resin tuning
right print is before resin tuning left print is after. Prints are 75mm long printed with .05mm layers
I had a chance to do some tuning of the print exposure and pigment concentrations in the resin I am currently using with the vat. The test prints I was making were somewhat overexposed/underpigmented causing a loss of sharpness in the prints but early on the most important thing I needed to do was to run prints to test the release characteristic of the vat so good enough was good enough. On my dlp printer I actually have a program to help me do resin and exposure tuning (DIY And Technical Information: – flexvat.com) but because of the way the form1+ prints I had to use a different method.
Exposure and pigment concentration testing involves making a single layer exposure in a puddle of resin, doing this tells you two things the hardness of cure and the cure depth. Keep in mind that exposure mostly controls the hardness of cure and the pigment in the resin mostly controls the depth of cure and the depth of cure is what largely controls the sharpness of a print. For example, if you print a model that has horizontal holes and the bottoms of those holes come out flattened it could be overexposure but most likely your resin is underpigmented (you are printing .05mm layers but the cure depth is .25mm and you are continuing to expose already exposed layers when printing). If you seem to have problems with printed layers separating, prints never sticking to the build plate or constant print failures it could be underexposure but most likely your resin is overpigmented (you are printing .05mm layers but the cure depth is .04mm and layers are not sticking together). Resin manufacturers do thier best to make resins with characteristics that will work with the printers they are meant for and the resins generally work fine but standard resin pigment concentrations are always going to be a compromise.
To run a test I remove the printers build plate and vat and use an acrylic platform with a square cutout in the center, a separate acrylic “tray” sits on the platform over the hole and a piece of clear mylar sits on the tray (mylar can be found at office supply or craft stores), I put a puddle of resin on the mylar and make a single layer exposure (I open the printers lid after the exposure to stop printing). I take the mylar sheet with the single layer exposure and clean it using a spray bottle filled with 91% isopropyl alcohol this leaves me with a clean single layer print. If when cleaning the test print the print breaks up your exposure is too low. I cure that single layer with uv then peel the layer off of the mylar and cut it in half with scissors (so I can take a measurement that does not include edges or holes which can be thicker than normal). I then measure the thickness of the layer, if the layer is more than .15mm (for layer thicknesses up to .1mm) I add pigment to the resin, if the layer is less than .1mm I add clear resin to the test resin. Not that on average you can take an exposure that generally works and just play with a resins pigment concentration to control sharpness and eliminate printing problems.
Resin concentrations are going to be a compromise unless you want to mix resin for individual print layer thicknesses. You are shooting for an exposure that gives you a reasonable hardness of cure with a cure depth that does not degrade the sharpness of your print. I like as hard a cure as I can get because that allows me to print pretty extreme overhangs without supports.
Rule of thumb: the cure depth of the resin should not be more than 2 or 3 times the desired layer thickness (for example, with layer thickness of .05mm the cure depth should be no more than .15mm) and never less than the layer thickness
Technical info:
The pigment concentration I settled on (makerjuice sf, 4mL/L red pigment) gives me a single layer print thickness of .13mm, For printing .05mm layer thicknesses I could go down to a single layer thickness of .1 (or even .07 but with the possibility of attachment layer issues). I am still using a pretty high exposure (50) but I have successfully printed models using 30 and I will probably pick up more sharpness by lowering the exposure.
To make the test I use Preform OpenPF with this stl: resin test 1.stl (454.2 KB)
and a custom .ini material file (the file upload here is not allowing me to upload a .ini file so I have uploaded a pdf): form1plus_resin_test.pdf (274.3 KB)
The OpenPF version of Preform can be downloaded from the following links (links are from from the OpenPf Github page):
Mac:
https://s3.amazonaws.com/FormlabsReleases/Release/2.3.3/PreForm_2.3.3_release_OpenFL_build_2.dmg
Note: You can have Preform and Preform OpenPF on the same PC, I rename the OpenPF shortcut (icon) so that I can tell the difference between the Preform and Preform OpenPF programs. I suspect the same can be said for Macs.
The original material file can be found here: OpenFL/Form_1+_FLGPCL02_100.ini at master · Formlabs/OpenFL · GitHub
If you are going to work with this type of file you may want to download the notepadd++ text editor: https://notepad-plus-plus.org/ because programs like notepad do not handle this type of file well.