rim seam stiffness/tolerance stuff

jim beam wrote:

Chalo wrote:

I expect that it's also significantly cheaper than making a pinned
joint that won't cause a major blip on the brakes

with a pinned joint, the pin is fitted
and the two ends are pressed together. end of story. with welding,
once the weld is done, it requires machining of all surfaces, including
under the hooks. even when automated, there's no way that's going to be
cheaper than just fitting a pin.

The expensive part of doing a pinned seam is not seating the pin, it's
getting the cut straight and treating the ends with enough care so that
they match perfectly at the time the pin is seated. If it were
easy/cheap to do, than all pinned seams would fit perfectly, and many
don't.

The reason that I know welded seams are cheaper to do is because they
are getting more common all the time, at all price points. A general
trend like that in the bike business almost without exception means
that the ascendant technology has a lower cost than the older one.

Mavic clearly don't do a post-weld heat treat.

sorry, you can't say that based on visual inspection. i don't know
whether mavic heat treat or not, [although i know some rims are] but
there's no "clearly" about it.

I can't tell it from looking at a new rim; I can tell it from
tensioning a 48 spoke wheel and observing that the weld collapses and
bulges long before even the section drilled for the valve hole does.
If the rim were heat treated after welding, the weld would be stronger
in compression than any drilled section of the rim.

That's why
their rim joints are the the weakest part of the rim, and why their
rims can't support the same spoke tension as comparable pinned rims of
equal weight.

the material coherence of a welded joint is much better than that of a
pinned joint. i would therefore expect the fatigue strength to be much
higher.

You may be right about fatigue strength; I have never had a rim
extrusion fail in fatigue, though (eyelets yes, extrusion no). But the
ability of a rim to support spoke tension is chiefly a function of
circumferential compressive strength, and a pinned joint does not
compromise the rim's resistance to compression-- but a weld's
heat-affected zone does.

Chalo Colina

Chalo wrote:
jim beam wrote:

Chalo wrote:

I expect that it's also significantly cheaper than making a pinned
joint that won't cause a major blip on the brakes

with a pinned joint, the pin is fitted
and the two ends are pressed together. end of story. with welding,
once the weld is done, it requires machining of all surfaces, including
under the hooks. even when automated, there's no way that's going to be
cheaper than just fitting a pin.


The expensive part of doing a pinned seam is not seating the pin, it's
getting the cut straight and treating the ends with enough care so that
they match perfectly at the time the pin is seated. If it were
easy/cheap to do, than all pinned seams would fit perfectly, and many
don't.

that's because they're cheap, not because it's hard to do.


The reason that I know welded seams are cheaper to do is because they
are getting more common all the time, at all price points.

no dude, you can't say that. the u.s. market supports /much/ higher
prices than any other market, so this is where the expensive product
gets sold. in the u.k. for instance, i understand that the ma3 is
considered a "good" rim that outsells the open pro. that's not a welded
rim.

A general
trend like that in the bike business almost without exception means
that the ascendant technology has a lower cost than the older one.

i don't see how a production method involving:

1. cut
2. weld
3. machine outer surface
4. machine inner surface
5. machine under rim hooks
6. machine brake track

can /ever/ be cheaper than:
1. cut
2. pin

it's simply a function of what our market supports/customer demand. i'd
not go back to pinned rims unless the bike was a beater.



Mavic clearly don't do a post-weld heat treat.

sorry, you can't say that based on visual inspection. i don't know
whether mavic heat treat or not, [although i know some rims are] but
there's no "clearly" about it.


I can't tell it from looking at a new rim; I can tell it from
tensioning a 48 spoke wheel and observing that the weld collapses and
bulges long before even the section drilled for the valve hole does.
If the rim were heat treated after welding, the weld would be stronger
in compression than any drilled section of the rim.

kinda. depends on what the heat treatment is designed to achieve. if
it's precipitation hardening, yes, it would make it stronger, but that
may not be so good for the fatigue life - what i imagine would be the
primary objective. an unhardened welded rim is still better than a
pinned rim for fatigue.



