Frame Components Purchased

I pulled the trigger today on a McMaster-Carr order for components to build the frame.

I purchased extra T-slot nuts for work, so the final total for the printer will be less. I will factor this in later when I make the final total.

The 9mm diameter rod will be cut in half to be used as a guide rod. for the Z axis. The 5/16"-24 threaded rod will act as a lead screw to move the axis. Notice, I didn't purchase any 5/16"-24 nuts, which was a mistake.

An now time for some math:
A rod with 24 threads per inch would then need 24 revolutions to move the build plate up 1" .
The NEMA 17 stepper motor I plan to use has 400 steps per revolution.

That's 2.64583316 microns per steps!

That's a theoretical value, assuming no binding in the nuts, no play in the coupler between the motor and the threaded rod, and that the board is capable of sending commands in 1 step increments to the motor. This is also assuming I didn't screw up somewhere, as that seems to be very small. By comparison, the MakerBot Replicator 2 has a minimum 2.5 micron accuracy, while the Formlabs Form-1 has a minimum of 25 microns. When comparing the layer height, the MakerBot has a minimum of 100 microns, while the Formlabs printer still has a minimum of 25 microns. This is due to the nature of the materials used in the printing process. Since the MakerBot uses 1.75 mm  (0.069 in) filament extruded through a 0.4 mm (0.015 in) nozzle, the minimum effective layer height is now a function of the material being extruded. If it is extruded too thin, it will bulge outwards and the XY resolution will be compromised. Since the Formlabs printer uses Resin that cures via UV light, we don't have to worry about the change in width as a function of layer height. 

(source: buildyourcnc.com)

Since these calculations are very straightforward, I will experiment with rods that have different threads per inch. My goal with this printer is to increase the printer resolution, not speed. If 24 threads per inch and a slow speed get's the job done, great. 

Frame Modeled

After testing the projector's minimum distance and image size, I began working on the frame in Solidworks.
Below is the first revision:

(REV 1 of the Frame)

The Z axis moves on two smooth rods (5/16" or 9mm if I'm lucky) and uses a 5/16 threaded rod. This setup is the same as what is used on my RepRap, and is quite reliable and can provide very small layer heights. If I want to improve my layer resolution, I can always upgrade later to ACME rod, which is designed for high precision linear motion.

(Close up of the Z axis, coupler not included yet)

Two components have been designed to be 3D printed for the frame. The first is a holder for the NEMA 17 stepper motor and smooth rods. It will be mounted on the top of the frame. 

(NEMA 17 Holder)

The second component is a bearing holder for the bottom of the smooth rod. It will help to constrain the rod and allow it to still rotate. This is based on a Z stabilizer part found on Thingiverse, and should help increase part accuracy. I will use a helicoil shaft coupler to attach the stepper motor to the threaded rod, to reduce the chance of binding. 

(608zz Bearing mount with integrated smooth rod holders)

All parts will be available on Thingiverse as soon as I can convert them to STLs.

Testing the projector image size and minimum distance

(Minimum projection area of 6 in x 4.5 in at a distance of 10.5 inches)

I am trying to use the smallest image possible from the projector in order to maximize the effective resolution of my printer. The individual pixels will be smallest when the image is smallest. This distance could theoretically be reduced by modifying the optics of the projector, but it is nice to have the projector left unmodified so I can watch more shows on my ceiling when I get bored. If I see a need to modify the optics, I can always come back to the idea later. 

DLP Printing pt. 3: The Frame

Now I am beginning to design the frame. The first version will be made of 20mm x 20mm aluminum T-Slot extrusion, also commonly referred to as "80-20". This material is ideal for frames and prototypes since it allows anything to be mounted along the frame, and makes it easy to move components around. In addition, it is fairly inexpensive and much more robust than threaded rod. 80-20 has been used in many RepRap printers and has proved to simplify the build, decrease build time, provide more freedom to modify, and is incredibly sturdy. AlephObjects, maker of the LulzBot AO-101 has tested their printer while standing on it, driving it off road, and making it print upside down.

