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Top-Down SLA Printer
02-16-2015, 03:28 PM,
Top-Down SLA Printer
I thought we might be able to use on of the projectors at the space, but apparently that model splits the light three ways and passes through three separate LCDs before rejoining them. I think that might lead to far too much UV power loss. So I ordered a used DLP projector, which just got here. Arduino UNO, GRBL shield, and stepper drivers are on the way.

For now, the plan is to get the projector and Arduino working in unison. Once that's achieved, I'll acquire and figure out the bearings, screw drive, frame, and vat. I'll probably aim for a salt water float to reduce resin requirements.

Step one is to pull the projector apart and remove things that block UV. Namely, filters and the color wheel. Once that's complete, I get to reposition the lens to change the throw. The used projector I found has a throw of 5+ feet. For the projector I need to bring that down to about 8". Optionally, I may need to bypass the ballast and replace the lamp with UV LEDs. May do that eventually just for the performance, but we'll see.

To that end, anyone know if there's a small torx set in the toolbox? I don't have anything handy in the 2mm range.
02-20-2015, 10:46 AM,
RE: Top-Down SLA Printer
Didn't get a chance to tear into the projector, but the Arduino stepper driver shield was soldered up last Wednesday. The pololu-compatible A4988 stepper drivers arrived and I tested the Z-axis control last night. Nothing too exciting, but I didn't blow up the driver which is a good start.
02-23-2015, 06:08 PM,
RE: Top-Down SLA Printer
Any day you didn't blow up a stepper driver is a good day Smile

"If you didn't build it, you will never own it." - Barton Dring
03-04-2015, 11:17 PM,
RE: Top-Down SLA Printer
Played with the Z-axis driver and configured everything tonight. Went well, got the Z movement synced with the projector output.

Haven't pulled the projector apart yet, but that's next on the list. After that, the frame and belt drive. I think I've got it figured out so I can dip the platform into the resin/salt water bath without exposing any moving parts to the salt water. That should minimize corrosion and thus minimize friction on the drive components. Not entirely sure how I'm going to build the platform yet, but I'm thinking a sheet metal box dipped into the tank length wise.
03-11-2015, 09:52 PM,
RE: Top-Down SLA Printer
Resin test tonight. Started curing, but only after 3 minutes of exposure. Obviously not enough UV making it through the bits of the projector. Definitely need to strip it down. Don't know if I'll need a stronger UV source yet.
03-12-2015, 05:58 PM,
RE: Top-Down SLA Printer
I would love to see some pictures if you can!
03-12-2015, 06:09 PM,
RE: Top-Down SLA Printer
Pictures of what, exactly? At the moment I've got a GRBL setup with only a single stepper driver attached to a Greg's extruder for testing purposes and a separate projector. Not much to look at, yet.
03-18-2015, 10:56 PM,
RE: Top-Down SLA Printer
Drilled out the bolts on the projector today and started the teardown. Broke the color wheel off so I retain the encoder feedback to keep the driver from freaking out, but don't have the plastic wheel blocking UV. Began working on the light path to check for extra filters that may reduce UV output, but that's going to require more disassembling. Unfortunately the lens assembly on screws out so far even with the case removed so I'm definitely going to have to figure something out for that.
03-19-2015, 09:05 PM,
RE: Top-Down SLA Printer
Tore the projector down further. Removed the focal length ring and filed down the focus stop to allow focusing at very close range then put it back together and fired it up.


Got it to focus at about 8" or so with roughly a 4"x3" display which gives a resolution of about 0.099mm per pixel at the native 1024x768. Trying to decide if that's enough, or if I want to half that by using 2"x1.5". That would require extending the focus a bit more, but we can print that!

Without the color wheel in the way, I get a black and white image and that 200W xenon bulb puts out enough UV to cure in about 3 seconds at that range. Did some testing in the kitchen on wax paper curing resin and got smoke after 10 seconds; kind've expected since the curing process is exothermic plus the UV heat input.

I did introduce a flicker to the screen, so I think one of the connectors is lose but it should be easy to correct.
04-13-2015, 05:21 PM,
RE: Top-Down SLA Printer
Further investigation showed no loose connectors, but the flickering gets worse the longer it's on. Probably a heat-related issue. Maybe a loose heat sink? Insufficient airflow?

The threaded z-axis rods are on their way, as are the bearings. Have the GT2 timing belt (closed loop), pulleys, and everything else. Just need to build the frame. Thinking 6" Schedule 40 for the vat and 1/4" hobby board for the z-drive and projector support. Shouldn't take much for a small machine.

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