Park tension gauge test



Elsewhere, doubts have been cast on the accuracy of Park's modestly
priced blue bicycle spoke tension gauge.

Hmmm . . . I'd never tested my trusty (?) Park tension gauge!

It does notice whenever I add small weights or turn spoke nipples or
let the air out of a tire--what else can a simple spring do?

But what if it's been lying to me all this time and just flattering me
when I ask it whether pinching spokes together makes my spoke-tension
look fat? What if the tension is 50% higher than the calibration table
claims?

How could I enjoy visions of sugar-plums dancing through my head
tonight with this kind of uncertainty nagging me?

So I bent the ends of a helpless 2 mm straight steel spoke into
U-hooks, added some wire-rope thingies to stop the U-hooks from
straightening, hung the spoke from a ceiling rope, and dangled a crude
rope-and-2x4 swing from the spoke to allow loading a standard 195-lb
Fogel onto the spoke.

I stepped onto the swing and found . . .

That I swung so wildly on my piñata-style contraption that there was
no way to read the Park tension gauge, much less take a picture of the
festivities.

Alas, the vast stock of convenient weights at Fogel Labs totals only
about 100 real pounds on postal scales. (An inflated 110 pounds
according to the lying numbers stamped on the weights themselves.)

At first I feared that Christmas would be ruined, since I needed
something close to 200 pounds to represent a low-normal 90 kgf
spoke tension.

But then I remembered that several plastic buckets are kept around the
premises for . . . well, for important stuff like this.

Filled not too near the top, the first bucket weighed a handy 30
pounds. After filling all three buckets and checking that they weighed
30 pounds, I dangled 100 lbs of weights on a bar and three 30-pound
buckets of water from a 2 mm spoke:

http://i14.tinypic.com/4960dw3.jpg

http://i18.tinypic.com/2czqz6f.jpg

Click on the lower right for full-size images in Explorer.

The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
over 22, and then the camera angle makes it look a little higher. I
steadied the camera on a handy but slightly too-high stand.)

For a 2 mm spoke, the Park calibration chart shows this to mean a
tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
of ropes, bar, weights, buckets, and water in the picture.

Park 2.0mm spoke
mark kgf / lbs

off scale
17 51 / 112
18 56 / 123
19 62 / 136
20 68 / 150
21 76 / 167
22 85 / 187 <--~190 lbs of weights hung from spoke
23 95 / 209
24 107 / 235
25 121 / 266
26 137 / 301
27 156 / 343
28 179 / 394
off scale

I hope that this test pleases anyone who gets a blue Park tension
gauge tomorrow morning. (Or a gift certificate to places that sell
it.)

Merry Christmas!

Carl Fogel
 
P

Paul Hobson

Guest
[email protected] wrote:
> Elsewhere, doubts have been cast on the accuracy of Park's modestly
> priced blue bicycle spoke tension gauge.
>
> Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>

[...]
> http://i14.tinypic.com/4960dw3.jpg
>
> http://i18.tinypic.com/2czqz6f.jpg
>
> Click on the lower right for full-size images in Explorer.
>
> The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
> over 22, and then the camera angle makes it look a little higher. I
> steadied the camera on a handy but slightly too-high stand.)
>
> For a 2 mm spoke, the Park calibration chart shows this to mean a
> tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
> of ropes, bar, weights, buckets, and water in the picture.
>
> Park 2.0mm spoke
> mark kgf / lbs
>


> I hope that this test pleases anyone who gets a blue Park tension
> gauge tomorrow morning. (Or a gift certificate to places that sell
> it.)


Awesome set up Carl! I have but one request:
The hacks at Georgia Tech have brain washed me into believing that in
order to properly calibrate an instrument such as a load measuring
device, you need to gradually load the instrument up to near its max.
capacity, then unload it back down.

What you do from there is up to you, but I'd throw the data into MATLAB
and model the data using a least-squares fitting technique. Any chance
I could get a little more data out of you?

\\paul (from his parents' house)
 
E

Earl Bollinger

Guest
<[email protected]> wrote in message
news:[email protected]
> Elsewhere, doubts have been cast on the accuracy of Park's modestly
> priced blue bicycle spoke tension gauge.
>
> Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>
> It does notice whenever I add small weights or turn spoke nipples or
> let the air out of a tire--what else can a simple spring do?
>
> But what if it's been lying to me all this time and just flattering me
> when I ask it whether pinching spokes together makes my spoke-tension
> look fat? What if the tension is 50% higher than the calibration table
> claims?
>
> How could I enjoy visions of sugar-plums dancing through my head
> tonight with this kind of uncertainty nagging me?
>
> So I bent the ends of a helpless 2 mm straight steel spoke into
> U-hooks, added some wire-rope thingies to stop the U-hooks from
> straightening, hung the spoke from a ceiling rope, and dangled a crude
> rope-and-2x4 swing from the spoke to allow loading a standard 195-lb
> Fogel onto the spoke.
>
> I stepped onto the swing and found . . .
>
> That I swung so wildly on my piñata-style contraption that there was
> no way to read the Park tension gauge, much less take a picture of the
> festivities.
>
> Alas, the vast stock of convenient weights at Fogel Labs totals only
> about 100 real pounds on postal scales. (An inflated 110 pounds
> according to the lying numbers stamped on the weights themselves.)
>
> At first I feared that Christmas would be ruined, since I needed
> something close to 200 pounds to represent a low-normal 90 kgf
> spoke tension.
>
> But then I remembered that several plastic buckets are kept around the
> premises for . . . well, for important stuff like this.
>
> Filled not too near the top, the first bucket weighed a handy 30
> pounds. After filling all three buckets and checking that they weighed
> 30 pounds, I dangled 100 lbs of weights on a bar and three 30-pound
> buckets of water from a 2 mm spoke:
>
> http://i14.tinypic.com/4960dw3.jpg
>
> http://i18.tinypic.com/2czqz6f.jpg
>
> Click on the lower right for full-size images in Explorer.
>
> The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
> over 22, and then the camera angle makes it look a little higher. I
> steadied the camera on a handy but slightly too-high stand.)
>
> For a 2 mm spoke, the Park calibration chart shows this to mean a
> tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
> of ropes, bar, weights, buckets, and water in the picture.
>
> Park 2.0mm spoke
> mark kgf / lbs
>
> off scale
> 17 51 / 112
> 18 56 / 123
> 19 62 / 136
> 20 68 / 150
> 21 76 / 167
> 22 85 / 187 <--~190 lbs of weights hung from spoke
> 23 95 / 209
> 24 107 / 235
> 25 121 / 266
> 26 137 / 301
> 27 156 / 343
> 28 179 / 394
> off scale
>
> I hope that this test pleases anyone who gets a blue Park tension
> gauge tomorrow morning. (Or a gift certificate to places that sell
> it.)
>
> Merry Christmas!
>
> Carl Fogel


That is nice to know. Thanks.
That is a very imaginatively neat setup you used to test it too.
I wonder how the modest Park tool compares to the super fancy spoke tension
gauges?
 
