safe spoke elongtion?
Seb
on the dimensions I use, measuring the tension will require stretching the
spoke a variable amount. In reasonable designs, this varies from .5 to 3 mm.
How much is it safe to "stretch" a spoke? I'm guessing that less elongation
is better, but I think my readings are less likely to be influenced by
operator error or construction inconsistancies if the "stretch" is longer,
because such errors would this be a smaller component.
The data in Brandt's "The Bicycle Wheel" indicates to me that a stretch of 3mm
might be completely impractical, since it would represent an increase in
tension comparable to the spokes elastic limit. Elongation of .5mm seems to
apply about 500 newtons of extra tension. Is this a reasonable amount?
Is there a more precise way to find the tension increase for a given
elongation? My design allows me to calculate the final tension after
elongation quite precisely, but I'd need to subtract the added tension due to
elongation to get the "base" tension.
-Seb
jobst....@stanfordalumni.org
> I'm designing a tensiometer, and have one issue left to nail down.
> Depending on the dimensions I use, measuring the tension will
> require stretching the spoke a variable amount. In reasonable
> designs, this varies from .5 to 3 mm.
What is it you are trying to do that isn't accomplished by the
tensiometer you saw in "the Bicycle Wheel"? The tensiometer shown
there has features that others do not.
1. Spoke thickness does not affect readings, support and measurement
being made from the same side.
2. By using a precision micrometer, deflections produced by a small
test load can be accurately detected. For this a "zero on the fly"
must be made to cancel slight irregularities something this
instrument does.
3. A light test load has minimal effect on existing tension that would
otherwise be compromised as is common with tensiometers like the
Hozan.
4. Ball bearing support at the end of the test section prevents
friction from retarding spoke deflection (cosine error)
5. The four inch test span is reasonably large to permit high accuracy
with small micrometer read deflections.
I don't know what you propose to do in "stretching". This is not a
reasonable the way of measuring tension in wires.
Jobst Brandt <jobst....@stanfordalumni.org> Palo Alto CA
Seb
>tensiometer you saw in "the Bicycle Wheel"?
Actually, I'm not sure, since theres no specific dimensions or forces given
for the tensiometer in "the Bicycle Wheel".
In essence, I am attempting to apply "appropriate technology" design to the
tensiometer. I don't think the one in "the Bicycle Wheel" could be built
cheaply at home by a hobbiest with no special tools, which conflicts directly
with the philosophy of "appropriate technology", and (less directly) with the
spirit of "Do It Yourself".
I'm trying to design a reasonably accurate tensiometer that can be built for
less than $10 from items avaialble in any decent hardware store, or mass
produced for less than $1. I'm trying to make this design and the method of
its use freely available information.
Since "It is not nescessary to know the actual tension but only that the
tension has reached the desired mark", I figure an inexpesive tensiometer that
gives precise, scaled, and repatable (if not accurate) readings would be all a
hobbiest wheelbuilder needs to eliminate the problem that "final tension of a
wheel is affected by the mood of its builder."
Granted, I'm "cheating" by using a torque wrench to do the actual measuring,
but I figure most people would rather buy a nice, generally useful torque
wrench (which costs maybe $30) and make a cheap accessory tensiometer than buy
a tensiometer (which costs at the least I've seen $90) that they only use when
building (or maybe truing) wheels.
>The tensiometer shown
>there has features that others do not.
I appreciate its features, but feel I would have no need to duplicate them, or
benefit from doing so. Your design's features and functions do not seem
duplictable without precision machining and / or specialized parts, and it has
moving parts which complicate home construction. My design can be made with a
hand drill and a brazing kit, and has no moving parts.
>1. Spoke thickness does not affect readings, support and measurement
> being made from the same side.
Your design still calls for a table to calculate absolute tension based on the
measurements, correct? How much extra work would it be to make a seperate
table for each of a few spoke thicknesses (and maybe brands)? That's all that
would be required to compensate for spoke thickness when using my design.
Given a formula for spoke elasticity and the appropriate data for various
spokes, I could set up a spreadsheat to produce all the required tables, I
think. It could be verified with measurement- a precision tensiometer such as
your design would be very helpful there!
>2. By using a precision micrometer, deflections produced by a small
> test load can be accurately detected. For this a "zero on the fly"
> must be made to cancel slight irregularities something this
> instrument does.
