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NBull

Help to better underside print quality

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Posted · Help to better underside print quality

Hi

 

I have some bowl like shape i need to print. I know the best way (quality) is to print it with the opening down. but to save in support material and time I would like to print it with the opening up. and here comes the problems. This gives me a very bad finish on the underside.

I know it will never be as godt as the top side print, but again when using pva I think it should / could be better. so im looking for some tips.

 

1: Warping and deformation on the underside, special in the curved part. I can se that the pva is printede fine. so the pla must lift detach from the pva.

I have tried to lift the whole print 10mm and 15mm from the build plate (ideer was to give it a more uniform tempter) I see some improvements, but not sure if is a coincidence.

 

Changing "Support z/x/y distance" to give a better grip on the pva.
don't know if there some settings overriding this because i don't see any changes.

 

Speed, I have all set to 25mm/s so should not be a problem. 

minimum layer time is 10sek not sure if this should be higher or I will benefit more from a prime tower. (don't really use prime tower they have a tendency to break of midway)  

 

2: Shape simplifikation. perhaps it's also due to warping! but parts of the bottom seam to be simplified. e.g. if you print a ball the bottom will be more edgy like if the polygon count is smaller then the top half. if that makes sense.

 

In general I have problems with the print quality at the underside og my parts. so any tips will be appreciated. 

 

Printer: UMS5

PLA: localbrand temp 200-225c (I see same problem with Ultimaker pla) 

PVA: PrimaSelect PVA+ temp 180-210c (I generally print a bit over recommendation 215c at lover temp it tends to stig a bit in the print core, same with Ultimaker pva. don't know if the temperature gauge can measure incorrectly on the B core?)

 

UMS5_150319.3mf

 

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Posted · Help to better underside print quality

Please show photos of the problem.

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Posted · Help to better underside print quality

Well that's an issue, i'm already begun sanding 😕 so it's not easy to see any more. and the print in the printer is not ready until Monday. (The item in the picture is flipped, what you see as top was printed facing down)

Bottom1.thumb.jpg.491128263250e643acf86cc0fdb738fc.jpg

 

This is from another print. in Ultimaker pla but it's the same problem. the print gets this inward bumps, thats only on the pla an not in the pva. 

 

001.thumb.jpg.bddc75f42458912a472d90bbcce94fe8.jpg

 

 

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Posted · Help to better underside print quality

Hi NBull,

 

I'm not sure if this help, but I've seen this kind of problem when printing with overhang close to the bed. After switching off the bed and using glue with PLA, this phenomena disappear.. Also had some more problem with white color filament. I've also learned that the light colored filament always radiate less heath when cooling down, compared to the darker colors.

So a hot print bed in this combination is "kind of a" no no.. May be if we're using a raft or a skirt can reduce this problem, but I have not tried this way.

 

Thanks

 

Torgeir.

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Posted · Help to better underside print quality

That looks like the angle of the printed piece and the layer thickness created the stair-step. If notice, it happens on the longest slope and evens out on the angles with greater attack.

 

I sliced something to demonstrate that.The images on the left has a greater angle from the buildplate. The image has a much lower angle (more horizontal) and has a stairstep that is much more prominent.

 

 

SamplingEdge.thumb.jpg.f0f60815ce7a8240fb90bdf5003e9166.jpg

 

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Posted (edited) · Help to better underside print quality

Hi Torgeir


Thanks for the input. I agree that this mostly occurs close to the bed, also why I tried to lift the hole print. I have not that much success in printing with the bed off though. but Ill give it a go again. what Is best tape or glue?

 

800144909_ScreenShot2019-03-18at08_19_29.thumb.png.7551ec3a2a1c3300b129163ab09c5d3a.png

 

I haven't thought of the filament colour, affecting the cooling. I will try a black, although I only have UM's tough pla in black, so maybe not the best comparesent, since tough pla reacts diffrent then normal pla in general.

 

 

Hi kmanstudios

 

Thanks for the input, but It's not the stepping. I'll see if i can clarify the question better. Here's a picture of a top and bottom side from the same print. stepping is more or less the same on both sides. it's the inward dent thats the problem. I know it's some type of warping.

