Ronno6

Do any of you guys use a Hozan C-737 Spoke Tensionometer??
I have used one for many years, but have never been certain about the calibration.
The tool was accompanied by a chart depicting the spoke tension plotted against the
deflection reading on the dial indicator.
For reference, one complete 360° sweep of the dial indicator is 0.10mm. That deflection
translates to about 40kgf tension on a 14ga high carbon steel spoke (useless for SS ?)
The graph pretty much goes vertical in the kgf value (max 150kgf shown) when the dial indicator approaches 0.15mm deflection on the dial indicator. That is the limit of the graph.
Using the musical pitch method seems to reconcile at about 0.19mm on the dial indicator.
I have typically used 0.18mm to 0.19mm as the proper tension range for 14/15/14 spokes, and a tad higher
for 14ga straight (0.20mm reading.)
All spokes I use are stainless.

As these readings are off the graph, I do not know what the actual tension is....

Does anyone have experience with this tool?

JohnDThompson 

We used them at Trek. I calibrated them using a strain gauge with known tension on a spoke.

N.B. my experience is that they didn't stay calibrated for very long, but then again, we were churning out dozens of wheels a day.

FBinNY 

Like other tension meters, this one has a baseline offset based on the thickness of the spoke that's being measured. Then chart therefore needs to be specific for every spoke gauge.

In any case, I'm no sure I understand the problem. Are you saying that you tension your wheels to over 150kgf and the meter doesn't go that high.

FBinNY 

If it's simply a question of calibrating, it's not a difficult DIY needing no exotic or specialized equipment. For one method, you'll beed a spoke & nipple, some metal objects to hold them at both ends and apply tension, then some rope, a tree and a friend of known weight of roughly 100kg.

Use the rope and brackets to improvise a rope swing on a tree branch with the spoke midpoint. Have your friend sit to load the swing, then take a tension reading. This establishes the correct value at that weight, and the tool can either be adjusted to the chart, or the chart values offset to match the reading.

If you have no chart, you can generate one using the same method and a few friends with weights spanning 50kg or so to the top. You only need two, but using 3 or 4 will help correct any errors caused by a single error.

When you're finished, don't forget that whatever calibration you get is still only right for that spoke gauge. If you want to measure various spokes, you have to generate charts for each.

Ronno6

I suppose that I should have stated that the included graph had 3 spoke gauges listed: 14ga, 15ga, and 15-16-15ga, each having their own curve.

The dial indicator would keep spinnin' 'round and 'round, depending on the tension of the spoke: the higher the tension, the more revolutions it would make. As such it could measure tension far in excess of 150kgf. 150kgf is just the highest tension shown on the chart, at a maximum graphed indicator reading of 0.150mm.
What I am saying is that, using the deflection indicated by the indicator, I am applying tension in excess of the included chart.
But, again, the chart is given for high carbon steel spokes; I would have to believe that SS has a different modulus of elasticity, hence the actual tension would differ from that on the graph.

I usually try to get proper spoke tension using the musical note method (depending on spoke length and gauge), then use the tensionometer to achieve uniformity to the best of my ability.

FBinNY 

There isn't enough difference in Youngs Modulous between Stainless and Carbon steels to fret over. If you're readings are beyond the chart, either you are in fact building overly tight wheels, or the unit needs recalibration.

Probably time to find a tree and recruit a friend or two.

Ronno6

John Allen describes the G pitch of a properly tensioned 292mm long straight gauge spoke as being "approximately 1/3 of the yield strength of good-quality spokes," but never specifies what that force is on that spoke in kgf.

Where can I find a value for that specification?

I really don't want to gang up a bunch of heavy friends til a spoke breaks, but I guess I could keep adding weight to the rope swing spoke til I achieve the G pitch......

gsa103

You're over thinking it.
A spoke with a 90kg weight hanging off it has a tension of 90kgf.
The reason to achieve a specific pitch is when you don't know the tension, and want to calculate the tension based on the pitch (and linear density of the wire).

FBinNY 

The cross section area of a 2mm (0.80") spoke is about 0.005sq". You can use 75,000psi as a rough guide for minimum tensile strength, so breaking load is in the range of 375#s or so.

Actually it's a bit lower since the shear strength at the elbow is roughly 80% of tensile. Likewise the tensile at the root of the threads. So any friend under 300#s is safe.

The above are very conservative figures for the alloys in annealed condition. Heat treating, and cold working processes can more than double these values.

FBinNY 

Yes, I guess I should have mentioned that my method gave a direct reading of tension load. I omitted it because I thought it was obvious.

