Actually, as I mentioned in the "Violins/Fiddles" thread, the 'scratchiness' is partly WHERE the wheel touches the strings.

The other problem is the same as the violin bow - if too much pressure is put on the string, you get that scratchy sound.

I have found that if you use the right amount and type of wool (was 'cotton' actually available?!!!) and lift the string to the right height above the wheel, so that the STRING IS NOT ACTUALLY TOUCHING the wheel, but the wool acts as a bow buffering the direct contact of the wheel, the 'scratchiness' totally disappears.

Kinda like how some brass instruments are played to sound in some cultures - they would fail an audition for a 'Western' brass band because of the 'tone' .... if you listen to badly set up and played instruments for long enough, then they all 'must' (traditionally!) sound like that....

:~P