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  1. #1
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    Reputation: WheresWaldo's Avatar
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    Spoke Tensiometer Calibration Device

    I decided a couple of months ago that I wanted a way to double-check the calibration on my 10+ year old TM-1. Without sending it back to Park Tools, there is no cheap way to do this yourself. My goal was to design a calibration rig that was cheap, easy to build, and has repeatable accurate results. I have gotten much further along and have a working version of the Spoke Tensiometer Calibration Rig. It is still missing a part (Thrust Bearing) and there are a couple of things I would change but here it is:





    In the picture above the spoke is being pulled with 102.7 kg so the spoke tension is 1000 newtons. I double checked my Park Tool TM-1 chart together with my rarely used TM-1 and it was close. The TM-1 was one marking too low with a 1.8 mm spoke. So here is the parts list.


    • 2 - 2020 Series x 200 mm T-Slot
    • 2 - 2020 Series x 500 mm T-Slot
    • 4 - 2020 Series Corners (or 3D printed equivalents)
    • 8 - M5 x 10 mm Button Head Screws
    • 8 - M5 T-Slot Nuts
    • 1 - M8 x 35 mm Button Head Screw
    • 1 - M8 Washer
    • 1 - M8 Flat Thumbscrew
    • 1 - M8 x 200 mm Threaded Rod
    • 1 - M8 Hex Bolt
    • 2 - M8 Acorn Nuts
    • 1 - 8 mm Roller Thrust Bearing
    • 2 - M8 Clevis Rod Ends
    • Small Crane Scale (150 kg or more capacity)
    • 1 - Brass Spoke Nipple
    • Some 3D Printed Parts


    This list will build the model with the items I would do differently. The difference is that the pictured version uses an M6 Threaded Rod and that should change to an M8 or M10. It is not a strength issue, it is a space issue. Besides this you need a few drill bits and a way to drill straight holes. Some Allen Head Hex Wrenches and some time to print the 3D parts and putting it all together. Total cost building this was under $80 USD.

  2. #2
    Rub it............
    Reputation: frdfandc's Avatar
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    How much would have it cost to send to Park for recalibrating?

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  3. #3
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    I was thinking of checking mine with a 2x4 and a big sack of concrete.
    But, yours is a lot nicer!
    BANNED

  4. #4
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    @frdfandc, no one cares

    @duriel Yep, that works too!

    I built this because;

    1. I could,
    2. I wanted to share,
    3. Commercial ones, and there are a few out there, cost anywhere from $400 - $700 USD,
    4. I built my own tensiometer and wanted to calibrate it myself.
    5. Lastly, I don't want to send my TM-1 through the postal service.


    Here is how I perceive its use: Once you figure out what spoke tension you want to build to, lets say for sake of argument you want a front wheel spoke tension of 1100 newtons. Turn on the scale with no spoke attached. Place a single front spoke in the rig. Tighten the wheel until the it reads 112.2 Kg (N = Kg X g or conversely 1100 N / 9.80665 = 112.2 Kg in our example). Measure the tension with your Tensiometer of choice. You now have the exact deflection reading for that exact type of spoke for this particular wheel build.
    Last edited by WheresWaldo; 2 Weeks Ago at 06:42 PM.

  5. #5
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    Quote Originally Posted by frdfandc View Post
    How much would have it cost to send to Park for recalibrating?
    I don't think cost is the real issue with doing this. It more that:

    1) The Park TM-1 is not a precision device. There is no guarantee that if you send it back to Park, it will be calibrated right.

    2) You drop the TM-1 once and that in itself can throw it out of calibration, not to mention tiny screws that loosen including the arrow that points to the numbers. Back to square one. There is also no guarantee it won't get tossed around in the mail and thrown out of calibration even before you receive it back from Park.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  6. #6
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    Quote Originally Posted by Lombard View Post
    I don't think cost is the real issue with doing this. It more that:

    1) The Park TM-1 is not a precision device. There is no guarantee that if you send it back to Park, it will be calibrated right.

