Loose spoke won't tighten

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raleighnut

Legendary Member
Good spokes have their threads rolled, not cut so there should not be a stress point at the end of the threading (as would be the case with a cut thread) wether they are butted, double butted or bladed in section. John, the guy who builds my wheels, has a 'hand cranked' thread rolling machine on his wheel bench, but then he can rebuild 'any spoked wheel from a pram to a Ferrari' and does.
He's very popular with vintage motorcycle racers especially the sidecar and Morgan 3 wheeler racers.
 
Location
Loch side.
I've just had a squint with a magnifying glass and my front bike light.

You could not have described that better had you been looking over my shoulder.

Clean cut and a tiny burr - the bit of thread.

Happily, I've no need to ride the bike because I have a couple of others, and I'm only out at weekends at this time of year.

I will gently suggest to the mechanic the other spokes are stress relieved.

He he.... and if he doesn't know what stress relieve is or hint that he will "pre-stress" the spokes, find another wheelbuilder.
 
Location
Loch side.
Good spokes have their threads rolled, not cut so there should not be a stress point at the end of the threading (as would be the case with a cut thread) wether they are butted, double butted or bladed in section. John, the guy who builds my wheels, has a 'hand cranked' thread rolling machine on his wheel bench, but then he can rebuild 'any spoked wheel from a pram to a Ferrari' and does.
He's very popular with vintage motorcycle racers especially the sidecar and Morgan 3 wheeler racers.

Rolled threads still have a stress riser even though such devices don't remove any thread. A spoke is 2mm thick at the end. By rolling on a thread some of the metal is moved from the root of the thread to the peak of the thread. This means that the spoke shaft is 2mm, the roots are 2mm-X and the crests are 2mm +X. The average thickness remains 2mm but you have to have an area thicker and an area thinner in order to achieve this. Of the thread was cut, the crests would have been 2mm and the roots 2mm-minus a bit.

In spite of this, rolled threads are still better. A cut is never as smooth as a roll and rough valleys make for big stress risers.

Further, the die that rolls the thread is designed to give a U-shaped root rather than the traditional V-shaped root in the thread, again reducing but not eliminating the stress riser.

What the OP saw through his magnifier was the first crest of the first thread. The root is where the spoke breaks because that is the first weakest spot on the spoke and the spot that carries the most tension of all the other threads.

Spoke Thread.jpg


Here's a photo of a thread rolled with my Morizumi spoke threader. Look at the point where the thread starts on the left and note the first root, that's where a spoke breaks if it doesn't break at the head on the other side.

This illustrates why double-butted spokes are more durable. The spoke's middle section, the shank, is drawn to a lesser diameter - typically 1.8 or 1.5mm and is thus the thinnest part of the spoke. The spoke then flexes in this section rather than at the second-thinnest section, the first thread. But because the shaft is smooth without any stress risers, it has an infinite fatigue life. A double butted spoke will never break at the shaft but will fatigue if the wheelbuilder doesn't understand how to stress-relieve the spoke.
 
Last edited:

mrandmrspoves

Middle aged bald git.
Location
Narfuk
Rolled threads still have a stress riser even though such devices don't remove any thread. A spoke is 2mm thick at the end. By rolling on a thread some of the metal is moved from the root of the thread to the peak of the thread. This means that the spoke shaft is 2mm, the roots are 2mm-X and the crests are 2mm +X. The average thickness remains 2mm but you have to have an area thicker and an area thinner in order to achieve this. Of the thread was cut, the crests would have been 2mm and the roots 2mm-minus a bit.

In spite of this, rolled threads are still better. A cut is never as smooth as a roll and rough valleys make for big stress risers.

Further, the die that rolls the thread is designed to give a U-shaped root rather than the traditional V-shaped root in the thread, again reducing but not eliminating the stress riser.

What the OP saw through his magnifier was the first crest of the first thread. The root is where the spoke breaks because that is the first weakest spot on the spoke and the spot that carries the most tension of all the other threads.

View attachment 74409

Here's a photo of a thread rolled with my Morizumi spoke threader. Look at the point where the thread starts on the left and note the first root, that's where a spoke breaks if it doesn't break at the head on the other side.

This illustrates why double-butted spokes are more durable. The spoke's middle section, the shank, is drawn to a lesser diameter - typically 1.8 or 1.5mm and is thus the thinnest part of the spoke. The spoke then flexes in this section rather than at the second-thinnest section, the first thread. But because the shaft is smooth without any stress risers, it has an infinite fatigue life. A double butted spoke will never break at the shaft but will fatigue if the wheelbuilder doesn't understand how to stress-relieve the spoke.

I couldn't have put it better myself!
(Mainly because you are far more knowledgeable about spokes than I am!!!!)
Thanks for sharing your knowledge I enjoyed reading this.
 
OP
OP
Pale Rider

Pale Rider

Legendary Member
...update...

Took the wheel to the bike shop today.

Their take was to replace the spoke, see how I get on, then maybe go for a full rebuild/different spoke choice if more break.

Apart from owt else, they are too busy building Christmas bikes to do a full wheel rebuild before the New Year.

The spoke was replaced while I waited, even though it had to be cut and threaded because they didn't have the correct length.

That's a bit of a faff, and the disc rotor and cassette need to come off.

Apparently my cones were a bit loose, so they've been tightened.

All this for a fiver in the coffee jar and a £1 box of Maltesers.

I've used the shop on and off for 20 years, and done a few favours for them, so we have an informal mates' rates arrangement.

Still a good effort to do the wheel straight away, I was expecting to leave it.
 

Rohloff_Brompton_Rider

Formerly just_fixed
...update...

Took the wheel to the bike shop today.

Their take was to replace the spoke, see how I get on, then maybe go for a full rebuild/different spoke choice if more break.

Apart from owt else, they are too busy building Christmas bikes to do a full wheel rebuild before the New Year.

The spoke was replaced while I waited, even though it had to be cut and threaded because they didn't have the correct length.

That's a bit of a faff, and the disc rotor and cassette need to come off.

Apparently my cones were a bit loose, so they've been tightened.

All this for a fiver in the coffee jar and a £1 box of Maltesers.

I've used the shop on and off for 20 years, and done a few favours for them, so we have an informal mates' rates arrangement.

Still a good effort to do the wheel straight away, I was expecting to leave it.
That's a nice update with a good result.
 
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