First Real Project

My friend Bob is a rock star. Well, he's the bass player in a band, I don't know if that counts. Anyway, the band is called Phoenix Rising and Bob did the logo design. Probably more than a year ago he did a graphic design job for me and I suggested I could make a key chain for him with the band's logo on it. So right on schedule, I finally got it done. It's not really a key chain, though, it's 3/16" thick aluminum and over 2" x 3". I decided to call it a "plaque" and put a couple holes for screw mounting to a guitar case or something.

It's a simple design, an etching with a profile cut out. I really didn't have a suitable bit to do the etching with. I bought a Dremel engraving kit with a mix of grinding and engraving bits in it. I assumed the bits all had a 1/8" shank as most do. I've got a 1/8" collet just for Dremel bits. Unfortunately the engraving bits were 3/32" shanks. So I went ahead and used my drill chuck to hold the bits. This is considered bad form, drill chucks aren't designed to take side loads, but the engraving was only 0.015" deep and went slow. I'm not terribly happy with the cuts, but after breaking a small bit doing PCB milling a year ago, I was reluctant to invest in another high-quality engraving bit without being sure what I wanted.

I did a couple of tests in a vinyl sheet material. I mounted the stock over a sacrificial plexiglass piece and held it with the same hold-down clamps I use for my vise. I ran the engraving program and everything went fine.

Then I switched to the 1/4" collet and mounted a 1/8" bit to cut the profile. I immediately realized my first error when I brought the head down. With the stock mounted so close to the surface of the table, the head with the short 1/8" end mill won't come down far enough to cut through the stock. So ends practice run number one.

One of the greatest challenges with this mill is the work envelope. You've got to plan ahead to make sure the bit can get every where it needs to go without running into the limits of the machine. I took some measurements and figured I needed to raise the work surface 1/2". I even took off the lower Z-axis limit switch to get a little more room. Fortunately, I had in the works a large tooling plate I mentioned in my last post. I didn't have any holes in it, so I had to take a quick detour from this project.

I mounted the tooling plate, and found the center rear edge. I then made a number of holes on a 1/2" grid clustering them on either side of center figuring I didn't need too many holes in the middle. Anything small enough to fit in the space in the middle likely could go in the vise just fine. Tapping lots of holes is tiring. I lost focus at one point of the drilling phase. My wife called me while I was in the middle of transiting the spindle from the left to the right side. I took the call and when I finished I assumed the head was at the target location and proceeded to drill the hole. Then I looked at the DRO and realized I was a little more than 1/4" short of the target. I made another hole to pair up with it, so now I've got 2 holes that are off the 1/2" grid, but they're actually in a pretty useful spot for holding the vice.

After completing the drilling and taping of the tooling plate, I mounted the sacrificial piece and another vinyl practice piece. I ran the engraving job again, then did the first roughing pass of the profile with the 1/8" bit. I've been using Cam Bam to generate the gcode. It supports "tabs" to hold the inner material in place while the profile is cut. The size of the tabs I chose turned out to be too small. I switched to the final finishing pass with a 1/16" bit and the tabs broke free. So I doubled the size of the tabs. A valuable practice run...

The blank stock mounted:

Engraving:

Profile cut:

You can see the tabs in the above picture. I had to grind them off and clean up, of course. This was a bit of a drag. The final milling pass was pretty clean so to have to grind and sand was a bummer. If I had to do it again I'd drill the holes first and screw the stock down. This would leave the complete perimeter free so the tabs wouldn't be needed. That's OK, I got a feel for the tabs and I know what the correct size is and what I'm up against for future jobs that don't have any interior holes for securing.

After milling, I painted the face gloss black, let it cure and sanded it with a random orbital sander. This left the black only in the engraving path. I took a shot at polishing the aluminum with my Dremel. I bought some polishing compound and hit the sides and the back. I figured the back isn't going to be seen so it would be good practice. It's not perfect, but it shows promise. Polished aluminum looks really nice.

Bare aluminum in the hands can feel a little dirty, so I sprayed on a clear coat enamel. And here is the final piece: