Hi Seth,
I'm not sure why drilling out that hole would impact a wah-wah sound.
However, I don't think you need to worry about the structural
integrity of the shaft system from that hole. If you need that wood
brace (which is subject to seasonal movement) to support a *metal*
shaft that is much more rigid than anything else in the instrument,
you are in trouble. It is instead drilled out to allow the shaft to
pass through it, not to support the shaft. In fact you want to
minimize contact between the shaft and anything else to reduce
friction. Therefore your ideal system would contact the body only at
the head and tail bearings.
Maybe someone else can think of a reason for the wah-wah, but my only
guess would be that the shaft wasn't *perfectly* straight and that
the loading pressure of those drones was causing an intermittent rub
between the shaft and the brace that was manifest as sound like that.
But that's only a guess.
Regarding the bearings, it looks like he's used a wooden bearing for
the head (the wooden rod) and probably for the tail as well, but it's
not visible. Marc Reymen has posted details on the list in the past
of how to make these (they are fairly simple to make), but suffice it
to say that a well-constructed wood bearing from lignum vitae will
probably last longer than the rest of your gurdy and require less
maintenance. Marc makes them from lignum vitae, which was used to
make industrial bearings for steamships, mills, etc. It works more
like a metal than a wood, and is almost indestructible. You might be
ale to get similar results from some other woods like cocobolo (it's
often used to make self-lubricating guides for bandsaws) or even
osage orange/hedge apple, but I haven't tried these. The really nice
thing about a wood bearing is that if you do get any grit into the
wood bearing the grit gets incorporated into the bearing rather than
scouring the bearing and/or shaft, as can happen with metal or
plastic bearings.
Best,
Arle
On Mar 15, 2007, at 2:14 PM, Seth Hamon wrote:
I was looking at the building of the luteback hurdy gurdy on http://
www.edmonds.de/body6.html . What is the reasoning behind drilling
the hole in the first rib for the shaft 4mm larger than the o.d. of
the shaft? I know he said it relieved the wah wah sound problem he
was having.. It just seems as though this would take away some of
the structural integrity of the shaft system.. Is this a common
practice for the construction of a hurdy gurdy. It does appear that
he didn't use any kind of bearings for the shaft. It seems to be
set directly into the wood. Cheers, Seth
