One man's epic journey to create a personal 3-dimensional printer
without breaking the bank.
Monday, January 6, 2014
For your viewing pleasure
In case you are interested and have about 8 minutes to kill, here is a video I shot while the Dalek was printing. I have a float on a lever in the resin tray (on the left side) that blocks an opto interrupter. Every 10 layers the printer checks the sensor and if it is unblocked it triggers a relay that turns on a fish tank air pump. Air is pumped into the resin jar and forces resin up the tube to the vat. the hissing sound is a pressure relief valve (a small hole in the cap) on the jar. Without it the resin kept flowing for quite a while after the pump stopped. You can see I eliminated the power tilt and went with a passive design. The tray is hinged on one side and allowed to lift and fall back by itself. The thud is the sound of the tray dropping back down. Interestingly, You see that after the first few layers there is almost no movement of the tray. Once the build platform gets some distance from the floor it doesn't have the suction when it lifts. Exposures with small surface areas release so easily that the tray often doesn't lift at all. Unfortunately that also makes it difficult to tell if there has been a printing failure, such as the part separating from the build platform. I changed the front of the resin tray to clear so I could spot a failure before it made a big permanent blob and ruins the Sylgard.
The first couple layers get a longer exposure (about 9 seconds) to stick it to the build plate. After that the exposure is 5.5 seconds per layer. The Z axis lift is also higher for the first few layers. I found that after about 5 layers I only had to lift about 1/8". That helped cut some time off the total print run.
I also changed the vat floor. My first floor was a piece of 1/4" Plexiglas with a Sylgard 184 coating. I have since switched to regular double thick glass. Nothing special just plain glass. By using glass I can heat cure the sylgard in a toaster oven in about 40 minutes instead of waiting 24 hours for it to cure at room temp. I made the Sylgard layer a little thicker and so far it has held up well, 5 or 6 prints with no noticeable degradation. Also added is a red plexiglas filter/shutter that blocks the lens before and after printing to eliminate accidental exposure during set up and clean up. you can hear it being moved out of the way just before the projector comes on the first time.