 

(the profile of a 20mm x 20mm aluminum extrusion. source: eBay)

My main goal is to use as little material as possible to reduce cost and simplify building the printer. It's worth investing in a m5x0.8 mm tap to add tapped holes to the end of your extrusions. McMaster Carr sells both the extrusions and various connectors. It is worth buying the extrusion on their website, but a corner block sells for $10 each! This quickly adds up. Luckily, there's thingiverse! Printing a corner block on my RepRap prusa with 0.35mm layer height took roughly 20 minutes and cost about $0.16! 

Here are some excellent extrusion components:

Corner Block -- These work incredibly well and are ~60x cheaper than the aluminum ones for sale!

90 Degree Corner Backet -- These also work very well, although the overhang is tricky. Blowing on it worked until I got light headed.

In addition, I will be uploading all parts I make onto Thingiverse. Follow me, and make sure to print a Toothbrush holder.

DLP Printing pt. 2: The projector

The projector is the most important component to a DLP printer. DLP stands forDigital Light Processing, and is a technology developed by Texas Instruments to project light. I'm not going to go into many details about the technology, as it doesn't really matter for the printer. All that is important is that there is a filter that blocks UV light from being projected, and we need to fix that. The projector replaces both the X and Y axis of a typical FDM printer by projecting the desired layer shape onto the build plate. The projected image is black and white, and the white region is where the resin cures. A simple way to visualize this process is to think of an MRI or CATScan. An objected is "sliced" like deli meat into many thin layers. The printer recreates each layer on top of each other sequentially until the object has formed.

(LEFT: the desired shape. RIGHT: the sliced version. source: Wikipedia: Rapid Prototyping) 

After a week of eBay hunting, I came across a used Optoma EP716 DLP Projector for only $40. This projector is capable of resolutions up to 1400x1050, and has a 200W UHP (Ultra High Performance) mercury- arc bulb. It came with a working bulb, which is strangely difficult to come across on eBay, and the only thing missing was the remote. The projector arrived yesterday and is in decent condition, with only a couple of scratches. After watching an episode of Late Night with Jimmy Fallon on my ceiling while lying down, I decided it was time to get to work.

(my baby! source: eBay listing)

Optoma datasheet

Key components for a good Projector:

• MUST be DLP (a Texas Instruments technlogy. Read more about it here)
• A high wattage lamp. The higher the wattage, the stronger the light and the faster the cure time
• Avoid LED. These are harder to get enough UV light from. It seems as though it is possible to use a LED projector, but there will be much more work.
• A high resolution. The build area and resolution of your prints is directly proportional to the projector resolution. The projected image is the X and Y axis, while the lead screw moving the build plate is the Z axis.

DLP Printing pt 1: The Basics

After some research, it seems as though the next step in the 3D printing revolution will be in the form of Stereolithography (SLA). This process differs in a couple key ways from PLA, and has its own benefits and downsides. SLA works by exposing a portion of a UV curable resin to light waves in the correct spectrum to selectively harden that area into plastic. 3D systems pioneered this technique in the late '80s and has been the leader in commercial grade printers since then. Only recently has it been made available to consumers. The newly announced Formlabs Form 1 printer is the first truly competitive SLA device, competing with the highest quality Fused Deposition Modeling (FDM) printers such as the MakerBot Replicator 2.

(image source: Wikipedia: Stereolithography)

Just like the RepRap, people have begun to construct their own versions of SLA printers. There are two main ways to harden the polymer: via a laser pointer, and with a projector. Lasers are harder to cool and cost much more than a projector, so most DIYers use a projector. Not any projector will work though. It seems as though DLP projectors are needed to crank out the UV light needed to cure the polymer.

Some great sources on DIY DLP projectors are below:

Better Printer Blogspot

3D Homemade Blogspot

The legend: Gary Hodgson's DLP printer

LemonCurry Wiki

(my attempt at making a diagram of the set up)

These have been my guides in the design of my printer. I aim to make everything freely and openly available, and will upload all parts to Thingiverse to help start a new wave of DLP printers. This is part 1 of many chronicling my build, I hope it serves to be a helpful guide. Enjoy!