On Sun, 24 Dec 2006 21:52:58 -0600, "Earl Bollinger"
<[email protected]> wrote:

><[email protected]> wrote in message
>news:[email protected]
>> Elsewhere, doubts have been cast on the accuracy of Park's modestly
>> priced blue bicycle spoke tension gauge.
>>
>> Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>>
>> It does notice whenever I add small weights or turn spoke nipples or
>> let the air out of a tire--what else can a simple spring do?
>>
>> But what if it's been lying to me all this time and just flattering me
>> when I ask it whether pinching spokes together makes my spoke-tension
>> look fat? What if the tension is 50% higher than the calibration table
>> claims?
>>
>> How could I enjoy visions of sugar-plums dancing through my head
>> tonight with this kind of uncertainty nagging me?
>>
>> So I bent the ends of a helpless 2 mm straight steel spoke into
>> U-hooks, added some wire-rope thingies to stop the U-hooks from
>> straightening, hung the spoke from a ceiling rope, and dangled a crude
>> rope-and-2x4 swing from the spoke to allow loading a standard 195-lb
>> Fogel onto the spoke.
>>
>> I stepped onto the swing and found . . .
>>
>> That I swung so wildly on my piñata-style contraption that there was
>> no way to read the Park tension gauge, much less take a picture of the
>> festivities.
>>
>> Alas, the vast stock of convenient weights at Fogel Labs totals only
>> about 100 real pounds on postal scales. (An inflated 110 pounds
>> according to the lying numbers stamped on the weights themselves.)
>>
>> At first I feared that Christmas would be ruined, since I needed
>> something close to 200 pounds to represent a low-normal 90 kgf
>> spoke tension.
>>
>> But then I remembered that several plastic buckets are kept around the
>> premises for . . . well, for important stuff like this.
>>
>> Filled not too near the top, the first bucket weighed a handy 30
>> pounds. After filling all three buckets and checking that they weighed
>> 30 pounds, I dangled 100 lbs of weights on a bar and three 30-pound
>> buckets of water from a 2 mm spoke:
>>
>> http://i14.tinypic.com/4960dw3.jpg
>>
>> http://i18.tinypic.com/2czqz6f.jpg
>>
>> Click on the lower right for full-size images in Explorer.
>>
>> The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
>> over 22, and then the camera angle makes it look a little higher. I
>> steadied the camera on a handy but slightly too-high stand.)
>>
>> For a 2 mm spoke, the Park calibration chart shows this to mean a
>> tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
>> of ropes, bar, weights, buckets, and water in the picture.
>>
>> Park 2.0mm spoke
>> mark kgf / lbs
>>
>> off scale
>> 17 51 / 112
>> 18 56 / 123
>> 19 62 / 136
>> 20 68 / 150
>> 21 76 / 167
>> 22 85 / 187 <--~190 lbs of weights hung from spoke
>> 23 95 / 209
>> 24 107 / 235
>> 25 121 / 266
>> 26 137 / 301
>> 27 156 / 343
>> 28 179 / 394
>> off scale
>>
>> I hope that this test pleases anyone who gets a blue Park tension
>> gauge tomorrow morning. (Or a gift certificate to places that sell
>> it.)
>>
>> Merry Christmas!
>>
>> Carl Fogel

>
>That is nice to know. Thanks.
>That is a very imaginatively neat setup you used to test it too.
>I wonder how the modest Park tool compares to the super fancy spoke tension
>gauges?


Dear Earl,

Well, there are two kinds of tension gauges . . .

The Park gauge is just a spring arm (hammer post) with a long needle
attached to the hammer-shaft. The hammer post pushes against the
middle of a short spoke span, which is supported by two end posts
(anvil posts).

Where the needle ends up on the gauge depends on two things.

First, how thick is the spoke? The hammer post hits a thick spoke
sooner than it hits a thin spoke, so readings begin sooner for a thick
spoke, higher on the scale. This is just an offset, but it's
considerable for even small differences in spoke thickness.

Second, how much does the spoke bend under the spring pushing the
hammer? This mostly depends on how much tension is trying to keep the
spoke straight, but there are other factors.

Friction, for example, confuses things. When the hammer bends the
spoke, it tries to drag the spoke inward over both posts. This raises
the tension slightly, so the lower the hammer force, the less
frictional distortion. The Park posts are just fixed, polished metal,
but I think that more expensive gauges may have roller-posts to reduce
friction.

The thickness and material of the spoke also confuses things. The
thicker the spoke and the stiffer its material, the more it resists
bending just by its own stiffness.

Higher marks mean higher tensions. Mark 20 on the Park calibration
tables means 68 kgf for a round steel 2mm spoke, 89 kgf for a round
steel 1.8mm spoke, 80 kgf for a round titanium spoke.

For a round 3.3mm aluminum spoke, mark 36 (way up there!) means only
89 kgf. The 3.3mm thickness of the spoke means that the hammer hits
the spoke much sooner and stops at much higher marks.

Steel motorcycle spokes are so stiff that the Park tool may be useless
because its spring isn't powerful enough bend the massive spokes. You
can get readings, but it's about like trying to weigh a 2 pound
package accurately on a bathroom spring scale intended for 100 to 200
pound objects--the range is wrong.

Here's a 3.5mm (4mm elbow butt) spoke (modest for a motorcycle) next
to a 2mm straight spoke (husky for a bicycle):

http://home.comcast.net/~carlfogel/download/spokes.jpg

Here the obviously 0-tension 3.5mm section of motorcycle spoke reads
almost 25 on a Park gauge:

http://i11.tinypic.com/2me5zec.jpg

Here the obviously 0-tension 2mm bike spoke reads 0 on a Park gauge:

http://i18.tinypic.com/2wp5s2c.jpg

And here's the back of the Park gauge:

http://i10.tinypic.com/47i07xv.jpg

One end of the \/ spring fits into the slotted head of the long
adjustment screw on the left. The back of the "hammer" post is the
round gray spot to the right of the spring post. The "needle" is the
large black squeeze-handle.

Click on the lower right in Explorer for full-size images.

The Park gauge and the Wheelsmith gauge are the inexpensive ones and
use this simple spring and calibration table approach. Park Tool will
re-calibrate a gauge for a fee. Here's a page showing a few brands:

http://www.sheldonbrown.com/harris/tools/wheel.html#tensiometers

More expensive tension gauges use a different approach. The red DT
gauge on Sheldon's page uses a built-in micrometer to measure how far
the spring-load hammer moves _after_ it first touches the spoke. Then
you figure out from tables what that movement means. The idea is to
use the geometric calculation approach, but it still ends up
calibrating for spoke thickness and material and so forth. You can get
dial indicators or even more expensive digital indicators, but they
both just measure how far the hammer moves the spoke sideways.

I don't know of any tests comparing the accuracy of the simple spring
and needle Park and Wheelsmith style gauges versus the micrometer
reading of hammer movement.