Since I don't know what it really means, I can't say its something I ever
wanted or not. I'll grant its not a feature of my design. Will that
negatively affect a hobbiest wheel builder who desires to use a tensiometer
primarily to ascertain if his new wheel has enough or to much tension?
>3. A light test load has minimal effect on existing tension that would
> otherwise be compromised as is common with tensiometers like the
> Hozan.
Actually, by posting this thread, I was trying to figure out how much "test
load" is ideal for a design like mine. How much is "light"? What do you
suggest?
In this case, a light test load would produces changes that are hard to
acsertain accurately without precise alignments or measurements. I could
concievably reconfigure my design to use a very lightweight torque wrench and
very small deflections, but I was shooting for something a hobbiest could
build cheaply and quickly, and use with a minimum of opperator error.
>4. Ball bearing support at the end of the test section prevents
> friction from retarding spoke deflection (cosine error)
Would smooth round posts with lubrication at all 3 points of contact (2
loaded, 1unloaded) in my design do nearly as well?
>5. The four inch test span is reasonably large to permit high accuracy
> with small micrometer read deflections.
I was thinking of a total 6.6mm (1/4 inch) deflection over 10 cm (4 inches,
simply because that fits well on most spokes). Is that far off from what your
rig does? I can't say what my design accomplishes relative to yours without
knowing the dimensions and forces you use.
>I don't know what you propose to do in "stretching". This is not a
>reasonable the way of measuring tension in wires.
"a tensiometer measures the deflection of a spoke over a given span in
respones to a standard load". Assuming the endpoints do no move, is it
possible to deflect a span without elongating it? To me, it seems is
impossible to measure spoke tension using a tensiometer without "stretching"
the spokes at least a bit- if not the spoke being "deflected", then all the
other spokes in the wheel, so as to move the endpoints of the "deflected"
spoke!
However, it may very well be the rig you used, and perhaps other tensiometers,
cause less elongation in the deflected spoke than I was planning on. That is
exactly why I asked how much is reasonable. If the answer is "none", what is
the mechanism used?
Perhaps I could ascertain the folly of my plans myself if you would be so kind
as to point out where / how I could get some precise, accurate spoke
elongation data? I trust you are as reasoanble as I if not much more so.
Still, I'm quite bull headed and would rather not take your word for the
infeasability of my design without doing my own analysis and experiments.
-Seb
john m schmidt
You first need to a little more studying. You personally need to
fully understand stress and strain. YOU need to study a strength of
materials book. You are asking questions that show ignorance of the
physics. How can you design something when you don't understand the
technology / physics behind it ?
You also need to investigate all designs that already exist that
measure tension in a cable or rod. You should probably do a QFD
(quality function deployment) and a "house of quality". The
Wheelsmith tensionmeter seems pretty simple.
I personally like the true rim method. If you start with a true rim,
build the wheel evenly and keep the rim true, then the spokes are
going to be pretty much evenly tensioned. I also feel the spokes by
hand. Tried plucking / tone method but gave up pretty quick.
regards and good luck, John
jobst....@stanfordalumni.org
By the way, why so secretive. This reminds me of speaking to a spy
with dark glasses and hat drawn low in Casablanca.
>> What is it you are trying to do that isn't accomplished by the
>> tensiometer you saw in "the Bicycle Wheel"?
> Actually, I'm not sure, since theres no specific dimensions or
> forces given for the tensiometer in "the Bicycle Wheel".
> In essence, I am attempting to apply "appropriate technology" design
> to the tensiometer. I don't think the one in "the Bicycle Wheel"
> could be built cheaply at home by a hobbiest with no special tools,
> which conflicts directly with the philosophy of "appropriate
> technology", and (less directly) with the spirit of "Do It
> Yourself".
You say that as though it were trivial measurement while in fact it is
not. Deflecting the spoke from its straight path causes a length
change which if large will change its tension. The instrument shown
deflects the spoke 0.013" in a 4" span, which gives an angle of 0.37
degrees. Spoke length change for that angle is 0.000021" and bending
is kept small enough so that it does not materially affect readings
for spoke thicknesses of 1.6 to 2.0mm diameter wire.
