We’ve been noticing that some of the circular holes on our prints haven’t quite been coming out as an actual circle. More specifically, when a circle is along the z-axis, the top and bottom of the circular hole end up a little flat. And when I say top and bottom of the hole, that’s in relation to the orientation of the part when it’s printing, not the orientation of the part itself.
(PLA printed with 0.4mm nozzle and 0.3175mm layer height)
This is due to a combination of the drooping of the bridging on the arch and layer height. It's still mostly a circle, which may be good enough for many applications, but the flats on the top and bottom of the circle can cause some trouble when trying to tap the hole or put in heat set inserts. In order to reduce the flats and get a more accurate circle, I tried adding small points tangent to the top and bottom of the hole.
To start, I tested adding an extra 0.25mm and 0.5mm to the top and bottom of the holes as well as printing an unaltered hole for comparison. I tested this on 4mm, 5mm, 6mm, and 7mm holes to see if the size of the point added would need to be scaled up with the hole size or not.
After a quick test print out of PC filament using a 0.4mm nozzle with 0.3175mm layer height, the added 0.25mm tangent points on all holes looks like it’s turned out the best circles. The added 0.5mm tangent points on all holes look like they’ve gone too far in the opposite direction and are too pointed. The points so far do not appear to need to be scaled up with the increasing size of the holes, but the sizes of the holes tested are relatively close to each other. The next step in this project will be to test both the 0.25mm tangent point and the 0.5mm tangent point on larger diameter holes such as 15mm, 20mm, and 25mm holes.
7mm holes from left to right unaltered, 0.25mm point, 0.5mm point
6mm holes from left to right unaltered, 0.25mm point, 0.5mm point
5mm holes from left to right unaltered, 0.25mm point, 0.5mm point
4mm holes from left to right unaltered, 0.25mm point, 0.5mm point
Unaltered 7mm hole has flat areas on the top and bottom of the hole
7mm hole with 0.25mm tangent point is visibly more circular than the unaltered hole
7mm hole with 0.5mm tangent point is too pointed
I hope this helps everyone print more circular circles along the Z-axis. I’ll also post an update soon about how well this works with larger hole diameters so be sure to check back to see the results.