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Sinking the Pan

A critical part of making a good pan is to get the shape of bowl right on the initial sink.

A common cause of notes that oilcan/pop is that the shape of the bowl prior to shaping was not correct in relation to the finished shape of the pan. Similarly, notes that are marginally stable - the ones that it's tough to get in tune, and will be the first ones to go out of tune - are also often victims of a poor bowl shape. Nine times out of ten, these problems occur on the LOWEST RIM NOTES on the pan.

Another side effect of getting the shape of bowl wrong in relation to the finished pan is that the pan will tear during the shaping process. This problem is what put me on the trail of really analyzing the relationship between the two shapes.

In my experience from talking to other builders and tuners, and from what I've seen on various "how-to" videos, not nearly enough attention is paid to the shape of the bowl. It's not sufficient to simply say "The pan needs to be 8 inches deep and spread 23 inches" or something along those lines. There are many bowl shapes that can be produced with such a measurement system. We need a much more precise system.

Marking Before Sinking

The first thing I do is to mark the pan with a circular grid. I find the center of the drum, and then use a template to mark radial lines from the center of the pan to the rim of the pan every 22.5 degrees. This essentially divides the pan into 16 segments.

Following that, I use a ruler to make marks 2", 4", 6", 8" and 10" from the rim. I draw concentric circles around the pan on these lines. I refer to these lines by their distance from the rim; so if I talk about the "four-inch line" I'm referring to a line drawn 4" from the rim of the pan.

The finished, marked pan is shown at right. Having the pan properly marked like this helps tremendously in giving my eye a lot of feedback as to the shape of pan as I'm sinking it. There's very little guess-work involved in the progression of the bowl shape as the pan gets deeper.

Sinking the Pan

I use the rounded sinking tip on the large sand rammer to sink the pan. I used to run this through the foot-pedal regulator so that I could vary the speed of the hammer, but these days I'm just running it straight out of the compressor tank at around 110 psi. This makes for a very agressive sinking process. It's also not for beginners, you need to be very confident about what you're doing and how to control the tool before you do this.

To sink the pan, I usually right on the 2" line and work around the pan in a giant spiral towards the middle. I'll do this repeatedly, sometimes starting a further into the pan than the 2" line. As the pan gets deeper, I will increasingly start these spirals from lower and lower into the drum.

Once the shoulder of the pan is within about 1/8" of the sink profile, I'll switch over to the 2" diameter smoothing tip and smooth out the entire pan. From here on out I'm running the airtools through the footpedal so that I can control the pressure very carefully. The steel smoothing tip has relatively sharp edges, and it's easy to cut the drum near the shoulder area, so I often switch hammers in this region and use the 1 1/2" plastic tip on the smaller sand rammer in the shoulder region.

As the pan is smoothed out, it will settle very close to the finished sink profile.

Sinking the Pan in a spiral motion using the 2" round sinking tip. Checking for balance using a straight edge and square Re-marking the Shoulder line. The circle will be drawn using the circle tool. The line being marked is the 7" line, the line below it on the drum was originally the 6" line before the pan was sunk. Starting to smooth the pan using the smoothing tip. The left side is smoothed, the right side has not yet been touched.

Keeping the pan Balanced

I'm constantly measuring the depth of the pan as I sink it, to make sure it stays balanced. Its remarkable to me how many finished pans are not balanced. By balanced, I mean that if you draw a line on the pan a certain distance from the rim, the steel at every point along that line will be the same depth unless its inside a note panel. This sounds like common sense, but if you measure many pans you'll find they are not properly balanced. Often these pans have a wild range of quality in their notes - some work nicely, while others are just awful, and no amount of tuning them is going to fix that - the bowl need to be balanced first.

As the drum gets deeper, the lines will "move" across the pan and need to be re-marked. For example, a line that was marked 6" from the rim will become 7" or more from the rim as the pan is sunk. To properly measure the shape of the bowl, we need to re-mark these lines.

I stay away from the shoulder region with the 2" steel tip. Using the 1 1/2" plastic tip on the small sand rammer for the shoulder region. Almost finished with the sink. Notice that the area between the shoulder and the rim is almost flat.

Marking a line on the pan

I frequently refer to a particular "line" by its distance from the rim of the pan. So for example I talk about the 4" or 6" or 7" line. These lines are concentric circles a certain distance from the rim of the pan.

To correctly mark a line on the pan, I place the ruler as shown at right. In this case, the line being marked is the 7" line. So in this instance, I placed the ruler's 7" mark right on the lip of the pan, and then marked the position of the end of the ruler on the pan (far right).


Concentric Circle Tool

The traditional method of using a ruler and just holding it a fixed distance from the rim of the pan as one walks around the drum is not very accurate, as the ruler tends to "wander". I developed a circle drawing tool to draw concentric circles around the pan. This method draws very precise circles on the pan.

The two holes in the bottom of the tool are for different size Sharpies.

The tool is made using some Radio Control Plane wheels and a hinge. There is a clamp that allows the length of the pipe to be adjusted and held. THe small black bump at the bottom of the pipe near the pen is a metal insert that acts as a counterweight.

Measuring the depth of a point

To measure the depth of a line on the pan I use a straight edge and an adjustable set-square. This way, there is no "eyeballing" involved - the measurements are accurate and repeatable.

The first step is to mark the line accurately - so I'll use the ruler to measure, say, the 6" line, and then use the Circle Tool to make a 6" circle around the pan. The lines creep constantly as the pan is sunk, so it's always a good idea to check that what was the 6" line a few minutes ago is in fact still the 6". Remember, I'm striving for accuracy and repeatability. Numbers don't lie.

I set the length of the adjustable square to the depth I'm trying to achieve. So for example, if I'm trying to sink the 6" line to a depth of 4 3/32", I'll set the square to 4 3/32" plus a correction of the depth of my straight edge. In my case, the straight edge I lay across the drum is a piece of 1" aluminum angle. So, I can conveniently just add 1" to the desired depth on the square.

I lay the straight edge across the pan, and then put the square on the straight edge. I'll slide it towards the pan so that it just touches the surface of the pan. If it touches below the line, then the pan is too shallow. If it touches above the line, then the pan is too deep.

I make sure that every intersection of every radial and concentric line is at exactly the same depth. When they're set correctly, the bowl is the right shape and well balanced. The tolerance I use on the ruler is 1/64", which is around 0.4mm.



Free Pan Software

I developed some computer software that is freely available in the downloads section of this site. This software provides a relatively easy way to see the relationship between the bowl shape and the finished shape of the pan. It only runs on Windows, my apologies to all you MAC and Linux users out there - it might run under WinE, though.

The drawing at right shows a screenshot. The left most white column at is where you to enter the "line" numbers in, the next white column is the depth of the "sink" profile for that line, and the third white column is the depth of the "finish" profile.

There are some toggle switches you can play with on the bottom left, and you can add a caption to your profile. Also, you can save and load profiles, so you can come back to them and modify them as your pan building skills evolve or you encounter problems that you'd like to correct over time.

The default profile pre-loaded into the software is the shape for the sink and finished profiles that I use for my Heritage pans.

There's a rudimentry help section. I'd value feedback on the software if you decide to download and use it.



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