One Step Back, 2 Steps Forward

      So, I've been doing a lot of printing on my 3d UV DLP printer lately, making little tweaks here and there. A few months ago, my friend Tristram Budel http://3dprinterplans.info/tag/tristram-budel/ was kind enough to send me one of his high-quality machined build vats. The frame of it is machine from a solid piece of aluminum, and he uses (I believe) FEP sheets to coat the vat bottom. He also uses a thin piece of borosilicate glass http://en.wikipedia.org/wiki/Borosilicate_glass

      I've been printing increasingly larger models on my 3d printer, and I think I hit a limit. As some of you know, the amount of force required to 'peel' a slice of a model off of the bottom of a vat can require a tremendous amount of force. Unfortunately, it was too much for the vat, and the borosilicate glass bottom broke, showering resin all over my mirror, projector & electronics, ugh...

The Remains of the vat

      After a lengthy process of cleaning up spilled semi-hazardous resin, I began to plan on how to fix it. I located several EBay auction for borosilicate glass. Most of these auctions were selling panes of glass that act as a stable build surface for FDM printers.http://www.ebay.com/itm/Borosilicate-glass-for-RepRap-3D-printers-214mm-x-200mm-x-3-3mm-/321241665891?pt=LH_DefaultDomain_0&hash=item4acb7ed163

      Borosilicate glass is used for it's optical transmission properties. Shown here is a few comparisons between several types of glass http://www.sinclairmfg.com/datasheets/optical3.html . Ultimately, I decided to take a chance. Instead of shelling out 25$ for a pane of glass, i decided to use a 5mm thick piece of polycarbonate plastic (Lexan)  that I had laying around from another project.

Polycarbonate - aka - 'bulletproof glass' or 'Plexiglass' has fairly decent transmission properties. It does NOT transmit deep UV, but it looks like right around 390nm or so it starts.

Spectral transmission for polycarbonate

Polycarbonate pane 155x155mm x ~5mm

      I knew that I was going to need a vat coating, I went ahead and ordered a few samples of FEP sheeting from CS Hyde http://catalog.cshyde.com/viewitems/films/fep-pfa-clear-ptfe-film?&bc=100|1002 . I ordered 1 sheet that was self-adhesive and 1 sheet that was not.

Taking a picture of  sheet of plastic is difficult at best...

The aluminum frame and walls all cleaned off, ready for a replacement

      I replaced the broken borosilicate glass with the plexiglass pane. I decided to use the FEP sheet that had the self-adhesive and I immediately regretted the decision. As soon as I peeled the FEP from the backing, it curled up and stuck to itself. It took a little doing to get the FEP properly placed on the plexi, and even then I was plagued by bubbles. Of course AFTER the fact, I did a little research on how to properly put down adhesive-back sheets (stickers, window tinting, etc...), so maybe next time, I'll have a little better luck, or use the non-adhesive version.

      I added in a generous amount on silicone sealant, and remounted the vat back on my machine. I was initially concerned that the plexi might block more UV light than the original, but after a few test prints, I was fairly convinced that there was no significant difference to the optical UV transmission for the lamp I was using.

All back in working order

     One new feature I added to my printer was a peristaltic pump (http://en.wikipedia.org/wiki/Peristaltic_pump) that I ordered from China. It was originally intended as a small aquarium medication pump. At first I was wondering how I was going to control this feature through Creation Workshop. Should I add a motor driver section? Should I have the controls automated? What G-Code could control this? In the end, I realized that I was completely over-thinking this, and I added a simple DPDT (double pole - double throw) switch connected to a 5v power supply. This allows me to control the direction of the pump. 

      I drilled 2 holes in the cap for the resin. The tube went through one hole in the cap, and the other hole is used for venting. I used a small fuel-line hose that I bought from an auto-parts store to extend the short hose of the pump. I also used a few short segments of brass tubing to connect the various hose lengths together, and to act as weights for the end of the hoses.  I did a few tests with some water and a few glasses to verify that the pumping system was working properly. The flow rate was good, no leaks, everything looks like a go!

     I mounted the peristaltic pump system in my printer. I used the word 'mounted' a little loosely here. It's actually just wired into the power supply and placed in the area that I want it. I did a few tests pump resin in and out of the vat and back into the bottle. It looks like everything is working well. Now I don't have to detach my vat to drain it, or use a syringe or funnel to get the resin back in resin container. In the next day or so, I'll probably FDM print a mount plate for the switch and pump and zip-tie a few cables.
The only thing I would change about this set-up is using BLACK tubing. I'm concerned about light curing leftover resin in the tube. Instead of changing everything, I may either spray-paint the tube, or wrap some tape around it to block out light.

I can use the fill/drain tube to add/remove resin from the vat

I would HIGHLY recommend getting a cheap peristaltic pump, a length of tubing and a switch to make your own system.

More to come later.
-Steve

Resin tray rebuild and UV Resin testing.

Last week, I purchased some UV resin specifically designed for 3d printing from 3DInk http://buy3dink.com/p/59/uv-resin . It arrived yesterday and I immediately started conducting a few print tests. One of the first things I noticed is that the resin was much less viscous than the SolarEZ resin I tried before. The 3DInk resin flowed almost like water. Again, I put a few drops in a sandwich bag and placed it on my resin tray.

I fired up my software and picked a nice slice from the 'Goldberg Sphere'. The resin cured within seconds! Good progress so far. The next step was to test the adhesion (or hopefully lack of adhesion) to my polycarbonate resin build tray. I used a silicone spray and paper towel to grease up my build tray, and I place a small amount (few drops) of resin on the tray to be exposed.

The remains of my first build tray.

Unfortunately, The resin firmly adhered to the build tray. No amount of coaxing could remove it. I decided polycarbonate might not be the best choice, or I might have to use a thin film of Teflon coating on the polycarbonate. Either way, this build tray was toast. 

Shown here is the resin stuck to the tray.

I found a nice small pane of soda glass I had been saving, and re-tried with a few more drops on an un-coated pane. Even un-coated, the resin did not adhere very well to the glass. I was able to slide a few test prints off the pane.

Some test object slices of the 'Goldberg Sphere'

New build tray

I used some aluminum channel stock I had lying around along with the glass pane to construct a new build tray of the proper size. I used silicone sealant on all bottom edges and the corners to ensure a proper watertight seal.

I think this new build tray will do the trick. The last thing I need to do is finish the arm that connects to the ZAxis and dips into the resin. I've already added a leveling system to the bottom of the build tray on the printer. I may have to add a small leveling system (some screws) to the build arm.