That's why
their rim joints are the the weakest part of the rim, and why their
rims can't support the same spoke tension as comparable pinned rims of
equal weight.

the material coherence of a welded joint is much better than that of a
pinned joint. i would therefore expect the fatigue strength to be much
higher.


You may be right about fatigue strength; I have never had a rim
extrusion fail in fatigue, though (eyelets yes, extrusion no). But the
ability of a rim to support spoke tension is chiefly a function of
circumferential compressive strength, and a pinned joint does not
compromise the rim's resistance to compression-- but a weld's
heat-affected zone does.

Chalo Colina

we've touched on this befo excess spoke tension does not increase
the strength of the wheel - there's no reason to do it. if you
experience loosening problems, you need to go with nipple "glue".

Nate Knutson Wrote:
Yesterday I built up a Rhynolite / XT 756 / DT 2.0/1.8 wheelset, 32h
for both. These are the cheap Rhynolites - all silver, I think brushed
and not anodized, not machined, and not welded. These are maybe the
14th and 15th wheels I've built, and I've built 4 other Sun rims
previously.

Since these are for me and are probably never going to be used with
rim
brakes, I basically paid little attention to radial trueness and
tension balanced them fairly precisely using a tensiometer, and then
made the necessary small adjustments for lateral trueness. When you do
this, the radial trueness at all areas except the seam basically comes
out as a reflection of the rim's precision. At the seam, there are
some
additonal factors having to do with the construction of the rim there,
as well as some other stuff that I'm kinda in the dark about.

The idea of building wheels this way is that in order to correct
signifcant radial errors that are still there after the tension
balance
is good, you'd have to throw tension balance out the window in those
spots, since that's how much change in tension is needed to produce
much change in radial trueness.

What I'm wondering about is this: on at least one one of these rims
(can't remember now), the seam had a significant radial dip (error
inwards toward the hub, not outward). With tension balance looking
good, the rim was maybe 1.5 - 2mm in there. So you'd need to have some
spokes stupidly loose there to make things look good. This is pretty
normal, especially for Sun. However, some rims behave in the opposite
way at the seam. They want to have outbound errors and need
tighter-than-average spokes to be radially true at the seam. And I
built an Aerohead once (sleeved seam, I think) where I wasn't willing
to sacrifice much radial trueness for tension balance, and it wanted
to
have one spoke at the seam be really, really tight and an adjacent
one,
coming from the other flange and on the other side of the seam, be
really loose.

Can someone who knows what they're talking about explain how exactly
this works? I assume that it all has to do with different seam joining
and rim forming processes producing different effects, but what's the
explanation for why the rim I just built wanted to have a dip at the
seam where others go outward? I realize that the rim probably had a
flat spot there to begin with, but can some joining processes make the
rim more elastic there, causing it to respond differently to the same
amount of tension as the rest of the rim? If it's just a flat spot
(and
I'm guessing that's all it ever is), then what causes that and what
joining processes is it an inherent problem with? If the type of
irregularity I'm describing usually or always are just simple flat
spots, then is the same true of high spots at the seam? Or in those
cases, is something going on that makes the rim stiffer there, like
sleeves providing unwanted reinforcement? What types of joining are
actually the best and worst at minimizing irregularities at the seam?
Does anyone who's built a lot with many of the current brands and
models have an opinion about which are CONSISTENTLY good about seam
stuff? (I've noticed that it can vary a lot from rim to rim and
perhaps
model to model).

Thanks in advance.
Nate Knutson
My experience with Sun rims is that they lack consistency.
The rim joint, sleeve, and cutting/facing of the ends of the extrusion
are from quite good to quite poor. The sleeved area is stiffer and
less responsive to spoke tension. If the pre-alignment provides for
proper tensioning and the cutting/facing is in good alignment, you can
attain less than .3 mm error in radial and lateral true with 5% spoke
tension balance.
I have built over 200 wheels with Sun Rims. Rhyno Lites are in the
category of poor consistency. I have recycled them when they build
like you are describing, but I have also spent an extra hour or so
working with the rim(s) to get good alignment/radial/lateral true with
5% spoke tension balancing. With the right tools, patience,
experience, and rim extrusion that can handle the forces you can get
attain a much rounder and straighter wheel while keeping the spoke
tension well balanced.


