Alternative ways to calibrate a spoke tension meter

lefthanded · Feb 18, 2023

I got one of these ZTTO TC-02 spoke tension meters. Of course it's not calibrated and its readings are way off. Does anyone know of a calibration method that does not involve a crane scale?

I'm thinking I could measure the spring force required to obtain a specific millimeter reading on the gauge with a kitchen scale and some simple maths.
What's missing is the knowledge how much force it takes to deflect a spoke (of a given diameter) by a certain distance (between the bolts where it rests on) for a specific tension.

Any ideas?

arnea · Feb 18, 2023

Sure.

Spoke tensiometer calibration ghetto style

Many people have built devices to calibrate the spoke tensiometer. Some of those devices are really beautiful. Like this Swiss-made tool: Blackcat wheels: Spoke tensiometer calibration jig - production version! Or simple food fixtures with crane scale. Like this one: Spoke Tension Meter...

www.mtbr.com

lefthanded · Feb 18, 2023

arnea said:
Sure.

Spoke tensiometer calibration ghetto style

Many people have built devices to calibrate the spoke tensiometer. Some of those devices are really beautiful. Like this Swiss-made tool: Blackcat wheels: Spoke tensiometer calibration jig - production version! Or simple food fixtures with crane scale. Like this one: Spoke Tension Meter...

www.mtbr.com

..and without the use 100 kg of mass ;-)

evernorth · Feb 18, 2023

lefthanded said:
..and without the use 100 kg of mass ;-)

Not really. You need a reference that you know the exact value. And 100-125 kgf is the typical value needed for wheels.
Doing it halfarsed would be pointless since we are speaking about calibration

Maybe ask someone who has a calibration jig to do it for you

lefthanded · Feb 18, 2023

evernorth said:
Not really. You need a reference that you know the exact value. And 100-125 kgf is the typical value needed for wheels.
Doing it halfarsed would be pointless since we are speaking about calibration

Well, what I want to do is a calibration, too. Just with some added math because I measure a different quantity. It's the working principle of spoke tension meters that the force and deflection are the same for all spokes of the same kind. I can measure the deflection, and I can measure the deflection force. I only need to know what deflection force corresponds to what tension.

evernorth said:
Maybe ask someone who has a calibration jig to do it for you

I will be very suprised if anyone I know has such a thing. It usually would be me, but obvisouly I don't have one

TandemBear · Feb 18, 2023

lefthanded said:
I got one of these ZTTO TC-02 spoke tension meters. Of course it's not calibrated and its readings are way off. Does anyone know of a calibration method that does not involve a crane scale?

I'm thinking I could measure the spring force required to obtain a specific millimeter reading on the gauge with a kitchen scale and some simple maths.
What's missing is the knowledge how much force it takes to deflect a spoke (of a given diameter) by a certain distance (between the bolts where it rests on) for a specific tension.

Any ideas?

Dan Burkhart did exactly this! I was needing the very thing, as my Ice Toolz spoke tension gauge had a very limited calibration chart to begin with, which was then rendered useless by years of use and myriad other spokes being used (Mavic Ksyrium aluminum, for example).

So I came across this video and it's an ideal solution:

I made mine with hardwood, which is less than ideal. A steel square tubing rig like Dan's is far better. But for my uses, it's just fine. I think my guage's error is probably greater than the flex my wooden jig imparts on my calibration.

Good luck.

lefthanded · Feb 18, 2023

TandemBear said:
Dan Burkhart did exactly this!

What was the result?

TandemBear said:
So I came across this video and it's an ideal solution:

This is exactly what I don't want to do, hence alternative ways

TandemBear · Feb 19, 2023

So you want to figure out a way to use math to determine deflection values for a given spoke material and cross-section?

Spoke materials vary from brand to brand, and spoke shapes and diameters vary from model to model. So if you WANT to find some magic formula to calculate expected deflection values for a given spoke, then great. Have at it.

But when building and servicing various wheels, I don't want to go through the rigamarole of making guesses, assumptions and plugging in values of varying accuracy to determine an end result of questionable veracity. This is about the LAST thing I'd want to do when repairing and building quality wheels is my end goal. I'd much rather simply KNOW what deflection values are.

