Repairing a Bike-Light Mount With 3D Printing

3D printers have amazing possibilities for making our world better, but unfortunately lots of the things that people print on them have little or no useful value.  From an environmental outlook, 3D printing is far from perfect.  The world doesn't really need to be filled with little plastic dinosaurs, cars, or sculptures of people.  My goal for this project was to make an environmental argument for why 3D printing can be a net-positive.  

As an example, I decided to use 3d printing to repair my bike light.  More exactly, it was my bike light's handlebar mount that needed fixing. It's a NiteRider MiNewt 600 Cordless Rechargable Headlight and I broke the section that connects the light to the handlebar clip. At TechShop, I was able to successfully design and print a repair part.

Tools:  

Calipers
Audodesk 123D, or other CAD software.
3D Printer (or printing service).  I used Makerbot, Type A Machines, and Objet.

Step 1: CAD Your Replacement Part

My first step was to recreate the part of my bike mount in CAD.  Using a set of calipers, I measured the mounting parts of my light and recreated the necessary shape.  I used 123D, a free CAD software produced by Autodesk, available at http://www.123dapp.com/123d.

It isn't necessary to replicate all of the part's feature's exactly.  Identify which dimensions are critical for attaching the light and then finish it off however you like. It's important to remember that your final part will probably be made out of a material that is less strong than the original.  Add extra support and keep in mind the orientation you will end up printing in.  If you are using a Makerbot or other FDM (filament-type) printer, the material will be much weaker in some directions than others.  One tip for getting a good finish is to add small fillets (~0.05" or so) to all of your part's edges since most printers aren't effective at creating sharp corners.  

I exported the shape as an STL file to bring to the 3d print software.

Step 2: Send to the Printer

I used a Makerbot Replicator printer to print my first attempt.  The Makerbot uses a software called ReplicatorG that imports an STL, slices it into the necessary number of layers, and calculates the tool path for the printer to follow for each layer.  

It's important to position the part correctly on the virtual build platform.  With ReplicatorG, you have the option of adding support material, making it possible to print overhanging parts.  I used this because it let me print it an orientation that was much more structurally sound.

Send it to the printer and watch it go!

I was also able to print my model on an extremely high-end 3D printer called the Connex 300 by Objet.  These work using inkjet-like nozzles that deposit layers of extremely tiny plastic resin droplets that are cured using UV light.  These printers cost about 100 times more than the $1750 Makerbot Replicator and have at least 10 times higher precision.  The material that the Objet uses costs about 20 times more than the ABS and PLA that Makerbots use, but the Objet can mix hard and soft materials to produce objects with exactly the stiffness and flexibility that you desire.  

Step 3: Test It Out!

I attached each of the clips onto the intact part of my mount and tried them out.  They required a tiny bit of modification with an Xacto knife, but I was really impressed with the fit overall.  

• My first version (the blue one) broke almost immediately because I had printed it in an orientation that was very weak.  It did fit very nicely on the light and was stronger than the others in it's non-sliced directions.  
• The Objet version (the gray one) fit superbly.  It has a glossy surface finish and looks exactly as if it was a rendering in CAD.  It is able to flex a bit without breaking.  I printed two.  One broke along the two thin fins on top, the other is still going strong. 
• My intelligently-oriented Makerbot versions (the white ones) were quite impressive.  They fit almost as well as the Objet ones and were sufficiently flexible in the desired locations.  One broke in the same place as the Objet one, the other is still going strong.  

I was pretty happy with the performance of the Makerbot prints, especially considering they have approximately 1/10th the resolution, 1/20th the material cost, and 1/100th the machine cost of compared to the Objet!  Future steps would include redesigning my part to be less fragile.  Another thing to try out is laminating the Makerbot parts with a thin layer of resin for added strength.  

Step 4: Weigh the Benefits

So, from an environmental perspective, did my 3D prints have a net-positive benefit?  

From the beginning, my goal was to provide light for myself while biking.  Since my light doesn't serve its purpose without a mount, I have the choice between buying a whole new light system, or replacing or repairing the mount.  The bike light itself has a fairly large environmental impact (and embodied energy) mainly due to its electronics and metal parts.  From an environmental perspective, the cost of using several grams of plastic to print a mount is justified because I have extended the lifetime of the much-higher-impact light (or avoided needing to buy a new lighting system).

In this case, buying a replacement mount was also an option.  It is a much smarter option than throwing away the light and getting a whole new one, however it's hard to say how it compares to printing one yourself.  On one hand, the replacement mount contains more plastic than the printed ones and it needs to be shipped to me, probably from China.  On the other hand, it may last 5-times as long as the 3D printed versions I made.  Al Dean has done a neat article on the pros and cons of 3D printing in for repair.

On thing is clear.  It definitely makes sense to try 3D printing for repairs when there is no option of getting a replacement part (for example the gas cap on a particular old lawnmower).  You will be extending the lifetime of a relatively-high-impact device through the use of a relatively-low-impact piece of plastic, (hopefully eliminating the need to buy a whole new lawnmower).

Another use for 3D printing that makes sense environmentally is upcycling.  I think of upcycling in this case as "using 3D printing to add new useful functionality or extending the lifetime of items, especially items that will be thrown away." For example, in  Project RE, Samuel Bernier upcycles a glass jar into an orange-juicer with a 3d-printed cap.

Finally, one consideration with 3D printing is material choice.  Often, it becomes necessary to print out 2 or 3 test-parts before a reaching a satisfactory final print.  There's currently no good way of recycling the ABS test-prints that I've made, so they end-up in the landfill.  One option I have is to test out my designs in PLA (corn-plastic) and print a final version in ABS or send to a high-end printing service.  I can then crush up the PLA prints and (theoretically) compost them.