3d printing notes 2

Vat Stuff

The vat is where the rubber meets the road.

My 3d printers vat is made of .5″ (12.7mm) cast acrylic (not extruded).  Cast acrylic does not have locked in stresses, so when you clean it with a solvent (like alcohol) it does not crack. After you saw or drill extruded acrylic it will start cracking as soon as you expose it to solvents. Making a vat out of cast acrylic is a bit more expensive but being able to clean your vat without it falling apart makes up for that big time.

I make my vat so that the outside edges are 5″ X 7″ (This allows for a print area of 102.4 mm X 76.8 mm (for a 1024 X 768 pixel resolution projector at 0.1 mm print resolution or 51.2mm X 96.0 mm for a 1080 X 1960 projector at 0.05mm print resolution) or any variations up to about 4.5″ X 6.5″ (the resin uses the edges around the build plate as a reservoir). This size also allows me to use pre cut 5″ X 7″ photo frame glass (I’m not in to deep and exotic, if picture frame glass works for my vat floor that’s good enough for me).

Why are the vat walls so thick (.5″):  If you cut (have cut) the pieces of the vat with a reasonable amount of accuracy all you have to do to construct a vat is to run a line of (thick) acrylic adhesive on the edges and hold the parts temporarily together on a flat surface then clamp or strap the parts together until the adhesive sets, the edges are essentially self aligning. Try that with 0.125 or even 0.25 thick acrylic sheet. Also, after the adhesive sets a flat vat wall bottom allows you to attach the vat floor glass easily with just a thin bead of silicone sealant (I place a sheet of sand paper on a flat surface and sand the bottom of the vat smooth before attaching the vat floor glass).

The care and feeding of my Sylgard 184 vat floor coating.

I use Sylgard 184 as a vat floor release layer (I am going to try other release layers as time permits), and I have found several things affect the Sylgard 184 vat floor layer.

One of the most important issues is vat tilt/build plate lift timing. If you lift the build plate before or at the same time you tilt the vat after your layer exposure you might as well have not created a vat tilt mechanism at all.  I have found that if you tilt the vat to the point where the part releases then lift the build plate you are going to be a lot better off.  A slow tilt is best, if you are in a hurry you are going to find that you are going to have the sylgard wearing out quicker and parts peeling off of the build plate (resin shrinkage also has a part in this).  If you hear the build plate “snapping off” the vat floor then something is wrong, either the vat floor release layer is worn out or the build plate is lifting too soon (before the tilt releases the part from the vat floor), the vat floor release and build plate lift should be relatively smooth with only light sticking even when the entire build plate is releasing from the vat floor. I also think (my opinion only) that the thickness of the Sylgard release layer has an effect on the part releasing from the vat floor. I use a thickness of about 3mm, I have used thinner layers and have found that thinner layers do not work as well.  My belief is that the thicker layer “stretches” more as the part is peeling from the release layer making the release easier. When 3d printing resin is exposed it can get hot and if over exposed the resin can possibly get hot enough to damage the sylgard release layer, very short exposure times I think may also be problematic (this is admittedly speculation on my part). I run exposure tests to get the minimum exposure needed to get a good layer and to adjust layer thickness (more on this in another note).

I drain and clean my vat after every print unless I am making multiple prints one after the other without problems (failed prints etc).  This is what I do: drain the vat of resin back into the resins storage container through a re-usable coffee filter (cheap, fine metal mesh, cleanable with alcohol).  Then I rinse the vat with water and shake as much water out as I can then spray with alcohol (92%) from a spray bottle (avoid breathing the spray), rinse with water again, spray with alcohol again, then wipe off any “shadows” on the vat floor with a piece of microfiber cloth or “sham wow” dipped in alcohol then a last light alcohol spray on the vat floor to “wet” the vat floor (so that it dries without spots), then I set the vat on edge to dry.

Sorry about jumping between inch and metric measurements.  3d printing is mostly metric but a lot of easily available parts are inch.





This entry was posted in 3d printing. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *