Calibrating Park Tool TM-1 spoke tension meter

For discussions about bikes and equipment.
User avatar
SimonCelsa
Posts: 314
Joined: 6 Apr 2011, 10:19pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby SimonCelsa » 6 Oct 2017, 5:55am

Yes, a good effort Des 49.

Very similar to what I have in mind except I do not possess the spring balance so will have to use my body weight as the calibrating mass.

The only let down with the suspended mass calibration is that the Park Tool TM1 instructions state that the meter should be used in the horizontal plane. Whether this makes much of a difference I'd have to check.

Good, simple idea anyway. I've nearly finished my calibration device although I got stuck in the baby bouncer last night and it took a while to extricate my thighs from the bouncing arrangement,

All the best, Simon

Brucey
Posts: 26880
Joined: 4 Jan 2012, 6:25pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Brucey » 6 Oct 2017, 9:34am

SimonCelsa wrote:Yes, a good effort Des 49.


+1

.....The only let down with the suspended mass calibration is that the Park Tool TM1 instructions state that the meter should be used in the horizontal plane. Whether this makes much of a difference I'd have to check.....


the pivoted mechanism in the tool isn't mass-balanced in the plane of movement. I think this offset weight means that there is a small torque exerted around the pivot when the gauge isn't horizontal, and this may affect the reading. I don't know if this is really significant or not (the spring is strong and the parts are built light), but if you want to test for this, you ought to see double the error when the gauge is used twice on a vertical spoke, once each with the tool facing left and right.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Des49
Posts: 462
Joined: 2 Dec 2014, 11:45am

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Des49 » 6 Oct 2017, 2:36pm

SimonCelsa wrote:The only let down with the suspended mass calibration is that the Park Tool TM1 instructions state that the meter should be used in the horizontal plane. Whether this makes much of a difference I'd have to check.


This doesn't seem to make much difference, as Brucey alludes to as well. When I have a wheel in the jig and hold the TM-1 vertically or horizontally there doesn't seem to be any noticeable difference on a well tensioned spoke. Maybe there is more likely to be a difference in looser spokes. My set of scales are pretty heavy themselves and need to be hung vertically, they used to be used for mainly weighing out hundredweight sacks of spuds by my grandfather.

SimonCelsa wrote:I got stuck in the baby bouncer last night and it took a while to extricate my thighs from the bouncing arrangement,


That would be an interesting one for the fire brigade to be called out to!

I did a few measurements this morning:-

With an 80kg load on a 1.8mm spoke the TM-1 indicated 21, which is 105kgf on their chart. With 96kg load the gauge indicated 22.5 which seems to be 124kgf.

With a 2.0mm spoke and a 96kg load the TM-1 showed 25 which is 120kgf.

So my gauge is over-reading a substantial amount.

I have just completed a nice DT Swiss RR440 asymmetric rim, Ultegra 6800 hub 32h, 2.0mm PG spokes on drive side, tensioned to 27 on my gauge (which should be close to the max recommended for this rim of 120kgf), NDS DB2.0/1.8mm spokes comes out at about 21, which should be about 80kgf on my gauge. It feels a very nicely balanced build on an 11 sp hub thanks to the asymmetric rim.

As a further reference I have a Spa built front dynamo hub on a family member's bike, this is very tight and actually shows 25 on my gauge for a 1.8mm spoke. So even allowing for my gauge to be about 25kg over the top this wheel is still very tight and it feels it too.

Also I measured a Zipp 202 set of wheels, these use bladed spokes of 2.2x1.0mm and Zipp say that they use tensions of 100kgf front and RDS, 65 rear NDS. On my gauge the DS comes out at 15 which equates to 126kgf on the chart, again an over reading of about 26kg. The NDS measures 7.5 on the gauge which equals 65kgf on the chart, which looks about right. So maybe the gauge is accurate at lower tensions and over reads about 25kg on the higher tensions seen with normal wheels and normal round spokes.

I haven't tried to adjust the gauge to correct it yet, the adjustment can only be done in half turns so I wonder how tunable it actually is.

I have been building my own wheels for over 30 years with no issues and only got the gauge a couple of years ago. It is useful to check the relative tensions of spokes but obviously the actual values given need to be used carefully.

Brucey
Posts: 26880
Joined: 4 Jan 2012, 6:25pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Brucey » 6 Oct 2017, 2:57pm

the meter is adjustable for calibration purposes; one end of the spring bears against a screw threaded piece the can be set in a different position, once the spring is unhooked.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Des49
Posts: 462
Joined: 2 Dec 2014, 11:45am

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Des49 » 6 Oct 2017, 3:09pm

Brucey wrote:the meter is adjustable for calibration purposes; one end of the spring bears against a screw threaded piece the can be set in a different position, once the spring is unhooked.

cheers


Haven't tried yet. The spring rests in the slot of the screw so any adjustment can only be in half turn increments. I should try out of interest to see how many turns equates to how many kgf.

