Keychain Production

Motivation

For Cal Poly's open house week, I took on making our annual CNC machined bottle openers. Each year, the machine shop makes commemorative bottle openers/keychains to show off the capabilities of our machine shop and raise some money. These keychains are machined live in front of prospective students, alumni, and their family. Additionally, a key quality of the bottle openers is that they are personalized with a persons name.

Design

I wanted to incorporate a curved surface into this keychain, mainly for the visual aspect and good feel in the hand. This definitely increased the machine time, but it also sold more keychains (at least that's how I justified it...). Using fun surfacing toolpaths could leave different fun effects on this surface. The backside, which is flat, is machined first to allow for easy fixturing for the second op, which machines the curved surface.

Timeline and Fixturing

I had about 2 weeks to go from concept to production for this project, so I chose to limit my fixturing setup to save design and up front machine time. The keychains are small enough that multiple first and second ops could be machined at once on a pallet system, however I simply did not have time (or stock) to invest in such a fixturing setup.

Instead I opted for a single first op and second op machined at the same time (1 complete keychain per cycle). While this meant there would be a lot of time lost to swapping stock and operations, I decided for my timeline and relatively low volume of production (~200 parts) that this was a worthwhile sacrifice. This made the fixturing much simpler, with first ops held in talon grips, and second ops could then be held in simple softjaws. This also made loading and unloading simpler for the operators, which weren't always myself.

Second operation in softjaws

First Operation in talon grips

Empty softjaws

Prototype keychains to test surfacing toolpaths

Open House Production Run

I tuned and tweaked the toolpaths and loading procedure until I had the machine time down to about 3min 45s, and loading time to about 30s. This resulted in about 12 parts per hour. While not amazingly fast, I was happy with the process for being created in such a short time and producing some very nice keychains.

Open house was super successful, and we made/sold about 70-80 keychains, many of them personalized. We were making them about just as fast as they were selling, which was good. We also got to talk to lots of admitted students and parents about CNC machining and Cal Poly's engineering program.

Jake talking about keychains

Jake loading the personalization fixture

Me talking about Cal Poly's engineering program

Explaining gcode and CNC machining

Testing the matlab generated gcode on a scrap piece

Personalization

To allow for engraving names onto the back (flat) side of the keychain, a special fixture was 3d printed. Because the loads imparted are very low when engraving, this fixture served fairly well. However, as the day went on, the nylon printed fixture soaked up coolant and swelled, causing the engraving depth to sometimes be too deep.

A matlab script was created to take a persons name as a string and generate the gcode needed to engrave the name using the Haas text engraving canned cycle (G47).

Testing how many characters fit on one keychain. A plus of 3d printed clamps is the tool survives when you crash.

My personal keychain featuring the date wrapped around the hole.

Production Run #2

For our shop tech end of year bbq, I was comissioned to create a personalized keychain for every shop tech (~75 people!). For this run I managed to lower the cycle time slightly, and added a small 2023 engraving to the back of the keychain.

"Your clones are very impressive, you must be very proud"

To help get a faster, more consistent engraving, I created a palletized engraving fixture. With two people, one loading/unloading keychains into the pallets and one changing programs/ loading pallets in the machine, the cycle time was actually extremely fast. Cole and I managed to engrave all ~75 keychains in under an hour

Pallet base plate

Pallet installed with keychains ready to engrave

Post engraving pic of Cole

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