[Part 2] Mechanical Design and Fabrication

"To make the mechanical body of the Peteometer, I spent roughly about ten hours in the machine shop making friends with a lathe, sanding gears, milling machines..."

In this post, I am going to show off some of my machining skills as well as the end result of the Peteometer casing. While I am waiting for the package, I can start machining some parts that will house all the electrical components as well as the flow meter. This is also very crucial since I'm using a light detection method to read off the flow meter where the frequency range for the light detection (infrared + 650nm diode laser) overlaps greatly with the general spectrum of the room light. In order to minimize noise as well as inaccurate measurements, proper casing is crucial for this project.

Now, the electric circuit components have to be shielded from the ambient environment (pretty standard procedure for all electronics designs around us), therefore I have roughly drawn a blue print in my mind before I made my first cut on a aluminum sheet

The above picture shows a completed casing. It is basically made of two sheets of metal, aluminum for the outer chassis and stainless steel for the back cover. This material choice comes from the following three most basic reasonings.

1. Anything that is going to cover the front of the device should look aesthetically pleasing. Therefore, aluminum sheet metal with anodized surface is used for the front external casing.
2. The electrical circuit elements have to be well shielded. Aluminum cannot provide this.
3. The back cover will serve as a mounting point for the whole device. Stainless steel has the right stiffness vs. machinability and therefore a perfect candidate for this purpose.

I believe to some degree that machines are better off in reading numbers and measuring things. But sometimes they can fail and, for this case, I have to make sure that the flow meter gratings are visible from the outside of the device. So I am going to make a narrow linear cut on the location where the flow meter will be located.

Once I did all the markings, I clamped the aluminum sheet metal on the lathe from both ends and started to mill using a 3/32 bit. My first attempt failed because I kept getting jagged edge. Then I simply changed to an almost brand new mill and it worked great. But I had to keep spraying on WD40 while making slot to prevent frictions as I thought that frictions are responsible for any resulting irregular edge.

I said earlier that I'm using anodized aluminum sheet. So it comes with a protective plastic cover with it. It should only be removed after any required machining is done since this protects surface finish. When you take the sheet off, it will look flawless.

After removing the plastic cover, the result is shown in the above picture. Please note the effect of constantly spraying WD40. The reduced friction makes the cut looks almost the same as the ones made by EDM machines (Electric Discharge Machine) which is often used to cut sheet metals. The milling speed was 2400rpm, which is considerably fast to avoid, of course, jagged edge.

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