin with. It means you are printing at a much higher volume per second, which means the nozzle pressure is high, so as soon as you get any pauses, the head will ooze.

Print it at 0.1mm layers, and print all the parts at the same speed, so the head pressure stays constant. Consider not doing the z-lift, as the UM2 z-moves aren't very fast, and will just add more time for oozing (or experiment with increased z-acceleration, as I mention in my 'Myth of Z-speed blog post in respect of the UM1).

Also it looks like you aren't printing on the glass? If you want good surface finish on the bottom, that's really the only way to go.

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Let me know what can be done to improve the surface finish.

 

I guess I'm not sure what the problem is. Is it those tiny holes you don't like in the pattern? Or is that supposed to be there? Or is it the gaps in the curved lines? Or do you not like the diagonal infill? Or is it something completely different. The images you show look very pretty but one person's "beautiful" is another person's "ugly" so I think you have to be more specific.

For the diagonal infill - to make it almost invisible you have to get the leveling perfect. I would do bottom layer .2mm but then you need the leveling at all 4 corners accurate to about 1/10 of that or .02mm or 1/5 the thickness of paper. This is best done by printing a skirt only. Stopping the print. Adjusting. Repeat. Until all 4 corners are perfect.

For tiny holes and gaps - this is slicer issues. You could make the pattern bigger. I've done very well with Cura as you can see on one of my cell phone covers (this was a practice run). Look at the detail in the edge of the arm:

new experiment with single extruder

 

edit: note that the left side of this image the bed was too low and the right side was good. That was something I had to adjust.

 

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@gr5, yes the designs are beautiful but the holes are not part of the design. I have problem with those tiny holes as well as the surface finish. It is really rough and i am sure no one would want to use that as a cell phone cover.

I figured that alignment has to be right to print a perfect case. But levelling in UM2 is not straight forward. It uses a 3 point leveling system. Most of the time the front two corners are ok but the two corners at the back are slightly bent inward. With only one screw to adjust i really cannot get a even leveling.

I somehow figured out a way to get rid of the holes using a combination of design changes and slicer adjustments. But the new problem now is warping. I see that the bottom two corners of iPhone case warp inwards. I am printing using PLA @ 220 on a Kapton tape with heated bed turned off. I will post the pictures of the warping. Because of the warp the fit is not right.

Uma

 

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@uma - can you show a photo of the warping? If it's lifting off the bed, then this is easy to fix. But if the warping is instead *not* lifting off the bed yet still causing it not to fit the phone, then the fix is to adjust your cad model for shrinkage.

This is a problem for other technologies as well such as injection molds where you have to have the mold with a different angle of the part so that after it shrinks the angles shrink to 90 degrees. Weird stuff like that.

Anyway, please post photo.

 

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[...]

This is a problem for other technologies as well such as injection molds where you have to have the mold with a different angle of the part so that after it shrinks the angles shrink to 90 degrees. Weird stuff like that.

[...]

 

The slicer software which could do such corrections automatically would wipe all other slicer software away... (@Daid: I'm aware that this is very far away! :smile: ) But just imagine...

 

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PLA does not stick to Kapton without heating the bed. The "standard" temperature is 70 Celsius, but some people print at lower temperature (down to 45 Celsius).

About the gaps in the print, I don't think will work, even with a smaller nozzle diameter. The reason is that the width of the lines that compose the model varies continuously. Even at 100% infill, any slicer could not plan a path that would fill any tiny gap. Some improvement in this respect would be to increase the flow, but this will generate other issues (e.g. blobs).

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the width of the lines that compose the model varies continuously

 

You'd be surprised! Most slicers know that the gap is for example only .2mm so they will will extrude (in this case) 50% to try to perfectly fill that gap.

I'm not sure if Repetier host takes this into account when displaying the traces - I think instead it always shows .4mm wide traces. Or maybe I'm wrong about repetier host.

 

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I think the issue is not having a gap of .2 mm width for a length of, say, .5 mm, but rather having to fill a triangle with the smal base of .2mm and a height of, say, 1 mm.

I can agree that one can print certain pieces on cold Kapton, but I don't think is a good practice in general, thpugh it could save some energy. For the given context, it's a warp-certain case, since the walls at the corners of the case would definitely create enough tension while cooling to warp the base.

That's just what I've learned and experienced :)

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image 2

image 1

image

@gr5 please find the attached images. The warp is two dimensional. From the side view you can see that the right most edges are caved in. In both front and back views, the edges are caved out. Adjusting for shrinkage is ok provided the design has a repeatable shrinkage pattern. I dont see that happening.

