Calibrating Park Tool TM-1 spoke tension meter

[philvantwo]

Is this the winning entry for the most untidy garage of all time?

[Des49]

nice work!

One comment I would make is that the reading on this (or any other similar) tension meter is critically dependent on the gauge of the spoke. A spoke that is nominally 1.8mm could be +/- 0.05 (or more) and this will make a big difference to the reading that you get. If you have not done so already I would suggest that you measure the spoke that you use for calibration purposes using a micrometer and act accordingly.

cheers

Thanks! Crude, but hopefully effective.

I must admit I didn't check the spoke. Having just measured it, it may be marginally over 1.8mm, but I only have a very cheap fibreglass Rabone micrometer. Fine for checking seatposts but not such fine tolerances on small spoke diameters. I may be able to borrow a quality digital micrometer this afternoon.

[Des49]

Is this the winning entry for the most untidy garage of all time?

Ha! The other side is a (little) bit better! But yes, I will admit it does need a good sort out, I started a month ago, but have lots to do yet. Still having trays of apples from last autumn and chitting potatoes thrown in amongst it all doesn't help. There never seems enough space.

[Brucey]

nice work!

One comment I would make is that the reading on this (or any other similar) tension meter is critically dependent on the gauge of the spoke. A spoke that is nominally 1.8mm could be +/- 0.05 (or more) and this will make a big difference to the reading that you get. If you have not done so already I would suggest that you measure the spoke that you use for calibration purposes using a micrometer and act accordingly.

cheers

Thanks! Crude, but hopefully effective.

I must admit I didn't check the spoke. Having just measured it, it may be marginally over 1.8mm, but I only have a very cheap fibreglass Rabone micrometer. Fine for checking seatposts but not such fine tolerances on small spoke diameters. I may be able to borrow a quality digital micrometer this afternoon.

black spokes are especially troublesome, because they sometimes have a coating on them that contributes to the thickness of the spoke but does not increase its stiffness in bending.

Tension meters (with a few exceptions) produce a deflection reading that

a) effectively includes the thickness of the spoke and
b) the bending stiffness of the spoke (which varies with the diameter cubed) is allowed for in the lookup tables

Coated black spokes throw the reading out twice over.

The bending stiffness of the spoke becomes important if the applied load in the three-point bend is high enough; in essence with thicker spokes the relative contribution of the elastic deformation (in bending) of the spoke becomes a larger proportion of the whole whenever a higher force is used; by contrast if a lower force is used the spoke behaves more like a flexible taut cord for normal spoke thicknesses. The manufacturers often choose a higher force simply because this reduces the errors that might arise because the spoke is not quite straight to start with, and live with the variation in reading with spoke thickness etc by having lookup tables.

If you look at fig 4 (p5) here
http://www.ihpva.org/HParchive/PDF/hp53-2002.pdf

you can see data taken using a Hozan tool. Try to ignore the fact the horizontal calibration is crazy (yeah, you get more deflection if the tension is higher, that makes sense... ) and that the vertical axis is a log scale. The thing to bear in mind is that the curves for 16G and 15G spokes are nigh-on identical apart from an offset which corresponds very closely with the difference in the spoke diameter, i.e. even at the high force/low span used with this tool, the spokes are behaving like a taut cord when they are skinny enough (which NB is less true for the 14G readings). If the readings were taken with lower force from one side only (instead of having a tool that include the spoke thickness in the deflection measurement) then there would only be a small error arising with variations in spoke thickness (and indeed variations in spoke material too).

As I understand it, Brandt's tension meter tool design uses a one-sided measurement at a low force and therefore gives meaningful readings (over a small range of different spoke thicknesses and materials) without need of a lookup table. However it presumably also requires that a 'zero' is taken on the spoke to start with, in case the spoke is not quite straight.

Swings and roundabouts, eh....

In any event if you take a typical tension meter and 'calibrate it' (even if it is just noting the reading it gives) by using it on an identical spoke at the desired tension, then it should be good for that build, provided the tool itself isn't damaged or the spring force varies in the meantime. If you want accurate readings then you should repeat that procedure whenever you change to a different type (thickness especially) of spoke. When I have measured spoke diameters, they have varied slightly from one box to another, even with the same make, enough to alter the readings you would get on a typical tension meter.

cheers

[drossall]

Is this the winning entry for the most untidy garage of all time?

No.

[Des49]

As I understand it, Brandt's tension meter tool design uses a one-sided measurement at a low force and therefore gives meaningful readings (over a small range of different spoke thicknesses and materials) without need of a lookup table. However it presumably also requires that a 'zero' is taken on the spoke to start with, in case the spoke is not quite straight.

Swings and roundabouts, eh....

In any event if you take a typical tension meter and 'calibrate it' (even if it is just noting the reading it gives) by using it on an identical spoke at the desired tension, then it should be good for that build, provided the tool itself isn't damaged or the spring force varies in the meantime. If you want accurate readings then you should repeat that procedure whenever you change to a different type (thickness especially) of spoke. When I have measured spoke diameters, they have varied slightly from one box to another, even with the same make, enough to alter the readings you would get on a typical tension meter.

cheers

Having tried to measure my spokes I found it wasn't quite so easy. Just to be correct I do not have a micrometer, but a cheap plastic vernier, and then borrowed a higher quality vernier. The spokes seemed to vary enough (thickness and roundness) and the calipers enough for me to think that, as you suggested above, it would be best just to check the Park TM-1 on each type of spoke. I do not build wheels that often and it isn't that much of a pain to do.

