WheresWaldo

This was originally posted in my thread on 3D printed bike accessories and mounts. I have built a working version of the Spoke Tensiometer Calibration Rig. As pictured 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 500 mm T-Slot
• 2 - 2020 Series x 200 mm T-Slot
• 4 - 2020 Series Corners (or 3D printed equivalents)
• 4 - 2020 Series Corner Plates (or 3D printed equivalents)
• 24 - M5 x 10 mm Button Head Screws
• 24 - 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 - M8 Hex Nut
• 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

Tools to build it

• 8 mm drill bit
• 4 mm drill bit
• 3 mm hex wrench
• 5 mm hex wrench
• 3D printer or equivalent off the shelf parts.
• Time

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 way to drill straight holes. Total cost building this was under $80 USD. I will post an updated picture and a Thingiverse link to all 3D printed parts used.

I have a second design I am working on that replaces the threaded rod with an acme lead screw for smoother operation and uses a base load cell and digital readout.

Here is how I perceive its use. For example you wanted to build a front wheel and your desired outcome is a 1200 N spoke tension:

1. Turn on the scale with no spoke attached, this will tare the scale (zero it) with no tension at all.
2. Attach spoke you are using for this build into the rig, it should be obvious how.
3. Turn the wheel until the Kg scale reads 122.4 Kg. (newtons = kilograms x gravity or conversely 1200 N / 9.80665 = 122.4 Kg in our example)
4. Measure your deflection with the tensiometer of your choice.
5. Use that deflection to build your front wheel.

No more guessing, no more charts. If you need to ask, I designed and built this:

• Because I could
• I wanted to share
• I designed my own DT Swiss style clone tensiometer and wanted to check its calibration as well as double check my Park Tools TM-1

Hoopdriver

Thanks for posting this. It certainly would work to satisfy the question about whether my Park tool is still on the money. I wonder about the accuracy of some of the cheap chain scales, though.

dedhed

Are there any provisions on the meters to recalibrate them?

WheresWaldo

Some of the scales will let you calibrate them with a known weight. I happen to have a calibration weight set that is 2.5 kg total and I have tested my particular scale and it was on spec, YMMV. I don't remember if this scale allows recalibration as I lost the one page instructions.

That is also why I have a second version in mind that uses a larger load cell and a digital load cell indicator, those have a lot more flexibility in how you verify that the load cell is reading correctly. The problem is I was trying to keep the design under $100 USD, which I did. The load cell and digital indicator raises the price by $40 - $60 USD.

As I mentioned in the OP, My Park TM-1 was reading one mark higher than normal, so if it registered a 21 on the scale the real reading was a 20, that was measuring a few 2.0 / 1.8 / 2.0 double-butted Wheelsmith spokes I had laying around.

63rickert

Before doing all the work involved in building that rig consider sending the tool back to Park. They have calibration service.

Nessism

Awesome work! Love it when someone takes on a project like this!

Question: have you checked at lower tensions? The knock against the TM-1 is that the spring force is too high to accurately read at say 60kgf. Also, have you checked the Park app for accuracy when using oval spokes such as CX-Ray's? There chart doesn't match these but Park has an app, but some confirmation would be nice.

WheresWaldo

@63rickert, you miss the entire point of this project. Of course I could send it back, but why? And now I never have to.
@Nessism, My thought on this is why have a chart at all? And if your tensiometer drifts over time, why fret? The TM-1 lists for $85, remarkably the cheapest tensiometer on the market. Building this turned out under $80. Also my stash of CX-Rays are under a pile of boxes in my garage, so I haven't checked with those yet. I have checked this against some Wheelsmith and DT Swiss round spokes.

Before beginning a wheel build you already have in mind a target spoke tension for front and DS rear wheels. Maybe it is based on experience or maybe it is based on some other limiting factor like rim strength. You may already have the spokes in mind, say Sapim CX-Rays, for example. Just pop a CX-Ray in the device before the wheel build and turn the adjusting wheel and when you reach the desired tension, measure the deflection. That is it, no chart, no wondering if the chart is right, just build. If you went cheap and bought a Chinese clone of the Park TM-1 or a clone of the DT Swiss TETTA or TETTD it won't matter, because basically you are calibrating it for each and every build. It is also much harder to lose a machine like this compared to a chart printed on paper, and no internet access needed to use the online Park application.