> I'm trying to design a reasonably accurate tensiometer that can be
> built for less than $10 from items available in any decent hardware
> store, or mass produced for less than $1. I'm trying to make this
> design and the method of its use freely available information.
If you look at the Wheelsmith instrument, you'll see that it has two
pieces of stamped sheet metal, a spring and a pivot pin. That's hard
to beat in simplicity but it is not as accurate as the instrument in
the book because it has friction and measures across the wire. It
also cannot be checked for proper zero or be adjusted for kinks in
spokes.
> Since "It is not necessary to know the actual tension but only that
> the tension has reached the desired mark", I figure an inexpensive
> tensiometer that gives precise, scaled, and repeatable (if not
> accurate) readings would be all a hobbiest wheelbuilder needs to
> eliminate the problem that "final tension of a wheel is affected by
> the mood of its builder."
I think you have a contradiction there. Knowing you are at the
desired mark IS determining the actual tension. I don't see how else
you can define that.
> Granted, I'm "cheating" by using a torque wrench to do the actual
> measuring, but I figure most people would rather buy a nice,
> generally useful torque wrench (which costs maybe $30) and make a
> cheap accessory tensiometer than buy a tensiometer (which costs at
> the least I've seen $90) that they only use when building (or maybe
> truing) wheels.
The torque wrench is not free and it is not sensitive enough to give
you what you want. Fine instrument torque wrenches (1-50 in-oz) are
at least as expensive as a good tensiometer.
>> The tensiometer shown there has features that others do not.
> I appreciate its features, but feel I would have no need to
> duplicate them, or benefit from doing so. Your design's features
> and functions do not seem duplicable without precision machining
> and / or specialized parts, and it has moving parts which complicate
> home construction. My design can be made with a hand drill and a
> brazing kit, and has no moving parts.
That is the crux of the matter. Why do you think tensiometers cost
as much as they do. The instrument must be largely non invasive and
that requires precision. What you seem to be looking for is far
easier to achieve by building a wheel as described in the book and to
know what tone a spoke of the appropriate tension makes. You'll
notice that tension specifications are not offered with most rims, so
that is in itself your problem to solve.
>>1. Spoke thickness does not affect readings, support and measurement
>> being made from the same side.
> Your design still calls for a table to calculate absolute tension
> based on the measurements, correct?
That's only because its production was too small (less than 200) to
have a special gauge dial, something that could be done electronically
today.
> How much extra work would it be to make a separate table for each of
> a few spoke thicknesses (and maybe brands)? That's all that would
> be required to compensate for spoke thickness when using my design.
> Given a formula for spoke elasticity and the appropriate data for
> various spokes, I could set up a spreadsheet to produce all the
> required tables, I think. It could be verified with measurement- a
> precision tensiometer such as your design would be very helpful
> there!
Brands of spokes makes no difference. All the ones of interest are
steel and and its modulus of elasticity is well defined. Thickness
only enters into the problem with more than the customary range of up
to 2.0mm diameter. Flat spokes do not change the readings.
>>2. By using a precision micrometer, deflections produced by a small
>> test load can be accurately detected. For this a "zero on the
>> fly" must be made to cancel slight irregularities something this
>> instrument does.
> Since I don't know what it really means, I can't say its something I
> ever wanted or not. I'll grant its not a feature of my design.
> Will that negatively affect a hobbiest wheel builder who desires to
> use a tensiometer primarily to ascertain if his new wheel has enough
> or to much tension?
I don't think you understand the problem or you wouldn't say what you
do. The hobbyist needs to get a good reading at least as much as the
professional wheel builder.
>>3. A light test load has minimal effect on existing tension that
>> would otherwise be compromised as is common with tensiometers
>> like the Hozan.
> Actually, by posting this thread, I was trying to figure out how
> much "test load" is ideal for a design like mine. How much is
> "light"? What do you suggest?
About 2kgf gives a deflection of around 0.4mm, a useful deflection yet
one that does not change existing tension because the length change it
causes is diminishingly small.
> In this case, a light test load would produces changes that are hard
> to ascertain accurately without precise alignments or measurements.
> I could conceivably reconfigure my design to use a very lightweight
> torque wrench and very small deflections, but I was shooting for
> something a hobbiest could build cheaply and quickly, and use with a
> minimum of operator error.
