Tuning a Bar

I'm going to briefly go over my process for tuning a bar. I start by drilling rows of dents starting in the center of the bar, making them as close as possible. I sort of use the previous tuned bar as a reference for about how far out from the center I will drill rows of dents.

Then I grind down the sharp edges between all the dents. This creates more surface area to drill additional dents in the next layer of drilling. 

I don't even check the pitch of the bar until I've drilled about 3 layers, at least for the larger bars that is. I know I need to remove a good amount of material from the underside so checking the pitch would just be a waste of time to do it so early on. 

When I'm ready to start checking the pitch, I finish grinding a layer of drilling and the place the bar in a bucket of water because the grinding heats it up a good bit. The temperature affects the pitch of the bar, so I need it to be room temperature when checking the pitch. It only takes a few seconds to cool down. 

For a tuner I actually use an app on my phone called DaTuner. It's amazingly precise and accurate and can easily pick up a pitch. 

When you strike a bar, there is more than 1 pitch that results. There is the fundamental and overtones. For my vibraphone, I will be tuning the fundamental and first overtone. The other overtones would require a stroboscopic tuner because they are in such a high register. Also they aren't very noticeable anyways. To tune the fundamental you hold the bar near a nodal point and strike in the center. For the first overtone, you balance the bar in the middle and strike on a nodal point, or about 1/4 into the bar. These 2 pitches need to be the same note 2 octaves apart. For the bar in picture (C4), the fundamental pitch needs to be C4 and the first overtone needs to be C6. 

Changing the fundamental pitch is done by removing material from the very center of the bar. Changing the first overtone is done by removing material closer to the nodal points. If you remove material in between those locations, you can change both pitches at the same time. So for tuning I check both pitches after each layer of drilling and then drill another layer based on how much each pitch needs to change. When you first start tuning a bar, the first overtone is closer to the target pitch than the fundamental, but as you tune the fundamental pitch quickly catches up and passes it if you're not careful. After tuning 3 or 4 bars I found a very uniform pattern in how much the pitches are affected based on drilling locations. As I get closer to the target pitches, the fundamental will drop far easier than the first overtone. One more item to note is that I am tuning all of these bars until each pitch is about 30 cents sharp of the target pitch. I still need to drill the holes for the string and clean the surface of the bars, which will affect the tuning. Later on I will go back and fine tune each bar.

Below shows the progression of tuning C4. This does not show every layer but every few layers.