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In this section we propose the building of a standardized test rig that can be built low cost and can permit a larger base of people to participate in the testing of ideas. The idea has been discussed in this Yahoo Group thread
Standard Test Vats and Cells
Microscope Slide Mini-vat
We use a regular 1mm thick microscope glass slide and apply a 3mm high thread of silicone on a square perimeter. The volume of this mini vat is not as important as the height the resin you will pour inside can reach. Bottom-up DLP methods use resin depths in the vat no lower than 3 and up to 6 mm. The minimum depth is important to keep the curing slice as far away from the influence of air oxygen, which inhibits the curing reaction by free radicals (with Photoinitiators such as BAPO and H-Nu470)
To avoid the curing of the zone of resin immediately in contact of the silicone thread, we draw a thick black line around the perimeter of the mini-vat, on the reverse side of the microscope slide (not inside the mini vat!). We do this to avoid the creation of a thickened edge around the cured slabs, due to capillary effects between the resin and the silicone (meniscus effect), as well as for keeping the mini-vat's clean and reusable. We don't want the resin sticking to the silicone.
Enclosed Cell Vat
To permit for testing in controlled conditions for top-bottom, bottom-up and even lateral exposure setups, an enclosed standardized cell can be build as follows:
A PVC tube with 20mm internal diameter is cut into rings of 10mm height and glued to a transparent 30x40mm window. In the pictures below I used a PMMA 3mm thick slab, but Cellulose Acetate or microscope slides can also be used.
Use tight fitting Polyethylene caps to shut the cell tight. Pierce 2 holes in the cap to be able to close the cell with the resin filled in the PVC ring untill the rim. Air should be able to escape fully leaving no air bubbles in the cell. A little resin will escape through the holes when pressing down. Once the cap is inserted, clean the excess resin off and stick black electric tape over the vent holes.
Test Rigs
Enclosed Cell Test Rig
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DLP Projector Test Rig
Sketch
The Rig made from Meccano
| Front View | Top View | Side View | Orthogonal View |
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Another proposed mini vats are made from regular microscope glass slides and cover slides. These are typically made from common glass (transmission spectrum) and let near-UV light through.
Every setup should ideally be calibrated with a commercial resin, for effective comparison.
Simple Table Hole Test Rig
Geometry
- Distances between modules: A = 10mm
Black Box Test Rig
Geometry
- Distances between modules: A = 10mm, B = 50mm, C =100mm
Optics Module (Proposal)
- Glass plane for thermal separation
- Optical step wedge OR Slide timer
- Box is completely lined in black
- Box contains vent shutters to allow ventilation by chimney effect
Implementation Example
Place the slide in a rig, I built mine out of Meccano parts, easy and moddable. This rig will help positioning the mini-vat repeatedly in the same position and perfectly level, so as not to create an uneven, wedge shaped slab.
The lamp
The lamp I use is a standard GU10, 220V 50W Tungsten Halogen incandescent bulb with reflector and front glass cover.
I mounted it in a tin can to fix the lamp distance and a switch to make time measurements consistent. I didn't paint anything black, as the bulb reflector makes that feature rather irrelevant.
This lamp's front cover should filter out any UV light it produces. The blue spectrum content of incandescent bulbs is comparatively low against the UHP bulbs used for DLP projectors. The GU10 bulbs are rated at 400-500 ANSI Lumens, compared to the 1500-3500 ANSI Lumens of DLP projectors. A final comparison between this test rig and complete DLP printer must yet be done to calibrate the whole process.
dufas_duck Test Rig
Common components
Build Area Module (Proposal)
- Glass pane
- N x Top glass panels with spacer elements
- Temperature of build area: Room temperature: 21ºC
Lamp Module (Proposal)
- Bulb: Philips D2S Xenon bulb, 35W Nº 85122 (data sheet)
- Buy online: ebay international
- Ballast: Universal 35W HID Ballast amazon, ebay 1, ebay 2
- Reflector: None, box is completely black
- Power source: 12V
Resin System
- Calibrate: Solarez UV Epoxy (link)