Try building a cheap microscope.
>>4. Ball bearing support at the end of the test section prevents
>> friction from retarding spoke deflection (cosine error)
> Would smooth round posts with lubrication at all 3 points of contact
> (2 loaded, 1 unloaded) in my design do nearly as well?
No but your method would not cause any length change in the
measurement length so friction is not a problem. There are a few
problems in your design, one of them being that the three pegs cannot
be in a straight line because deflections need to be kept to size that
is far smaller than what a pin that could support the load could take.
The concept is good but it defies execution in the range of forces
involved.
>>5. The four inch test span is reasonably large to permit high
>> accuracy with small micrometer read deflections.
> I was thinking of a total 6.6mm (1/4 inch) deflection over 10 cm (4
> inches, simply because that fits well on most spokes). Is that far
> off from what your rig does? I can't say what my design
> accomplishes relative to yours without knowing the dimensions and
> forces you use.
There is the killer. Deflections must be kept to less than 0.5mm
(0.02") or the measurement will be too intrusive. That is to say, the
measurement result will be rim and spoke length and number dependent.
>> I don't know what you propose to do in "stretching". This is not a
>> reasonable the way of measuring tension in wires.
> "a tensiometer measures the deflection of a spoke over a given span
> in response to a standard load". Assuming the endpoints do no move,
> is it possible to deflect a span without elongating it? To me, it
> seems is impossible to measure spoke tension using a tensiometer
> without "stretching" the spokes at least a bit- if not the spoke
> being "deflected", then all the other spokes in the wheel, so as to
> move the endpoints of the "deflected" spoke!
I think the above paragraph was dealt with earlier. Cosine error can
be so small that it has no stretching effect on the spoke.
> However, it may very well be the rig you used, and perhaps other
> tensiometers, cause less elongation in the deflected spoke than I
> was planning on. That is exactly why I asked how much is
> reasonable. If the answer is "none", what is the mechanism used?
> Perhaps I could ascertain the folly of my plans myself if you would
> be so kind as to point out where / how I could get some precise,
> accurate spoke elongation data? I trust you are as reasonable as I
> if not much more so. Still, I'm quite bull headed and would rather
> not take your word for the infeasability of my design without doing
> my own analysis and experiments.
Give the concept some more thought. Maybe you can devise a
configuration that can be made to work. The concept is not bad but it
seems to lie beyond implementation in the constraints involved.
Seb
|
|By the way, why so secretive. This reminds me of speaking to a spy
|with dark glasses and hat drawn low in Casablanca.
What value would my last name add to the conversation? If I was a published
autor or otherwise felt a need to reference my credentials, it might be
pertinant. Since I have no credentials, I prefer to go by a simple nickname,
and just explore some ideas ather than my personal history.
If by "secretive" you mean not posting the details of my design, check for
another thread, called "home project tnesiometer palns and analysis-
comments?" (sic- my typing was that bad)
On some news readers, its not given its own thread identifier.
|>> What is it you are trying to do that isn't accomplished by the
|>> tensiometer you saw in "the Bicycle Wheel"?
|
|> Actually, I'm not sure, since theres no specific dimensions or
|> forces given for the tensiometer in "the Bicycle Wheel".
|
|> In essence, I am attempting to apply "appropriate technology" design
|> to the tensiometer. I don't think the one in "the Bicycle Wheel"
|> could be built cheaply at home by a hobbiest with no special tools,
|> which conflicts directly with the philosophy of "appropriate
|> technology", and (less directly) with the spirit of "Do It
|> Yourself".
|
|You say that as though it were trivial measurement while in fact it is
|not.
No, I had not assumed it was. I felt it went without saying. I think the
fact that I felt the need to design a device for the purpose, and had some
admiteded desing quandreis, showed the non-triviality.
|Deflecting the spoke from its straight path causes a length
|change which if large will change its tension. The instrument shown
|deflects the spoke 0.013" in a 4" span, which gives an angle of 0.37
|degrees. Spoke length change for that angle is 0.000021" and bending
|is kept small enough so that it does not materially affect readings
|for spoke thicknesses of 1.6 to 2.0mm diameter wire.