Brandt's seems a great design, this seems to be manufactured by Wheel Fanatyk. Appears reasonable value for those who build wheels a lot:-
http://www.wheelfanatyk.com/store/digit ... ption=Dial
Tempting, but not that easy to justify!

If you look at fig 4 (p5) here
http://www.ihpva.org/HParchive/PDF/hp53-2002.pdf

That was interesting. I use tone to check evenness of spoke tension at various points in the build, but my ears are not going to tell things too accurately.

[Samuel D]

Brandt’s tensiometer design is clever in several ways, but in practice it is still noticeably affected by the spoke’s bending resistance (for extremes of gauges at least), and for that reason Wheel Fanatyk provides a look-up table that can be found here.

In a recent moment of madness when an American friend was flying from California to Paris, I had him bring me this tensiometer. It should last decades in my use but that doesn’t justify its price (unless by some happy accident I end up owning a bicycle shop!). I see it as a homage to Jobst Brandt and his inspiring idealism rather than a merely utilitarian object.

I’d like to photograph its details and share my thoughts about it on this forum, but that might take a while because my macro lens is currently out of action.

[Des49]

I would love to know your thoughts on the Wheel Fanatyk, in due course when you get your lens sorted out.
Handy to get someone to bring it over for you, the $50 shipping and current exchange rate are not favourable.

Did you get the digital or dial version?

[Samuel D]

I got the dial version, both because it was cheaper and because I prefer not to have batteries and electronics in such a long-lived, occasionally used tool.

Not only is the shipping pricey and the exchange rate unfavourable, but there are also customs fees and VAT to worry about. It was having a friend come over that lured me into the purchase.

Alright, I’ll see what I can do about a few photographs and a write-up as soon as I have the opportunity.

[Des49]

I got the dial version, both because it was cheaper and because I prefer not to have batteries and electronics in such a long-lived, occasionally used tool.

Sounds sensible reasoning and what I was thinking too.

Alright, I’ll see what I can do about a few photographs and a write-up as soon as I have the opportunity.

Thanks! Will keep an eye out for it.

[Brucey]

the link for a PDF of the chart is here
https://www.dropbox.com/s/yy9vy8gzsf2hn7e/WF%202018%20Chart.pdf?dl=0

and the illustrations below the chart show quite well how the tension meter works.

FWIW with this tension meter if you measure 0.30mm deflection then this signifies a tension of

126kg for a 1.7mm spoke
123kg for a 1.8mm spoke
115kg for a 2.0mm spoke

in other words if you only build in spokes of about that gauge, you don't really need to bother with the calibration chart; the errors arising are small.

However do note the extreme importance of the 'zero' setting; should the zero not be accurate and thus cause the deflection reading vary by +/- 0.05mm ( 0.002") then this will constitute a tension error of > +/- 20kg. Very few spokes, once fitted to a wheel, are likely to be consistently straight within the tool span, such that the zero reading need not be checked for every spoke.

cheers

[Samuel D]

Will keep an eye out for it.

The lens problem was easily resolved and I’ve now put up some photos in this thread.

FWIW with this tension meter if you measure 0.30mm deflection then this signifies a tension of

126kg for a 1.7mm spoke
123kg for a 1.8mm spoke
115kg for a 2.0mm spoke

in other words if you only build in spokes of about that gauge, you don't really need to bother with the calibration chart; the errors arising are small.

True. But since I had to consult the chart anyway to convert deflections to tensions, I found this not to be a great advantage. It would be a bigger advantage if you used the tool often and got to know the deflections you want.

[Dsan]

Hi, I'm new to this forum, and start with a question about spoke tension of the zipp 202 Firecrest clincher.

According to zipp, the sapim cx-sprint have 2.25mm width and 1.25mm thickness. If you use the park tool tension web app, for these spoke measures, 100kgf correspond to 17 in the park tool tm-1 tension meter. Am I right?

[mercalia]

I would love to know your thoughts on the Wheel Fanatyk, in due course when you get your lens sorted out.
Handy to get someone to bring it over for you, the $50 shipping and current exchange rate are not favourable.

Did you get the digital or dial version?

[youtube]ahyjuV951Ro[/youtube]

[Airsporter1st]

it appears to be a knock-off of someone else's design. It uses a digital depth micrometer to measure the defection under an applied spring pressure. The absolute deflection is (as with the park meter) a combination of spoke thickness and spoke flexion. I think that calibration rests on two main things

1) zeroing the digital gauge at the right point in the meter's stroke and
2) the preload and spring rate of the spring

presumably there are instructions regarding both items but if the spring rate is wrong then the calibration of the meter will be suspect outside of a narrow range in which it is checked/set. Presumably there is a calibration chart that is supplied with the meter.

cheers

One of the others that appears below the listing includes a picture of the chart (which goes up to 200kg). Its interesting to note that the body of the chart has been deliberately greyed out - seems the rip-off merchants don't want anyone else to rip off their data!!!!!