Spoke Tensiometer Calibration

No,  but I've been wondering about this myself.  At the moment I just check it against a friends guage but I was considering building something using a weight, a lever for a bit of multiplication and a spoke.  Not sure I'll ever get round to it really though.   

Seen lots of pictures of wooden frames holding a spoke under tension with a strain gauge connected to one end. They look simple enough to build.

I've seen some very nice looking ones with aluminium T slot profile and a crane gauge. It doesn't look difficult but I bet there are some obvious mistakes that people have made.

I was trying to avoid the strain guage as then that needs calibrated as well

I was trying to avoid the strain guage as then that needs calibrated as well

For the level of accuracy required would a torque wrench not suffice? 

I'm thinking something like a 1100mm length of 25mm box section, put a big M14 bolt through one end, and 1000mm away from it put another with something to act as a bushing, some 16mm OD / 14mm ID tube cut to ~16mm long and a couple of washers would probably do.  Bolt that one to your workbench.  Drill a spoke hole 100mm from the fulcrum on the perpendicular side.  Bolt a plate to your workbench with a ~2.5mm hole for the J bend.  Then double check my maths but your spoke tension is then 10x whatever the torque wrench says (or 125Nm ~ 125kgf if you want to make the math's really easy put the torque wrench bolt 9810mm from the fulcrum) )

TBH, the gauges are mostly precision rather than accuracy.

As wheel building is more about consistent tension, as long as the spokes are tight enough, it's not hugely important. (ex wheelbuilder, but haven't built any for a couple of years.)

And it's not even as if we have any really bendy rims about these days. Can still remember trying to get old GEL280 and GL330 straight. Had a range of about 1/4 of a turn on the spoke from being too loose to pretzeling the rim. 🤪 

I'd focus on improving the gauge, make it precise!

Posted by: mert

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As wheel building is more about consistent tension

That's pretty much where I'm at actually.  I've found that going round a wheel and making sure all the tensions are close has made the biggest difference to any work I have to do.  The torque wrench idea is interesting though

I'm already getting consistent tension and while building them tight enough, I've not had any spokes pull through the rim (which is where the 120kgf limit usually comes from), just thought it might be a fun little project.

I'm already getting consistent tension and while building them tight enough, I've not had any spokes pull through the rim (which is where the 120kgf limit usually comes from), just thought it might be a fun little project.

TBH after struggling with a few sets of Stans rims, I've given up and now just over tension them.  So far no issues.  The 120kg limit just gives too little tension on the NDS to actually keep them straight. Adding ~20% solves that.

If they crack they crack, but the alternative was hanging them from the garage roof as never to be used spares which is equally a waste.

In future I'm sticking with asymmetric rims or rims with higher / no quoted spoke tension limits. 

I do build with washers though which probably helps the rim.

The last set of Stan's I built were 100kgf and we're a pain to keep straight. I did the same and upped the tension until they worked. It's the only time absolute tension has been an issue.

Would be interesting to know what absolute tension actually works though 

I keep mine callibrated by refusing to use it. I tune them instead. Much less faffy.

And always close enough.

Yes I have.  I based it around a luggage scale.  Since the luggage scale range was limited to 40kg it was attached to the spoke via a 3:1 lever.  Some threaded rod added tension, 30kg on the luggage scale 90kg at the spoke.   Any error in the scale is magnified by 3 though if that is a concern.  I did not want to pay for a 120kg load cell!.   Mine was a welded frame and  a fun little project.    Only did this as I build my own tensiometer as I refused to pay £90 for the park one.

Seen lots of pictures of wooden frames holding a spoke under tension with a strain gauge connected to one end. They look simple enough to build.

Doesn't that still rely on the calibration of a strain gauge? 

Wouldn't the simplest way to 'calibrate' a tensiometer (in a home setting) be to build a rig where a known weight(s) was suspended from a spoke and to apply the tensiometer to that spoke and looking for consistency/drift in the readings over time and with use? 

[discuss]

Yep, hanging known weights off a spoke, or lever would be more reliable over time. A strain gauge or crane scale is perhaps more versatile and would certainly take up less space when not in use. I'm not sure where I would keep 120kg of weights and the system for attaching them to a spoke.

Just order one from AliXpress 

Never seen one on AliExpress. Got a link?

I wouldn't trust the accuracy of anything purchased on aliexpress without properly traceable calibration. 

Found it. £290! Who in rather would spend that on one, let alone one from AliExpress 

Most calliper type spoke tension meters are just comparators and IME it is simply about getting consistent tension across the wheel rather than absolutes. Might be a bit different if you’ve got a DT Dial Gauge type and you’re building lots of super light carbon builds. Speaking as an ex bike mechanic with 20+years wheel building experience