Need some help understanding this…
A 50×50mm square
With a circle in the center having an outer diameter of 30 mm and an inner diameter of 20mm.
But what I am getting is a 50.4 x 50.3mm not out of the usual but the 30mm OD of the circle being under at 29.6 and the ID of the circle being 19.6. I again understand the ID being off from say over extrusion but I would also expect the OD the be larger by say .4 to .6mm.
It was printed in ABS on a custom printer, .2mm layer and .4mm nozzle at 50 mm/sec. Using RAMPS MEGA and MarlinRC8. I did check the stl and dimensions are correct there. Is this normal?
It is driving me crazy any help is greatly appreciated.
Because circles aren’t handled as continous arcs, they’re interpolated as line segments approximating the circle. The problem you’re seeing isn’t one of extrusion, it’s more basic than that.
I had the same issue with ID. Try different slicer and extrusion width.
Along the line of what Stephen mentioned if you increase the STL resolution of the circle geometry you will get closer to what you intend. However, a 0.2mm offset on an arc is pretty typical. I find that is the clearance I need to design into high resolution cylinders to get them to fit snugly and still pull them apart again.
Yep. Even “well tuned” - which I define as a proper filament diameter and steps per mm based on your extruder, with a 0.4mm nozzle holes come out 0.4mm too small. It’s a slicing thing. Just adjust for it in CAD if you can.
I usually do a simpler thing, on outer parts reduce 0.3 mm and on the internal parts reduce 0.3 mm, that helps a lot
What was it sliced with? Slic3r has a horizontal size compensation feature that should improve this significantly. Of course, depending on which one your’e using now, switching to a slicer with a different extrusion volume algorithm might fix the problem (or make it worse).
Thanks for the advice, it was sliced in Cura btw. I will look at the stl resolution.
If, the internal diameter is 10, make it 10.3, that way the abs have some tolerance to shrink (or expande in this case)