Month: March 2010

The bass bar is a piece of spruce about 6 mm wide that runs the length of the top underneath the bass foot of the bridge. It provides rigidity for the top and enhances the lower frequencies. Its proper installation is critical to the tone of the instrument.

The first step is to cut a piece of spruce to the proper length, plane it to width and cut the proper shape with a knife.

We then glue some temporary cleats to the top to hold it in place and chalk fit the bassbar to the top. Its location is critical and must fit exactly the entire length.

Once it fits perfectly, we glue it in place.

The bassbar is then shaped using small planes. Thicker in the bridge area and thinner in the lungs.

Like we did for graduating the top, we use resonate frequencies to fine tune the shape of the bassbar.

The top is now complete. We are ready to put the body together.

The top is now ready to receive f-holes. The location and size of the f-holes is very critical to the tone and function of the violin. The first step is to accurately locate the holes.

After the holes are located, I cut out the holes.

Then, using a hand saw I cut out the shape of the f-holes.

Finally, with a very sharp knife we blend all of the curves to produce a beautiful pair of f-holes.

We are now ready for the last step for the top, installing the bass bar.

The steps for continuing with the top are the same as for the back. The next step is to cut the purfling channel and install the purfling.

Then using the gouge, we bring the arching down to the level of the purfling.

Now, as for the back, we refine the arching using finger planes and scrapers, cut the sgusciatura and blend the arching to the channel. we have now finished the outside of the top.

To do the inside, we gouge out the excess wood to a uniform thickness of about 4 mm. The top does not have the same graduation pattern as the back. Rather, it is essentially uniform in thickness. Sometimes, depending on the wood, it is a little thinner in the upper and lower bouts and a little thicker in the bridge and sound post area. Using finger planes and scrapers, I bring this top down to about 3.2 mm all over.

As with the back, the top is tuned using resonate frequency readings and stiffness calculations.

The top is now finished except for cutting the f-holes and installing the bass bar.

With the back done, we turn our attention to the top. The steps are the same as for the back.

First we glue the pieces together. Again a perfect joint is required.

Next we use the ribs to layout the outline.

We saw just outside the layout lines.

Rough in the arching.

Finish the outline and purfling platform.

we are now ready to purfle and finish the outside arching.

With the thickness of the back carved to nominal values, it is time to tune the plate. We want the plate to vibrate freely but we also want it stiff enough to provide carrying power. These two goals are at cross purposes so we have an optimization problem.

Using the work of Carleen Hutchins, I sprinkle tea leaves on the plate and vibrate it with a signal generator and amplifier. I look for two resonate frequencies, F5 and F3. I examine the pattern formed by the tea leaves. From the pattern and the resonate frequency, I can tell where to remove more wood. I also weigh the plate and calculate a number that is proportional to the stiffness of the wood. Finally, I also look at the range of frequencies at which the leaves still vibrate. I find that as I get closer to the optimal thickness, the leaves will only vibrate over a range of a few Hertz for a given resonate frequency. That is when it is time to stop removing wood.

Here is a picture of the pattern I get for F5. This is also called the ring mode for obvious reasons.

Here is a picture of F3.

Here is the finished back.

Now, on to the front.

With the outside of the back done, we turn to removing wood from the inside and graduating the plate. The first step is to remove the bulk of the unnecessary wood. I use a gouge and take the entire inside down to a thickness of about 6mm.

Next I layout the graduation pattern. Since this is a Strad model, I use a variant of the system described by Sacconi. For this outline and arching shape, I find that this system gives very reliable results for the tone and carrying power of the instrument.

Again, using the gouge, I carve the graduation pattern to about 0.5 mm above the nominal values.

Now, using finger planes and scrapers, I clean up the gouge marks and take the thickness’s down to nominal values. Now we are ready for tuning the plates.