Re: [Harp-L] comb design/structure

["Vern Smith" <jevern@xxxxxxx>]

Many of the puzzling design features of plastic combs are there to prevent 
warping as the injection-molded comb cools.  The plastic is squirted into 
the steel mold as a hot liquid.  Then it starts to cool and shrink. As it 
comes from the mold, it is solid but still hot.  IF one part of the harp 
cools and shrinks faster than another part, warping can result. If you tried 
to injection-mold a comb the shape of a wooden comb, it would be a crooked 
mess when it finally cooled down.

Thick and thin cross sections cause warping.  In a harp, the thin sections 
would be in the middle of the harp and the thick sections would be at the 
ends.  The thin sections cool and shrink faster than the thick sections. The 
ends and the back are hollowed out with grooves and openings of various 
sizes to help them cool as fast as the partitions between reed chambers.

The bar you refer to was no doubt put there as a brace to prevent warping.

Because the air passages in the reed chambers are very large with respect to 
the slot that is mostly blocked by the reed, you won't notice any 
differences related to air flow under the bars..

And of course we all know that the material of a comb does not perceptibly 
affect the sound of the harp.  ;o)

Vern
Visit my harmonica website www.Hands-Free-Chromatic.7p.com

----- Original Message ----- 
From: "Marc Molino" <mmolino54@xxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Thursday, July 05, 2007 6:41 AM
Subject: [Harp-L] comb design/structure


> If you look into the hole of a diatonic harp, why do some models have a 
> bar running horizontal across the middle of the comb (e.g. Golden 
> Melodies) and some have none (e.g., Marine Bands)? Is this a manufacturing 
> issues w/ plastics vs. wood? Are there plastic combs that do not have such 
> a bar? Are there wood combs that do have this bar? It does not seem to 
> have any impact upon the sound, but it would seem like it should affect 
> airflow somehow...
>
> Curious,
> Marc Molino
>
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