I’ve been building a stereolithography (SLA) printer recently. This is a different 3D printing technology that is capable of much finer details than typical FDM printers, but is a lot more finickey and not as commercialized. All of the commercially available SLA printers are in the $3k-ish price range. There aren’t any existing RepRap-type models that you can download the parts and print yourself, nor are there any Printrbot-type sub-$1k entry level models but apparently SeemeCNC has a BYOProjector kit for $400. There are a couple on the horizon (such as Peachy Printer) that are promising but as of this writing still vaporware. So… if I want one, I have to build it myself, with parts I found in my basement.

So, what’s an SLA printer?

SLA Printers work by curing liquid resin in a vat by shining UV light on it. Some SLA printers use UV lasers to draw the pattern for each layer; others use projectors to print the whole layer at a time. I opted for the latter, because it meant fewer moving parts and quicker print times. Once the layer is cured, the print bed moves and the next layer can begin.

There are two approaches to constructing an SLA printer, top-down and bottom-up.

Top-down printers submerge the print bed in the vat of resin so that the resin just slightly covers it. The UV light is shined from the top, and then the bed moves down to make room for the next layer. This means your maximum build height is the depth of your vat, but it also means that you must fill your vat with that much resin ($$$) in order to get that tall a print. However, it also skips the need for a peel step, as is required in…

Bottom-up printers place the UV light source under the clear vat floor, so the light is shining from the bottom of the print. After each layer is cured, the build plate moves up a step so the next layer can begin. This requires much less resin, but the print will then be stuck to the build plate AND the vat floor. The vat floor is coated with a nonstick material, but a step to peel the print off the vat floor is still nessesary, and is generally achieved by tilting the build plate or the vat slightly. Bottom-up designs also put your precious light source under your resin vat, so leaks could be catastrophic. I’ve worked around this by using a mirror. Magic!

Flexvat is a very experimental design, that I don’t believe is used in any commercial SLA printers. Instead of a rigid vat bottom, a flexible sheet is tensioned over the bottom of the vat. I have a couple materials to try for the vat bottom, once I get my resin in the mail, but I also have some clear acrylic sheets and another Nema 17 motor on hand in case I have to abort this plan and go with a tilting rigid vat.

My in-progress build

So it turns out I’m not a very good engineer. Good engineers draw out what they’re going to do before they do it. They measure things to make sure it’s all going to fit. I sit down with a pile of parts and smash them together until I get something like what’s in my head, and then I end up re-doing it 5 times over because I didn’t measure things and it doesn’t fit.

Anyways, here’s what I’ve got. Current BOM:

FDM Printed Parts: Mirror Bracket (only one side, mirror it in your slicer for the other side) Z carriage Motor Mount & smooth rod block Knurled knob Z-coupler

FDM part yet to be designed: Vat brackets Projector Shutter Projector optics spacer (edit: ended up not needing)

Other parts: MakerBeam kit (OpenBeam will work too, it’s just what I had) RAMPS/Mega Nema 17 motor (PB Simple) Vat (acrylic and acrylic solvent; the PVC in the pic is just placeholder) Flexvat bottom (FEP film or other materials maybe?) First Surface Mirror (source) DLP Projector Aluminum build plate (source) Servo 2x 8mm Smooth rods (PB Simple) 5/16″ Threaded rod (PB Simple) 2x LMU88 Bearings (PB Simple) M3 hardware (PB Simple) Delrin Acme Nut (PB Simple) Big-Ass Bands to affix flexvat bottom (source)



Parts listed as “PB Simple” means that these were from the box of parts I had left over after I upgraded my Printrbot Simple Maker’s Kit to a Printrbot Simple Metal.

Total build cost is about $300 right now. Your price will vary based on a) your ebay skills (the projector is the most expensive component), and b) whether or not you have an old Printrbot to cannibalize or if you have to buy those parts.

For the projector, the most expensive part of the whole build, any DLP projector will work. However, some modifications (like breaking off the color wheel) can result in better cure times. Additionally, higher projector resolution = higher print quality. You may also need to adjust the minimum focal distance of the projector, which it is my understanding that you just print out a spacer and add it to the optics assembly. I’ll… let you know how that goes.

Software

Creation Workshop is free software that will slice, and then it will feed code to your printer while also feeding images to your projector.

The firmware is a modified version of Marlin. It is modified to turn off extruders and thermistors so that your printer doesn’t say “OMG NO THERMISTOR SHUT DOWN EVERYTHING.” Which it will do. I also had to activate the servo function and set it to 1 servo.

I’ve also swapped the Z and Y axis pinouts because the Z-axis pins on my RAMPS board are busted. So everything in my G-Code still says Z, but the current actually goes to the pins silk-screened Y on the RAMPS board. Other than that, everything’s the same!

What comes next?

Well, resin is coming in the mail. A lot of “will this work” depends on the resin. Also on order are some heavy-duty rubber bands to try and affix the flexible vat bottom. The weeny little rubber band in the picture is just there to hold some cellophane on to simulate where the vat bottom will be. I’m just going to have to science the vat construction a bit because I have no idea what I’m doing.

I need to design and print some brackets to keep the vat securely in place.

I need to figure out this servo thing. So, when the printer is moving from one layer to the next, the projector turns “off” to prevent curing the resin when it’s not suppose to. However, “off” just means projecting a black image, which still has a fair amount of light. A shutter, attached to a servo, will swing into place during each peel/layer change to prevent extraneous curing. I know Marlin can handle a servo, but I don’t know where to plug it in on the RAMPS board. I’ll also haven’t tried yet, so I’ll figure it out. I hope.

My projector (a used InFocus LP70 off ebay) currently has a minimum focal distance of about 1.5 meters. That’s no good. I need it to be like 10-15cm. Apparently this is achieved by adding a spacer in the optics assembly. Well, I have the projector opened, but it needs Torx screwdrivers I don’t have to get the optics off. To MicroCenter!

And assuming all that works, then there’s the fun fun calibration extravaganza! 😀