At first, the micrometer sounds more accurate, but then you realize
that the Park needle is almost 7 inches long. I suspect that the more
expensive gauges may be more accurate, but that much of the accuracy
lies in polishing and rollers to reduce friction.

You can compare the DT Swiss and the Park calibration tables to get an
idea of the practical outcome.

Here's the DT Swiss pdf, with a conversion graphs and tables starting
on page 9:

http://www.dtswiss.com/data/files/MAN_EN_51202133804.pdf

Here's the Park calibration table:

http://www.parktool.com/products/documents/TM_1table_2005912_4301.pdf

For practical wheel-building (as opposed to insatiable curiosity), the
Park gauge seems to be accurate enough to get the spokes to the right
absolute tension (say 110 kgf) and accurate enough to get them to the
same tension (very small differences between spokes are noticeable).

Cheers,

Carl Fogel
 
On 24 Dec 2006 19:32:24 -0800, "Paul Hobson" <[email protected]>
wrote:

>[email protected] wrote:
>> Elsewhere, doubts have been cast on the accuracy of Park's modestly
>> priced blue bicycle spoke tension gauge.
>>
>> Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>>

>[...]
>> http://i14.tinypic.com/4960dw3.jpg
>>
>> http://i18.tinypic.com/2czqz6f.jpg
>>
>> Click on the lower right for full-size images in Explorer.
>>
>> The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
>> over 22, and then the camera angle makes it look a little higher. I
>> steadied the camera on a handy but slightly too-high stand.)
>>
>> For a 2 mm spoke, the Park calibration chart shows this to mean a
>> tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
>> of ropes, bar, weights, buckets, and water in the picture.
>>
>> Park 2.0mm spoke
>> mark kgf / lbs
>>

>
>> I hope that this test pleases anyone who gets a blue Park tension
>> gauge tomorrow morning. (Or a gift certificate to places that sell
>> it.)

>
>Awesome set up Carl! I have but one request:
>The hacks at Georgia Tech have brain washed me into believing that in
>order to properly calibrate an instrument such as a load measuring
>device, you need to gradually load the instrument up to near its max.
>capacity, then unload it back down.
>
>What you do from there is up to you, but I'd throw the data into MATLAB
>and model the data using a least-squares fitting technique. Any chance
>I could get a little more data out of you?
>
>\\paul (from his parents' house)


Dear Paul,

The Park gauge may work the way that you want. You squeeze the tool to
open its jaws, pushing against a spring--loading it to its maximum?

Then you slap it onto--

Er, then you carefully fit it onto the spoke and let go of the squeeze
handle, letting the spring push the hammer post against the middle of
the spoke section. The needle drops down from mark 45 (as stiff as an
i-beam) to whatever lower mark and tension level the spoke's
resistance will sustain.

That is, the tool works in the opposite way from a spring bathroom
scale, where the spring starts at no load and is then loaded when you
step onto the scale, but only to whatever your weight is.

A bathroom scale designed like the Park tool would consist of a
platform hanging from the ceiling by a powerful coil spring. You'd
force the platform to the floor with a huge lever, lock it to the
floor, step onto the platform, release the lock, and see how high the
spring raised you off the floor.

As for heaving more variations of ~200 pound weights around and trying
not to spill the water all over the floor, I think that my bad back
and I will have to regretfully decline. My interest was whether the
gauge was reasonably accurate in absolute terms for roughly ordinary
bicycle spoke tensions.

If you're curious, you can emai the folks at Park Tool about their
calibration service and how they arrived at their calibration table. I
suspect that Park has tested their gauge far more extensively on a far
more elegant version of my crude setup.

Here's the Park calibration table:

http://www.parktool.com/products/documents/TM_1table_2005912_4301.pdf

And here's the tool's page:

http://www.parktool.com/products/detail.asp?cat=16&item=TM-1

Calvin Jones at [email protected] might be able to answer your
questions.

Cheers,

Carl Fogel
 
It's good to see the concept of instrument calibration is known by
most tensiometer manufacturers. However,the instrument that I
designed when writing "the Bicycle Wheel" was calibrated on a Tunis
Olsen tensile tester, the same one on which the stress-strain diagrams
for spokes were made. In addition to being calibrated, it can be
zeroed on the spoke to be tested a feature not found on others.

http://www.tiniusolsen.com/

For most wheel building at that time, no calibration curves were
needed in practice, because wheels were nearly all 36-spoke Mavic MA-2
wheels and knowing the deflection of the dial micrometer for proper
tension was just a number used to check whether the spokes were tight
enough and not too tight by checking a couple of them on the finished
wheel. On my own tensiometer, that value is 0.013" for right side
rear spokes.

Rick Hjertberg at FSA has my two prototype instruments that I gave him
when he opened his shop, here in Palo Alto. These subsequently led to
the production of the Avocet instrument, that was marketed by DT in
Europe.

http://tinyurl.com/7ogpr

http://tinyurl.com/75glz

There are several design criteria that make these instruments more
accurate than some, the Hozan in particular. Spoke bending is kept
small to not cause plastic deformation as well as minimizing elastic
interference from spoke stiffness. For this reason the test span must
be as long as practical, at about four inches.

The test load is be small for the same reasons as well as that large
deflections affect spoke tension. Typically, the Hozan gauge will
show tension in a zero tension spoke because it uses a high test load
over a short span.

To accurately read deflections from light test loads, a precision
display is required which requires either a long pointer or for direct
readings, a precision gauge, or a vernier as on the Wheelsmith.

The instrument should be one hand operated with no net force applied
to the spoke, using a load anvil with a radius to avoid localized
bending. In addition the FSA unit uses ball bearings as span supports
to avoid stiction when the test load is applied.

Finally, the FSA instrument has a rotatable bezel that allows zeroing
the instrument on spokes that are not perfectly straight. This is
done in one hand operation with the thumb that is free to rotate the
bezel. The value of this feature is evident only on instruments that
measure deflection on the same side from which the spoke is supported.
The dial should be at zero before applying the load. This layout has
the advantage in not including spoke thickness in the measurement.

Most tensiometers do not address all these design criteria for one
reason or another. In the instrument built by FSA, as with writing
the book, I wanted to cover all aspects so that none of the common
problems could occur. There were no tensiometers available at the
time I designed mine, and therefore, I was not influenced by prior
art.