 

Top

top.thumb.jpg.9ef14ad1040295304d85b7df51de06e4.jpg 

 

Bottom

bottom.thumb.jpg.9f3734b44f364d4742d34d33e4651cab.jpg

 

 

003.jpg.c72ac88a89d9f291b592e59deec6d721.jpg004.thumb.png.db18b84249bd87a1c4e525eba9317e06.png

Edited by NBull

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Posted · Help to better underside print quality

Yeah, the dent is a separate issue, But the 'topographical map' look of the surrounding area is looking to be the stairstep due to the angle of the curvature. You can see it in your slice.

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Posted (edited) · Help to better underside print quality

Hi kman


I appreciate you taking the time. But I think we are talking a bit past each other. I don't have a problem with the steeping. I know this is an unavoidable effect of angle vs layer hight do to the way a 3d printer works. It's the dent's/warping I can't get rid of 😉 

 

Edited by NBull

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Posted · Help to better underside print quality
1 minute ago, NBull said:

I don't have a problem with the steeping.

Ohhhh...my mistake. Duhhhhhhh.........

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Posted · Help to better underside print quality

Print is done. And the underside turned out better than expected regarding the dents. But the shape simplification is easy to see. 

 

Like shown in the picture, you can see that the curved edge, is more edgy like its made of straight surfaces (low polygon)

But in the slicer its a nice round shape.

 

Is this some simplification happening in the printer (doubtful). Or Cura that do this before exporting, but don't show it in the slicer?

It only happens on "overhang" bottom curves not the top ones.

 

008.thumb.jpg.ab1f218c0c54c99008241c1e3119d53e.jpg

 

009.thumb.png.e2ff096f98b159baa4ca138dd1fa6587.png

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Posted · Help to better underside print quality

I think you are seeing a pattern that is not there.  The blue lines sort-of match what the part looks like but really I think it's a perfect curve except there are 2 horizontal lines each at a different layer.  I'm not sure what causes those 2 lines - it could be that the Z axis didn't move the correct amount or it could be under or over extrusion just near this one corner caused by a speed change.

 

If this printer is pretty old I would clean the Z screw and add one drop of oil to each of the vertical rods.

 

If you decide to use tape - use any painters tape - most commonly found in blue but also green (frog tape).  You want the widest possible tape.  You MUST clean it with isopropyl alcohol.  If you don't then the part won't stick very well to the tape and may come loose during printing.

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Posted · Help to better underside print quality

Hi Gr5

 

When looking at it, it looks like more then one layer is off (from the curve) And it doesn't feel round. I will not reject it's maybe only some layers that causes the problem. still a problem 😉 but it don't look that way.

 

011.jpg.b2c96cc3759ec9fa1bc63bf3e2be6f0c.jpg

 

I don't really have a z-axis problem, beside that it's not accurate (size) I can make a pretty perfect cube and 45degree overhang. If there where layers with problems it should be consistent right? the problem is only there when printing a curved overhang.

 

wall.thumb.jpg.12d8a16ab3cdd65d9bd361d64e78d407.jpg   45c.jpg.87fc4cbc3e017f433fa08b91fb311347.jpg

(there's a little shift at the bottom of the overhang, that was do to a fillement break)

 

Regarding the painters tape. To be honest I feel a bit let down, One of the reasons I upgraded to the s5 was to get the aluminium building plate and the enclosure with better heat control. now I have to go back to painters tape, and no heat.  

 

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Posted · Help to better underside print quality

Well with PLA and trying to get perfect details then you want as little heat as possible. The Aluminium build plate wasn't meant for PLA and inclosure is also not wanted for what you want to achieve. Its more meant for engineering materials. Different materials require different methods to gain the best results. 

To get a good curve on the bottom of a PLA print you don't want any heat on the bed or the rising heat will make the edges curl up too much and give bad results. A 45deg shape will always give a better result than a full curve on the bottom as a curve has a steeper angle the gradually gets less. 

I normally put a small 45 deg angle at the base where the steep part of the curve would normally be is to avoid this or I use breakaway support material.

You can also reduce the layer height to reduce the amount of overhang of filament for each layer. 

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