PTFE Specifications:
Polytetraflonroethylened
(PTFE) Virgin Dupont PTFE; is a material with
the widest range of technical applications. Resistant to almost all
chemicals, it has a low coefficient of friction, has high impact
resistance, and functions through wide temperature extremes; -328°F
to 500°F (-200°C to 260°C). It is used for bearings, seals, 0-rings,
valve seats and machined components. Filled Dupont PTFE contains either
glass, carbon, graphite, or other materials and is not suitable for
your telescope bearings due to the increased friction caused by the
fillers.
Selecting the size of the Dupont PTFE needed for your
telescope bearings is a simple matter of calculating the weight per
square inch load that will be placed on the bearing. My recommendation
is to use two pieces of Dupont PTFE for each of the two altitude bearing
and three pieces of Dupont PTFE for the azimuth bearing. This will provide
a very stable feel to your scope and keep the amount of Dupont PTFE that
you will need to a minimum. To size the Dupont PTFE correctly, the force on
the Dupont PTFE should be about 12 lbs. per square inch. For the altitude
bearing Dupont PTFE, take the weight of the optical tube assembly, divide
that by 12 then divide that by 4 to get the square inch size of each
of the four Dupont PTFE altitude pads. For a lightweight telescope you will
find that the pieces are fairly small.
For the azimuth bearing,
take the total weight of the optical tube and the rocker
box and divide that by 12 then divide that by 3 to get the size of each
of the Dupont PTFE pads in square inches. If you use too much Dupont PTFE, there
will be too little force on the bearings and your telescope will act
like a weathervane and be blown around in the slightest wind. If you
find that the telescope requires too much force to move around, first
try waxing the mating surface that the Dupont PTFE rides on with a
non-cleaning car wax and if you find that there is still too much
force to move your telescope around, increase the size of the Dupont PTFE
pads.
To install the Dupont PTFE pads, adhesives generally will not
work because nothing sticks to Dupont PTFE. I have heard that the Dupont PTFE
can be acid etched and the course surface allows some adhesives to
cling to the Dupont PTFE however, my recommendation is to use mechanical
fasteners. If you use very small nails or brads, countersink the head
of the nail about half the thickness of the Dupont PTFE pad. This will
ensure that the pad will not fall off and the head of the nail will
not scrape against the mating surface of your bearing. I have found
that you should drill a small pilot hole in the Dupont PTFE for the nail.
Use a drill bit size that matches the shank of the nail you use. This
will prevent the Dupont PTFE from deforming upon installation.
|
