Outer wall is around 0.20mm wider per side on small or big prints. Slicer problem??

[juangiluruguay 0]

Hello. I came to notice that my prints are around 0.40mm BIGGER on the outside, and around 0.40mm SMALLER.

It is critical when printing mechanical parts, specially if they have to assembly with each other.

Just made a figures test from 30 to 150mm, and I have the same deviation in the measurements inside and outside; ALWAYS around 0.40mm with either small or big print; BIGGER in the outside, and SMALLER inside.

I came to think that might be something with CURA and not the printer, because, my nozzle is 0.40, and seems that the deviation on each side is 0.20mm, that is, half of the nozzle size, and therefore, it might be that the slicer takes the center of the nozzle, as reference for the print size? instead of taking the "center" plus 0.20mm, so, the outside of the wall will determine the final dimensions of the print??.

To be honest, I don't remember if it happened before, but I do remember to have to give bigger tolerances in order to fir some parts into other.

Could somebody help me, or point me in the right direction?

Is very frustrating to have to deal with making a design, deal with printer and materials, and ... after all that effort, the outcome is not as expected

[GregValiant 1,142]

What is "Experimental | Slicing Tolerance" set to?

[ahoeben 1,888]

2 hours ago, juangiluruguay said:

ALWAYS around 0.40mm with either small or big print; BIGGER in the outside, and SMALLER inside.

 

Try setting the Horizontal Expansion setting to -0.4 (or 0.4 lower than what it is currently set at).

[juangiluruguay 0]

Hello Greg, thank you for your reply.

That setting I never used before, and was unmarked. 

I consider that unmarked is not activated?? is that right?

As soon as I put the check on it, I saw that the option on it is "Middle"

According to the help menu, it is for the vertical tolerance in the sliced layers.

I don't see that it could be related to the horizontal offset I have.

Has anybody else noticed this before?

I use Sketchup 2018, with settings on measurements on 0.00 and generate STL directly form Sketchup.

That file I load un CURA.

[juangiluruguay 0]

Hello Ahoeben. Thank you for your help.

 

Took me a little to find that setting. Is under "SHELL" settings.

Never understood that setting, and has no value in it. 

It makes sense, but I am going to try 0.2 first, maybe it is per side, and it will be another 0.2 in the other side, making a total of 0.4

I will try it right away!!!

Never ever came trough anybody complaining about this, and I was guessing that the software should do it by default, taking in consideration the nozzle size.

I will report after printing something, thank you.

[GregValiant 1,142]

That setting can have un-intended side effects in the X and Y.  Setting it to Middle is the correct thing to do.

 

Regarding aHoeben's suggestion, you can print two calibration cubes side-by-side and set the Per Model Settings for one of them to the Horizontal Expansion of your choice.  That way you can tell if Middle or Horizontal Expansion made a difference.  

 

[juangiluruguay 0]

Hello Greg, thanks for joining.

I just made a 1.5 hour test model, and will reply as soon as I have it ready.

About 2 cubes side by side.. Is it possible to print 2 pieces with different printing settings? I have never tried that. It could be useful to do tests like that.

If it is possible.. Up to how many settings in how many prints can be used at the same time??

 

One way or the other, is disappointing that is not printing as expected by defect (size wise)...

Ok.. in some cases maybe this offset could be useful, because of expansion and contraction of different materials, having only a STL file but still.. I never guessed that this could be a standard problem. I don't go deep in settings changing what I don't know.

 

Is there some standard procedure to calibrate something related to horizontal dimensions?? given the amount of different materials in the market and their behavior...

[GregValiant 1,142]

There are two supremely useful tools on the left side of the screen.  Support Blockers and Per Model settings.  A support blocker is a special mesh (part)  you can bring in.  It can be sized, moved, rotated into position to block support.  It can also have it's own set of special settings that are different from the rest of the things on the build plate.  It can be used to add, or to subtract things (a cutting mesh).  There is a plugin available in the Marketplace that provides round support blockers if the rectangular ones aren't the right shape.

 

Any regular model can have special settings as well.  Not all settings are available in Per Model settings, but a lot are.  Click on the model you want to be different and select "per model" settings.  Then add the settings you want to be different and change the values for that setting.

 

[juangiluruguay 0]

Hello Greg,

I haven't really played with CURA in very long time. Before was much more simple.

I just now notice that there are 2 settings you can play with, and makes a lot of sense what you are saying about 2 models side to side, to compare changes.

I have enough plugins in Sketchup to go crazy trying to remember how to use them, and now.. CURA has also plugins, and probably for a good reason too. 

I guess I have to dive deeper into it, as well as try to learn more about using the software which can make improvements on the prints.

But,, truly.. this out of the box offset of almost half millimeter on even small parts... was a surprise for me.

Just wondering if I did something wrong, or if it happens to everybody, and even perhaps.. from which revision of CURA.

Printing now at -0.2mm horizontal offset (half of the total I have noticed).

Another hour to go...

[juangiluruguay 0]

Ok, I am here to report that the Horizontal offset works really well.

Has to be used as expected with HALF of the total measured offset because the print has 2 walls, one on each side of the print, so, the offset value will double!

What I measured now I think is as good as can be expected, and I am very happy.

Now I can share or take STL files and make models with real measurements, not adjusting measurements for my printer!!

Thanks to all of you who helped, and be welcomed to add more information in case it is relevant.

Maybe I can learn another new tricks.

 

Still surprised that I have not heard of this issue, that, without any input on that field, will not be handy for people assembling pieces with each other.