Spoke length calculation

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Samuel D
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Re: Spoke length calculation

Postby Samuel D » 8 May 2017, 12:44pm

PhilD28 wrote:If you contact spa I'm sure they will measure the rim erd for you and suggest or supply the correct spoke length to match the very rim they are sending, problem solved.

I called them and they were slightly reluctant to be pushed for a recommendation, just in case the parts don’t fit (or, I suspect, the amateur builder wrongly thinks they don’t fit and returns them). However, the gentleman on the phone did divulge 298 mm for this build when gently prodded.

I’ll order that length and not hold Spa to it if it’s wrong.

Samuel D
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Re: Spoke length calculation

Postby Samuel D » 27 Jul 2017, 11:08pm

UPDATE.

Today I tackled this build at last. It took me most of the afternoon, following the step-by-step instructions in the second half of Jobst Brandt’s wonderful book.

To my great pleasure and excitement, the wheel came together beautifully. I took some photos of the process with my phone.



Spa Cycles supplied the raw material to be transmuted into a wheel. Note the only specialised tool: a spoke key.
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Lacing by the book. I used regular chain lubricant on the spoke threads and rim eyelets. The sofa got a protective blanket.
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The fully laced wheel.
Image



I used the upside-down fork as a truing stand, with my thumb braced against the fork as a gauge, periodically reversing the wheel to get the dishing right. Spa’s SONdelux wheel in the foreground was useful as a guide to tension (comparing the tones of spokes plucked near the nipple).
Image



The finished article with a tyre mounted. Inflating the tyre reduced spoke tension by more than I expected. It’s a 23 mm tyre so needs high pressure.
Image



And with that, I took off for a 40 km test ride. I confess there was a ping or two when I leaned the bicycle as far as I could in a straight line. I suppose there was some residual spoke wind-up. But then silence.

This was an unusually satisfying job. I think I’ll have to find an excuse to do it again!

By the way, the 298 mm spokes came up to about the base of the slot in the nipple.

Brucey
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Re: Spoke length calculation

Postby Brucey » 27 Jul 2017, 11:46pm

nice work, that!

IIRC when you start out it is about five cups of tea per wheel... it gets less the more you do.... :wink:

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Samuel D
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Re: Spoke length calculation

Postby Samuel D » 28 Jul 2017, 9:46am

I should hope so!

By the way, I observed several things I’d read about while building this wheel:

  • tyre pressure reduced spoke tension
  • spoke tension perceptibly reduced bearing preload in the hub (any idea if this is because the hub is compressed axially or the cups are stretched radially* or both?)
  • bearing preload was too tight from the factory, but not by a lot, and I wouldn’t have wanted it to be too loose instead, which would have complicated truing and dishing
  • there was much less grease in the hub than I like (I added plenty)
So I recommend building a cup-and-cone hub into a prestressed wire-spoked wheel to anyone who’d like a practical class in material properties. It gets you thinking (so much so on this first occasion that I had to take periodic breaks to rest my tired brain).



* Or, more accurately, allowed to expand by the stretching hub shell, since I think the cups are merely pressed into the shell.

Brucey
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Re: Spoke length calculation

Postby Brucey » 28 Jul 2017, 10:31am

re the change in preload; it could be either or both, depending on the design/dimensions of the shell and the way the parts fit together. I have had cartridge bearings go loose in a built hub (where before they were a light press-fit in the bare hub) so there is definitely a small change in the radial dimensions of the flange once the spokes are tensioned.

cheers
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NATURAL ANKLING
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Re: Spoke length calculation

Postby NATURAL ANKLING » 28 Jul 2017, 10:32am

Hi,
I would not worry much of the effect of spokes on the bearing.
For spinning the wheel whilst trueing, if its crunching then slacken off the bearings, if you can feel play it might be to little to worry about for trueing, feeling and seeing is different, if you can see the play then tighten a bit.

Grease won't harm the hub so yes add some, we won't talk about grease type, will be here to xmas otherwise, any grease is better than no grease.

Did you stress relieve spokes? that's grip parallel spokes.
Good practice even though it not rear which is very important.

Its standard practice to leave a little slack ( you could just feel it with fingers on the spindle before mounting wheel) then tighten the QR to remove play.....just............

Edited- Cartridge bearings would be no adjustable of course.
NA Thinks Just End 2 End Return + Bivvy
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.

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NATURAL ANKLING
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Re: Spoke length calculation

Postby NATURAL ANKLING » 28 Jul 2017, 10:35am

Hi,
Rear wheel building will run to several pages not just the two :lol:
NA Thinks Just End 2 End Return + Bivvy
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.

Samuel D
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Re: Spoke length calculation

Postby Samuel D » 28 Jul 2017, 10:44am

Brucey wrote:I have had cartridge bearings go loose in a built hub (where before they were a light press-fit in the bare hub) so there is definitely a small change in the radial dimensions of the flange once the spokes are tensioned.

Interesting.

NATURAL ANKLING wrote:Did you stress relieve spokes? that's grip parallel spokes.

I did, yes. I’ve never seen anyone do this job, so I wasn’t exactly sure how much force to use. I used leather motorcycle gloves and squeezed as hard as was reasonably comfortable (less comfortable by the time I’d done them all). That felt like putting a lot of force into the components.

I’m not worried about the interaction of spoke tension and bearing preload, just intrigued to find that it was practically noticeable.

I have no reason to build a rear wheel now, but perhaps the occasion will arise. It’s a pity my girlfriend broke her rear wheel just before I’d built my first wheel rather than after, or she could have saved a few euros and I could have had the experience of building a rear.

MikeF
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Re: Spoke length calculation

Postby MikeF » 28 Jul 2017, 4:08pm

A first wheel build is rather satisfying.
Rather than pluck the spokes I find it quicker and easier to let the shaft of a screwdriver bounce onto the spokes. You can easily tap several in succession doing that. Also if the wheel is symmetrical each spoke should have the same "ping".
"It takes a genius to spot the obvious" - my old physics master