First prints, sizes problems
Hi all,
So i built the kit and managed to fight through the initial problems with the PLA totally not sticking to the textured sheet. The next thing i noticed is that my prints are slightly undersized, i have an object with what is supposed to be 22mm hole in the middle, on the finished print the hole reads 21.5mm on calibers in all directions. this i think is fairly significant, since the parts were ment to house a bearing that will not fit. I would not like to make my parts oversize because that messes up with everything else on the drawings where some parts are machined and some printed.
Is there a calibation somewhere for this, or some standard process to go through to validate this and adjust this?
RE: First prints, sizes problems
The scale is calibrated using points embedded in the heat bed. If you ran the full calibration cycle, X, Y, and Z accuracy is generally pretty good. 1% or better - and most do a lot better than 1%. E.g., I see better than 0.1%. Also, if you've adjusted belt tension after running a calibration cycle, well, calibration is 100% dependent on belt stretch so you'd want to rerun cal after adjusting the belts.
Holes are probably the exception since they depend on scale plus extrusion rates. If you haven't printed a calibration cube, that'd be my next step. It allows a check of scale and extrusion rate. You need an accurate caliper or micrometer to measure the cube wall thickness. Essentially you are checking that when printing a 0.42 mm wall you are getting a 0.42 mm wall.
RE: First prints, sizes problems
@tim-m30
alright, thank you for the tips, is there a standard cube somewhere or should i just go and print one?
There is the one for the extrusion thickness i found, which i can measure with the micrometers easy enough, i'll see if have time to run these tests later today and report the results.
thanks again,
Janne
RE: First prints, sizes problems
@lekonna
https://help.prusa3d.com/en/article/extrusion-multiplier-calibration_2257
RE: First prints, sizes problems
I ran the calibrations on the device again.
printed the test cube part, the wall thickness seems to range from 0.428 - 0.435 which i think should be fine, for sure its not the reason for the half a mill of discrepancy. The outside diameter seems to be almost dead-on, but its difficult to tell with that part, so i printed another part. Here the outside diameter seems to hold well but the hole is again undesrsized, though not that much anymore, maybe due to this being not as thick as the original part in z?
Anyways, i'm very happy about the quality of the print otherways, i dont see obvious artifacts. I tested with a dial gauge, the x axis is consistently few 0.01 of mm short on steps, the y axis seems to be much closer to true. Maybe i'll just have to keep in mind that the parts will not be accurate and modify the models accordingly.
RE: First prints, sizes problems
I've not researched the coefficients of expansion for Polylactic Acid - but it's not unreasonable to expect some shrinkage from print temps to room temps.
https://www.e3s-conferences.org/articles/e3sconf/pdf/2018/07/e3sconf_eenviro2018_01007.pdf