Jobst Brandt
 
On Sun, 24 Dec 2006 19:39:14 -0700, [email protected] wrote:

>Elsewhere, doubts have been cast on the accuracy of Park's modestly
>priced blue bicycle spoke tension gauge.
>
>Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>
>It does notice whenever I add small weights or turn spoke nipples or
>let the air out of a tire--what else can a simple spring do?
>
>But what if it's been lying to me all this time and just flattering me
>when I ask it whether pinching spokes together makes my spoke-tension
>look fat? What if the tension is 50% higher than the calibration table
>claims?
>
>How could I enjoy visions of sugar-plums dancing through my head
>tonight with this kind of uncertainty nagging me?
>
>So I bent the ends of a helpless 2 mm straight steel spoke into
>U-hooks, added some wire-rope thingies to stop the U-hooks from
>straightening, hung the spoke from a ceiling rope, and dangled a crude
>rope-and-2x4 swing from the spoke to allow loading a standard 195-lb
>Fogel onto the spoke.
>
>I stepped onto the swing and found . . .
>
>That I swung so wildly on my piñata-style contraption that there was
>no way to read the Park tension gauge, much less take a picture of the
>festivities.
>
>Alas, the vast stock of convenient weights at Fogel Labs totals only
>about 100 real pounds on postal scales. (An inflated 110 pounds
>according to the lying numbers stamped on the weights themselves.)
>
>At first I feared that Christmas would be ruined, since I needed
>something close to 200 pounds to represent a low-normal 90 kgf
>spoke tension.
>
>But then I remembered that several plastic buckets are kept around the
>premises for . . . well, for important stuff like this.
>
>Filled not too near the top, the first bucket weighed a handy 30
>pounds. After filling all three buckets and checking that they weighed
>30 pounds, I dangled 100 lbs of weights on a bar and three 30-pound
>buckets of water from a 2 mm spoke:
>
>http://i14.tinypic.com/4960dw3.jpg
>
>http://i18.tinypic.com/2czqz6f.jpg
>
>Click on the lower right for full-size images in Explorer.
>
>The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
>over 22, and then the camera angle makes it look a little higher. I
>steadied the camera on a handy but slightly too-high stand.)
>
>For a 2 mm spoke, the Park calibration chart shows this to mean a
>tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
>of ropes, bar, weights, buckets, and water in the picture.
>
>Park 2.0mm spoke
>mark kgf / lbs
>
>off scale
>17 51 / 112
>18 56 / 123
>19 62 / 136
>20 68 / 150
>21 76 / 167
>22 85 / 187 <--~190 lbs of weights hung from spoke
>23 95 / 209
>24 107 / 235
>25 121 / 266
>26 137 / 301
>27 156 / 343
>28 179 / 394
>off scale
>
>I hope that this test pleases anyone who gets a blue Park tension
>gauge tomorrow morning. (Or a gift certificate to places that sell
>it.)
>
>Merry Christmas!
>
>Carl Fogel


An email asked me exactly how much force a Park tension gauge applies
through its spring. I could have sworn that I did this once, but it
was easier to hang some weights, measure things, and take a picture
again than to try to find the old post.

A quick check confirmed that the force pushing against a spoke is not
enough to make me say "ouch!" when I substitute my finger, much less
anything more colorful.

So I used Fogel Labs state-of-the-art small-force testing apparatus:

http://i13.tinypic.com/4gs7hoj.jpg

The cut-off plastic bottle dangling from the fishing line holds four
50-cent penny rolls.

Click on the lower right in Explorer for an image large enough to show
that the pointer (removed and lying on the white paper) would indicate
mark 19, judging by the square hole that holds the triangular pointer
in the black arm.

(The spoke bent into a skeleton-grip with its tip ground into an
ice-pick is for making holes in things like fingers and plastic
bottles.)

With their plastic wrappers, the four penny rolls weighed 4.7, 4.7,
4.8, and 4.8 ounces on U.S. Post Office electronic scales. The
variation is due to grime adding weight, worn-off metal reducing
weight, and the infamous debasement of the currency:

http://www.finishing.com/112/84.shtml

Briefly, pre-1983 pennies weighed 3.1 grams, post-1983 pennies weigh
2.5 grams, and 1983 pennies are a hideous and irresponsible mixture
of both weights.

See the letter near the bottom of that page from Ray Simon that
explains how to demonstrate our lightweight modern coinage with a
ruler, a knife edge, and a dime's worth of pre- and post-1983 pennies.

Anyway, 4.7 + 4.7 + 4.8 + 4.8 ounces of pennies is 19.0 ounces. Add
another ounce for the plastic bottle and fishing line, and rounding
errora, and that's 20 ounces of force supplied by the spring at around
Park mark 18. Another roll of pennies pulled the arm down to about
mark 30.

It's 165mm from the center of the pivot to the fishing line, and 10mm
from the center of the pivot to the center of the hammer arm, so the
leverage is about 16.5 to 1.

So the spring applies about 16.5 x 20 ounces of force, 330 ounces,
about 20.6 pounds, to the middle of a spoke section supported by two
massively braced posts 100mm apart.

Cheers,

Carl Fogel
 
N

Neil Brooks

Guest
[email protected] wrote:

> So I used Fogel Labs state-of-the-art small-force testing apparatus:
>
> http://i13.tinypic.com/4gs7hoj.jpg
>
> The cut-off plastic bottle dangling from the fishing line holds four
> 50-cent penny rolls.


We should all be EXTRA nice to Carl this holiday season. It seems he's
finally going through his change... ;-)

Happy Holidays, all!
 
O

Ozark Bicycle

Guest
[email protected] wrote:

<snipped for clarity>

- on tensiometers -

>
> For most wheel building at that time, no calibration curves were
> needed in practice, because wheels were nearly all 36-spoke Mavic MA-2
> wheels


"Wheels were nearly all 36-spoke Mavic MA-2 wheels"??? When was this?
Was this here on Earth as we know it? Or in alternative reality? What
about rims from other makers? Ambrosio, Fiamme, Rigida, Super Champion
(Wolber), Weinmann, etc?
 
[email protected] wrote:
> A bathroom scale designed like the Park tool would consist of a
> platform hanging from the ceiling by a powerful coil spring. You'd
> force the platform to the floor with a huge lever, lock it to the
> floor, step onto the platform, release the lock, and see how high the
> spring raised you off the floor.


But this bathroom device would not be for determining weight. It would
be for body fat percentage.
First you would try fitting your wrist through various sized stockade
type holes to find the best fit to determine your bone-size type, then
you would consult a massive laminated card that would be quite unweildy
and would probably not fit in the bathroom, what with all the levers
and things.

Joseph
 
C

* * Chas

Guest
<[email protected]> wrote in message
news:[email protected]
> On Sun, 24 Dec 2006 19:39:14 -0700, [email protected] wrote:
>
> >Elsewhere, doubts have been cast on the accuracy of Park's modestly
> >priced blue bicycle spoke tension gauge.
> >
> >Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
> >
> >It does notice whenever I add small weights or turn spoke nipples or
> >let the air out of a tire--what else can a simple spring do?
> >
> >But what if it's been lying to me all this time and just flattering me
> >when I ask it whether pinching spokes together makes my spoke-tension
> >look fat? What if the tension is 50% higher than the calibration table
> >claims?
> >
> >How could I enjoy visions of sugar-plums dancing through my head
> >tonight with this kind of uncertainty nagging me?

<snip>

Carl,

Thanks for going to all of the trouble to test and publish your results.
I've been toying with the idea of getting one of the Park TM-1 Spoke Tension
Gages. I've seen a lot of them on eBay but the noobs keep paying more than
the "Buy it Now" prices.

