On 1/10/2019 9:04 PM, Mark J. wrote:
Wheel building questions (including "religious" questions to
replace the political ones with which RBT has become
saturated).

Background: I am re-rimming a wheel.
Hub: Powertap GS, 24 spoke (NOT disc)
Spokes: Sapim CX-ray bladed straight-pull
Old Rim: Velocity A23 O/C (offset) 700C non-eyeletted rim
New Rim: DT 411 (also offset), uses DT-supplied/mandated
nipple washers.

Original build tension measured with a Park tensiometer,
drive side tensioned to Velocity's recommended max, even
tension on each side.

Other: I'm ~170 lbs and strong enough though not as in days
of yore, but bike is geared quite low so on the steep stuff,
the hub sees a fair bit of torque. Tires 700x25, typically
105-110 psi. Paved road use except for a handful of miles.

I built the original (Velocity) rim in 2015, had no problems
until recently (9900 miles later). Now I notice the rim
starting to crack at the spoke holes (only the pulling
spokes on the drive side). Wheel was still rideable and
true when I unlaced it, so the cracks weren't severe yet.

NOTE: I KNOW (IMHO) that I'm pushing the margins with this
build, so if I can only get 10,000 miles and 3 years out of
a wheel like this, I'm OK with that, but I'll be happy to
get more. I have plenty of more durable/reliable wheels,
but I've had fun with this wheel, and fun is why we're here.

QUESTIONS:

Q1: I don't use thread compound or linseed oil, and would
rather not start now. I lubricate threads and nipple/washer
contact with light grease. What is a reasonable minimum
non-drive-side tension to be confident the spokes won't loosen?

I'm partway though tensioning the new rim, and think I can
get the NDS up to ~80 kgf if I push the DS up to DT's
recommended max tension (1200 Newtons, or 122 kgf). I'm
confident 80kgf is plenty on the NDS, but I may want to put
less than max tension on the DS (and thus less that 80 kgf
on the NDS) to give me more margin on the cracking problem.

Q2: Do we suppose DT's (and/or Velocity's) max tension
recommendation has enough margin that stress-relieving the
spokes won't overstress the nipple holes? I reefed on the
last build pretty hard at stress-relieving time, Could that
have weakened the rim in a way that only showed up 10,000
miles later? I have belonged to the church of
stress-relieving for a long time, but my faith is weak.

Q3: (let the religious wars begin!) I would think that
stress-relieving is of primary benefit with J-bend spokes.
Does it really help with straight-pulls?

Notes: I have studied the sacred writings of the Jobst, on
multiple occasions, though I'll admit I'm having a hard time
fully grokking his stress-relieving argument.
I just did it 'cause "why not?" Now I'm quavering.
Also note that with bladed straight-pull spokes, any spoke
wind-up would be immediately obvious ('cause bladed), and
anyway perhaps impossible because the entire spoke,
including the head, just turns on you.


Right now my inclination is to tension the DS at the
recommended limit, stress-relieve just a little less
vigorously than last time, hope that the nipple washers that
DT mandates (and supplies) will spread out the stress better
at the nipple holes, expect at least 10k miles of
usefulness, and hope for more.

Thoughts? (esp. on questions Q1, Q2, and Q3 above)

Mark J.

24h is probably less robust than a 32 but you have a 24h hub
so here we are.

Yes most of the effect of brief overtension after build is
to straighten/seat the spoke heads at the bend so I agree
you should see minimal change with a straight spoke. Still
and all, any slack ought to be taken up then.

We like linseed oil as it lubricates well during build and
after set will still move with a spoke wrench, unlike
anaerobic thread lockers. I built with oil for years but
that was back when rims were heavy and wheels were nearly
all 36h.

I can't quantify 'reef' but 'enough to seat spoke heads' may
be less than 'this is how strong I am'.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971