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ciclopez

"Analyzing your first print" missing

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Hi,

I'm a new Ultimaker user triying to improve my prints.

Some pages of the Wiki and some old forum posts point to this webpage (http://techwall.net/analyzing-your-first-print) as a must-read to understand what's going on when the finish of a print is not good enough.

It would be very helpfull if someone could publish a copy of that page or some short guide on how to analyze a print.

Thanks!

 

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You should really take a chance here, you would get personalized feedback ! However, I think i'm the same and like some "reference" data to process and try to do by myself. And I agree some FAQ would be cool.

Anyway, you can find the page here: http://web.archive.org/web/20130526014427/http://techwall.net/analyzing-your-first-print

(in general you can find a lot with the "internet archive waybackmachine"

Cheers

 

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ok, here is one of my first prints (and problems):

IMG_0122.jpg

http://www.thingiverse.com/thing:71593

There is a slight X/Y offset at half height, where it should be flat.

I sliced it with Kisslicer and the G-code seems to be ok:

pifpafsliced.jpg

It's printed in PLA with this settings:

0.2mm layer height

0.8mm wall thickness (2 loops)

30mm/s outer loop

50mm/s inner loop

70mm/s infill

20% infill

220ºC

 

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You are getting good results! That print looks pretty good.

Okay - I see the offset. I've seen this before - it's annoying and difficult to fix.

The problem is that PLA shrinks when it cools. The longer the part, the stronger the forces and the more the walls are pulled inward.

So on the lower half of the part, you have a length 3X as long so there is 3X as much force shrinking the part. Then when you print the upper half, the cube portion, you have 1/3 as long as the lower half so there is 1/3 the force trying to pull the walls in so it prints properly (larger). The problem is only noticable in one axis because you only shrunk one axis.

I do not know any good solutions other than a heated chamber. A heated bed is not enough - you need to cover the entire 3 sides of the UM and hardest of all, the top (typically with a large cardboard box open on one side large enough to not touch the bowden tube).

Another possible solution is to reduce infill. The sides and the infill are what are pulling. But the top of that lower half has a solid layer which probably does at least 60% of the pulling. Maybe reduce top/bottom thickness to .4? This will not help much at all. Putting holes through the part (top surface to bottom surface) would help as this would reduce the pulling stresses. You might be able to cut the pulling by 70% this way but it requires access to the original cad files and cad software.

The best solution in my opinion is to modify the cad. Increase the lower part (that shrunk the most) by the amount it shrunk. In other words use calipers to measure the offset and increase the lower part by that amount.

If you print in ABS you will have much worse shrinking issues.

 

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Lower temps won't help. The shrinking doesn't start pulling until PLA becomes a solid. I think around 80C or so. If you can keep the air around the print at 70C until the print is complete that should help. This is usually accomplished with a heated bed at 70C and enclosing sides and top and moving stepper motors outside the box (put them on end of rods and get rid of belt) so they don't get so hot.

Normally this isn't needed for PLA as the shrinking is minor. But for ABS you really need this. I am told. Because ABS shrinks much more than PLA.

I have a heated bed but don't use it very often.

 

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I could be completely wrong about the cause as the piece on the left doesn't seem to show the same problem. Being twice the width might help but I'm not sure why that would help.

Certainly shrinkage causes all kinds of obscure problems but I'm not certain that is the problem here - it just seems very likely.

 

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