Thus the use of this jig. I get a wheel in the shop, I remove a spoke and determine its ACTUAL deflection values for THAT spoke with MY meter as it's currently "calibrated." No guesswork, no math, no assumptions, and thus no questionable results.

I'll admit that I'm NOT that concerned about perfectly accurate "end" spoke tension values. Once I'm in the 110-120 kgf range, I'm fine. Unless I'm finding myself in that unenviable position of having DS spokes reaching maximum tensions, while the NDS spokes are barely high enough to be considered "acceptable." And this is EXACTLY why I use my jig - so I know I'm within enough error to be at the tensions needed. At the same time, it's CONSISTENT tensions throughout the wheel that I know are most important and result in the most durable, reliable wheel.

But perhaps I'm misunderstanding your entire goal here. Take my experience for what it's worth.

lefthanded · Feb 19, 2023

TandemBear said:
So you want to figure out a way to use math to determine deflection values for a given spoke material and cross-section?

No, not really.

I want to know, say how much force by my tension meter does it require to deflect a DT Swiss 2.0/1.8 mm spoke tensioned to 1000 N by 2.8 mm.

If I know that, I use a kitchen scale to set the tension of the spring in the tension meter with a kitchen scale:

The force needed on the kitchen scale can be easily calclated from the levers. Then I tweak the spring tension until I read a deflection of 2.8 mm.

I would call this a real calibration, and we could all calibrate our ZTTO TC-02 to the same reference chart (maybe even the one that comes with the tool).
Just measuring the response with a jig isn't really calibrating the measurement device but is only creating a look-up table for a randomly adjusted tool.

So if anybody has a ZTTO TC-02 and a jig and has a good (verified) reference chart (preferably the original chart for 2.0-1.8mm), could you share your chart and the "weight" from the sketch for any point in the chart?

TandemBear said:
I get a wheel in the shop, I remove a spoke and determine its ACTUAL deflection values for THAT spoke with MY meter as it's currently "calibrated."

Sounds like a lot of work. Neither DT Swiss nor Park Tool recommends this approach, AFAIK. Why would need to recreate your look-up table for every wheel? A DT 2.0 mm spoke is a DT 2.0 mm spoke. No?

Mikevdv · Feb 19, 2023

I used two bathroom scales and a chunk of metal between them with a hydraulic jack. I had this crap laying around

it was fussy as you had to tighten each nipple
Individually to ensure the tensions were the same but got the job done

Crane scales can be had cheaply on AliExpress

J.B. Weld · Feb 19, 2023

lefthanded said:
I got one of these ZTTO TC-02 spoke tension meters. Of course it's not calibrated and its readings are way off.

Curious, how do you know it's way off?

scoon · Feb 19, 2023

I have built hundreds of wheels during my 30 years behind bars. Even though what you are trying to do is not recommended, I really appreciate your creativity and honestly look forward to what you discover.

arnea · Feb 19, 2023

lefthanded said:
The force needed on the kitchen scale can be easily calclated from the levers. Then I tweak the spring tension until I read a deflection of 2.8 mm.

How do you plan to tweak the tension of the spring? Best you could do is to preload it, but it's not the same thing.

lefthanded said:
I would call this a real calibration, and we could all calibrate our ZTTO TC-02 to the same reference chart (maybe even the one that comes with the tool).
Just measuring the response with a jig isn't really calibrating the measurement device but is only creating a look-up table for a randomly adjusted tool.

So "reference chart" isn't a "look-up table"? I looked at the images in the web and as expected TC-02 has dial that is calibrated in mm, so one needs reference chart or look-up table to convert mm to N-s for particular spoke.

lefthanded said:
So if anybody has a ZTTO TC-02 and a jig and has a good (verified) reference chart (preferably the original chart for 2.0-1.8mm), could you share your chart and the "weight" from the sketch for any point in the chart?