Unlike the Park CC-3 Chain Checker - where all of my chains tested OK, if I
buy one of these I'll probably have to re-adjust the spokes on all of my
wheels (about 12 sets). Ignorance is bliss!

Season's Best...

Chas.
 
J

jim beam

Guest
[email protected] wrote:
> On Sun, 24 Dec 2006 21:52:58 -0600, "Earl Bollinger"
> <[email protected]> wrote:
>
>> <[email protected]> wrote in message
>> news:[email protected]
>>> Elsewhere, doubts have been cast on the accuracy of Park's modestly
>>> priced blue bicycle spoke tension gauge.
>>>
>>> Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>>>
>>> It does notice whenever I add small weights or turn spoke nipples or
>>> let the air out of a tire--what else can a simple spring do?
>>>
>>> But what if it's been lying to me all this time and just flattering me
>>> when I ask it whether pinching spokes together makes my spoke-tension
>>> look fat? What if the tension is 50% higher than the calibration table
>>> claims?
>>>
>>> How could I enjoy visions of sugar-plums dancing through my head
>>> tonight with this kind of uncertainty nagging me?
>>>
>>> So I bent the ends of a helpless 2 mm straight steel spoke into
>>> U-hooks, added some wire-rope thingies to stop the U-hooks from
>>> straightening, hung the spoke from a ceiling rope, and dangled a crude
>>> rope-and-2x4 swing from the spoke to allow loading a standard 195-lb
>>> Fogel onto the spoke.
>>>
>>> I stepped onto the swing and found . . .
>>>
>>> That I swung so wildly on my pi�ata-style contraption that there was
>>> no way to read the Park tension gauge, much less take a picture of the
>>> festivities.
>>>
>>> Alas, the vast stock of convenient weights at Fogel Labs totals only
>>> about 100 real pounds on postal scales. (An inflated 110 pounds
>>> according to the lying numbers stamped on the weights themselves.)
>>>
>>> At first I feared that Christmas would be ruined, since I needed
>>> something close to 200 pounds to represent a low-normal 90 kgf
>>> spoke tension.
>>>
>>> But then I remembered that several plastic buckets are kept around the
>>> premises for . . . well, for important stuff like this.
>>>
>>> Filled not too near the top, the first bucket weighed a handy 30
>>> pounds. After filling all three buckets and checking that they weighed
>>> 30 pounds, I dangled 100 lbs of weights on a bar and three 30-pound
>>> buckets of water from a 2 mm spoke:
>>>
>>> http://i14.tinypic.com/4960dw3.jpg
>>>
>>> http://i18.tinypic.com/2czqz6f.jpg
>>>
>>> Click on the lower right for full-size images in Explorer.
>>>
>>> The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
>>> over 22, and then the camera angle makes it look a little higher. I
>>> steadied the camera on a handy but slightly too-high stand.)
>>>
>>> For a 2 mm spoke, the Park calibration chart shows this to mean a
>>> tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
>>> of ropes, bar, weights, buckets, and water in the picture.
>>>
>>> Park 2.0mm spoke
>>> mark kgf / lbs
>>>
>>> off scale
>>> 17 51 / 112
>>> 18 56 / 123
>>> 19 62 / 136
>>> 20 68 / 150
>>> 21 76 / 167
>>> 22 85 / 187 <--~190 lbs of weights hung from spoke
>>> 23 95 / 209
>>> 24 107 / 235
>>> 25 121 / 266
>>> 26 137 / 301
>>> 27 156 / 343
>>> 28 179 / 394
>>> off scale
>>>
>>> I hope that this test pleases anyone who gets a blue Park tension
>>> gauge tomorrow morning. (Or a gift certificate to places that sell
>>> it.)
>>>
>>> Merry Christmas!
>>>
>>> Carl Fogel

>> That is nice to know. Thanks.
>> That is a very imaginatively neat setup you used to test it too.
>> I wonder how the modest Park tool compares to the super fancy spoke tension
>> gauges?

>
> Dear Earl,
>
> Well, there are two kinds of tension gauges . . .
>
> The Park gauge is just a spring arm (hammer post) with a long needle
> attached to the hammer-shaft. The hammer post pushes against the
> middle of a short spoke span, which is supported by two end posts
> (anvil posts).
>
> Where the needle ends up on the gauge depends on two things.
>
> First, how thick is the spoke? The hammer post hits a thick spoke
> sooner than it hits a thin spoke, so readings begin sooner for a thick
> spoke, higher on the scale. This is just an offset, but it's
> considerable for even small differences in spoke thickness.
>
> Second, how much does the spoke bend under the spring pushing the
> hammer? This mostly depends on how much tension is trying to keep the
> spoke straight, but there are other factors.
>
> Friction, for example, confuses things. When the hammer bends the
> spoke, it tries to drag the spoke inward over both posts. This raises
> the tension slightly, so the lower the hammer force, the less
> frictional distortion. The Park posts are just fixed, polished metal,
> but I think that more expensive gauges may have roller-posts to reduce
> friction.
>
> The thickness and material of the spoke also confuses things. The
> thicker the spoke and the stiffer its material, the more it resists
> bending just by its own stiffness.
>
> Higher marks mean higher tensions. Mark 20 on the Park calibration
> tables means 68 kgf for a round steel 2mm spoke, 89 kgf for a round
> steel 1.8mm spoke, 80 kgf for a round titanium spoke.
>
> For a round 3.3mm aluminum spoke, mark 36 (way up there!) means only
> 89 kgf. The 3.3mm thickness of the spoke means that the hammer hits
> the spoke much sooner and stops at much higher marks.
>
> Steel motorcycle spokes are so stiff that the Park tool may be useless
> because its spring isn't powerful enough bend the massive spokes. You
> can get readings, but it's about like trying to weigh a 2 pound
> package accurately on a bathroom spring scale intended for 100 to 200
> pound objects--the range is wrong.
>
> Here's a 3.5mm (4mm elbow butt) spoke (modest for a motorcycle) next
> to a 2mm straight spoke (husky for a bicycle):
>
> http://home.comcast.net/~carlfogel/download/spokes.jpg
>
> Here the obviously 0-tension 3.5mm section of motorcycle spoke reads
> almost 25 on a Park gauge:
>
> http://i11.tinypic.com/2me5zec.jpg
>
> Here the obviously 0-tension 2mm bike spoke reads 0 on a Park gauge:
>
> http://i18.tinypic.com/2wp5s2c.jpg


at last! great post.

