MakerGear Forum

Simplify 3D

When making vertical holes, I've noticed the extrusion width of the circular outlines that surround the hole seem to be undersized relative to the extrusion width used everywhere else. This results in concentric rings that just barely touch, or even have gaps in some cases, which can often result in the whole shell outline getting pushed out of the finished part when inserting screws. If I adjust the extrusion width and multiplier to make the extrusion fatter, then it over extrudes all the other lines. S3D just seems to undersize the concentric circles used to create shells around vertical holes. Anyone else ever noticed this or know of a solution?

i dont get that at all BUT if your talking small dia holes like for screws etc then excessive coasting and or a neg restart distance can give you something like that. a very high retraction can cause it a bit too

These aren't gaps at the end point of a circle, they are gaps between the extrusion lines of concentric circles. For example, the printer will make an outline around the hole using three concentric circles, then start doing the regular infill pattern beyond that. The extrusion lines on the infill pattern blend together just fine, but the extrusion lines of the three concentric circles are not fat enough and don't blend or even leave outright gaps. I'll try to get a picture next time I see it. It's a problem that has been bugging me for a long time, but with this current project I'm working on that uses hundreds of holes to make sorting screens it is really noticeable. It tends start blending better the higher up the layer stack it goes. First layer is the worst.

From that picture it looks great. If your z gap is to big I have noticed small holes being more problematic. Usually if you are leaving gaps you are under extruding a tad or coasting to much.

Can't really see that too well on the picture, but how many perimeter outlines are you running? It's a bit hard to explain, but if S3D doesn't have room to fit a full thread in a gap, it either rounds up or rounds down. If you want S3D to fill in as much as it can, set the Perimeter layers to 1, and on the Advanced tab in S3D, check the Allow Gap Fill When Necessary button, and set Allowed Perimeter Overlap to 0 %. That fills everything possible with infill. (I pretty much always print with a single perimeter.)

I've noticed that circles tend to run a lot faster, especially small ones like those. The circle outlines might not be sticking quite as well, they are standing up a little taller, and not quite squishing together as well. So if you have to keep multiple perimeters, you might try slowing that first layer waaaay down, and changing the direction (inside to out/outside to in) to see if it gives a better result.

Circles in STLs are really just made up of lots of tiny lines, so there should be in theory no difference between "circular" perimeters and long straight ones. Maybe what is happening is that the interior perimeters are being dragged in towards the center?

You can't see the defect in the picture because the gaps are too tiny, I would probably need a real camera with macro mode to get the image rather than a cell phone. The gaps actually occur equally on all layers, not only the first ones like I previously thought. It is just harder to see them as layers increase, but if you hold the finished part up to the light you can see the gaps run all the way though. I'm currently using three perimeters, but I can see where dropping that to just one would actually fix the problem since the gaps only occur on each side of the second perimeter. The reason I'm using three is to produce the thin wall frame around the screen without having infill in the middle of it, which makes it print faster. I could always put the wall on a Process2 with three perimeters and then the hole plate being on Process1 set to have only one perimeter.

I'm still curious why this even happens though. It's almost like there is some phenomenon that occurs when doing tight circles which makes the extrusion bead slightly more narrow than when doing a straight line. Centrifugal force from the circular motion maybe? I can increase the extrusion multiplier to get rid of the gap, but then everything else over-extrudes to the point of being rough and hole diameters shrink beyond the point of acceptable tolerance.

On normal perimeters, if you set the start points all at the same spot is the first 5-10mm a little thin also?

pyronaught wrote:........I can increase the extrusion multiplier to get rid of the gap, but then everything else over-extrudes to the point of being rough and hole diameters shrink beyond the point of acceptable tolerance.

Rather than doing that....in the Layer tab, you can increase the width of the extruded thread by 10-15%, just for the first layer. It might hide those holes in the surface, although the gap is still going to exist through the print. But it might be the quickest way to compromise the speed versus the fill. (Also be sure to set your Outline Overlap on the Infill tab to at least 10-15%. That makes sure you get a good bond between the infill and the outlines. 10% or less for S3D v3.0 and 15% for S3D v2.2.)

Jules wrote:

pyronaught wrote:........I can increase the extrusion multiplier to get rid of the gap, but then everything else over-extrudes to the point of being rough and hole diameters shrink beyond the point of acceptable tolerance.

Rather than doing that....in the Layer tab, you can increase the width of the extruded thread by 10-15%, just for the first layer. It might hide those holes in the surface, although the gap is still going to exist through the print. But it might be the quickest way to compromise the speed versus the fill. (Also be sure to set your Outline Overlap on the Infill tab to at least 10-15%. That makes sure you get a good bond between the infill and the outlines. 10% or less for S3D v3.0 and 15% for S3D v2.2.)

Your previous suggestion of just using a single outline fixes the problem quite well, and I think it actually speeds up the print time for that screen shown above due to reducing the number of circles that has to be drawn on each layer by 66%. Making the fill lines between the circles slightly longer should not effect print time as much, but removing 606 circle movements from each layer should really make a difference in the print time. Thanks for the idea!