----- Original Message -----
Sent: Wednesday, February 05, 2003 7:50
AM
Subject: RE: ShopTalk: Frequency meters
and deflection boards
I've
had a Brunswick freq analyzer for several years...one of the early things I
learned was the effect of clamping on frequency. When I bought it, I
also bought a calibration shaft, and it turns out that what you actually do to
calibrate the machine is change the clamping location. Sooooo as
it turns out, the correct clamp length for my **system** (and I'll elaborate
on that a little more in a minute) turns out to be about
4".
I
mentioned the clamping "system"....here's what that includes: The base
of the machine has a v shaped slot that the grip is clamped into (you have to
measure shafts with grips on them...I have a whole drawer full of split
grips). The shaft is clamped by a plate with one end resting on the
base, and the other has a v-shaped slot that matches the one on the
base. The clamping force is applied by a screw type mechanism with a
slip arrangement that allows the handle to slip when it reaches a certain
torque (I have no idea what that quantity is, but the instructions say to turn
it until you get three clicks. This is similar to the clamp knobs on the
Golfsmith FA.
One
day I noticed that the clamp arrangement was squeaking, and like any good
engineer, I took it apart and greased it. Lo and behold, suddenly my
frequencies jumped. I "recalibrated" and found that I needed to shorten
the clamping length to get the same frequency. What had happened was
that by lubricating the clamp, I enabled it to get tighter before the torque
limiters started slipping, thus the clamp pressure had increased, resulting in
an increase in measured frequency.
Enter the PCS Equalizer...The way the Equalizer works is that it
measures a shaft against an arbitrary standard and assigns a frequency to
it. You then measure the frequency of that shaft in your machine, and
compare the measured frequency with the standard frequency to get a conversion
factor. That conversion factor then generates a set of curves similar to
the FM precision curves, but calibrated to your freq analyzer, clamping
system, and all. Soooo.....
The
bottom line is that if I wanted to, I could make a shaft read in a wide range
of frequencies, all of which would be correct for the configuration of
clamping length, pressure, and grip. The key is to get a good comparison
standard and try to be as consistent as possible in how you clamp the
shaft.
Having said that, I do notice that sometimes the electronics get fooled
by a dark colored shaft. I noticed that sometimes a black graphite shaft
would read quite a bit lower than others. What I figured out was that
the electric eye that counts the times the shaft goes by it couldn't always
"see" the shaft and missed counts, which leads to a lower indicated
frequency. Solution is to keep some strips of lead tape handy and wrap
the shaft where it is in the path of the sensor. Also helps to have a
good strong light behind you pointing toward the sensor. Steel shafts
reflect light better, so they don't seem to suffer from the
problem.
Sorry for the long note, but hopefully it is useful to
someone.
Royce
Dave
You
are correct. That was a very good test. It opened my eyes. The clamping
mechanism is more important than the electronic side because it is where all
the variable seems to lie. The electronics are pretty well governed by
design and components used while the clamping mechanism as well as the bench
and its stability are where most of the deviations seem to lie between
machines. I for one liked your home made unit because yours broke the CPMs
down to less than one. I would like to have one that breaks it down to
tenths which I think is overkill but that is just me.
Charlie
B
