Settings in Cura which you might want to experiment with when you're printing with PLA / Tough PLA:
Line width: 0.4
Wall thickness: 1.2
Top/Bottom thickness: 1.2
Speeds: 40
Jerks: 20
Horizontal expansion: -0.03
walls: 3
Settings in Cura which you might want to experiment with when you're printing with PLA / Tough PLA:
Line width: 0.4
Wall thickness: 1.2
Top/Bottom thickness: 1.2
Speeds: 40
Jerks: 20
Horizontal expansion: -0.03
walls: 3
Thank you both for your help. Your info dialed in the outer dimensions for me almost immediately. It looks like the key for my inner dimensions appears to be playing with ranges of negative values for horizontal line expansion (and perhaps getting a smaller nozzle since I’m printing very small parts).
I’ll echo what @gr5 said: design inner holes with a diameter approximately 0.4mm larger.
For example, I am attaching PLA and/or Tough PLA to acrylic sheet cut on my Glowforge with M3 screws. I design in Fusion 360 with diameter 2.8 to account for 0.2mm kerf from the laser and 3.4mm in the PLA part. This is usually a snug fit. I could probably go to 3.5 if I wanted the bolt to slide easily.
In general, if I want a printed part to slide inside another, I will design about 0.2mm clearance for a smooth sliding join. If I want a tight fit I might use 0.15mm.
most of these parts are under 40mm in longest dimension. Many much smaller.
All of these dimensions came from trial and error. Also, first layer squish will make the hole smaller there. Do test measurements on a hole opening further from the bed. It’s easy to open the first layer up to match the rest with a small knife.
I’m using 0.4mm nozzle with 0.1 layer height.
i do notice that horizontal holes in vertical walls tend to be about 0.1 mm larger than the vertical holes.
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gr5 2,224
Cura knows to offset the lines by half the nozzle width. So that's not it.
However vertical holes are always printed too small. Add around 0.4 or 0.5mm to every vertical hole diameter in CAD.
Also other things you can do to improve other dimensions:
Make all printing speeds the same and around 35mm/sec or even 25mm/sec for super accurate. Disable jerk and acceleration control (this will make ringing worse but will make dimensions more accurate).
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