Setting up a new DLP projector for my 3d printer.

For a while I have wanted to be able to print higher resolution parts with my 3d printer and have more flexibility in adjusting the usable build area (XY build area size) so I decided to upgrade to a high def (1080 X 1920 pixel resolution, aka 1080p) projector from my unmodified Toshiba T95 (1024 X 768 pixel resolution) projector. I decided to go the used projector route to upgrade and found an Acer H6500 “with issues” at a very good price on ebay. The description of the projector on ebay led me to believe that the problems with the projector were mechanical rather than electronic so I took the risk and purchased it (electronic problems are a show stopper, mechanical problems you can often fix or work around). It turns out that the projectors main cooling fan had somehow broken two of the 4 “legs” that hold the fan centered in it’s assembly and the fan blades were hanging on the edge of the fan housing so the projector was not able to cool itself and would go into thermal shutdown soon after being turned on.  This problem apparently caused a cascade of problems within the projector. At some point in the past it appears that the projector lamps reflector cracked (probably from the fan issue) and the color wheel was broken possibly from thermal stress or a piece of glass from the lamps reflector. The lamp, however, worked fine even with a small piece of the reflector missing (I have ordered another lamp, why tempt fate).

This was all good with me. The first issue I went after was the fan, after some disassembly I removed the fan (a 4 inch “muffin” fan)  and repaired the damaged support legs with superglue (the breaks were clean and fit back together flush) the fan had also been attached to a metal housing where the metal had been stamped out to exactly match the support legs of the fan so I wire tied the broken legs to the housing as an added precaution. Next came the color wheel, I am not a fan of removing or modifying color wheels or any projector modifications for a 3d printer because it’s a good way to get yourself in trouble (and not being able to use the old one for the super bowl, summer evening movies on the patio etc.).  But since the previous owner of the projector was so kind as to pre-destroy the color wheel for me wheel I decided,  just this once, to do the deed. I grabbed a wire cutting tool that had a very small tip and began very carefully and gently nipping away at the remaining glass on the color wheel. The glass is extremely fragile and broke away with very little effort and I was able to remove the glass all the way down to the motor housing. You may ask why I didn’t just  remove the color wheel entirely, the answer is, if I had, the projector would not work. The projector requires a “sync” signal from a sensor on the motor to tell it the rotational position of the color wheel so it knows what image to show for a particular color wheel filter segment, without this signal you will have a very confused projector.  After re-assembling the projector there came the moment of truth, I plugged it in hit the power switch and…  It worked just fine. I plugged it into a hdmi video feed and it projected the video perfectly although in black and white.

I mounted the projector to my 3d printer then leveled and squared the projector, vat and build plate using a leveling block I made out of spirit level and a small block of corian. To level and square my 3d printer I set the leveling block in the vat floor first and noted the position of the bubbles (I mark the positions with a fine point sharpie) then I place the leveling block directly on the lens barrel of the projector in the same orientation as it was when I took the level in the vat. I adjusted the projector mount until the bubble positions matched the vat to make the vat and projectors projected image plane reasonably parallel (I parallel the build plate in a similar way).  I have found that I get near perfect parallel and alignment of my printer using this method, however, since the projectors optics project “up” some slight additional adjustment beyond leveling was needed for the projector, these adjustments were made while setting up the build area in Creation Workshop.

Connecting the projector to the  3d printers computer and setting the resolution: After mounting the projector to the 3d printer and adjusting the projector mount and tilt assembly to line up. It was time to connect it to the computer. In order to be able to use the full resolution of a high definition projector (1920X1080 resolution) it is best to connect through a digital video connection, DVI or HDMI.  If you use the vga connection on your computer you may not able to go higher than a resolution of around 1400 X 1050 or so. The video card on my computer had both DVI and HDMI so I connected the projector via HDMI. Note that there are DVI to HDMI adapters available so if your computer has DVI and VGA and the projector has HDMI and VGA you can use one of these: DVI-D Single Link Male to HDMI® Female adapter with a HDMI cable to connect your computer and projector using the computers DVI connector. After connecting the projector to the computer I turned on the projector then the computer and let the computer boot to the Windows desktop.  I have both a monitor and projector connected to the 3d printers computer that work in a “dual monitor extended desktop” configuration. To set the projector resolution I right clicked on the Windows desktop then clicked on “Properties” (Windows XP) then clicked the “Settings” tab and set the projectors resolution to 1920 X 1080 (for a 1080p projector). Monitor resolutions can be set in a similar way on the different versions of windows, there may also be dedicated utility programs for adjusting monitor resolutions.

Note: The projector will appear as a monitor, select the projector and set the resolution to 1920 X 1080 (for a 1080p projector), if the projector does not allow you to set this resolution these are the usual suspects: you are using a VGA connection to the projector that does not support the resolution of the projector, you are using a vga splitter of some sort (this may limit the resolution of the projector to the resolution of a lower resolution monitor). Your video cards driver software is not up to date or it is using the generic widows driver (rare).  If you only have one video output on your computer you should consider purchasing and installing an inexpensive video card with DVI/HDMI connectors, this will make your life much easier in the long run.  3d printing is not a video intensive operation any video card with the correct connectors from a reputable manufacturer will work, many will come with 2 output connectors.

Using eye protection (welding goggles, #5 filter) I used a digital caliper to set the projected image on the vat floor to roughly the build size X axis width (my build area is 144mm(X) X 81mm(Y) for a resolution of 0.75mm).  I measured the top and bottom width if the projected image and adjusted the projector mount until they were equal in size then the diagonals (if the diagonals are equal the image is square). After making sure the image was squared up I finished sizing the projected image to the width of the build area X axis(144mm), the Y axis measured 81mm as expected.

The Acer H6500 projector is waaay brighter than the Toshiba (and waaay waaay hotter. I think I am going to have to move the projector shutter higher to keep it from burning). Before removing the Toshiba I measured a patch of white projected on the vat floor with a photographic light meter and made a note of the reading. When I installed the Acer I Made the same measurement and the Acer was more than 2 “stops” brighter.  With the Toshiba my exposures were 14 seconds with the Acer that exposure time will go down to under 3 seconds. I may end up using the eco mode setting with the Acer not to extend the life of the bulb (for 3d printing it’s going to last forever anyway) but to lengthen the exposure time. I believe short exposure times may quicken the deterioration of the sylgard vat floor release layer by making the resin being exposed very hot very quickly, possibly hot enough to damage the sylgard (this is an opinion).

Layer exposure testing note: I test for exposure times using a 1 layer stl file printed using Creation Workshop. To use the test file I place some resin on a sheet of mylar and place that mylar on the vat floor. I then expose the resin for X amount of time and clean the resulting layer with a 92% alcohol spray. If there is no layer or the layer falls apart the exposure is too low. If the exposure is too low for the next test I will add 1 or more seconds to the exposure and repeat the test until I have a good layer. When I get a good layer I will uv cure it and measure it’s thickness with a caliper, in general I like a thickness of no less than about 0.02 thicker than my layer thickness and no more than about o.o6 thicker, I control the thickness with yellow pigment (after determining the exposure).

HL

 

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