Fitting Teflon Bushings

[John Musselwhite]

At 05:33 PM 3/7/99 -0800, Del wrote:

>choose a larger pin or gluesize the hole.  I didn't bother with the blunt
pins
>sold at a frightful cost by S&S.  I used standard pins -- they thread
easier and
>cause less damage to the second bushing as they pass through -- and cut
them with

With respect to Del,  part of the beauty of servicing Teflon actions is you
can push the pin part-way out, carefully ream the hole and then push the
pin back in. It requires minimum movement of the pin through the wood and
places less strain on the bushings as well as allowing for greater accuracy
in the pinning. By design the rounded ends of the finished pins cause no
damage to the second bushing as they pass through.

>a sharp flush cutting side cutter.  Contrary to popular belief the
residual burr
>won't cause any trouble at all.  It doesn't cause any trouble with felt
bushings
>either, but I'm sure it will take more than facts to convince anyone of that.

I agree with the burr not affecting cloth bushings if the cut is good. With
the above technique cut pins have great potential to damage the
freshly-reamed teflon surface when you push them through, eliminating that
extremely valuable service technique. As for the expense of finished pins a
"set" is about $4.  I've never actually seen one wear out although I
suppose it's possible, and if the pins are tight in the wood you could
re-use them with new bushings unless they're visibly damaged, old or bent.
Check them with a Radio Shack pocket microscope if you want to make sure.
When you compare the cost and time spent re-bushing a set of hammers with
cloth to the $20 for a new set of bushings and pins the Teflon system is
much faster and cheaper in the long run. In the time it takes simply to
prepare a set for rebushing with cloth every hammer can be repinned with
new Teflon bushings and the piano back in service.

>long.  I could carefully press the cutting end of the reamer all the way
through
>the first bushing and cut the second bushing using the first as a guide to
keep
>the hole straight.  I would then -- again, very carefully -- pull the
reamer out,
>turn the fork over and repeat the process cutting the first bushing.  I
would then
>verify the fit and friction of the pin before assembly.  Make sure that
you have
>the same amount of friction in each bushing.  With just a bit of practice
this
>became a one-shot operation.  Once you have verified this you can assemble 

Rather than doing it one-shot and risking damage to the guide bushing, have
the reamer sticking out from the broach holder just the thickness of the
bushing. Press the pin part way out, carefully press the reamer straight
in, turn once and pull it out. If it doesn't feel right, do that again.
Then press the pin back in and repeat on the other side. Check your work
with a friction gauge making sure the flange travels smoothly and keep the
friction as low as possible without totally eliminating it. 

Excessive friction in these centres is a major problem, IMO. In addition to
the loss of power and heavy touch, if I recall my thermodynamics correctly
friction translates into heat and I have some concerns about the effect of
even slightly heated metal rods running through a precision-reamed Teflon
bushing, especially as the assembly is exposed to the effects of gravity as
it cools. 

>center.  Check overall friction of the center and trim the pin.  Don't
worry >about the slight burr.

As long as you never want to press the pin out again without replacing the
pin and perhaps the bushing. 

>The resulting bushing was solid, quiet and trouble free.  And durable.  Yes, 

Not to mention easy to service once you know how. 

>The Teflon bushing was and is a much maligned development.  In fact, it was 

Absolutely!

>true that they were introduced as a cost cutting measure replacing another
>problematic part, the felt bushing.  There is nothing inherently wrong
with that.

I have heard pianists complain that the Teflon introduces an artificial
connection to the natural flow of wood, leather and felt. Mind you, I've
heard the same complaints about plastic keytops and vinyl bench coverings,
so who knows?

>Piano manufacturers should be constantly looking for ways to reduce their
costs.

I would agree in the case of mass production pianos, although I'd prefer
that they look for ways to improve their efficiency rather than just
"reduce costs". With the high-quality instruments they should be looking at
ways to improve their art regardless of the cost. When you're spending that
much money on a piano, a few thousand extra for a properly-built soundboard
and a balanced action doesn't seem too much to ask.

>What got lost somewhere along the line was that just as much care was
required to
>properly install and fit the Teflon bushing as was needed with the felt
bushing.

I think the problem was just that they were different and there wasn't
enough information about what to do with them. 

>The Teflon bushing has now gone
>into history as a terribly bad idea along with the general use of plastic
in piano
>actions.  Too bad, I remain convinced that the Teflon bushing was really
quite a
>good idea and handled properly -- and with some further development work
-- might
>well have freed the industry from the problematic felt bushing.

Spoken like a true engineer, Del!    B-})  

			John

John Musselwhite, RPT -  Calgary, Alberta Canada
Registered Piano Technician   http://www.musselwhite.com
email: john@musselwhite.com