Getting closer to reshelling my SE/30. . . Printed my version of the brightness knob, finally:
Clarity isn’t perfect obviously with FDM printing, especially with something this thick. Early on I had a hell of a time printing with this, but eventually dialed in great settings for printing on my Prusa Mini+. A few tips I picked up when trying to print ”light pipes” for LEDs in clear filament:
1. Reduce the amount of directional cross-hatching by aligning layers to print the same direction every time. In this case, because the object is round, I am using a 100% infill, concentric pattern achieved by bumping up perimeters to 8 which basically eliminates the infill setting and keeps the nozzle moving in circles the whole way (with one exception below).
--Note that while this may not be crystal clear, it’s a much nicer effect than you would get from a grid-like monotonic infill that alternates 90 degrees every layer! All of that cross-hatching will result in tiny overlapping air gaps which scatter the light. Aligning the nozzle direction every layer helps reduce that.
2. Thicker layers are better here. If this was a single-walled vase-mode print, thin layers may work to your advantage, but the knob needs to be strong and rigid. In this case, thicker layers will put down bigger filament “tubes” to permit the light vs. lots of thin layers that might have more air gaps between them scattering light. YMMV, of course, but I find with thick stuff, a .2mm layer height has better clairty than thinner.
3. Get your temps right. For Taulman T-Glase which this is, I find 220C to be the right temp to avoid scorching and to get good layer adhesion, and 330 for the first layer to compress and stick nicely to the bed. Running the fan is also recommended. I run it at 40% after the first few layers.
4. Be mindful of overhangs (this model). My model prints in two parts to avoid supports. The knob itself prints with the post end up, slowly coning to the center. However, there is a moment after printing the keyed hole for the post that it needs to print a small bridging layer. If you adjusted your model to use 8 perimeters to get perfect concentric infill as recommended above, check the first bridging layer at 19mm. For me, the slicer created circles in thin air for that are supposed to bridge—but they wont. This would have been a disaster since the filament would just dangle down the middle and probably booger up the point that needs some precision where the post will go. To correct this, I added a modifier at 18.8-19.0mm to change to 2 perimeters. The slicer took the cue to draw simple, straight bridge lines and cross-hatched this area for two more layers for perfect bridging. This is directly under the pin and over the post that will be glued anyway, so not a concern for transparency. The concentric areas everywhere else are maintained.
This stuff is apparently PETT, a close cousin to PETG. It’s really tough stuff, It sticks great to PEI beds, and you can wet sand the seams and polish with fingernail buffing tools if you like. If you print this filament at 240, it gets all goopy and the pin sags into the center. At 220 it is beautiful.
Resin would be better, but I will be very happy with this I think.