OK, that's exactly the sort of info I was asking for. Thank you. That is
indeed very difficult to replicate, or even approximate, with a home built
tool.
|> Since "It is not necessary to know the actual tension but only that
|> the tension has reached the desired mark", I figure an inexpensive
|> tensiometer that gives precise, scaled, and repeatable (if not
|> accurate) readings would be all a hobbiest wheelbuilder needs to
|> eliminate the problem that "final tension of a wheel is affected by
|> the mood of its builder."
|
|I think you have a contradiction there. Knowing you are at the
|desired mark IS determining the actual tension. I don't see how else
|you can define that.
The words in quotes are from your own book (p. 118 3ed), and contain the
entire contradiction. How would you define the difference?
|> Granted, I'm "cheating" by using a torque wrench to do the actual
|> measuring, but I figure most people would rather buy a nice,
|> generally useful torque wrench (which costs maybe $30) and make a
|> cheap accessory tensiometer than buy a tensiometer (which costs at
|> the least I've seen $90) that they only use when building (or maybe
|> truing) wheels.
|
|The torque wrench is not free and it is not sensitive enough to give
|you what you want. Fine instrument torque wrenches (1-50 in-oz) are
|at least as expensive as a good tensiometer.
Yes, so I am finding. They can be built farily easily and calibrated with a
test mass, but that still isn't free, and might be an equal waste of time.
|That is the crux of the matter. Why do you think tensiometers cost
|as much as they do. The instrument must be largely non invasive and
|that requires precision. What you seem to be looking for is far
|easier to achieve by building a wheel as described in the book and to
|know what tone a spoke of the appropriate tension makes. You'll
|notice that tension specifications are not offered with most rims, so
|that is in itself your problem to solve.
I had no sure indication that is was not possible to design an inexpensive
tnesiometer, and it didn't seem harmful to try. The worst that might have
happened would have been I;d ruin a test wheel.
There's been a lot of debate as to whether the "mini taco" and "tuning harp"
method work for all wheels. Your own book stats the "mini taco" method only
works for certain road wheel designs, and probably not for any MTB wheel.
|>>1. Spoke thickness does not affect readings, support and measurement
|>> being made from the same side.
|
|> Your design still calls for a table to calculate absolute tension
|> based on the measurements, correct?
|
|That's only because its production was too small (less than 200) to
|have a special gauge dial, something that could be done electronically
|today.
OK, that's nice and saves a little time over looking at a few tables. I have
time.
|>>2. By using a precision micrometer, deflections produced by a small
|>> test load can be accurately detected. For this a "zero on the
|>> fly" must be made to cancel slight irregularities something this
|>> instrument does.
|
|> Since I don't know what it really means, I can't say its something I
|> ever wanted or not. I'll grant its not a feature of my design.
|> Will that negatively affect a hobbiest wheel builder who desires to
|> use a tensiometer primarily to ascertain if his new wheel has enough
|> or to much tension?
|
|I don't think you understand the problem or you wouldn't say what you
|do. The hobbyist needs to get a good reading at least as much as the
|professional wheel builder.
Well, its certainly not your responsability to explain the problem.
I do wonder, if the Wheelsmith tensiometer "can't be properly zeroed", how
does itn "zero on the fly", and why is it so useful?
|>>3. A light test load has minimal effect on existing tension that
|>> would otherwise be compromised as is common with tensiometers
|>> like the Hozan.
|
|> Actually, by posting this thread, I was trying to figure out how
|> much "test load" is ideal for a design like mine. How much is
|> "light"? What do you suggest?
|
|About 2kgf gives a deflection of around 0.4mm, a useful deflection yet
|one that does not change existing tension because the length change it
|causes is diminishingly small.
If tension / length is chaged, by a known amount, why can't the addtional
tension be calculated and cancled out? Is it likely to be harful to the
spoke?
|> Would smooth round posts with lubrication at all 3 points of contact
|> (2 loaded, 1 unloaded) in my design do nearly as well?
|
|No but your method would not cause any length change in the
|measurement length so friction is not a problem. There are a few
|problems in your design, one of them being that the three pegs cannot
|be in a straight line because deflections need to be kept to size that
|is far smaller than what a pin that could support the load could take.
|The concept is good but it defies execution in the range of forces
|involved.