This has been a useful exercise to learn about the gauge. I look forward to someone doing a more sophisticated analysis than my crude rig.

Brucey
Posts: 26880
Joined: 4 Jan 2012, 6:25pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Brucey » 6 Oct 2017, 7:40pm

IIRC in addition to the spring adjuster, I think the pointer is adjustable where it mounts on the arm. Whatever adjustment is made on the spring mounting, it results in about x4.5 movement of the pointer. I think that in order to get the correct adjustment, you need to be able to move the pointer about 2 divisions on the end of the arm, else half turns on the spring adjuster leave you between correct settings.

Remember that the scale reading comprises of two elements; a thickness-of-spoke element and a deflection-of-spoke element. I have a suspicion that (nominally) the gauge may be calibrated so that the 'gap' between the three fulcrums is actually the scale measurement, in some multiple of 0.001" increments (-a hypothesis which can be tested by using a straight edge and a digital Vernier caliper, zeroed to the end fulcrum diameter). If so it will be impossible to satisfy the 'fit' to a calibration curve across the full range if

a) the spring can only be adjusted in large (ish) increments and/or
b) the spring rate is slightly wrong
c) the middle fulcrum moves through enough of an arc to throw the geometry off (so that the normal component of the load is not as desired)

It might be that the spring adjuster can be made to work better by having a second slot cut in it, so that it can be adjusted in quarter turns instead of half-turns.

you can see the layout and approximate geometry of the device here;
Image
Image

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Jezrant
Posts: 607
Joined: 14 Dec 2007, 8:11pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Jezrant » 11 Oct 2017, 8:43pm

Brucey wrote:BTW I intend to build a device that allows one to check the calibration of tension meters. Once I have it up and running, maybe I could offer a calibration checking service to others?

cheers


I'd be interested in that. A couple of years ago I had mine checked against Woodrup's DT and it seemed to read the same, but I still have lingering doubts as to its accuracy. :?

cheers :)

User avatar
Mick F
Spambuster
Posts: 39631
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Mick F » 12 Oct 2017, 8:48am

Because the Park Tool device uses a spring, it would need to be calibrated now and again unless you could take the tension off the spring when not in use.

Same as a torque wrench. Release the spring down to zero before you put it back in its box.
Mick F. Cornwall

mercalia
Posts: 6677
Joined: 22 Sep 2013, 10:03pm
Location: london South

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby mercalia » 12 Oct 2017, 10:18am

Jezrant wrote:
Brucey wrote:BTW I intend to build a device that allows one to check the calibration of tension meters. Once I have it up and running, maybe I could offer a calibration checking service to others?

cheers


I'd be interested in that. A couple of years ago I had mine checked against Woodrup's DT and it seemed to read the same, but I still have lingering doubts as to its accuracy. :?

cheers :)


me 2

User avatar
fausto99
Posts: 165
Joined: 19 Sep 2011, 10:06am

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby fausto99 » 12 Oct 2017, 7:30pm

Anyone used one of these? If so, any comments on calibration?

http://www.ebay.co.uk/itm/Bike-Bicycle- ... 0005.m1851

Brucey
Posts: 26880
Joined: 4 Jan 2012, 6:25pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Brucey » 12 Oct 2017, 11:35pm

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
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
bicyclejourneys
Posts: 89
Joined: 29 Oct 2011, 3:28pm
Contact:

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby bicyclejourneys » 16 Oct 2017, 10:55am

Hi,

I've discussed my readings from my TM1 with Spa Cycles... I mentioned the readings I had from my old set and the name of the builder. It was said that builder had a tendency to build very tight. So the readings I'm getting for the Spa Cycle built wheels will probably be correct and the TM1 isn't reading high!

This is the readings on the old Spa Cycle wheels:

Sputniks

Front 23 Sapim Race
NonDS 24 Sapim Race
DS 29-30 Sapim Strong

Recommended to aim for on a heavy loaded bike:


Sputniks

Front 21 - 105 kgf Sapim Race
NonDS 20 - 95 kgf Sapim Race
DS 26 - 135 kgf Sapim Strong

Pretty much the readings Colin mentioned :D
Born To Cycle

Jezrant
Posts: 607
Joined: 14 Dec 2007, 8:11pm

Re: Calibrating Park Tool TM-1 spoke tension meter

Postby Jezrant » 17 Oct 2017, 5:24pm

bicyclejourneys wrote:Hi,

I've discussed my readings from my TM1 with Spa Cycles... I mentioned the readings I had from my old set and the name of the builder. It was said that builder had a tendency to build very tight. So the readings I'm getting for the Spa Cycle built wheels will probably be correct and the TM1 isn't reading high!

This is the readings on the old Spa Cycle wheels:

Sputniks

Front 23 Sapim Race
NonDS 24 Sapim Race
DS 29-30 Sapim Strong
[b]


That sounds vaguely familiar.
viewtopic.php?t=19189&start=60