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
-----Original Message-----Dave
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of [EMAIL PROTECTED]
Sent: Tuesday, February 04, 2003 11:13 PM
To: [EMAIL PROTECTED]
Subject: Re: ShopTalk: Frequency meters and deflection boards
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