Of course most people don't need or want a device like this, that isn't why I did this. Also note that I freely gave all the information away, so there isn't any money making intention here.

About 10 years ago I had two heart attacks while riding my bicycle with my daughter. I passed both off as breathing cold air on the two January rides. My cardiologist at the time was frantic when I came in the following week and the first thing he said after seeing my test results was "you should be dead!" When I asked why I wasn't he specifically told me that all the cycling I was doing is the only thing that saved my life. An every other day stress test that strengthened other areas of my heart. Since I literally (correctly used in this instance) owe my life to cycling, projects like this are my way to give back to the sport that saved my life!

Dan Burkhart 

Many, if not all of the calibration rigs I have seen bear a remarkable similarity to the one I built about six years ago, and posted a youtube video of the build. Whether I was copied, or the design was so basic and generic that it dawned on several minds independently, I can't say.
At any rate, it was the use of bladed spokes like CX Rays and DT Aerolites that was the impetus for me to build the fixture.The calibration chart that came with the tension meter showed calibration for spokes that were an approximation of those spokes cross section, and not a very close one at that.

WheresWaldo

Thanks @Dan Burkhart, your video was one of the references I saw early one. This also takes inspiration from Universal Testing Machines like the Zwick made machines and others.

I like to consider myself a Maker, and 'Makers make ****!' I also wanted to give back to the community the best way I knew how.

WheresWaldo

Updated image

Dean51 

I've been there too.....welded some bits from my scrap pile and used a digital scale that I had purchased for another project.

Dean


IMG_2439

WheresWaldo

@Dean51, thats a pretty hefty rig.

Unfortunately for me I don't know how to weld and I had a bunch of spare extrusion from my 3D printer builds, Cycling is just a hobby/passion and I build my own wheels, so this rig was a natural step beyond just owning a tensiometer.

bluehills3149

I used a cheaper but much less elegant method. Drill a spoke sized hole in a c shaped bit of metal. Attach the other end (assume a J spoke) to a piece of metal with a spoke sized hole (I used a stainless metal ruler with a hole) and suspend from something about chest high and solid using a strong clamp (I used my fire escape stairs). From the C shaped metal, attach a large bucket. Fill with some bricks, measure tension and weigh the bucket. Repeat by adding more bricks (or water, or metal or your kid sister - anything) and graph the results. It does not matter on the weight as long as you plot the results and get a repeatable plot of force vs tension.

fietsbob

Amateur builder,, as an individual , tension of 1 spoke , relative to all the others in the wheel , ought to be adequate

unless you feel a need to use a tension data number, dictated from outside authorities to need to have a standardized calibration reference



Like doing an engine overhaul from a service manual that states the importance of bolt torque values , for fitting the Cylinder, head to engine block..


Guitar player, wheel building relative pitch was enough (a 30 + year old wheel set still OK)








...

AnkleWork

Most people perceive that a number on a screen is absolutely correct, while in actuality digital readouts accrue more errors than other methods. Without timely regular recalibration of the scale to traceable standards the posted method really can't tell much.

There is a past thread here detailing a much simpler calibration fixture using known weights to load the spoke, which can easily give much better results.

Nessism

This place kills me sometimes. Dude creates a super cool piece of kit and the peanut gallery invents ways to put it down.

Dean51 

+1 or more.

Dean

AnkleWork

Coolness is better than results, right?

WheresWaldo

I really don't mind the absurdity of the naysayers, really. This place is much better than RBR. If all I wanted was to be stoked, I would have asked my wife instead.

Besides, an absolute number is not what it important, as all the cynics here will tell you, it is repeatable results with a modicum of accuracy that is important. At least the rig is repeatable.

davidad

If you wanna keep your feet dry stay away from here. Many of us violate rule #2 . Look up ten good rules.

flanso 

+1

AnkleWork

Among others there's:

Hoopdriver

Really? I doubt that very much. I'd say that most people believe the number to be reasonably accurate but not absolutely correct (unless you're talking about a bathroom scale, which most people believe to be wrong on the high side).

What do you mean by this? Any measurement device will have some error, but how can a single device accrue errors?

"Timely" to me means "opportune". What does it mean to you in this context?

We all must frequently recalibrate our tools for communication.

AnkleWork

Sorry, I can't explain your language usage, but you could probably look up answers to all your questions.

Darth Lefty