I am able to move the projector on my DLP based 3d printer up and down in relation to the vat easily because the backbone of the printer is a MP4 heavy duty photographic copy stand. The projector is mounted on the copy stands movable carriage. This allows me, with some additional adjustments, to change the size of the build area if I need to. The Creation Workshop software that I use for slicing and control allows me to size the build area and let the print resolution match the build area or set a resolution and let the build size match that resolution without affecting the size of a printout (10mm cube will print as a 10mm cube at any resolution or build area size). What follows are instructions on how that’s done and some generic information on sizing and squaring the projected image on the vat floor.
Setting up the 3d print build area and letting the resolution match: I will use the X axis of the desired build area and a 1080p projector (1920 X 1080 resolution) as the basis for the following calculations. Let’s say I want a build area 144mm wide along the X axis (the Y axis will be calculated later). Divide 144 (the desired width) by 1920 (the projectors width resolution in pixels) this will equal 0.075. Use this number (0.075) to multiply the projectors height resolution in pixels by (1080 X 0.075=81) which gives you the height of the build area in millimeters. Incidentally 0.075 (75 microns) will also be the build areas XY resolution in millimeters. Make a note of these numbers as width, height, resolution.
these are the formulas without the talk.
DesiredBuildAreaWidth / ProjectorWidthResolutionInPixels = XYBuildResolution
ProjectorHeightResolutionInPixels * XYBuildResolution = DesiredBuildAreaHeight
Setting up a 3d print resolution and letting the build area match: Lets say you want to print at an XY resolution of 0.05mm (50 microns) multiply 1920 (the projectors width resolution in pixels) by 0.05 for a build area width of 96mm, multiply 1080 (the projectors height resolution in pixels) by 0.05 for a build area height of 54mm. Make a note of these numbers as width, height, resolution.
ProjectorWidthResolutionInPixels * DesiredResolution = BuildAreaWidth
ProjectorHeightResolutionInPixels * DesiredResolution = BuildAreaHeight
Entering the build area information into Creation Workshop
Your projector should be on and operational. Open Creation Workshop (beta 3), Click “Configuration” (gear icon) > click “Machine Config” tab, select the profile you want to use from the “Profile in Use” list (just use Default_SLA). Both your monitor and the projector should be in the “Select Print Display Device” list. You may be able to determine which is the projector by clicking on the selections in the list, in general, the selection with the resolution of “Width” 1920 and “Height” 1080 will be the projector for a 1080p projector or “Width” 1024 and “Height” 768 for a low def projector (you can also use the “Machine Control” tabs “Show” button to determin which is the projector), in any case, figure out which is the projector and make sure it is selected. Note that the “Select Print Display Device” fields are automatically filled by Creation Workshop, you should not enter any settings in these fields. In the fields under “Axis Length” enter the X and Y numbers you made note of earlier and enter a Z axis size appropriate to your printer. Enter any other settings in Machine config as needed then click the “Apply” button. Note that the Z axis resolution is separate from the XY axis resolution and is set in “Configuration” > “Slice Profile Config” > “Slice Thickness (mm)”. “Slice Thickness” is your Z axis resolution and it can be set independently of the XY axis resolution, for example, you can have 0.1 mm Z axis resolution and 0.05mm XY axis resolution.
At this point you have to set up the projector to project the correct sized image on the vat floor. You will need an inexpensive digital caliper and eye protection such as welding/brazing goggles (goggles with a #5 filter work very well and can be had for about $10.00). Your projector should be on and operational before starting the following operations. Setting the projector to a lower brightness mode, if supported, may make things a bit easier. In Creation Workshop click “Configuration” (gear icon) then click the “Show Blank” button. The projector will project a blank image that clearly shows the “frame” of the projectors image area, what you need to do is to set your caliper for the build area width you made a note of earlier and lock it. Set the projectors zoom in the middle of it’s range then position your projector so that you get a focused image on the vat floor as close to the desired image size as possible, use closeup lenses if needed. Measure the top and bottom width if the projected image and adjust the projector mount until they are equal in size (if they are not equal the projected image plane and the vat floor are not parallel) then measure the diagonals (if the diagonals are equal the image is square). Use the projectors zoom to fine tune the width of the projected image to the build area width. Don’t worry about the height it will be the calculated height (ok, go ahead and measure it if you want to). Mark or tape the projector lens settings.
You can set up or change your 3d print area for any size or resolution you want, if you use the techniques explained above and your 3d prints will print the same size as you designed them regardless of resolution or build area size you select.