Finishing the surfaces

So obviously I don't want my vibraphone to look like a scrap metal yard. So my next step was to smooth out all the surfaces of the bars. This is done by sanding only. I didn't want my bars to be so smooth that there are reflections on them. I did all the sanding parallel to the length of the bar to give it a uniform grain along the bar's length. The sanding process was done in 3 stages or layers.

First I used an 80 grit sanding belt on my belt sander. I applied all surfaces except the top surface of the bar to the flat part of the belt sander. The belt sander was good for quickly removing large scratches but was not very smooth. It was also great for creating rounded edges simply by applying an edge to the sander and then slowly pivoting about that edge. I did not apply the top surface because it produced an uneven grain because the surface of the belt sander was not perfectly flat and some portions of the bar would get sanded more than others.

Then I used 80 grit sandpaper. Even though it was the same grit as the belt sander it made the surfaces much smoother when done by hand. Using wet sandpaper lets the sandpaper last longer.

The final layer was done with 150 grit sandpaper. This completely smoothed out every surface and gave everything a nice "polished" look.

Here is the finished result. I was immensely pleased with how they turned out. There were a few dings and scratches here and there that were too deep to be removed, but I'm not too worried about it. Next up is fine tuning, which will require a good deal of patience.

Drilling String Holes

At this point I can finish out tuning all of the keys. Using my new A-Frame I positioned all the keys and amazingly everything fit perfectly on the A-Frame using the measurements from the template. I didn't have to make any changes. String has proven to be a really useful tool for lining things up. I used string to mark the center point between the naturals and accidentals, and also to mark the center of each beam to mark where to screw in the screw eyes I'll be using to suspend the bars and string.

Luckily I didn't have to redraw the drill hole lines on the bars. I bought a drill press vise from Harbor Freight Tools because I didn't trust myself drilling holes at angles while holding the bar with my hand. It took a while to correctly position the vise so that the drill bit enters at the correct angles.

All bars now have string holes drilled and countersinked. Next up is fine tuning, which will take a good bit of time to complete.

The A-Frame

If you don't know what the A-frame is, it is the portion of the frame that suspends the keys. It consists of 4 beams under the bars parallel to the alignment of the string holes in the keys. This part was very tricky to figure out the exact measurements I would use. Ideally, the string holes are drilled through the nodal points of the bars perpendicularly, but they also have to line up when all the bars are in place. So there has to be some compromise on their location and angle. I decided to determine the nodal point again of every 3 bars or so. The nodal points are now in different locations than they were before any tuning was done.

I had this poster board that I decided to use as a template or stencil of sorts. I positioned all the bars on it with the exact space between each bar that I wanted. It was just barely too small so I extended it to fit the last bar. Then I traced the corners of all the bars.

I then positioned string over the nodal points that I just measured. I had to position it as a best fit line through the nodal points because they don't line up perfectly. With the string taut over the nodal points I marked the lines where the string holes will be drilled on the bars as well as the poster board.

Then I made some measurements on the lengths of the beams that needed to be cut. I'll spare the boring details on how those were determined. Then I cut them to length with a miter saw.

I lined up the beams using my template and then screwed them together. For all purposes of joining pieces of wood together for the frame I first set the pieces in place with wood glue and let them set with clamps.

I used a drill bit smaller than the width of the screws to drill "pre-holes" for the screws. This prevents splitting the wood by driving the screws straight into the wood. I also used a countersink bit to allow the screw head to sit at or below the surface of the wood.

This multi-function oscillating tool worked great for smoothing out the surfaces where different beams are joined together.

Here is the complete A-Frame with the tools used to put it together. That tool in the middle is called a T-Bevel. It was used to find the angle that each of the four beams are positioned on the end pieces. This allowed me to cut the four pieces connecting the pairs of beams together at the proper angle.

Initial Tuning Complete

The most time consuming and monotonous task of the project is now complete. For all bars the fundamental and first overtones are tuned to about 30 cents sharp of their desired pitch. For the highest 7 bars (B5-F6) I only tuned the fundamental pitch. Eventually the first overtone becomes too high to tune without a stroboscopic tuner and you won't really even notice when it's being played.

Next I will be purchasing the wood and other hardware to construct the frame. I haven't decided which type of wood to use yet.  After I build the A-frame then I will drill the string holes in the bars, finish their surface, and then fine tune to their exact pitch. I have to build the A-frame first so I get the holes drilled at the correct positions and angle so all the string holes line up correctly.

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.