I was under that impression too, but if there is a polarizing layer that is 90 degrees to the one in the LCD itself, then it may help pass more light. I'll have to experiment. I just can't believe that a decent flashlight (120+ lumens) could barely make a dent in the spectrometer readings when passed through a white image (Windows Notepad opened full screen) on the LCD.

 

Slow for the moment, but hopefully I can get some kid free time for Fathers Day

I hope to pick up a router table tomorrow. That will allow me to round off the corners of the vat, as well as put a decent finish on the LCD mounting plate.

 

Progress! Managed to get the vat assembled and the bottom edge routed to a 1/8" radius. That should minimize any chance of tearing the film when I go to stretch it across the vat.

You can see in the pictures some of the corner braces I printed to assemble the vat. They just clip in place with binder clips. Worked quite nicely.

 

This red acrylic did a fantastic job at filter out short wavelength light. I have a few cheap flashlights made up now with various wavelengths of LEDs, and a 405nm LED was filtered so much I could see the die pattern clearly.

I'm not 100% thrilled about the strength of the walls of the vat seeing as they are only 1/8" thick. It was all Tap Plastics offered. I can get thicker stuff, but I would have needed to order a larger sheet and cut it myself. I was lazy and had Tap cut these for me

To increase the strength, I'll probably glue in some 1/4" square strips of acrylic into the corners to brace them a bit. I don't want the corners to break when I'm man handling it while stretching the film over it.

 

I only buy cell cast acrylic. Extruded acrylic is a big no no in the aquarium world (another hobby I'm deep into) due to it's tendency to absorb moisture, swell, and crack. We shall see how this works out though. The solvents in the resin may not play nice, but maybe the solvents in the daylight cure resins are less aggressive than the UV cure.

Speaking of resins... I was talking with Bucktown Polymers last week. They have a selection of daylight cure resins (peaks around 470nm) that they can formulate to your needs, but buying the stuff seems to be a painful experience. No matter how many times I asked, I couldn't get a straight answer from them as to what kinds of volumes I could buy from them. At least from the website, you can either buy a 250mg sample bottle (one color only, yellow), or a 20kg pail. Asking them over email if I could buy in smaller quantities just lead me in circles with no apparent answer. Buying from these guys would have been great, as they have a good number of options in any color I could want, and being a US based company, the shipping would have been reasonable. They just don't seem to want to deal with the likes of us. Going to try again today to see if I can get a straight answer

 

I had thought about that, but I just don't want to have to deal with packaging it all up, pigmenting it, and possibly selling it (I wouldn't have any need for 20kg of resin EVER).

 

I'm sure they are similar. The big advantage from getting the OB ones and not the Harbor Freight ones is that the Harbor Freight ones only come in a kit. You can't get them individually if you break one. I broke one when I used PB Blaster as a lube, which was a mistake. WD-40, while not really a lubricant, work way better. Tap Magic would be ideal. Regardless of where you get them from, they are a massive time saver.

As for progress, it's been slow. We have had a few family vacations over the last two months with has eaten into my weekend project time. Right now, I'm in the process of fixing the fence on my router table so that I can trim down the top plate to mount the LCD. The injection molded fence isn't exactly flat, so I'm building up a new outer surface that will be a little more true. I have the frame squared up now and the Z-axis actuator in its final position (for now at least). The first build is going to just use the LCD backlight until I can get a decent backlight setup sorted out.

 

Interesting idea with the vacuum pump. I was planning on just having the vat frame sit a little lower than the upper surface of the LCD so that it tensions the FEP film once the vat is in place. That basically kills two birds with one stone (tensioning the film, and getting the film as close to the LCD as possible). But the vacuum pump would work well to get the film to suck down to the top glass of the LCD, as it would sit on the assembly tape otherwise. That will be something I will have to play with once I have a working system.

As for the air bubbles, I had thought about that. Wouldn't using a perforated build surface also take care of this issue? I know that there is still a small likelihood of small bubbles remaining on the build surface, but small issues like this should only appear on the first few layers, as everything is submerged for the remaining build time (won't be introducing any air back into the resin).

Anyway, some interesting ideas staccers. Care to share any pictures of your printer?

 

The Photocentric printers we one of the devices that pushed me into making my own. The price is pretty reasonable compared to DLP solutions, but I wasn't all that thrilled with the resolution. Still, good for them for being one of the pioneers in this realm of rapid prototyping.

 

Looking good scarab. I may have overlooked it, but what resin did you use?

 

It's been a little slow, but I'm hoping to get back on it in earnest very shortly. Some of the time has been spent cleaning my garage so I can work on projects, the eternal bathroom remodel, kids (!), some short vacations, and of course that ultimate destroyer of motivation, work Starting another 3D printer build didn't help either, but at least that project is going together quickly.

I am going to continue to work on the LCD transmission issue. I have made a series of flashlights with various LEDs of differing wavelengths (8000K white, 4500K white, 3000K white, 405nm, 420nm, 455nm, 460nm, 470nm, plus more, but not needed for this experiment). With these, along with a better test rig (something more solid for the LCD will make me feel better, as they are a little delicate), and I should be able to come up with a reasonable idea as to just what we can do with the iPad LCD.

The first stab at a working printer is most likely going to be with a stock LCD, so cure times will be slower, but at least I can prove out the vat, LCD, Z-axis, and control system.

 

You don't want something like that, unless your LCD is the same size as the LED. It will create a hot spot directly over the led, and the perimeters of the vat will not cure at the same rate. You want a larger array of smaller 3W LEDs covering the entire LCD area for even coverage. Chinese 3W LEDs are dirt cheap, and with the leads being exposed, it's pretty easy to just epoxy the thermal slug if each led to a heatsink and solder the LEDs in series parallel arrays. You could do an array the size of an iPad display for about $100 with heatsink and drivers.

 

It will work to a point, but I still don't think it's the best choice. Fresnels are good for taking off angle light and turning it parallel to the axis of the light source (straight down, or in our case, straight up). You would still need to use multiple high power LEDs to cover the area, but with a fresnel, the light intensity will be more even than if you didn't use one.