Top plate graduations

Measuring variables

During graduation you will have to measure the following criteria:

a) Area thickness You will use the thicknessing caliper to measure the thickness in the area you are working on. See the Tools section for a description of the thicknessing caliper.

b) Mode frequencies These depend on the stiffness of the plate. The M5 frequency is the most important. Refer to the section on plate tuning to learn how to measure these frequencies.

330-360 Hz here is the accepted range. It shouldn't be more than the M5 in the back plate.

Look at Fig. 1 which describes how areas on a plate affect the mode frequencies. Therefore, for example, removing material in the central section number 1 lowers both the M5 and M2 frequency.

c) Weight Plate weight influences the ease with which the plate gets excited by the bow. 60-70 grams range for a finished plate with bassbar often considered is ideal. Too heavy a plate doesn't resonate freely enough.

d) Flexing Apart from measuring using instruments, you should also get a feel for how the plate feels in your hands. Flex the upper and lower bouts, twist the plate along its axis, flex the small areas in the bouts.

e) The stiffness index One of the numbers which describe the stiffness, weight and arching is the stiffness index. It really combines the a) and b) into a formula. The formula is (M5 frequency squared) * weight = stiffness index.

The ideal number in this test is 8 000 000 for the front and 14 000 000 for the back.

For our finished plate it is (333 squared) * 68 = 7 540 452.

Generally, the goal is to create a plate that is as lightweight as possible, while retaining as much stiffness as possible.

Graduation patterns

Before you start removing material, you should have an idea what graduation pattern you will choose.

a) membrane - uniform in thickness all over the plate
b) common - the most used system with the central part thicker
c) reverse - thinner in the center
d) spine - thicker along the center line

Each of these patterns has its acoustical qualities, which ideally are matched to the correct arching. It all depends on what sound you want from the violin.

In our violin we will use the common pattern which is also the pattern Stradivari used in many of his violins. This pattern is also best if you need to get the M5 frequency as high as possible.

Concrete numbers

In Fig. 2 you see the averages for 48 Stradivari top plates. The thickness maps are here for reference only so that you have some idea of the real thicknesses. Bear in mind that Stradivari used first rate wood which allowed him to graduate the plates thinner than you probably will be able to.


Now you know what to check for, so you can start removing material.
  1. Use a small thumb plane. Make sure you don't remove too much wood in one place. Make the transitions between areas of different thickness as smooth as possible. Avoid overthining spots.
  2. Keep checking the variables mentioned at the top of the page. Create a table for your measurements, like the one below, to mark your progress.

Plate 4 mm uniform thickness:
mode 1mode 2mode 5Plate weight
117 Hz208 Hz401 Hz85 gr

  1. When you start getting close to finished, switch to your scraper and finish the surface smooth.
  2. Measure again all variables and make a record.

Finished plate:
mode 1mode 2mode 5Weight
89 Hz155 Hz333 Hz68 gr

The plate is finished for now. The numbers will still change after you have cut out the f-holes and after the bass bar has been added but not by too much. You can now proceed to the Cutting the F-holes.

Back plate graduations

Graduation patterns

a) bulls eye - thicker in the center in the for of a circle
b) spine - thicker along the centerline

Concrete numbers

In Fig. 3 you see the averages for 48 Stradivari back plates. You can distinctly see the bulls eye pattern used here.

  1. Use a small thumb plane.
  2. Keep checking the M5 frequency and the weight of the plate. Create a table for your measurements, like the one below, to mark your progress.

Starting plate:
mode 1mode 2mode 5Plate weight
* Hz* Hz430 Hz143 gr

Finished plate:
mode 1mode 2mode 5Weight
* Hz* Hz364 Hz107 gr

Masters: 14 177 072
(364 squared) * 107 = 14 177 072

Category: Tuning