v-bar/capo repair: Seiler pictures 2

[Overs Pianos]

Hi David,

>Ron,
>
>Looking at the jpg of the capo bar I notice how V shaped it is...not 
>rounded...comments
>
>David Ilvedson, RPT
>Pacifica, California

The apex of the bar is still rounded, but to a very small radius, 
around 1.25 mm. Mind you, I don't get down with a light and check 
each bar. But occasionally we'll get out the drills to compare the 
profile, just to check that we're not getting too far away from what 
we are aiming for. The overall section of the bar needs to be 
V-shaped, preferably with a slight concave on the sides. This helps 
to reduce the sectional area for heat escape from the apex during the 
heating phase. It still will have plenty of sectional area for the 
self-quench. The bar needs to be dressed up after it is hardened. 
This will remove much of the concave that we put in prior to 
hardening.

If the section of the bar is made round it will be very difficult to 
harden.You'd have to pour in so much heat that the filler would be 
blistering and burning, and there would be a risk that whole bar 
might get so hot that it wouldn't self quench (its also not too good 
for plate to have a hot section while the remainder is cold). With 
the profiles we are using these days, we only mildly scorch the 
filler coats. We have a grab bag of heat shields which have evolved 
over the years and these also are a help.

Back in 1995 a certain piano company's 'expert' criticised the V 
shape profile we'd been shaping the bars to. The representative wrote 
a scathing report which was delivered to a leading Australian 
Conservatorium, in an attempt to discredit me as a technician. Since 
the company, at the time, weren't actually hardening their bars they 
clearly didn't understand the process we were using. Since that time, 
the said company is now hardening their capo's. I wonder if their 
views have changed since 1995?

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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Web http://overspianos.com.au
mailto:ron@overspianos.com.au
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