For the SSC interview series, we asked Eric Au of Metro Grade Goods to share a little bit about slingshot design, and his process of making slingshots.

How long have you been in design, and what is your design background?
I have been an Industrial Designer for almost a decade. My previous professional design and creative experience comes from a marketing and graphic design firm and freelance fashion/editorial photography. I hold a Bachelor’s of Fine Arts (in Ceramics and Photography) and Master’s Degree in Environmental Design (Industrial Design).

I’ve always had a shop space of some kind, and my craftsmanship ranges from experimentation in the shop to formal training on equipment.

What got you interested in designing slingshots?
Slingshots were a by-product of my hobby of compound bow archery. As most would do, you would scour the internet for things to read and see about your hobby and I came across a few video on YouTube that showed a way to modify a wrist braced slingshot to shoot arrows. I was in love with this idea since the setup time for a quick arrow shooting session was complicated and laborious. I quickly made an arrow shooting slingshot from an inexpensive, commercially available slingshot and was bored quickly since I was used to the very fast flight of a carbon arrow leave the string of a compound.

The more I shot it, the more I reconsidered why I was shooting arrows when steel ball bearings were way easier to carry around and grab when I wanted to shoot. Thus, began the journey to find out how deep the rabbit went (and I am still not seeing the bottom).

Again turning to the internet for guidance regarding better slingshots, I discovered the forums and the community at large. There I found an incredible resource for all sorts of shapes and band types. As I began to understand the mechanics of slingshot shooting, the frames that were shown just didn’t meet my personal needs, so I started making my own, in the way I knew how to make things.

Almost 4 years later, I am still coming up with new designs, new ways of attaching rubber to sticks and discovering new or old materials that never really been seen on the business end of a slingshot.

Without giving away your secrets, what is your process for designing slingshots?
Design a slingshot is like finding a pair of gloves, they all have 5 fingers and a palm, but not all gloves fit just right.

When I start a fresh design, I have to first ask myself: will I shoot it? My primary goal since the beginning, has been to improve my own personal target shooting ability. In order to do that each slingshot shape I design, I must be able to shoot and do so, well. In that respect, my sling-craft is a very selfish endeavor. I don’t hunt, but I do like the calming, relaxed solitude of the pre-shot routine, draw cycle, concentration and hopefully, successful hit on the target.

The design of the slingshot is actually inconsequential, I can’t tell you how I come up with designs because most often, they are just shapes that I see or the way my hand wraps around an object. It’s mostly done by feel and then translated into a shape. That shape is either hand drawn and then I trace the shape in Adobe Illustrator.

Here is an example of Eric's process.

This video was made for his YouTube channel, subscribe below:
https://www.youtube.com/channel/UCnOjUmR3Z9FOojG_EQPC0pA

While in Illustrator, I can smooth out curves (or introduce them), add perfect radii to corners and tweak the dimensions freely and easily. I’ve been using Illustrator for more than 15 years so this is what I am most comfortable with, any vector based drawing program (AutoCAD, Inkscape etc). Once the outer profile is established, I move to adding details like counter sinks for screws, breaks in the surface, chopping it up into parts for lamination, editing digitally really comes into it’s own here.

Once the digital fabrication is done, I move onto the prototyping with wood or plastic. Lately, I have been favoring the use of a small CNC router, this helps me make an accurate ‘first try’ and allows me to test out hardware.

To program the CNC to cut the design, I first export the Illustrator file into a SVG (scalable vector graphic) and open it up into an open source CAM software called MakerCAM. This web browser-based software is powerful, but limiting, but I’ve learned to make it work for me. There are other software packages I have yet to try, but this works for now. Once the paths are made, I export the G-Code (NC file) and load it up into another piece of open-source software, Universal G-Code Sender (UGS)

UGS connects and talks to the Arduino based CNC machine which has the GRBL firmware (open-source g-code interpretation software). If all the checkboxes are marked, I press go and anxiously watch as the profile and features are slowly cut from the material mounted on the bed.

Many revolutions later, the block or part is pulled off the bed. If it’s a whole slingshot, I will use a combination of router work and hand shaping to get it to the final form, or if it’s a part, I will incorporate it into the work and move on. From there, it’s sanding and finishing time. Depending on the combination of materials, this can be either minimal or a 2 hour affair.

The results are always a surprise as one can only pre-visualize and anticipate so much.

What is the slingshot design you’re most proud of creating?
That’s a tough answer to give, I enjoy the craft as much as I love shooting so I can’t exactly give ONE design preference. My flow between designs is organic and I tend to saturate myself with one design at a time to get the best version of it. After I feel I’ve exhausted that outlet, I move onto something different. That way, I am never bored or feel I am making one of something too much.

There is always something to be said about consistency, but I am more consistency inconsistent!

If I had to choose ONE design, which likely won’t be repeated again is the Café Racer. It took all my brain power to visualize everything before I even touched raw materials. I doubt that there will be another slingshot made from a motorcycle piston head.

(The Café Racer by Eric Au: http://metrogradegoods.com/metro-made-the-spanish-cafe-racer/)

Another example of Eric's work, the Oren Slingshot based off the Kill Bill series:


Do you have a preference in slingshot design, either grip or fork type? Or would you say your more of an “inclusive” designer and not held down by anything specific...
I have a few preferences regarding shooting styles. For TTF shooting, I favour a solid pinch grip. For OTT shooting, I much prefer a high thumb support. For BB shooting, I lean towards pinch grip (and OTT).

This leads me to make a variety of frame designs but they all seem to gravitate towards a smaller scale. Being of Chinese descent, my hands are medium sized and I had mentioned before that I tend to make slingshots that I would personally shoot. Luckily, a smaller slingshot, with the right design, can still be held with larger hands.

We are in what a friend calls “the golden age” of slingshots, so much variety, materials, world-wide connection, even different rubber compounds. I’ve never traveled so much just to shoot the same cans and targets that I would normally shoot at my own range.

I can’t wait to see what is around the bend.

Eric's work landed him an interview with the CTV which can be seen here: