Pooling around touch points

Hi folks.

So today I’m puling the first real Durable ‘engineering fit’ parts out of the printer and cleaned up. I am amazed at the fit achievable with this printer. I’ve only allowed a tiny amount of tolerance for push fit parts, bearings are pushing into positions perfectly and cranks/cams are fitting the id of the bearings really well. I am seriously impressed.

Only one small issue, and it is small but it’s something I’ve noticed with most of the resins, not so much the white for some reason.

Flat bottoms are a problem, or to be more precise, flat surfaces with multiple touch points are a problem. If a surface is skewed from one plane only, and that surface is towards the bp, I get a rough surface around the touch points. Obviously there are more touch points on this surface as it’s upwards (on the printer).

With a couple of the parts that have finished this morning it’s obvious I could have oriented them better, but with another couple, because of the geometry, there’s no way I can avoid a flat-‘ish’ surface somewhere on the part. And in this case I’m printing Durable which has a certain elasticity which needs careful placement for tight fit surfaces.

How do you folks get around this problem? I’m reluctant to cut precision or loaded parts and glue them, there are threads on glue!

Any ideas welcome as always.

Many thanks.

That’s an issue that’s always going to be a problem with SLA printers, the laser will go through the current layer and if there’s uncured resin beyond that it will cure some of that extra material, which means that downward facing surfaces will have extra materials. Besides that, depending on the composition of the resin there will be some glow around the laser spot (sub-surface scattering) which will cure extra material as well. In some areas, like around the supports the resin won’t flow so easily off the print and will be subjected to multiple passes of indirect illumination from the laser.
Besides that, as the print builds up if a layer is significantly bigger than the layer before then it will be more fragile and will be more sensitive to movement as the tray moves to do the next layer.
What this all amounts to is that you’ll get extra material around supports, and then sometimes on the areas between supports you’ll get an arch where some of the resin has worn away due to the layer separation.

The best way to mitigate the issue is to orient the part in a different way and place supports in a way that you use as few as possible and the areas where you do have supports can easily be sanded afterwards. In the projects I do, sometimes I’ll split up parts so that the important surfaces can be oriented upwards or so that I can hide surfaces where the supports were.
Some of these issues will be improved in the Form3, the new printing technique places less force on the print because of how the bottom of the tray kind rolls/peels from underneath the print so that will result in less damage to fragile layers. The technique also means you would need less supports which is always good. Also, it’s possible that the way it’s working will result in a thinner amount of resin that the print will be submerged in which gives a smaller chance of the indirect curing (if the part isn’t submerged as much). The laser point is also oriented in a better direction and since it’s smaller it shouldn’t have as much indirect curing.

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