Printing inaccurately from model
Hello, my prints are not accurately matching my model. It is printing slightly off or there is a small scaling factor being applied, but I can't find the source of it. For instance, my model has a feature that is 7.894" (200.51mm), but this feature is printing at 7.876" (200.05mm). I verify this in my modeling software, create an .stl and import it into PrusaSlicer, and remeasure the feature within PrusaSlicer and it is the same, but the actual print is where I find the problem. Some observations: 1. I am using FreeCAD 1.0. This may be my first print since switching from FreeCAD 0.19 and I didn't have this problem previously, but would think an stl is an stl. 2. I am modelling in inches, but have exported with FreeCad set to inches and millimeters, with the same results in the final print. 3. The printer is MK3S+ purchased in 2021. The firmware has never been updated.
Any ideas? Thank you.
RE: Printing inaccurately from model
You are aware that plastic shrinks as it cools ? That deviation is well within the expected tolerance for this sort of factor. Its is also quite usual for holes to be slightly undersized too due to same/similar factors. Even with a well tuned printer. Many people take the production medium into account when designing things.
Beyond that make sure your printer is tuned and that you have no under/over extrusion (which has to be done on a per filament basis). You can also calibrate extruder steps per mm but Prusa printers generally don't need that as its all done at the design stage and QC is generally pretty good.
RE: Printing inaccurately from model
Neophyl, I really hadn't, I hadn't done prints previously that I was so worried about dimensional accuracy, but it seems obvious now. I guess scaling up the model to 100.2 or 100.3% before printing should correct the issue for me. Thank you.
Unrealistic expectations of accuracy crop up fairly often. Much of the blame lies with the ready availability of highly accurate micrometers and calipers but for some reason people don't complain so much when doing carpentry.
Part of the design process is adapting to the quirks of the medium. 0.2mm tolerance is about the closest you can get reliably so scale bearing points, threads and involutes accordingly. Where it really matters design with post-processing in mind. Just as you wouldn't expect a cast metal part to be ready without finishing think of printed plastic as the unfinished penultimate stage.
Expect your basic limit of precision to be around half the diameter of the standard nozzle, but:
If an error is proportional to the dimension then you may just be seeing thermal contraction: is your printer laying down hot plastic accurately - which then contracts as it cools?
Address this with calibration of your original design.
There are other minor distortions, most often of curves, caused by triangulation and rational approximation when translating ideal dimensions to practical printer movements. Trial and error will usually find an optimal value in a couple of iterations.
And the usual advice applies when making dimensionally critical blanks, build slightly oversize and machine to fit.
Cheerio,
RE: Printing inaccurately from model
Print at 100%, dimension comes out -.3% from model. Print at 100.3%, dimension comes out +.3% from model. Print at 100.15%, model comes out +.2%. Going to take a break...
So you've reached the point where you're adding and removing single perimeters - you *might* gain some additional control with:
Print Settings > Layers and perimeters > Advanced > External perimeters first
...but this will trade-off against overhang quality and corner precision.
Cheerio,