That's exactly what I was aiming to figure out from the "safe elongation" of a
spoke, or compute using spoke elasticity data. Thanks.
|>>5. The four inch test span is reasonably large to permit high
|>> accuracy with small micrometer read deflections.
|
|> I was thinking of a total 6.6mm (1/4 inch) deflection over 10 cm (4
|> inches, simply because that fits well on most spokes). Is that far
|> off from what your rig does? I can't say what my design
|> accomplishes relative to yours without knowing the dimensions and
|> forces you use.
|
|There is the killer. Deflections must be kept to less than 0.5mm
|(0.02") or the measurement will be too intrusive. That is to say, the
|measurement result will be rim and spoke length and number dependent
A flimsier rim would cause a diffrent reading, I hadn't considered that.
Nuts.
|Give the concept some more thought. Maybe you can devise a
|configuration that can be made to work. The concept is not bad but it
|seems to lie beyond implementation in the constraints involved.
I'd considered some alternate configurations, but they aren't fundamentally
diffrent in construction from Wheelsmith's design, and require similar
tolerances. With acess to a machine shop, building one might save me money,
but that wasn't my purpose.
-Seb
Seb
|fully understand stress and strain. YOU need to study a strength of
|materials book. You are asking questions that show ignorance of the
|physics.
I never concealed that ignorance. I laid out (in another thread) all the info
I had, and its sources. I wasn't trying to bamboozle anybody, or get a job,
so where's the harm?
| How can you design something when you don't understand the
|technology / physics behind it ?
With a little help and some refrence books?
|I personally like the true rim method. If you start with a true rim,
|build the wheel evenly and keep the rim true, then the spokes are
|going to be pretty much evenly tensioned. I also feel the spokes by
|hand. Tried plucking / tone method but gave up pretty quick.
There's a lot of debate as to whether that gives appropriate tension for
various wheels, especially for an occasional builder. Over time, it works
fine, but that''s no reason not to try to improve on it.
-Seb
jobst....@stanfordalumni.org
>> By the way, why so secretive. This reminds me of speaking to a spy
>> with dark glasses and hat drawn low in Casablanca.
> What value would my last name add to the conversation? If I was a
> published author or otherwise felt a need to reference my
> credentials, it might be pertinent.
Just the contrary. You can readily use your name because you have
nothing to hide or have said previously. Besides, it's rude to talk
to people with the visor of your armor closed, incognito. This is
part of common courtesy that doesn't hurt. You must not understand why
most contributors here do not hide behind "handles".
>> You say that as though it were trivial measurement while in fact it
>> is not.
> No, I had not assumed it was. I felt it went without saying. I
> think the fact that I felt the need to design a device for the
> purpose, and had some admitted design quandaries, showed the
> non-triviality.
Your suggestion that you have a simple way of measuring tension
implies that you think it is simple at best, or that those who make
them are unclear on the concept at worst.
>> Deflecting the spoke from its straight path causes a length change
>> which if large will change its tension. The instrument shown
>> deflects the spoke 0.013" in a 4" span, which gives an angle of
>> 0.37 degrees. Spoke length change for that angle is 0.000021" and
>> bending is kept small enough so that it does not materially affect
>> readings for spoke thicknesses of 1.6 to 2.0mm diameter wire.
> OK, that's exactly the sort of info I was asking for. Thank you.
> That is indeed very difficult to replicate, or even approximate,
> with a home built tool.
You would do well to build a prototype and investigate the effects
before proposing what you have. You are asking the net to do your
R&D, at least in the theoretical realm, before you have an idea of
how to accomplish this beyond sketchy ideas.
>>> Since "It is not necessary to know the actual tension but only
>>> that the tension has reached the desired mark", I figure an
>>> inexpensive tensiometer that gives precise, scaled, and repeatable
>>> (if not accurate) readings would be all a hobbiest wheelbuilder
>>> needs to eliminate the problem that "final tension of a wheel is
>>> affected by the mood of its builder."
>> I think you have a contradiction there. Knowing you are at the
>> desired mark IS determining the actual tension. I don't see how
>> else you can define that.
> The words in quotes are from your own book (p. 118 3ed), and contain
> the entire contradiction. How would you define the difference?
Vague insinuations will get you nowhere.