--
daveornee

jim beam wrote:

Chalo wrote:

But the
ability of a rim to support spoke tension is chiefly a function of
circumferential compressive strength, and a pinned joint does not
compromise the rim's resistance to compression-- but a weld's
heat-affected zone does.

we've touched on this befo excess spoke tension does not increase
the strength of the wheel - there's no reason to do it. if you
experience loosening problems, you need to go with nipple "glue".

That dog still won't hunt. Spoke tension is what allows a rim to carry
a load. I could squash even the strongest unlaced 700c rim I've got,
without resorting to dynamic loads like those I inflict on my bike's
wheels.

A wheel whose spokes go slack is on the verge of collapse, and can't
provide adequate lateral support to the rim section with unloaded
spokes. Since my wheels eventually fail from being bent laterally too
much to true, I think it's important to support my rims in lots of
places with enough spoke tension that they don't become unconstrained.
Mavic rims don't allow me to do that, while others of equal weight do.


Some of those others are even welded, which tells me that Mavic are
doing something wrong that compromises their rims' integrity. My guess
is that they are skipping the post-weld solution heat treatment to save
production costs, which results in rims that are weaker for their
weight than others.

Chalo Colina

Chalo wrote:
jim beam wrote:

Chalo wrote:

But the
ability of a rim to support spoke tension is chiefly a function of
circumferential compressive strength, and a pinned joint does not
compromise the rim's resistance to compression-- but a weld's
heat-affected zone does.

we've touched on this befo excess spoke tension does not increase
the strength of the wheel - there's no reason to do it. if you
experience loosening problems, you need to go with nipple "glue".


That dog still won't hunt. Spoke tension is what allows a rim to carry
a load. I could squash even the strongest unlaced 700c rim I've got,
without resorting to dynamic loads like those I inflict on my bike's
wheels.

A wheel whose spokes go slack is on the verge of collapse, and can't
provide adequate lateral support to the rim section with unloaded
spokes. Since my wheels eventually fail from being bent laterally too
much to true, I think it's important to support my rims in lots of
places with enough spoke tension that they don't become unconstrained.
Mavic rims don't allow me to do that, while others of equal weight do.


Some of those others are even welded, which tells me that Mavic are
doing something wrong that compromises their rims' integrity. My guess
is that they are skipping the post-weld solution heat treatment to save
production costs, which results in rims that are weaker for their
weight than others.

Chalo Colina

Chalo wrote:
jim beam wrote:

Chalo wrote:

But the
ability of a rim to support spoke tension is chiefly a function of
circumferential compressive strength, and a pinned joint does not
compromise the rim's resistance to compression-- but a weld's
heat-affected zone does.

we've touched on this befo excess spoke tension does not increase
the strength of the wheel - there's no reason to do it. if you
experience loosening problems, you need to go with nipple "glue".


That dog still won't hunt.

hmm.

Spoke tension is what allows a rim to carry
a load.

agreed.

I could squash even the strongest unlaced 700c rim I've got,

unsupported, yes. but that's not the loading the rim experiences when
laced.

without resorting to dynamic loads like those I inflict on my bike's
wheels.

A wheel whose spokes go slack is on the verge of collapse,

so jobst says, but i have yet to see the math on that.

and can't
provide adequate lateral support to the rim section with unloaded
spokes.

lateral loading involves tension /increase/, not decrease. a spoke
simply has to be present to offer lateral loading support.

Since my wheels eventually fail from being bent laterally too
much to true,

which is consistent with excess tension.

I think it's important to support my rims in lots of
places with enough spoke tension that they don't become unconstrained.
Mavic rims don't allow me to do that, while others of equal weight do.

high spoke count for your application is good. and that may well be
your experience with mavic rims. but it's still no logic for excess
tension.



Some of those others are even welded, which tells me that Mavic are
doing something wrong that compromises their rims' integrity. My guess
is that they are skipping the post-weld solution heat treatment to save
production costs,

solution heat treatment is not precipitation hardening. again, i don't
know what mavic are actually doing, but i still don't think you're
offering evidence of what their heat treatment history may or may not be.

which results in rims that are weaker for their
weight than others.

i accept your word on that!


Chalo Colina