Wheel Building Problem

[Tnark]

Group,

I thought I had mastered the art of wheel building – have built at least 10 wheels with 100% success rate, reliable operation, minimal re-truning following Sheldon Brown’s on-line instructions……until now.

Latest attempt….lacing a new but old Wolber Super Champion 700C rim onto a low flange Campy Record hub. For the first time I have tried DT double butted 1.8/1.5/1.8 spokes instead of the usual straight 2mm. I get initial tension and truing going well, but when I hit about 70 kgF tension, something seems to go twang, and the wheel suddenly takes on a awful bent fig-8 type shape. Loosen all spokes back and it all straightens up.

I’ve tried four times now, with the same result every time. A few more notes:

-Spokes and nipples are lubed
-it’s a 3-cross pattern with 296mm spokes
-spoking is symmetrical ie not the usual road dishing. This build is for a single speed, OLD = 130mm in a road frame
-I’m using a reliable Park Tools tension meter
-on last attempt I marked all spoke sides up near the nipples with a marker pen to keep track and remove any spoke twisting during tensioning, by appropriate over tensioning/back off. By the way, the double butted spokes wind up easily, it takes about ¼ of a turn of over tensioning and back off to remove spoke twist.

I’ve built this same type of rim a few years back for a 7-speed road setup with OLD 126mm and appropriate dishing, using DT Champion 2mm spokes and 3-cross spoking….no problems at all getting tension up to around 110 kgF on the drive side and wheel has been reliable.


Any suggestions as to what may be causing this? Seems the wheel is taking on a sudden unstable point at which it just goes chip shaped regardless of how carefully I tension it up. Should I try 2-cross or 4-cross pattern? Is it something to do with a symmetrical spoking? Do some rim/hub/spoking patterns just create a random unstable system? Or could the double butted spokes be causing something?

 

[tafi]

One thing you should be very carefull about with tensiometers (at least the Park one, I have used that in the past) is that they don't actually measure spoke tension, only the force required to deflect the spoke around a couple of posts.
This force does depend on tension but it also is VERY MUCH MORE dependent on the cross section of the spoke. The thicker the gauge, the harder it is to deflect and the more force will be measured at a given tension.

In other words, if a double butted spoke and a straight gauge spoke were tensioned the same and then measured, the straight gauge spoke would measure considerably more deflecting force, even though the tension is the same.

I think you're actually putting in a lot more tension than you think you are.

I use my own hands to test the level of tension and a tensiometer only near the end to ensure it is reasonably even around each side of the wheel.

I usually always use Competition (double butted) spokes but recently built a set with Revolutions on the front and the non-drive side rear and champions on the drive side. Despite putting a lot of force into tensioning, the Revolutions are so thin that the rear ones barely register on the scale.

 

[Tnark]

One thing you should be very carefull about with tensiometers (at least the Park one, I have used that in the past) is that they don't actually measure spoke tension, only the force required to deflect the spoke around a couple of posts.
This force does depend on tension but it also is VERY MUCH MORE dependent on the cross section of the spoke. The thicker the gauge, the harder it is to deflect and the more force will be measured at a given tension.

In other words, if a double butted spoke and a straight gauge spoke were tensioned the same and then measured, the straight gauge spoke would measure considerably more deflecting force, even though the tension is the same.

I think you're actually putting in a lot more tension than you think you are.

I use my own hands to test the level of tension and a tensiometer only near the end to ensure it is reasonably even around each side of the wheel.

I usually always use Competition (double butted) spokes but recently built a set with Revolutions on the front and the non-drive side rear and champions on the drive side. Despite putting a lot of force into tensioning, the Revolutions are so thin that the rear ones barely register on the scale.

Yes you are right, the Park tool measures deflection and this is greater for thinner spokes at the same tension as thicker spkes, BUT the tool comes with a scale for the various spoke sizes. I am measuring tension correctly, by reading off the 1.5mm scale for the tool. There is not way I am over-tensioning the wheel.

 

[tafi]

Then we are not using the same gauge. I use one with only one scale. Bugger, I thought that would be an easy fix.

I can only suggest then that the rim isn't up to snuff. Unless someone else has a better idea.

 

[alfeng]

What is your sequence for tensioning the spokes?

 

[Peter@vecchios]

Group,

I thought I had mastered the art of wheel building – have built at least 10 wheels with 100% success rate, reliable operation, minimal re-truning following Sheldon Brown’s on-line instructions……until now.

Latest attempt….lacing a new but old Wolber Super Champion 700C rim onto a low flange Campy Record hub. For the first time I have tried DT double butted 1.8/1.5/1.8 spokes instead of the usual straight 2mm. I get initial tension and truing going well, but when I hit about 70 kgF tension, something seems to go twang, and the wheel suddenly takes on a awful bent fig-8 type shape. Loosen all spokes back and it all straightens up.

I’ve tried four times now, with the same result every time. A few more notes:

-Spokes and nipples are lubed
-it’s a 3-cross pattern with 296mm spokes
-spoking is symmetrical ie not the usual road dishing. This build is for a single speed, OLD = 130mm in a road frame
-I’m using a reliable Park Tools tension meter
-on last attempt I marked all spoke sides up near the nipples with a marker pen to keep track and remove any spoke twisting during tensioning, by appropriate over tensioning/back off. By the way, the double butted spokes wind up easily, it takes about ¼ of a turn of over tensioning and back off to remove spoke twist.

I’ve built this same type of rim a few years back for a 7-speed road setup with OLD 126mm and appropriate dishing, using DT Champion 2mm spokes and 3-cross spoking….no problems at all getting tension up to around 110 kgF on the drive side and wheel has been reliable.


Any suggestions as to what may be causing this? Seems the wheel is taking on a sudden unstable point at which it just goes chip shaped regardless of how carefully I tension it up. Should I try 2-cross or 4-cross pattern? Is it something to do with a symmetrical spoking? Do some rim/hub/spoking patterns just create a random unstable system? Or could the double butted spokes be causing something?

Front or rear wheel? I'm thinking the wheel 'may' not be laced correctly but it's tough to say w/o seeing it.