Ronno6

So, 375# translates to 170kgf?? 375#/2.2lb/kg ??
That doesn't seem like very much.
That would translate to 56.67kgf if John Allen's assertion that the spoke is properly tensioned at approximately 1/3 of yield.........

FBinNY 

You have to read posts to the end. That's were I said that these were the most conservative values, and spoke tensiles could be more than double that.

OTOH - we also have to be careful about confusing yield and tensile strengths. IMO Mr. Allen's assertion is off and I suspect that he might have meant 1/3 of ultimate (tensile), not yield strength.

But as someone else suggested, you're over thinking this. You don't need to get super deep into the science as long as you're working within long established rules of thumb.

I was building wheels for years and even decades without ever having any idea about the tension. I developed decent, experience based, sense of what a "tight" felt like, and that has served me well, and still does. So, though I know the science, I don't think about a all when building wheels.

You have an instrument, take the time to calibrate it, or send it off to someone who can do it for you, then use it to advantage when you build wheels.

Darth Lefty 

The pitch actually has nothing to do with the stiffness of the spoke. (It definitely has nothing to do with the strength, which only matters when it yields.) The note is set by the inertia of the spoke going side to side, and the tension. You can do the math, the formulas are here:
https://en.wikipedia.org/wiki/String_vibration.


The John Allen article is here. His table corresponds to more or less the same kgf for straight and DB, 135-140 ish. That's the same kind of number you see from rim manufacturers. That means the DB spokes get higher strain, about 50 Mpa, he quotes strength as 150 Mpa or higher which is pretty plausible. Steel is amazing stuff.
Bicycling - Wheelbuilding: check spoke tension using musical pitch

I found lately that the Gates belt drive tension app for smart phones works fine for this, if you want to do it this way. There are also guitar tuning apps.

Dan Burkhart 

Roger Musson has an informative write up on tension meters on this page.
Wheelbuilding spoke tension and tensiometers
If you follow the page down to where he discusses calibrating your own tension meter, he has a link to my video showing the calibration device I designed and built.
It's a bit over the top for somebody who just builds the occasional wheel, but I build hundreds of wheels a year, and consistency is important.

Ronno6

FB, I apologize for using the numbers you applied without taking your caveat into consideration. I see that DT does, in fact, heat treat their spokes.I wold have to believe that other makers do as well. Things would be so much clearer if manufacturers published the strength values for their spokes.

Darth, I understand that the musical pitch is a result of spoke tension and other dimensions, not stiffness.

Dan, thanks for the links. Great info and insight.

Much of this is the result of some wheel failures I have seen lately.
My riding buddy has a Trek which he purchased new about 8 years ago.
While performing maintenance on his bike, I found several cracks on his rear wheel at the nipples. His wheel was WAY overtensioned, registering almost .30 on my tensionometer! Unless the bike shop had done that, they had to have come from the factory that way, because my friend had never touched them. Of course, I replaced rim and spokes.
I suffered a spoke failure on a front wheel recently. The wheel was 28 radial 14ga spokes tensioned as I usually do. The spoke broke at the nipple. Rim to flange orientation is correct. Maybe crevice corrosion??

From what I have been able to glean from the plethora of info on the web, proper spoke tension seems to be in the 100-110kgf range, except for the link Dan posted, The author uses 125kg as rule of thumb, and only a "little lower" if the rim manufacturer specifies lower figures.

I guess what this all boils down to is that, as directed, I need to calibrate my Hozan for the various spokes with which I build.

Thanks, y'all...

Darth Lefty 

Just some added references

Velocity
DT Swiss rim model R 460
which is 122 Kgf. All the other rims seem to say the same thing, even the fat bike rim which seemed a likely candidate to be different.

Wheel Tension Measurement | Park Tool has a list of Bontrager, Campy, Mavic, and Shimano wheels, with some values that seem strange, but are mostly in the 90-140 kind of zone, higher in the rear

Wheelbuilding spoke tension and tensiometers by Roger Musson, the author of one of the popular wheel building books

superstring

Ronno6, you might like to have a look at this:

Dan Burkhart 

What kind of a crackpot inventor came up with that idea?

superstring

Crackpot inventor?? I think it's pretty cool.

Darth Lefty 

It's hard to get credit on the Internet, isn't it? Even when your name is on it.

FBinNY 

Irony is not dead yet.

Dan Burkhart 

It was my lame attempt at self deprecating humor. If you didn't know, that was my video.
Oh, and thank you.

Ronno6

Yup. I have watched it.
Fascinating..............

Looks like I will be ordering special double-ended threaded spokes from my Spokesman......

Dan Burkhart 

I have since adapted the fixture to fit unaltered spokes.

superstring

Ahh.... I get it. Sorry, Dan, and yep, I think it's pretty ingenious.