I looked at the drawing and knowing how this type of tensiometer works your plan doesn't make sense to me. Perhaps I'm missing something obvious I cannot see how you could measure the force created by the spring using this method. You should put the kitchen scale between the end of spring and one arm - this is only way how to measure the spring force. But I cannot see how to do it in practice.

lefthanded · Feb 19, 2023

Mikevdv said:
I used two bathroom scales and a chunk of metal between them with a hydraulic jack. I had this crap laying around

That's a cool idea

Mikevdv said:
Crane scales can be had cheaply on AliExpress

I don't want to wait for a month, and I also don't want to build (and own) a jig. Just another item that's rarely used and would take up space.

lefthanded · Feb 19, 2023

J.B. Weld said:
Curious, how do you know it's way off?

It reads about 700 N for all my wheels, and I know that that's not the true tension in them. Experience.

lefthanded · Feb 19, 2023

arnea said:
How do you plan to tweak the tension of the spring? Best you could do is to preload it, but it's not the same thing.

Yes, changing the preload. What's wrong with that? That's how Park TM-1 is calibrated and I'm sure DT Swiss's meter, too.

arnea said:
So "reference chart" isn't a "look-up table"? I looked at the images in the web and as expected TC-02 has dial that is calibrated in mm, so one needs reference chart or look-up table to convert mm to N-s for particular spoke.

Yeah it is. What I meant, is the reference chart is a universal look-up table such that the readings of every "calibrated" device means the same. Adjusting the device at a small number of reference points to the reference chart / look-up table instead of creating look-up tables with dozens of data points over and over for randomly adjusted tools.

arnea said:
I looked at the drawing and knowing how this type of tensiometer works your plan doesn't make sense to me. Perhaps I'm missing something obvious I cannot see how you could measure the force created by the spring using this method. You should put the kitchen scale between the end of spring and one arm - this is only way how to measure the spring force. But I cannot see how to do it in practice.

The preload force of the spring between the handles (if that's what you propose to measure?) isn't relevant to know at all. What matters is the force required to depress the handle to a certain reading on the gauge. That I can measure with the setup I sketched. The exact same force (after the lever ratio) is pushing at the spoke.

We should all calibrate our TC-02's with a kitchen scale. We just need one person who creates that calibration chart with their jig. Anyone?

lefthanded · Feb 19, 2023

lefthanded said:
We should all calibrate our TC-02's with a kitchen scale. We just need one person who creates that calibration chart with their jig. Anyone?

I try to summarize how this could work:

Someone with a calibration jig adjusts their tension meter to the manufacturer reference chart (can be found at Spoke Tension tables – A database of tension meters and spoke tension charts). Let's say such that 102 kgf on a 2.0/1.8 mm spoke equals 2.80 mm reading. Then they verify that the manufacturer's reference chart is good in the first place and test the readings at the other tensions in the chart. This ensures that this device is able to reproduce the manufacturer's reference chart.

Then they use the proposed setup with a (digital) kitchen scale to measure the "weight" required for each millimeter reading in the chart. A scale that goes up to 3 kg is enough, I believe. It should be made sure that the angle of the lower handle of the tension meter is such that the force is pretty tangential, which is the case when the lower handle held at a small angle with the scale. I tested this and I can read the tension meter gauge and the kitchen scale no worse than 1% while pushing the meter onto the scale. It might require a little bit of patience and a hand that's not shaking. Alternatively, one could video tape the gauges while pushing down the meter slowly and get the readings from the video.

lefthanded · Feb 20, 2023

I took the TC-02 apart. Interestingly, the pivot is made from two thrust (axial) ball bearings, not from radial bearings.

lefthanded · Feb 20, 2023

This is how other industries do it

Nice that they have a dial that displays tension directly. Not even the $600 and $1500 DT Swiss Tensio meters have that. (Why DT up-charges $900 for a digital dial indicator would be a totally different topic.... Spoke Tensiometer)

lefthanded · Feb 20, 2023

That's a great idea to check the meter is still calibrated before

Put an allen key aside that you never use for anything else such that I won't be bent.

Alternative ways to calibrate a spoke tension meter

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arnea

Spoke tensiometer calibration ghetto style

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