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.

First 2 bars

I successfully tuned the first 2 bars (F3, F#3). It was very tedious and time consuming. Each bar took about 2 hours. My new 24-grit sanding belt is working very well.

Efficiency

Once both power tools were set up and ready to go, I started work right away. I started by using the disk sander to grind down the sharp edges of all the bars. I was amazed at how well this sander could do it. I made it about half way through the bars when the sanding disk become too worn out to be productive. I went to Home Depot and bought a few more of a coarser grit. These worked even better.

Once the edges were done, I was ready to start the tuning process. This process will probably be the most time consuming task and most likely very frustrating. You start by measuring out the midpoint of each bar and then drilling dents into the bar starting from the middle and gradually going outward toward the nodes. 

The next step is to take the bar to the belt sander and grind down all the bumps in between the drill dents. This will remove more aluminum and create an easier surface to then drill into the bar again. This process is repeated with smaller adjustments each time until you have the pitch you want. I quickly found out that the sanding belt I had was also too fine of a grit and wasn't removing the aluminum as well as I needed it to. I had to order new belts on Amazon because no local stores carried what I needed. So at the time of this post I'll have to wait for those to come in the mail. In the meantime I decided to do the first set of drill dents on each bar just to get something done while I could. Hopefully in my next post I'll be able to show the process to fully tune a single key.

New Toys

After 4 years, I thought I would never get any farther on my progress. The main reason I put the project on hold in 2011 was that I did not have the proper tools to do the job properly. My method of drilling with a hand drill and using a grinding wheel were so sloppy and would take way too long. And now that I have lots of time to spare I decided to make a few purchases to get back on track. Harbor Freight has some amazing sales and coupons. I managed to buy a dual sanding disk and sanding belt for $60 and also a drill press for $56, which are both insanely cheap.

On the sander, the disk function will allow me to grind the edges of the bars on the ends where I cut them with a hack saw. The drill press will make the drilling so much easier and faster than doing it with a hand drill, which was absolutely terrible. Also I'll be able to drill the holes for the string later on, which would be impossible with a hand drill. The belt function will allow me to grind smooth the underside of the bars where I drill into them.