Press-Fit Sundial — Joseph Negri

For the past three summers, I have been a counselor at Camp Casco, a week-long overnight camp for pediatric cancer patients and survivors. This as part of an activity on navigation, I decided to design and build a press-fit sundial to see how well the campers could orientate themselves to true north.

I am drawn to press-fit designs for the ability to make robust structures quickly with no additional tools needed for assembly. This is especially key when attempting a construction project large number of campers, aged 8-17, in a limited amount of time.

The design of the sundial was inspired by a fantastic Instructable for a paper sundial by arpruss. As part of arpuss's design, he developed a Perl script that would generate the dial face for your geographic location, which made it simple to adapt the design to the town in the Berkshires where the camp is located.

I modeled the sundial in Autodesk Fusion360. For a design like this, where tight tolerances are key for integrity of the structure, the use of a parametric modeling software is incredibly helpful, since it allows for changes to stock thickness that will propagate through the model. I also defined most of the geometry to be a function of the dial face diameter to allow for easy scaling.

a cross-spars were used to ensure dial face would be level and provide stiffness to the design

assembled sundial with dial face raster etched on laser-cutter

By fitting the design onto a single 12x24” sheet of cardboard, I could make a lot of these inexpensively. I experimented with raster etching the dial face, but this took ~25 minutes per dial (compared to 2 minutes for cutting the entire design), and the contrast of the text was not sufficient. Instead, I opted to screen-print the dial face, with the help of my friends Emily and Tim. This required reconfiguring the cut pattern, but the ratio of 12x24” sheet to sundial remained 1:1.

chamfer cuts on joints facilitate press-fit assembly

components for complete sundial on single 12x24" sheet

assembled sundial with screen printed face

campers sundials (mostly) pointing north

At camp, between campers and counselors, all 30 sundials were assembled correctly within 30 minutes. If you work with large groups of kids, you will appreciate how quick this is! Even a camper who has complete vision loss assembled the sundial on his own. I would like to think it was a credit to my design, but really he is just an incredibly talented kid.

I have now expanded the sundial design into a workshop on introduction to 3D modeling and laser-cutting. This workshop has been taught at Boston Makers, a community makerspace in Boston, and to the Harvard section of the MIT course How to Make Almost Anything.

teaching 3D modeling workshop at Boston Makers