Scalloped Flat Surfaces

Has anyone else ever come across the problem of Form 2 Printers leaving textured lines on flat surfaces? This has been happening to us since the last firmware update; our building roofs used to come out perfectly flat. Increasing the print angle does not mitigate the line texture, just makes tighter bands.

Any stories/suggestions would be greatly appreciated!

If the surface is exactly parallel to the build plate you won’t get these lines. Same thing for exactly perpendicular to the build plate.

You can see how the layering effects the surface finish by printing a sphere. It will be perfect on the sides and then have more layering at the top. This is similar to how a cnc mill works if you take only 2D cuts at set layer heights.

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Unfortunately, we can’t build completely parallel with the plate. The first layers become horribly warped and goopy if we try to print completely flat.

I’m perplexed because this never happened to us before the last firmware update, no matter what angle we printed the building at.

Those “stair-stepping” layer lines will be less pronounced if you print it at a larger and or if you print with a thinner layer height.

Hey there! Just to add on to what Craig said above me, this issue you’re seeing is almost assuredly do to a combination of the orientation, but maybe something in the mesh as well that’s causing it to behave this way.

As far as quick tips I can offer here, it maybe just take some experimentation finding an orientation that works for you. Typically we see these issues on parts with a very slight angle, because the standard layer lines that are in every print get stretched way out so they appear much larger and more regular. Given all of this, a steeper angle may help!

If you’d like our support team to take a look at the model for you and offer some more specific advice based on your particular case, please don’t hesitate to reach out to us at the link below and we’ll get back to you in just a few hours!

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Thanks, all, for the responses! I agree that a steeper angle would definitely get rid of the lines, but this still does not address my confusion as to why this has just started happening.

We have printed the same files several times, at several different orientations (some even flatter than these), and never had any problems until the last 2 weeks. 3 weeks ago we updated our firmware on our Form 2’s to the newest version. We are using Preform version 2.17.0, and printing at .05mm resolution.

Is there a feature included in the new firmware that may be causing this, such as the layers “overcuring” or the program interpolating layers differently than before? Has anyone else noticed a result such as this that wasn’t solved by correcting an orientation issue?

I realize it won’t be the most satisfying answer, but often these sorts of “things were fine up until recently” type questions are due to something super small and tiny that may have shifted over time. Maybe you were always on the verge of these issues appearing but it took one final variable to push you over the edge.

For example, in this case it could be due to the age of the resin, or even the compression/position of the resin tank shifting in juuuuust the right way over time. Again, not a great answer, but something like that is typically the culprit in these cases.

I’ll certainly ask around here at the office, but I haven’t heard any curing differences for White resin changing recently.

Based on the third image, it looks like the object is oriented in such a way that the roof is at a very slight angle which gives very few layers to try and create an angle for the surface, it will look better if you angle it more so that the roof is closer to a 45 degree angle to optimize the amount of layers on all surfaces.

SLA machines can create emergent periodic patterns as a form of MOIRE effect.

The layer height creates one kind of grid in the z axis.
The laser spot width is not the X/Y resolution, but the software and motors running the mirrors HAS to have a rounded off limit to how far over the laser can move with each subsequent layer. This is called Stepover, and its a second grid in the YX axis that is imposed upon the model.

Now add in that the flat surfaces of the model cut across these two grids at a specific and variable angle, and that is the intersection of these two grids… like the interference pattenr between two screen meshes that are layered and moved relative to one another… mathematical rounding of laser position combined with layer height, will result in a periodic artifact that is a form of 3D aliasing.

If you print a large enough dead flat surface- at ANY angle you choose- you will be able to see a periodic pattern to the layering in highly oblique incident light.
The frequency of this patterning will get worse in some orientations than in others.

Changing the layer height will change the pattern and reduce the height difference in the pattern.

Printing surfaces that are very close to parallel to the XY plane will create contour lines at the layer height… and becomes more noticeable because- unlike the laser, which can stepover a fraction of the spot width, the layer height is fixed and the next layer can not step up until the model data crosses a full layer height unit.

as you incline the surface to greater divergence from the XY plane the change in Z height becomes more robust and therefore reveals the more accurate profiling the laser is capable of… and the evident aliasing pattern becomes far more subtle.

Happy labor day everyone! Sculptingman… as I digest your response (thank you for being so detailed!), I wanted to bring up a new development in this line debacle. The building in the image above was printed at a relatively high angle - so the lines due to print layering were fairly subtle and easy to sand, as expected.

However, the lines you see on the angled roof in the center of the building appeared out of nowhere - and DO NOT follow the building’s print angle (see Preform screenshot). These lines are NOT visible in the .skp the building was created with or in the Netfabb-checked .stl. Any idea where these could have appeared from if not from the file?

Yeah, those lines definitely isn’t layer stepping.
Do you have some objects where they have coplanar faces? That would be parts where they aren’t intersecting but instead you have one exactly on top of the other.

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Nope, the surface with the lines in question was a single, triangulated face. This is a shelled building that passed the solid test in SKP, Netfabb and Preform.

I can see from the posted picture that that particular roof section has FOUR distinct sides- each of which is angled at a slight upward slope to the higher platform in the center. ( if the building was oriented upright. each of those four sides is modeled with a “fall” to the perimeter of that roof.)

Because of this slope, the face that was affected that falls to the criple is at a different angle to the raster of the printer than are the other faces. Each of those roof planes is is at a slightly different angle.

As I mentioned before, you can get a pronounced moire effect anytime the slope is so low that it can form an interference pattern between the Build Planes and the laser stepover.

These are really mathematical artifacts delimited by the z layer unit and the stepover of the laser in trying to calculate a path the laser can draw that will intersect an angled plane.
The software can not calculate to limitless decimal places… it has to round off to the stepover of the laser controller. So as an exaggerated example… let’s say the laser controller uses integer units. each path the laser can draw will be 1 unit greater or lesser than the previous profile.
When the plane is very shallow, the polygonal data might cross the Z height at X coordinates of 2, then 3.2, then 4.4, then 5.6, then 6.8 then 7.3
and the controller- unable to do fractional widths, will round those coordinates off to, 2, 3, 4. 6, 7, 7.
As you can see this creates a bigger jump in Z height between 4 and 6- and a shallower jump in height between 6.8 and 7.3- if the plane is flat- then this series of aliasing errors will repeat at a mathematically determined frequency as an artifact of the fact that the build height and the laser stepover are FIXED amounts, whereas the data is NOT.

the lines that appeared are PARALLEL to the build plate, relative to the orientation of the model.

If you printed the same model- with a different layer thickness- you might see these lines disappear, or get worse- depending on how the math works out.
But its WHY more angled flat planes print better, because the stepover of the laser is much finer resolution than the build height.

But you will ALWAYS see artifacts of this kind emerge when printing models with lots of flat planar surfaces.
If it is an issue you NEED to solve, then one solution is to REMOVE the roofs as separate parts that you can orient independant of the rest of the building.

The printer prints accurately enough that you should be able to fit printed parts back together without significant seams.

The issue there is not the problem you’re describing, that surface is angled at a degree where you shouldn’t see stepping like that.

Maybe it’s an issue with stability? The layers could be flexing over time, or maybe the lines could be something to do with a motor, could be it just needs some oil on the z-axis screw.

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