Well, I won't claim to be an expert, but I have done a fair amount of
work with teflon, mostly the early, thinner bushings. They can be
troublesome to get "just right."
With wool bushings we have a lot of options: remove material (ream);
pack the felt (burnish, using different sizes of burnishers, create
enough friction to heat up the fibers or not; sizing pin and wetting
agent, with or without heat); and lubrication.
With teflon, there is only the option of removing material. This
needs to be done with a parallel tool, and the fluted reamers Steinway
provides are good for that. But the problem is that the reamers and
the pins are precisely the same size (precisely within our realm of
measurement), and, in my experience, the result of reaming with a .
050" reamer for a .050" pin is somewhere around 6 - 10 grams of
friction, which is generally too much.
So how do you get that friction down? You have to remove a little
more material. I experimented with those "half size" reamers Pianotek
used to provide (maybe still does), graduated by .0005" (midway
between the .001" increments of the Steinway ones), and the result is,
in my experience, 0-2 gms, too little friction, and a wee bit of
wobble. There isn't anything between those sizes, to my knowledge. So
I have tried using "modified technique" of reaming with the standard
sized reamers, pressing against the sides, trying to make it even all
the way around the circumference of the bushing. I had some success
with that, but it's a little iffy.
What I have ended up with is initially sizing the bushing with the
fluted reamer, then following with a Mannino style reamer,
experimenting with size and amount of reaming. George Defebaugh used
to recommend rolling a centerpin on a table with a file to scuff it
up, and using that. That works, but doesn't last too long, as the
material of the pin is soft. The Mannino reamers are essentially piano
wire given the same treatment, with a segment roughed up. This raises
some filings around the circumference of the wire that act as cutting
surfaces, but making them is inexact (the precise size will vary - and
with teflon we are wanting to be within .0001 - .0003"), and they wear
down with use. (you can re-rough them with a file as needed). With
felt, it is more forgiving to use one of these. With teflon, you have
to be more careful and experiment.
One thing I have thought about but haven't actually looked into is
the possibility that metric sizes might be "just right" as an in
between size, and produce just the right friction with the fluted
reamer. If you have some, it might be worthwhile experimenting.
Standard pins (as opposed to Steinway's which are smooth both ends and
already the right length) work just fine in teflon (in removing a
standard pin, press it out from the side that wasn't cut, as the cut
side would score the teflon during removal).
In the end, once you figure out what will work for the particular
application, teflon is very easy to deal with, or can be. It's very
predictable, if you use precise tools and techniques.
Your 80g DW probably includes other sources of friction, though. Key
bushings, wipp cushions, capstans, knuckles, etc. The teflon probably
only accounts for about 10g or so. (And, of course, there is the
question of how much might be friction, and how much geometry, but
let's not go there for now <G>).
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu
On Dec 5, 2008, at 6:57 PM, Mark Dierauf wrote:
> Well, I managed to survive 30 years in business without having to
> deal with these by simply replacing teflon vintage parts, but now
> I've got an L action on the bench that needs sprucing up to ready
> for sale. Some of the keys are at 80g DW(!), and quite a bit of that
> excess seems to be in the hammer flanges. So I've gotten the "kit"
> from Steinway, but now I'd like to hear from the experts on the best
> way to proceed. My 1972 S&S Service Manual isn't much help ("ream
> the bushing accordingly", with a target of "3 to 6 grams"). This is
> one of the later teflon pianos, with the improved (ribbed) bushings.
> Any takers?
>
> Thanks,
>
> Mark Dierauf
>
>
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