>>> Granted, I'm "cheating" by using a torque wrench to do the actual
>>> measuring, but I figure most people would rather buy a nice,
>>> generally useful torque wrench (which costs maybe $30) and make a
>>> cheap accessory tensiometer than buy a tensiometer (which costs at
>>> the least I've seen $90) that they only use when building (or
>>> maybe truing) wheels.
>> The torque wrench is not free and it is not sensitive enough to
>> give you what you want. Fine instrument torque wrenches (1-50
>> in-oz) are at least as expensive as a good tensiometer.
> Yes, so I am finding. They can be built fairly easily and
> calibrated with a test mass, but that still isn't free, and might be
> an equal waste of time.
Oh oh. Here we go again. Next I see that you want to wind your own
springs and make steel shapes.
>> That is the crux of the matter. Why do you think tensiometers cost
>> as much as they do. The instrument must be largely non invasive
>> and that requires precision. What you seem to be looking for is
>> far easier to achieve by building a wheel as described in the book
>> and to know what tone a spoke of the appropriate tension makes.
>> You'll notice that tension specifications are not offered with most
>> rims, so that is in itself your problem to solve.
> I had no sure indication that is was not possible to design an
> inexpensive tensiometer, and it didn't seem harmful to try.
In that case I suggest you do that and don't use this forum as a
scratch pad for Idle conjecture. It's not as though you proposed
specific questions but rather you made a grand "open system" proposal.
>> I don't think you understand the problem or you wouldn't say what you
>> do. The hobbyist needs to get a good reading at least as much as the
>> professional wheel builder.
> Well, its certainly not your responsibility to explain the problem.
> I do wonder, if the Wheelsmith tensiometer "can't be properly
> zeroed", how does it "zero on the fly", and why is it so useful?
Try to imagine a way to do it and you'll see it cannot be done on any
other tensiometer because the measurement is generally made by the
depressing anvil. That is why my instrument starts out with an
undeflected spoke against which the dial of the micrometer is zeroed
(rotated) with the thumb before applying the load. For such small
deflections otherwise undetectable kinks in spokes can be nulled, and
they occur as is evident from use.
>> About 2kgf gives a deflection of around 0.4mm, a useful deflection
>> yet one that does not change existing tension because the length
>> change it causes is diminishingly small.
> If tension/length is changed, by a known amount, why can't the
> additional tension be calculated and canceled out? Is it likely to
> be harmful to the spoke?
Because it depends on spoke length, diameter, number, and rim
stiffness, all basically unknown effects. Therefore, making any
length changes is an invasion on what you want to measure.
>>> Would smooth round posts with lubrication at all 3 points of
>>> contact (2 loaded, 1 unloaded) in my design do nearly as well?
>> No but your method would not cause any length change in the
>> measurement length so friction is not a problem. There are a few
>> problems in your design, one of them being that the three pegs
>> cannot be in a straight line because deflections need to be kept to
>> size that is far smaller than what a pin that could support the
>> load could take. The concept is good but it defies execution in
>> the range of forces involved.
> That's exactly what I was aiming to figure out from the "safe
> elongation" of a spoke, or compute using spoke elasticity data.
Let me emphasize that paragraph. There would be no length change in
the gauge span and therefore no need for anti-friction bearings. The
size of the test load would determine the amount of length change
(cosine error).
>> There is the killer. Deflections must be kept to less than 0.5mm
>> (0.02") or the measurement will be too intrusive. That is to say,
>> the measurement result will be rim and spoke length and number
>> dependent.
> A flimsier rim would cause a different reading, I hadn't considered
> that. Nuts.
>> Give the concept some more thought. Maybe you can devise a
>> configuration that can be made to work. The concept is not bad but
>> it seems to lie beyond implementation in the constraints involved.
> I'd considered some alternate configurations, but they aren't
> fundamentally different in construction from Wheelsmith's design, and
> require similar tolerances. With access to a machine shop, building
> one might save me money, but that wasn't my purpose.
That design was made by Norm Ogle, a clever engineer and bike rider
who died of degenerative causes at an early age. I am surprised that the
instrument is as expensive as it is considering that it has so few and
simple parts. The spring requiring the most accuracy.
The instrument shown in "the Bicycle Wheel" was sold for about $250 at
the time it was on the market, the dial gauge being the main expense.