The summary from the post above: for parts that have height print on a heated Kapton tape or use a glue with Kapton?

One stone at a time. I am sure i can get a fitting case soon :)

 

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Okay - I'm not sure what you mean by "cave in" and "cave out" so I'm going to add arrows and explain what I see:

A copy

BLACK ARROWS

In the above image, the black arrows point to underextrusion most likely caused by different speeds for infill and exterior. Just go 30mm/sec or even 20mm/sec for the whole thing. This is a cell phone case - you want really good quality. It deserves 20mm/sec. It's not going to take days to print - just an hour or so. Go slow! Different speeds on exterior versus interior just doesn't work because it changes speeds too suddenly and the extruder doesn't catch up so you get this crap when it starts the exterior.

 

BLUE ARROW

Classic warping/lifting. Use 70C bed and/or glue and/or brim feature to keep this down and don't remove until it has cooled all the way down to 40C. Be patient.

 

 

 

B copy

GREEN ARROW

In this image the green arrow - what do you call that? I don't know what the heck causes that - maybe if the base was slightly above glass and the fan kept the plastic on the top side of the bottom below glass temp... I don't know. If you use glue and/or 70C bed and you let it cool gradually down to 50 or 40C before removing I don't think this will happen.

GRAY ARROW

What the hell? Is that just camera distortion? I hope so. Let's ignore this until you get the green arrow part fixed and then the sides might change shape to something I recognize like "elephants foot".

So in summary:

1) 20mm/sec for ALL speeds interior, fill, exterior, shell, whatever. Bottom layer also.

Okay if you want 30mm/sec you should be fine. But none of this 50mm/sec stuff. This will help the black areas and more. Quality will be better everywhere.

2) Set the bed to 70C. That is very important. It will affect many things possibly including - the green, gray, and blue arrow issues. Also I recommend a little glue stick spread around with a wet tissue so it is very thin - no bumps.

Brim is optional - if you still get lifting with glue and 70C, then add brim. This part should be EASY to keep down on the bed. I've printed parts twice this size with much more infill (not this simple flat bottom) and THOSE parts were hard - I needed heat *and* brim *and* blue. But you should be able to skip the brim. I think.

Take more pictures please and add colored arrows so I don't have to do the work of adding it myself.

 

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I think you tried to level the base after printing. Due to warping, the angle between the base and the lateral walls is greater that 90 degrees. When you brought the base flat, the walls went to outside, and perhaps a bit more bending caused the shape indicated with the green arrow above.

 

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photo 1

photo 2

photo 3

Warping is gone Yay!

Printed it at 70C bed temp with Kapton tape: Kept the speed constant throughout at 30 mm/s

The one thing i notice is under extrusion at the curves. Could that be a design issue as in the edge is too thin to be created. I made sure they are at least .4mm in width.

Another issue is the surface finish of the top layer (the surface that touches the cell phone). Because Slic3r tries to optimize movement it does the infill in a random order. As a result i see patches of infill on the top layer. The finish is not smooth. If this is normal i probably need to get a dremel to polish this off.

 

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I'm so glad you got good improvement simply by raising the temp to 70C. That probably won't be enough for larger things.

 

r. As a result i see patches of infill on the top layer. The finish is not smooth. If this is normal i probably need to get a dremel to polish this off.

 

I don't know slic3r well so I'm not sure what you can do other than make sure the top layer is supported with a few layers below.

 

Why do you care how this layer looks? It will be hidden against the phone.

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For the underextrusion at the curves - I'm not sure what to do there. I don't know slic3r. You could turn off combing if there is such a feature. You could maybe make the skin thicker? Or turn off infill? I really don't know. Did you look at the exact path the head makes? Consider loading up the gcode into repetier host (it's free and shows you the exact path and you can spot all kinds of problems there.

Or consider trying Cura just to get those curved underextruded spots better.

It really looks like something to do with the slicer.

 

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@gr5 The quality of prints seems improving but i am facing two problems

1) The strength of the case varies based on the type of material used. For instance, when i used blue material the strength is high the case doesn't crack that easily. But when i used fluorescent green material the strength of the case seems to be weak for the same thickness. In fact, the case crack right where the side of the case starts. Any pointers to improve the strength? increase temperature, increase layer thickness. I am currently using 220C @ .2 Layer thickness

2) The under extrusion problem is still the same. I tried using Cura also but the under extrusion is still the same.

 

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