Fwd: Re: [Harp-L] On Tolerances

["Tim Moyer" <wmharps@xxxxxxxxxxxxxxxxxxxx>]

Steve Shaw wrote:
> Cor, blimey, you "North Americans" and your pennies!  Are Canadian 
> pennies and US pennies the same size?  And how do they compare 
> with UK pennies (the real McCoy of course)?

I don't use a penny, I think the copper is too soft, and I can't get 
the proper grip on a penny.  I use a socket from a socket wrench 
set.  I'm not sure how well this description translates into other 
languages, but I can't think of a better description.  The socket 
I'm using is case hardened steel, and is a cylinder about 20mm in 
diameter, and 30mm in length (although the length isn't really 
important).  I find it's VERY important to use consistent pressure 
that is evenly distributed against both sides of the slot, or uneven 
reduction in tolerance will occur.  

Embossing will bring out every burr and defect in both the slot edge 
and the edge of the reed itself, as well as revealing any deviation 
in the reed angle in the slot.  I use a small (0.002") shim down the 
edges to get the reed centered again (works MUCH better than a 
wrench), and I sometimes use a small chisel drawn down the edges of 
the slot and/or the reed to deburr it or to remove overzealous 
reductions.  

I have found that embossing to reduce this tolerance has a profound 
affect on tone, making it far more brassy.  For this reason I like 
to not overly emboss, just enough to improve response and move the 
base of the reed farther down in the slot (a side effect of moving 
the socket up the slot over the reed).

-tim

Tim Moyer
Working Man's Harps
http://www.workingmansharps.com/