String pressure
I was thinking of doing more experiments, when I was considering whether I should use a truss rod or not in the build.
Unfortunately the pressure meters that I have access to only could take 5kg. An ordinary guitar with nylon strings got a pressure of about 10-15 kilos on each string. Since the strings are of metal and tuned a bit harder a balalajka would go past that.
Update: 6th of December: According to "Mel Bay's complete Balalaika Book", the string pressure on a prima balalaika is only around 8.3 kilos.
The balalajka got only three strings which should give it less pressure than a guitar, and therefore one could guess that a balalajka should survive without a truss rod to strengthen its neck. Due to the small size of the neck of the balalajka the pressure could affect it more, but if I were to use a truss rod it could all the same weaken the neck. This is because I would have to remove a relative high amount of wood to add the truss rod, you could have argues about this subject for hours and still not get anywhere.
The problem can in worst case be that the neck cracks. Other problems is that the neck can bend - the effect of this is not instance, but may appear over the years to come. See the pictures below. With a truss rod it would be possible to neutralize this.
This is the best picture that I could find that illustrates the problem, if you do a search on google you should be able to find better ones.
Others claim that using a truss rod or not also effects the sound very much, here is a link if you are interested. Click here!. I got no idea how this would affect me, since oak is an pretty unusual material in a guitar. This information has at least strengthened my decision not to use a truss rod, as a guitar that should have more pressure than my three-stringed balalajka. In the text they say that maple guitars without problem can stand the pressure without a truss rod.