>
> And here's the back of the Park gauge:
>
> http://i10.tinypic.com/47i07xv.jpg
>
> One end of the \/ spring fits into the slotted head of the long
> adjustment screw on the left. The back of the "hammer" post is the
> round gray spot to the right of the spring post. The "needle" is the
> large black squeeze-handle.
>
> Click on the lower right in Explorer for full-size images.
>
> The Park gauge and the Wheelsmith gauge are the inexpensive ones and
> use this simple spring and calibration table approach. Park Tool will
> re-calibrate a gauge for a fee. Here's a page showing a few brands:
>
> http://www.sheldonbrown.com/harris/tools/wheel.html#tensiometers
>
> More expensive tension gauges use a different approach. The red DT
> gauge on Sheldon's page uses a built-in micrometer to measure how far
> the spring-load hammer moves _after_ it first touches the spoke. Then
> you figure out from tables what that movement means. The idea is to
> use the geometric calculation approach, but it still ends up
> calibrating for spoke thickness and material and so forth. You can get
> dial indicators or even more expensive digital indicators, but they
> both just measure how far the hammer moves the spoke sideways.
>
> I don't know of any tests comparing the accuracy of the simple spring
> and needle Park and Wheelsmith style gauges versus the micrometer
> reading of hammer movement.
>
> At first, the micrometer sounds more accurate, but then you realize
> that the Park needle is almost 7 inches long. I suspect that the more
> expensive gauges may be more accurate, but that much of the accuracy
> lies in polishing and rollers to reduce friction.
>
> You can compare the DT Swiss and the Park calibration tables to get an
> idea of the practical outcome.
>
> Here's the DT Swiss pdf, with a conversion graphs and tables starting
> on page 9:
>
> http://www.dtswiss.com/data/files/MAN_EN_51202133804.pdf
>
> Here's the Park calibration table:
>
> http://www.parktool.com/products/documents/TM_1table_2005912_4301.pdf
>
> For practical wheel-building (as opposed to insatiable curiosity), the
> Park gauge seems to be accurate enough to get the spokes to the right
> absolute tension (say 110 kgf) and accurate enough to get them to the
> same tension (very small differences between spokes are noticeable).
>
> Cheers,
>
> Carl Fogel
 
J

jim beam

Guest
[email protected] wrote:
<snip>

> There were no tensiometers available at the
> time I designed mine, and therefore, I was not influenced by prior
> art.


and apparently not influenced by the need to worry about different wire
stiffness for different gauge spokes either.
 
R

Ron Ruff

Guest
[email protected] wrote:
> Rick Hjertberg at FSA has my two prototype instruments that I gave him
> when he opened his shop, here in Palo Alto. These subsequently led to
> the production of the Avocet instrument, that was marketed by DT in
> Europe.
>
> http://tinyurl.com/7ogpr


You forgot to mention it's best feature... the light yet stiff and
beautiful naked carbon fiber frame!

Seriously that looks like a nice device... is it the only one that
functions that way? The $400 DT unit looks like a fancy version of the
Park... or maybe I should give credit to Wheelsmith since they were
first.
 
On 26 Dec 2006 09:27:17 -0800, "Ron Ruff" <[email protected]>
wrote:

[snip]

>The $400 DT unit looks like a fancy version of the
>Park... or maybe I should give credit to Wheelsmith since they were
>first.


Dear Ron,

Actually, the Park and the DT tension gauges work differently.

The Park gauge measures only where the hammer needle ends up, starting
from the same place every time, no matter how thick or thin the spoke
is. It doesn't care how far the hammer actually pushed the spoke
sideways. The problem of where the hammer first touches the spoke is
handled by a table, not the needle.

The DT gauge measures only how far the hammer actually pushed the
spoke sideways. It doesn't care how far the hammer moved before it
first touched the spoke. The problem of where the hammer first touches
the spoke is handled by the micrometer, not the table.

Both kinds of gauge just give you a number. To find the spoke tension,
you look the number up in a table for spokes of that material (steel,
carbon, titanium, aluminum), shape (round or oval/blade), and
dimensions (2.0 mm, 1.8 mm, 2.6 x 1.4 mm).

Here's the Park table:

http://www.parktool.com/products/documents/TM_1table_2005912_4301.pdf

Here are the DT tables, starting around page 9:

http://www.dtswiss.com/data/files/MAN_EN_51202133804.pdf

Cheers,

Carl Fogel
 
Ron Ruff writes:

>> Rick Hjertberg at FSA has my two prototype instruments that I gave
>> him when he opened his shop, here in Palo Alto. These subsequently
>> led to the production of the Avocet instrument, that was marketed
>> by DT in Europe.


http://tinyurl.com/7ogpr

> You forgot to mention it's best feature... the light yet stiff and
> beautiful naked carbon fiber frame!


I thought that was a bit of classic Rich Hjertberg marketing. That
text on the Wheelsmith web site is also classic of his presentations.
Thee is no lack of hyperbole there.

http://www.wheelsmith.com/index_files/wsspokes.htm

To tear and compare, note that the introduction was written in a
different voice by the current owners of Wheelsmith, the Hjertberg
being out of the business for reasons best described by Gary Erickson
(of Cliff Bar) in his book, "raining the Bar".

http://tinyurl.com/ygp5ot

> Seriously that looks like a nice device... is it the only one that
> functions that way? The $400 DT unit looks like a fancy version of
> the Park... or maybe I should give credit to Wheelsmith since they
> were first.


In production, Avocet was first and they supplied DT. Wheelsmith got
theirs from a local bikie, Norm Ogle, a man of great skills. When
Rick said he wanted a tensiometer that didn't cost an arm and a leg,
Norm came up with this $25 item, two identical aluminum plates, a
spring and an axle. At the cost of manufacture and mechanical
simplicity, I saw it as a most beautiful and ultimately clever designs
of the time. As I said, I don't know what motivated others to not
include features that my instrument readily demonstrated when used. I
thought it was obvious but apparently not.

Jobst Brandt
 
[email protected] wrote:

> Friction, for example, confuses things. When the hammer bends the
> spoke, it tries to drag the spoke inward over both posts. This raises
> the tension slightly, so the lower the hammer force, the less
> frictional distortion. The Park posts are just fixed, polished metal,
> but I think that more expensive gauges may have roller-posts to reduce
> friction.


How much do you suppose friction might affect readings? In the other
thread where I posted a photo of my sanded (or similar process reduced
diameter) butted spokes, there is clearly a texture on the spoke that
would perhaps make friction a bigger issue with a solid post tool like
the Park. I wonder if my spokes were much looser than I thought.

Joseph
 
On 26 Dec 2006 13:45:26 -0800, [email protected] wrote:

>
>[email protected] wrote:
>
>> Friction, for example, confuses things. When the hammer bends the
>> spoke, it tries to drag the spoke inward over both posts. This raises
>> the tension slightly, so the lower the hammer force, the less
>> frictional distortion. The Park posts are just fixed, polished metal,
>> but I think that more expensive gauges may have roller-posts to reduce
>> friction.

>
>How much do you suppose friction might affect readings? In the other
>thread where I posted a photo of my sanded (or similar process reduced
>diameter) butted spokes, there is clearly a texture on the spoke that
>would perhaps make friction a bigger issue with a solid post tool like
>the Park. I wonder if my spokes were much looser than I thought.
>
>Joseph


Dear Joseph,

I don't know what the practical effect of the friction would be. But I
suspect that the friction for ordinary-finish spokes is pretty much
accounted for on the Park tables.

