One of my first tool purchases when I graduated from college was an air compressor. I wanted one my whole life, and I finally had the means to purchase one. It worked great for years, but along with usage and age came problems. The check valve in the tank leaked after a few years, several years later the unloading valve stuck so it couldn’t restart under pressure, the centrifugal starting switch flew apart at some point… but I always managed to bring it back to life. Its efficiency dropped over time, and eventually it would not build over 90 psi.

This compressor was 20 years old and designed for disposal rather than repair. I had already had picked up a large commercial compressor, so the logical course of action was to scrap the old unit. Destined for the scrap pile or not, I just had to know what failed. I took the compressor apart and discovered that the reed valves had cracked.

If you are not familiar with reed valves, they are pieces of sheet metal that seal against a hole in one direction and let compressed air pass in the other. During operation, pistons reciprocate in a cylinder compressing air and forcing it past the reed valves and into a tank. The compressed air is then restricted from returning from the tank by reed valves. In my particular compressor, this happens about 60 times every second in each of 3 cylinders!

I had already decided that compressors are considered disposable these days, that this particular one had dutifully served me for years, and that I needed to let it pass on to the great scrap pile in the sky. However, I was curious how much a replacement reed valve would cost if I naively decided to fix it. After some searching, I found the correct valve for my model number was available for only $2.37. WAS is the key term… it had been on backorder since 2005. Did I want to scrap my compressor for lack of a $2.37 sheet metal part that was once available? Obviously not. I decided to make a reed valve.

I did some research and found some hardened spring steel shim stock (strong sheet metal) that I thought would make an acceptable reed valve, ordered the shim stock, and tried to find a way to cut out the part. What is the most obvious way to cut thin sheets of metal? Snips?

Snips are my my preferred tools when I want to be intellectually humbled. I can think about the shape I need to cut, ponder best way to attack the sheet metal, be patient and deliberate… but the tin snips always do what they want. Not what I want. Convincing snips to cut a shape is like convincing cats to go somewhere that they don’t want to go. In the end you are cut, scratched, scraped, bleeding, confused, demoralized, and have only accomplished what your adversary wanted all along.

I put down my snips, picked up the internet, and decided to use SCIENCE to manufacture the reed valves. I found that it is fairly simple to electrochemically etch a complex shape from sheet metal without the plastic deformation and warping typical of other methods..

I am not going to go into the detailed science behind the project, but all that is needed is a DC power supply (12V battery or charger), some salt water, some alligator clips, some spray paint, a sacrificial piece of metal, and the sheet metal workpiece. Send me a comment if you want more details or suggestions for your own project.

The basic steps are:

• Lightly sand, clean, and paint both sides of the sheet metal workpiece (the paint will act as an electrical insulator).
• Scribe the desired shape onto one side of the workpiece. Make sure to scribe through the paint so that metal is exposed.
• Use alligator clips to attach the workpiece to the positive terminal of the power supply.
• Use alligator clips to attach to a sacrificial piece of metal to the negative terminal on the power supply.
• Place the workpiece and sacrificial piece in a plastic container filled with salt water. Make sure the workpiece and sacrificial piece do not touch each other.
• Watch the workpiece bubble for about 45 minutes.
• Remove the workpiece from the salt water and rinse thoroughly.

For this particular experiment, I used the used the old reed valves as a template and traced each lobe onto the workpiece with a scribe. The final results are pictured at the beginning of this post. It was little effort while things were set up, so I made two parts. Now I can fix my compressor again 20 years from now when parts are over 30 years on backorder.

Any advice I can give for the next DIYer that wants to cut sheet metal?

• Bend the attachment point for the alligator clips on both the workpiece and sacrificial piece so that they are not under the salt water. I discovered that the alligator clips were much more prone to electrochemical etching than the workpiece.
• I don’t know if the bubbles coming off of the workpiece were caustic or not.  I held my breath for the 45 minute duration just in case.
• If you want to etch a design onto a piece of metal rather than etching through the metal, the DC Power supply can be replaced with an AC power supply. This will visibly etch the surface, but it will not cut through the part.

UPDATE: I am more surprised than happy to report that the compressor works as well as ever with its new reed valves! I am adding a reminder on my calendar to update this post in 20 years. Stick around, and we will see if the custom reed valves last as long as the factory part did.