So welcome to the near impossible task of getting a perfect tolerance with a machine that is laying down melted plastic from a big chunk of suspended iron that is being pulled by a belt oover two large iron rods.
I am going to try to help you, but you are in for a lot of testing and fiddling, to get to where you need to be. My first recommendation is to not print the whole item with each test, and just print a shorter version. I hope you have Simplify3d, because the advice I am going to give you will be for it…
Bumps first: Everything @cobnut said, and then some. Read this: Print Quality Guide | Simplify3D Software
The zippering (bumps in a row) you are seeing is a combination of required retraction, and perhaps other issues. If you are using simplify 3d, start with the following and work from there. If you are using some other software, then you will have to see if you can find other settings that are similar.
Extruder TabRetractionRetraction Distance1 Extra restart-0.3 Coast at endCoasting distance0.2 Wipe NozzleWipe Distance5 Layer TabOutline Direction mess with on or off Advanced TabOoze ControlOnly retract when crossing open spacesmess with on or off Turn ON the rest here, such as force retraction, minimum travel, perform, and only wipe The objective here is to get the material that is drooling or forcing out during the release of pressure from the pause that happens either when the layer starts or when it stops.
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Now, the fact that your whole model is undersized is a little worrisome, but I am thinking maybe it is shrink. Its the easiest to fix. Since the inside and outside look undersized, I am thinking you can increase it. In S3d, under other, you can mess with horizontal compensation, which in your case would open up both the inside and outside. Failing that, resize the whole model, but set your “stop printing height” at the height you want the object to be under the “other” tab.
AND, you should understand that your tolerances are well within what you should expect. People need to understand this. When you are talking about a difference in width of .4mm on PLA, which (I believe with a .4mm nozzle swells to about .48) you are talking about a difference of less than 1/2 the hole of your nozzle on each side…
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One final note on inside tolerance. This is really an issue with too much material, but it is even a little more complicated than that. I dont know where you are from, but here in the states we have these large extruded foam toys for the pool we call “pool noodles.” If you take on of those, and squeeze in into the shape of a circle, you will see the outside of the circle is taut while the inside has squished foam in it. This is also what is happening when you print very small circles with an FDM printer. Extra material ends up inside, squished. This makes small holes smaller than they should be. There is no great fix for this in S3D, and is the primary complaint with slicers in general, that they simply do not take this into account. Your probably going to have to make the hole inside the model a little bigger to get to the exact tolerance you want. Or tap it out.
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Finally, some other things. I just did a massive print job that did not match within the tolerances that the customer wanted and that I would have expected, and it was a disaster. I spent a lot of time on trying to get the damn thing within tolerances. Finally I measured the STL. Sure enough, the STL was wrong. Make sure your first step is to not proceed from the assumption that the STL is actually correct without checking it somehow.
I hope you are getting paid well on this print, lol.
PS, as a side note, I don’t know if you saw the the great “tolerances” thread on here when 3dhubs implemented their tolerance rules when everyone gave feedback that was pretty much just all us talking and 3dhubs implementing it while it was still being discussed. This is a perfect example. I assume the part needs to fit exactly over something, and inside something else. But even PLA changes size as its printed, between melting point and crystallization, and changes size while it sits and absorbs or loses humidity. .4mm is very, very small. I am guessing if you measure that print in a few days, it could be much closer or farther off in size than when you took that photo. So good luck. Hope I helped.
