A working curve is the first step to creating settings for a new resin. If you arrived here before reading the Ember based working curve measurement, read it first as it goes more into the details and motivations for taking this measurement.
One does not need a DLP printer to make a working curve, just a printer where the dose per layer can be controlled or at least set to a low value (2-10 mJ/cm2 for most resins). This Instructable guides one thru making a working curve using the Form1+.
Step 1: First We Clean
The entire exposed optical path should be cleaned:
1) The glass side of the tray should be inspected for resin and finger prints. It can be cleaned with acetone and a wiper.
2) The PDMS window should be carefully cleaned with lens or microfiber cloths. This surface is easily damaged.
3) If the mirrors or dirty clean the dust of with compressed gas.
Step 2: Check the Light Intensity
If you want an accurate result the you need to know that the printer is outputting the correct amount of light. There is no point in taking the time to make a working curve without checking this first.
Step 3: Create the Test File and Print
One trick to making a working curve is to design a test artifact where the number of layers is known. The attached .stl consisted of panels ranging from 50 to 1250 microns thick. When a printer is set to 50 microns layers this should give 25 panels with different doses. The attached .ini file for the form gives an output of 13.3 mJ/cm2 per layer, which should be good for most 3d printing resins.
When you go to print the file, remember to leave the build head off. You want the print to form on the PDMS and the thickness to be dictated by the dose of light, not the position of the build head.
Step 4: Measure and Calculate the Working Curve
Once you have your 25 or so measurements (probably less as some of the layers will not form). Carefully clean off the film and measure the panels that formed.
You can calculated the dose as
spatially averaged dose = Laser Power / Laser Speed / scan line spacing * number of passes * optical efficiency * number of times the layer was exposed
An example set of calculations is attached.