    2) You drop the TM-1 once and that in itself can throw it out of calibration, not to mention tiny screws that loosen including the arrow that points to the numbers. Back to square one. There is also no guarantee it won't get tossed around in the mail and thrown out of calibration even before you receive it back from Park.
    I don't think it's that delicate. Something would have to bend to thrown it out of calibration. As you said, it's not a precision device; nor does it have to be. The tension of spokes in wheels work over a wide range. Absolute spoke tension is not that critical. You don't even need a tensiometer to build a reliable wheel.

    While this calibration device is nice, unless the weigh scale is calibrated, you're just calibrating one out of calibration device with another, and the calibration has no credibility, so I recommend checking the scale with a known weight of about 100kg.

  7. #7
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    Good job on the calibration device. Lots of plans for them on line too to look at for additional ideas.
    While ultimate tension readings are great I find the beauty of tensionometers is being able to quickly check for even tension, spoke to spoke on a given side. You can set ultimate tension however you like (meter, feel, tone) and use the meter for quickly setting spokes evenly to whatever that is.
    Good luck

  8. #8
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    Chinese electronics, although better than they were even 5 years ago, can be suspect. Yes the scale you use will make a difference and calibration of the scale is critical. I did check this particular scale with a small C6 calibration weight and it was on spec. but YMMV. My decision to build this was, as I mentioned to calibrate my 3D printed clone of the DT Swiss Tensiometer. I still have my 10+ year old TM-1 and it works for what it was designed for. While knowing the exact number of newtons a spoke is set to in a wheel has little significance in the real world, it is just nice to know you are in the ballpark and not significantly off. Using this rig my TM-1 was over-reading the tension so my wheelbuilds were not up to the tensions I expected. Not a real issue at the low end of the spectrum but when you are building at the higher end the actual amount it was off was not insignificant.

    When I searched for plans to build one of these, I saw quite a few forum posts that showed how someone built ones for themselves. Some threads even had suggestions on how to build one, but no one showed a complete parts list or suggested how to use one. There were a few commercial ones built by wheelbuilders that they sell on the side at 4 - 6 times the cost of this rig. I understand making money, I do that too, but there needs to be options for people that just are hobbyists and not professional wheelbuilders.
    Last edited by WheresWaldo; 2 Weeks Ago at 06:43 AM.

  9. #9
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    As a person who regularly calibrates machinist's tools at my job, my only real question is this: Do you have a set of calibrated weights to calibrate the scale? If not, then you are just calibrating a tool on an uncalibrated device. In that case, the 'sack of concrete' suggestion is really just as valid a method, and more efficient of time......
    "L'enfer, c'est les autres"

  10. #10
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    I have a Class 6 set of calibration weights, of course not the most accurate, but good enough for this application.

    Your suggestion of a "'sack of concrete' suggestion is really just as valid a method, and more efficient of time" has no basis in fact. It presupposes you 1. have a bag of concrete, and 2. that none has spilled out, and 3. you have a way to attach a spoke to something rigid and the 'sack of concrete'. Nice try

  11. #11
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    Spoke thickness variation makes a huge difference in accuracy. See https://www.wheelfanatyk.com/blog/tension-inaccuracy/

  12. #12
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    Quote Originally Posted by WheresWaldo View Post
    you have a way to attach a spoke to something rigid
    That's what the 2x4 is for!
    ... and I would use the spoke (to resolve the gauge issue) that I'm using on the wheel, so it would be accurate for my wheel!!!!
    BANNED

  13. #13
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    I made such device. Commercial price is 550 USD for base only or 650 USD for base + digital scale (steinberg, made in germany). Device can take also load cell - price on demand. More details here:
    https://www.blackcatwheels.ch/2019/0...ation-jig.html

    Spoke Tensiometer Calibration Device-v1_1.jpg
    Last edited by blackcat_wheels; 1 Week Ago at 07:38 AM.
    Custom wheels handcrafted in Switzerland
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    https://blackcatwheels.ch/

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