DT sold most of them in Europe, there being little interest here in
the USA at the time.
Chris Holliday
<jobst....@stanfordalumni.org> wrote in message
news:0iEG8.549$3w2....@typhoon.sonic.net...
>
> Just the contrary. You can readily use your name because you have
> nothing to hide or have said previously. Besides, it's rude to talk
> to people with the visor of your armor closed, incognito.
Imagine... Jobst calling someone rude.
Seb
|nothing to hide or have said previously. Besides, it's rude to talk
|to people with the visor of your armor closed, incognito. This is
|part of common courtesy that doesn't hurt. You must not understand why
|most contributors here do not hide behind "handles".
Nope, I don't understand. "Seb" is what my mother calls me, so I figure its
good enough for people I'm conversing with via open public correspondance.
I'm no more disguised here than I am in public. Comparing a nickname to armor
is faulty- its no more a disguise than dying your hair might be, and is used
for more or less the same reason. Iv'e got many friends from the net who I
know only by "handles", and even when I've met them and they have stayed at my
house, thier actual name was still irrelevant, and never came up.
I think the issue here reflects a sort of generational difference; to say
something is "rude" is to assume your culture applies to others. I find an
unwillingness to accept what somebody chooses to call themselves to be rude.
I'd never presume to ask somebody for thier "real" identity (as if there was
such a thing, outside of arbitrary governement standards) unless it was
directly pertinant (ie, to legal procedings)- that's common courtesy to me.
Doing otherwise is a sign of the kind of distrust I only expect form decpetive
people or legal officials.
|Your suggestion that you have a simple way of measuring tension
|implies that you think it is simple at best, or that those who make
|them are unclear on the concept at worst.
I thought maybe more expensive instruments had certain features I was willing
to do without, through some simplification, by accepting a larger margin of
error, and by using a measure of "brute force". However, I was unable to
describe this "simplefied" measuring device without a diagram and a page of
text. I don't think that suggests I think it is simple, or that other designs
are flawed.
I didn't mean to imply anything, and am suprised you felt those conclusions
could be drawn.
|You would do well to build a prototype and investigate the effects
|before proposing what you have. You are asking the net to do your
|R&D, at least in the theoretical realm, before you have an idea of
|how to accomplish this beyond sketchy ideas.
The net did not have to respond. If it had not, I'd have continued with less
information.
I didn't think my request was disruptive. I've seen some pretty sketchy ideas
and uninformed questions genrously answered without hostility or resentment-
that seems a normal and accepted purpose of Usenet.
|>>> Since "It is not necessary to know the actual tension but only
|>>> that the tension has reached the desired mark",
|>> I think you have a contradiction there. Knowing you are at the
|>> desired mark IS determining the actual tension. I don't see how
|>> else you can define that.
|
|> The words in quotes are from your own book (p. 118 3ed), and contain
|> the entire contradiction. How would you define the difference?
|
|Vague insinuations will get you nowhere.
It wasn't intened to be vauge, or an insinuation. It was just a direct
question.
The distinction seems present in your text, but you obviously feel
differently, so I probably mis-understood your text. If you care to clarify,
fine. If not, I would have accepted a clear stement of that, but I can't
"define" something I mis-understood.
|> Yes, so I am finding. They can be built fairly easily and
|> calibrated with a test mass, but that still isn't free, and might be
|> an equal waste of time.
|
|Oh oh. Here we go again. Next I see that you want to wind your own
|springs and make steel shapes.
I don't see that in what I said. Difficult, time consuming construction is
the opposite of what I wanted.
Indeed, it seems the deflections involved would be so small that such
lightweight constructions would be pointless in a design like I was
attempting.
|In that case I suggest you do that and don't use this forum as a
|scratch pad for Idle conjecture. It's not as though you proposed
|specific questions but rather you made a grand "open system" proposal.
A notable portion of usenet is idle conjecture, which nobody is compelled to
respond to. I'm sorry if my language seemed grandiose- I was just stating in
as clear terms as I could that I was not using the idea commercially (if it
was ever potentially useful in that way), and trying to prevent potentail
commercial (ab)use of ideas from other usenet contributors who were generous
enough to answer.
<Seb sniping some lengthy history / spoke info>
Thanks for sharing that truly interesting and informative discourse.
-Seb