Earl Bollinger said:<[email hidden]> wrote in message
news:[email hidden]...
Quoted message said:Aaargh!
By exhaustive testing, I've just determined that if you drop a Park
tension gauge onto a concrete floor from a height of six feet, the
gauge will begin to read ~250 pounds of tension instead of the ~190
pounds that it used to read when applied to a spoke hanging from the
ceiling and supporting ~190 pounds of weights.
Since it snowed all day, I went ahead and tested my new weight rig, a
63-kg weighted wooden platform that hangs from a spoke attached to the
ceiling and lets me add 110 kg of water to a plastic trash barrel.
The damaged gauge produces a nice, smooth, utterly useless curve that
parallels the Park calibration chart, suggesting that something bent
when it hit the floor.
I'm tempted to fiddle with the adjustment screw on the gauge, but I'll
probably just buy a new gauge and start all over again.
Oh, well, it could have been a $300 model . . .
Aaargh!
Carl Fogel
Well since it is already bent, can't you recalibrate it yourself?
I mean you did hook up a test rig a while back. It looks like it has a small
screw and nut affair for adusting something on the tool.
Of course it is hard to know if you got it right without comparing to
something though.
Dear Earl,
In effect, that's what I did last night.
After dropping the gauge on the floor, I laboriously hung known
weights from a spoke attached to the ceiling and applied the gauge,
getting a nice data curve for tensions from 138 to 383 pounds.
But the gauge reads ~60 lbs low for a ~190 lb load (smaller error at
lower tensions, larger error at higher tensions--the graph is a curve,
not linear).
So I'd have to heave a lot of weights to get anything as good as the
Park chart for a good gauge--and that would only tell me what a 2.0
round steel spoke does on my damaged gauge, not the popular 1.8 or any
of the other less common gauges on the two-sided Park chart.
I thought about bending what looks like the damaged central post back
to right angles, but that may not even be the problem--whatever went
wrong is likely to be so small that it's hard to see, and the post is
not much off true.
In a fit of late-night foolishness, I tried adjusting the screw to see
if I could the gauge to match a second round of weights. I put the
whole awkward rig back together, cautiously turned the adjuster by the
minimum half-turn allowed, and eventually got the gauge to read right
at the low end of the scale.
Encouraged, I started pouring 10 kg of water into my trash barrel and
checking the results. Apparently, whatever's bent doesn't have a
linear effect as things rotate. I kept adjusting, hoping that I'd find
that the initial adjustment had been a bit off, but by the time I got
up to about 300 lbs, 100 lbs short of the top of the Park chart, I'd
run out of travel on the long adjuster screw.
After heaving water buckets all night, two aspirin are starting to
help, but I'm ready to reconsider buying that 300-lb set of weights
rusting at the junkyard. Speken Metal wanted 35 cents per pound, and
I'd have to haul them out of the snow to my car, drive them over to
the weighing station, unload them and set them on the scale (even
though the weights are clearly marked!), load them back into the car,
and then lug them down into my basement.
One the one hand, the weights--after all that donkey-work--would then
be a lot easier and quicker to move on and off the test rig than
pouring buckets of water into a barrel and then draining it afterward.
On the other hand, it's a silly one-time procedure, and the barrel and
water are nearly free, much like cheap, unskilled labor. (Unless, of
course, the cheap, unskilled labor drops the gauge from up near the
ceiling, in which case a new gauge may be needed and everything has to
be repeated.)
Typing is a lot easier than testing.
Cheers,
Carl Fogel