You could test for accuracy by hanging known weights in the normal
spoke tension range on a spoke and comparing readings from a ~$60 Park
gauge and a ~$400 DT gauge. Possibly some bike magazine has compared
the accuracy of different spoke tension gauges, but I don't know of
any articles.

For practical wheel-building purposes, I suspect that the Park tension
gauge works fine. That is, it will give reasonably accurate absolute
tension (mine showed ~187 pounds for a known weight of ~190 pounds)
and it will show small tension differences--I've tested a number of
spokes with squeeze forces in 21 steps from 0 to 100 pounds, and the
gauge reflected the 5-lb squeeze force increase.

I doubt that it matters for practical wheel building whether your
absolute tension is 100, 110, or 120 kgf, any more than it matters
whether the tensions are all within 5 kgf or each other, or the rim is
true to within 0.1 mm, 0.5 mm, 1.0 mm, or even 2.0 mm.

In any case, your spokes are almost certainly looser than you think.
After all, on a narrow, well-braced 700c rim, Dianne's tests showed
that inflating the tire "to 120 psi dropped this spoke's tension from
about 99 kgf to about 83 kgf, a decrease of about 16 kgf or roughly 35
pounds."

http://www.geocities.com/dianne_1234/bikes/tension-inflation/tension-inflation.htm

So anyone who tensions spokes on a bare rim to 100 kgf is probably
actually riding around on spokes tensioned to only 83 to 90 kgf, a
considerably larger error than is likely with the Park tension gauge.

Cheers,

Carl Fogel
 
E

Earl Bollinger

Guest
<[email protected]> wrote in message
news:[email protected]
> On Sun, 24 Dec 2006 21:52:58 -0600, "Earl Bollinger"
> <[email protected]> wrote:
>
>><[email protected]> wrote in message
>>news:[email protected]
>>> Elsewhere, doubts have been cast on the accuracy of Park's modestly
>>> priced blue bicycle spoke tension gauge.
>>>
>>> Hmmm . . . I'd never tested my trusty (?) Park tension gauge!
>>>
>>> It does notice whenever I add small weights or turn spoke nipples or
>>> let the air out of a tire--what else can a simple spring do?
>>>
>>> But what if it's been lying to me all this time and just flattering me
>>> when I ask it whether pinching spokes together makes my spoke-tension
>>> look fat? What if the tension is 50% higher than the calibration table
>>> claims?
>>>
>>> How could I enjoy visions of sugar-plums dancing through my head
>>> tonight with this kind of uncertainty nagging me?
>>>
>>> So I bent the ends of a helpless 2 mm straight steel spoke into
>>> U-hooks, added some wire-rope thingies to stop the U-hooks from
>>> straightening, hung the spoke from a ceiling rope, and dangled a crude
>>> rope-and-2x4 swing from the spoke to allow loading a standard 195-lb
>>> Fogel onto the spoke.
>>>
>>> I stepped onto the swing and found . . .
>>>
>>> That I swung so wildly on my piñata-style contraption that there was
>>> no way to read the Park tension gauge, much less take a picture of the
>>> festivities.
>>>
>>> Alas, the vast stock of convenient weights at Fogel Labs totals only
>>> about 100 real pounds on postal scales. (An inflated 110 pounds
>>> according to the lying numbers stamped on the weights themselves.)
>>>
>>> At first I feared that Christmas would be ruined, since I needed
>>> something close to 200 pounds to represent a low-normal 90 kgf
>>> spoke tension.
>>>
>>> But then I remembered that several plastic buckets are kept around the
>>> premises for . . . well, for important stuff like this.
>>>
>>> Filled not too near the top, the first bucket weighed a handy 30
>>> pounds. After filling all three buckets and checking that they weighed
>>> 30 pounds, I dangled 100 lbs of weights on a bar and three 30-pound
>>> buckets of water from a 2 mm spoke:
>>>
>>> http://i14.tinypic.com/4960dw3.jpg
>>>
>>> http://i18.tinypic.com/2czqz6f.jpg
>>>
>>> Click on the lower right for full-size images in Explorer.
>>>
>>> The Park gauge reads about 22 on a scale of 0 to 45. (It's a little
>>> over 22, and then the camera angle makes it look a little higher. I
>>> steadied the camera on a handy but slightly too-high stand.)
>>>
>>> For a 2 mm spoke, the Park calibration chart shows this to mean a
>>> tension of 85 kgf, or 187 pounds, reasonably close to the 190 pounds
>>> of ropes, bar, weights, buckets, and water in the picture.
>>>
>>> Park 2.0mm spoke
>>> mark kgf / lbs
>>>
>>> off scale
>>> 17 51 / 112
>>> 18 56 / 123
>>> 19 62 / 136
>>> 20 68 / 150
>>> 21 76 / 167
>>> 22 85 / 187 <--~190 lbs of weights hung from spoke
>>> 23 95 / 209
>>> 24 107 / 235
>>> 25 121 / 266
>>> 26 137 / 301
>>> 27 156 / 343
>>> 28 179 / 394
>>> off scale
>>>
>>> I hope that this test pleases anyone who gets a blue Park tension
>>> gauge tomorrow morning. (Or a gift certificate to places that sell
>>> it.)
>>>
>>> Merry Christmas!
>>>
>>> Carl Fogel

>>
>>That is nice to know. Thanks.
>>That is a very imaginatively neat setup you used to test it too.
>>I wonder how the modest Park tool compares to the super fancy spoke
>>tension
>>gauges?

