Low Cost 3D Printing 3D printing is a process that takes a CAD file and “prints” an actual part from some material like plastic. Industrial printers cost tens of thousands of dollars, putting them out of the reach of most hobbyists. In the last few years, low cost printers have shown up and modelers on rocket forums have been asking about them. This report describes the experience I have had with a particular low cost printer. I am in no way an expert on 3D printing (or “rapid prototyping” as the industry calls it), nor are the statements I make about printer capabilities applicable to all printers. A friend at work bought a “Mosaic” hobby 3D printer from MakerGear http://www.makergear.com/ to see what it could do. James is a certified SolidWorks professional, so he knows his way around SolidWorks (SWX) and has written many VB programs to create parts libraries for our employer. As soon as he found out I was into rockets, he asked if there was anything I wanted to try printing. I have several rockets modeled in SolidWorks, but settled on testing the system with Chris Flannigan's beautiful D-Region Tomahawk he posted on Scaleroc. I used the SWX "scale" feature to scale the full-size model to fit a BT-60 tube (1.637 / 9.00 = 0.181888889). I wanted to print the fin shroud, lug, fins and fin attachments as a single unit that would slide over the BT-60 tube, and the nose cone.

It turns out the Makergear printer has a 5" x 5" x 5" work area, so we had to make some adjustments. For one thing, we had to split the nose cone into two parts

Next the whole fin assembly had to be broken down into separate parts. James was doubtful that the Mosaic would be able to print the fine bolt head detail, so he removed them from the CAD model.

After James cleaned-up my scaled SWX models, he followed these steps: 1. Model your concept in SolidWorks (or any good quality 3D software) and save the model

to a .STL format. 2. The 3d Printer (Mendel/RepRap process) will use a print software similar to Pronterface.

a. Within Pronterface is another software that runs called Skeinforge. (some people use Slic3r). This software is used to "slice" the .stl file into printable layers of gcode.

b. Once the gcode has been generated, Pronterface is used to send the gcode to the

printer. The process to create the gcode ran about an hour per part. The actual printing process took 2 to 3 hours per part, depending on the complexity of the part. The results were both amazing, but a little disappointing. Amazing that we took a part that existed electronically and created something you can hold in your hand, but the surface finish was less than I had hoped for. Those squarish pieces on the shoulder are supports created by the printer software to help support the wall during the print process. The printer feeds a plastic filament through a heated nozzle, applying it to either the table for the first layer, or the previous layer. Since it is molten as it leaves the nozzle (think hot glue gun) it can slump. There are very tiny ligaments holding the supports to the part which can be easily snapped-off. Sanding removes any trace of these. In fact one broke off while I was taking the pictures, leaving three still attached.

The nose tip turned out fairly well, but James discovered that as the print head got near the tip, it was moving so fast that it drug the molten material with it, leaving it skewed, looking like a soft-serve ice cream cone. I assured him I could fix that with some sand paper on my lathe. He came up with a fix on another rocket project, blowing through a straw to cool the layers as the print head got near the tip. That worked, and results looked great!

We discovered the fins will not print well. Since there was detail on both sides of the fin, it could not be printed flat on the table. James tried two different directions of printing the fin standing up, neither turned out very well.

The fin attaching rails were, to me, the coolest part! Since the printed fin did not work out, I decided to use balsa with a paper cover to obtain the sharp leading edge.

The shroud ended up being so thin (~1 filament thick), it really taxed the limits of the filament printing process…there are holes and gaps along the seam where the print head starts and stops each print layer. In the photo you can see another support ring that the printer software creates that is removed with a combination of cutting and sanding. I was not able to get the shroud to fit over the BT-60 completely—I was afraid it was going to split open, so I slid it on part way, then dry fitted the rail and fin to get a feel for what it would look like completed!

I kept sanding the ID to fit over the body tube, but it hung up about 3/4" down or so, on the area that did not print out well. The layer in that region had split, and wanted to grab the edge of the tube. Instead of designing the shroud to go over the tube, I redesigned it with a shoulder to fit in the BT-60 (and a built-in centering ring), and glued the lower motor mount paper centering ring into it.

As mentioned previously, I turned the tip of the nose cone on my wood lathe to get rid of the “curly-q” (now looking at the primered part photo, it looks like it needed a little more work ). I then thinned down some Bondo Glazing and Spot Surfacer putty w/ lacquer thinner to fill in the little voids and the seam running down the part. After sanding, it was interesting to see the pattern formed by the printer as it created the part. I then sprayed on a heavy primer called "Mr. Surfacer 1000" http://www.swannysmodels.com/Surfacer.html -- I let that dry thoroughly before sanding.

The fin rails were glued to the bottom shroud, the motor mount assembled, and everything was glued into the main body tube. I brushed on "Mr. Surfacer 500", sanded a bit, and applied some of the thinned Bondo to fill in larger voids.

The fins are balsa cores with some cardstock skins glued on to get that sharp edge on the leading edge of the fin. I filled the edges w/ some Elmer's Carpenters Filler and apply a coat of CA (superglue) to the paper to stiffen it. When the CA dries out, the paper feels like plastic!

A little more sanding and finishing on the paper tubes (I used thinned Elmer's Carpenters Filler for that) then an overall coat of primer.

Here is the finished model! According to Rocksim it will fly 588 ft on a D12-5 or 1015 ft on an E9-6. Hopefully it will fly at our next club launch, if the winds cooperate!

As I stated earlier, any of the statements I made about printer capabilities are applicable only to the MakerGear “Mosaic” low end printer. While I was a little disappointed in the surface finish and resolution, it is still very cool to be able to take a CAD model and make something you hold in your hands (the industry calls this “art to part”). There are two other members of my rocket club at work, and when James brings in our parts, we gather in his cubicle and giggle like school girls over the parts. With these hobbyist printers, it is not quite “click and print” … yet. There is some work involved in the conversion, and creating the gcode. A true gcode programmer might be able to tweak the program and get better results than we did.

The filament material used with this printer costs about $15 per pound. The nose weighs 1.53 oz. as-printed. The second shroud weighs 1.47 oz. The fin rails weigh about 0.04 oz. each. I am not sure how a professional printing bureau would charge for these parts as there is the conversion, coding, and actual printing time involved too. It turns out there is a whole world of hobbyist printers, mostly home-built units. A recent addition to the “under $1000” line is the Printerbot ($550 - $700 depending on model) from http://printrbot.com/ Here are some other 3D printer links from the “Hack a Day” site and others (sent to me by guys at work)… http://hackaday.com/?s=3D+printer+reprap http://hackaday.com/2010/08/29/from-repstrap-to-reprap-a-3d-printer-is-born/ http://hackaday.com/2012/02/08/yet-another-3d-printer/ This is a really high resolution printer that uses light curing resin http://hackaday.com/2012/04/05/3d-printer-with-insane-accuracy-uses-a-dlp-projector/ http://store.makerbot.com/ http://www.geek.com/articles/gadgets/printrbot-an-all-in-one-3d-printer-kit-for-499-20111121/ http://www.kickstarter.com/projects/printrbot/printrbot-your-first-3d-printer?ref=video Some well-known high end industrial printers are: Z-Corp http://www.zcorp.com/en/home.aspx Stratasys http://www.stratasys.com/ Objet http://www.objet.com A good reference to CAD and rapid prototyping is “Desktop Engineering” magazine – I get it free at work, and I think you can look at online content for free too. http://www.deskeng.com/ David Stribling NAR 18402 Sr