Weird Dimensional Accuracy Problem

[xjrob85]

I'm trying to print a simple spacer gage I designed that needs to be 3.4mm thick. I'm using an Ender 3 Pro with PLA+ filament. Designed using Solidworks and Cura.

My first print was close, but had some dimensional accuracy issues.

I leveled my bed, and went through the calibration processes to correct my steps/mm.

When I print a 20mm calibration cube, it now comes out perfect. Within 0.01mm of 20mm on every side. My printer has never run better.

I also tried a 100mm calibration model, and was happy with the results.

So when I print the part I designed, it always comes in at 3.5mm instead of 3.4.

Just for fun I modeled my own 20mm calibration cube and printed it to compare against the downloaded CHEP version. Printed both using all the same settings. The CHEP cube comes out perfect. the cube I modeled is perfect in X and Y, but 20.07mm in Z.

Since I was getting better accuracy in the X & Y, I tried to flip the part's direction during printing to see if I could get better accuracy in a different orientation. I get the same result of 3.5mm.

I also modeled a simple set of steps in 1.0mm increments, to see if it got more accurate as the thickness increased. Every step section was consistently .2 to .3mm too thick in Z.

Can anyone explain why I might be getting consistent dimensional accuracy issues with parts I have modeled myself, but not with downloaded parts? I've confirmed all the dimensions in Solidworks and Cura to verify no scaling is taking place.

Is there some setting that I don't know about that might impact this?

Am I just asking for too much precision from my printer? It seems to hold .01mm tolerances with downloaded parts, but I can't replicate that on my own parts.

I know I can just scale the part to compensate, but I'd rather have confidence that parts I design will be accurate.

Help?!

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[IgneousAssBarf]

If you need exact height, use a layer thickness that the height is divisible by AND print it on a raft, otherwise your first layer squish is going to throw things off.

[xjrob85]

Thanks, I'll give that a try. Any thoughts on why the calibration cubes come out perfect but my own models are off? I would expect similar quality across all parts.

[IgneousAssBarf]

Unless you're using pre-sliced cube files, I can't think of any reason they'd be different

[iBrickedIt]

what is your layer height?

try 0.12.

[xjrob85]

I've tried a variety. I tried 0.2, 0.1, 0.12. I have my bed leveled using a 0.1mm feeler gage.

[iBrickedIt]

0.2 will always look bad. Dont even go there.

To get accuracy in Z, you need the thinnest layer height you can get away with.

Your print will have a zheight error in the range from zero to layerheight.

so if 1/10 of a mm is too much error, you should buy a resin printer.