>
> Dear Earl,
>
> Well, there are two kinds of tension gauges . . .
>
> The Park gauge is just a spring arm (hammer post) with a long needle
> attached to the hammer-shaft. The hammer post pushes against the
> middle of a short spoke span, which is supported by two end posts
> (anvil posts).
>
> Where the needle ends up on the gauge depends on two things.
>
> First, how thick is the spoke? The hammer post hits a thick spoke
> sooner than it hits a thin spoke, so readings begin sooner for a thick
> spoke, higher on the scale. This is just an offset, but it's
> considerable for even small differences in spoke thickness.
>
> Second, how much does the spoke bend under the spring pushing the
> hammer? This mostly depends on how much tension is trying to keep the
> spoke straight, but there are other factors.
>
> Friction, for example, confuses things. When the hammer bends the
> spoke, it tries to drag the spoke inward over both posts. This raises
> the tension slightly, so the lower the hammer force, the less
> frictional distortion. The Park posts are just fixed, polished metal,
> but I think that more expensive gauges may have roller-posts to reduce
> friction.
>
> The thickness and material of the spoke also confuses things. The
> thicker the spoke and the stiffer its material, the more it resists
> bending just by its own stiffness.
>
> Higher marks mean higher tensions. Mark 20 on the Park calibration
> tables means 68 kgf for a round steel 2mm spoke, 89 kgf for a round
> steel 1.8mm spoke, 80 kgf for a round titanium spoke.
>
> For a round 3.3mm aluminum spoke, mark 36 (way up there!) means only
> 89 kgf. The 3.3mm thickness of the spoke means that the hammer hits
> the spoke much sooner and stops at much higher marks.
>
> Steel motorcycle spokes are so stiff that the Park tool may be useless
> because its spring isn't powerful enough bend the massive spokes. You
> can get readings, but it's about like trying to weigh a 2 pound
> package accurately on a bathroom spring scale intended for 100 to 200
> pound objects--the range is wrong.
>
> Here's a 3.5mm (4mm elbow butt) spoke (modest for a motorcycle) next
> to a 2mm straight spoke (husky for a bicycle):
>
> http://home.comcast.net/~carlfogel/download/spokes.jpg
>
> Here the obviously 0-tension 3.5mm section of motorcycle spoke reads
> almost 25 on a Park gauge:
>
> http://i11.tinypic.com/2me5zec.jpg
>
> Here the obviously 0-tension 2mm bike spoke reads 0 on a Park gauge:
>
> http://i18.tinypic.com/2wp5s2c.jpg
>
> And here's the back of the Park gauge:
>
> http://i10.tinypic.com/47i07xv.jpg
>
> One end of the \/ spring fits into the slotted head of the long
> adjustment screw on the left. The back of the "hammer" post is the
> round gray spot to the right of the spring post. The "needle" is the
> large black squeeze-handle.
>
> Click on the lower right in Explorer for full-size images.
>
> The Park gauge and the Wheelsmith gauge are the inexpensive ones and
> use this simple spring and calibration table approach. Park Tool will
> re-calibrate a gauge for a fee. Here's a page showing a few brands:
>
> http://www.sheldonbrown.com/harris/tools/wheel.html#tensiometers
>
> More expensive tension gauges use a different approach. The red DT
> gauge on Sheldon's page uses a built-in micrometer to measure how far
> the spring-load hammer moves _after_ it first touches the spoke. Then
> you figure out from tables what that movement means. The idea is to
> use the geometric calculation approach, but it still ends up
> calibrating for spoke thickness and material and so forth. You can get
> dial indicators or even more expensive digital indicators, but they
> both just measure how far the hammer moves the spoke sideways.
>
> I don't know of any tests comparing the accuracy of the simple spring
> and needle Park and Wheelsmith style gauges versus the micrometer
> reading of hammer movement.
>
> At first, the micrometer sounds more accurate, but then you realize
> that the Park needle is almost 7 inches long. I suspect that the more
> expensive gauges may be more accurate, but that much of the accuracy
> lies in polishing and rollers to reduce friction.
>
> You can compare the DT Swiss and the Park calibration tables to get an
> idea of the practical outcome.
>
> Here's the DT Swiss pdf, with a conversion graphs and tables starting
> on page 9:
>
> http://www.dtswiss.com/data/files/MAN_EN_51202133804.pdf
>
> Here's the Park calibration table:
>
> http://www.parktool.com/products/documents/TM_1table_2005912_4301.pdf
>
> For practical wheel-building (as opposed to insatiable curiosity), the
> Park gauge seems to be accurate enough to get the spokes to the right
> absolute tension (say 110 kgf) and accurate enough to get them to the
> same tension (very small differences between spokes are noticeable).
>
> Cheers,
>
> Carl Fogel


Thanks,
I was mainly curious as to if the accuracy of the Park Tools Guage
correlated Ok with the other tools.
I own a Park Guage, and it is acceptable for my skill levels in wheel
building and such endeavors.
 
Carl Fogel writes:

>>> Friction, for example, confuses things. When the hammer bends the
>>> spoke, it tries to drag the spoke inward over both posts. This
>>> raises the tension slightly, so the lower the hammer force, the
>>> less frictional distortion. The Park posts are just fixed,
>>> polished metal, but I think that more expensive gauges may have
>>> roller-posts to reduce friction.


>>How much do you suppose friction might affect readings? In the
>>other thread where I posted a photo of my sanded (or similar process
>>reduced diameter) butted spokes, there is clearly a texture on the
>>spoke that would perhaps make friction a bigger issue with a solid
>>post tool like the Park. I wonder if my spokes were much looser
>>than I thought.


> I don't know what the practical effect of the friction would be.
> But I suspect that the friction for ordinary-finish spokes is pretty
> much accounted for on the Park tables.


Stiction is a problem with these instruments and that is why I used
ball bearings to support the spoke. You can find how much effect that
has with your instrument by rotating it a few degrees about the spoke,
returning to the position from which you started. This releases
stiction and also shows the zeroing effect that is not present by
giving a different reading depending on where the instrument is
stopped. A common way of reducing stiction is to vibrate the subject
(spoke) by tapping on it, lightly yet sharply, without changing its
position.

> You could test for accuracy by hanging known weights in the normal
> spoke tension range on a spoke and comparing readings from a ~$60
> Park gauge and a ~$400 DT gauge. Possibly some bike magazine has
> compared the accuracy of different spoke tension gauges, but I don't
> know of any articles.


That will get you nowhere. That does not affect stiction which in a
sense is micro-welding. That is why I chose a rounded anvil to press
on the spoke.

> For practical wheel-building purposes, I suspect that the Park
> tension gauge works fine. That is, it will give reasonably accurate
> absolute tension (mine showed ~187 pounds for a known weight of ~190
> pounds) and it will show small tension differences--I've tested a
> number of spokes with squeeze forces in 21 steps from 0 to 100
> pounds, and the gauge reflected the 5-lb squeeze force increase.


I see bicycling is once more being so provincial that the term
tensiometer must remain foreign as do many other concepts in bicycle
hardware.

http://www.m-w.com/dictionary/tensiometer

> I doubt that it matters for practical wheel building whether your
> absolute tension is 100, 110, or 120 kgf, any more than it matters
> whether the tensions are all within 5 kgf or each other, or the rim
> is true to within 0.1 mm, 0.5 mm, 1.0 mm, or even 2.0 mm.


If you have access to better information, why not get it. Try
wiggling your tensiometer and see what you get.

> In any case, your spokes are almost certainly looser than you think.
> After all, on a narrow, well-braced 700c rim, Dianne's tests showed
> that inflating the tire "to 120 psi dropped this spoke's tension
> from about 99 kgf to about 83 kgf, a decrease of about 16 kgf or
> roughly 35 pounds."


That is only a problem for folks who use the instrument to tune the
wheel, every spoke reading the same value. This reminds me of gears
on bicycle, that some folks use to start at a traffic light running
through six to eight gears like a loaded highway truck. Gears are for
climbing hills, tensiometers are for assessing wheel tension, a couple
of spokes after final tensioning will do.

http://tinyurl.com/67gwc

> So anyone who tensions spokes on a bare rim to 100 kgf is probably
> actually riding around on spokes tensioned to only 83 to 90 kgf, a
> considerably larger error than is likely with the Park tension
> gauge.


That number isn't so fixed as it may seem, rims being of different
materials and cross section and having a different number of spokes.
An example of this effect is in "the Bicycle Wheel" just to avoid
great discoveries being made about this later. My spokes have the
tension that I measure. What is done with the wheel subsequently is
another matter.

Jobst Brandt