Stem bolt failure

Ron Ruff wrote:
Lou D'Amelio wrote:
Hands down, the unbeatable stem for reliability is Thomson. Both of
their stems (Elite and X-2) are milled from solid blocks of aluminum,
no welds.

Based on what? Forging is superior to milling from a solid block... the
best stems are all forged these days.

Some test data on stems can be found he
http://www.biketechreview.com/stems/summary.htm

Just to clear up something about Thomson stems - they are forged into a
rough aproximation of their final shape, and then are machined to the
final shape/finish. This is similar to what RaceFace did on their
Turbine cranks. RaceFace had to print "Forged" on the sie of their CNC
looking Turbine cranks because so many people got scared of CNC cranks
snapping back in the ultralight, multicolored MTB days of the early
90's.

Phil, Squid-in-Training wrote:

Chalo wrote:

Forging *can* make a stronger, more durable part than machining.
However, machining often allows the use of a stronger material, better
part geometry, or better finish and tolerances than forging, at the
same or lower cost.

This can't possibly be true across all economies of scale. If you were to
mill 10,000 stems versus forge 10,000 stems, I'm sure that the forging
process would save a whole heck of a lot of material. Sure, you need molds
and all that stuff, but you can recoup initial investment after X number of
stems.

You are absolutely correct, but then we're not discussing *all*
economies of scale. For really cheap bike parts, forged steel is hard
to beat. And if cost is no object, then you forge the
highest-performance alloy possible, then machine it to a precision size
and finish-- or you use even more exotic materials and techniques. But
when the criterion is maximum strength-to-weight, at a known acceptable
cost, in a comparatively low-volume item (e.g. a single manufacturer's
premium stem in a single size), then it's very likely that machining
will yield better results than forging.

I expect that the Thomson stem has higher strength, stiffness, and
longevity per unit weight than most if not all forged stems in the same
price range. And if that's true, then it's because machining the stem
allows the manufacturer better control over more relevant features at a
given production cost than he would have with a forging process.

Chalo Colina

Anthony A. wrote:

Just to clear up something about Thomson stems - they are forged into a
rough aproximation of their final shape, and then are machined to the
final shape/finish. This is similar to what RaceFace did on their
Turbine cranks.

Earlier, I tried to find the facts about this, but I was unable to
determine that Thomson stems were machined from forgings. The only
mention of forging anywhere in the L. H. Thomson website is in the
descriptions of the seatposts.

Chalo Colina

"Chalo" wrote in message
oups.com...
Phil, Squid-in-Training wrote:

Chalo wrote:

Forging *can* make a stronger, more durable part than machining.
However, machining often allows the use of a stronger material, better
part geometry, or better finish and tolerances than forging, at the
same or lower cost.

This can't possibly be true across all economies of scale. If you were
to
mill 10,000 stems versus forge 10,000 stems, I'm sure that the forging
process would save a whole heck of a lot of material. Sure, you need
molds
and all that stuff, but you can recoup initial investment after X number
of
stems.

You are absolutely correct, but then we're not discussing *all*
economies of scale. For really cheap bike parts, forged steel is hard
to beat. And if cost is no object, then you forge the
highest-performance alloy possible, then machine it to a precision size
and finish-- or you use even more exotic materials and techniques. But
when the criterion is maximum strength-to-weight, at a known acceptable
cost, in a comparatively low-volume item (e.g. a single manufacturer's
premium stem in a single size), then it's very likely that machining
will yield better results than forging.

I expect that the Thomson stem has higher strength, stiffness, and
longevity per unit weight than most if not all forged stems in the same
price range. And if that's true, then it's because machining the stem
allows the manufacturer better control over more relevant features at a
given production cost than he would have with a forging process.

The thing is, Thomsons aren't all that light. They look nice though. I see
what you mean though.

--
Phil, Squid-in-Training

On 29 Sep 2005 06:03:50 -0700, "Anthony A."
wrote:

Just to clear up something about Thomson stems - they are forged into a
rough aproximation of their final shape, and then are machined to the
final shape/finish. This is similar to what RaceFace did on their
Turbine cranks. RaceFace had to print "Forged" on the sie of their CNC
looking Turbine cranks because so many people got scared of CNC cranks
snapping back in the ultralight, multicolored MTB days of the early
90's.

But.. the strongest bit in a forging is the surface. Milling that away
seems to be pointless.

Jasper

"Jasper Janssen" wrote in message
...
On 29 Sep 2005 06:03:50 -0700, "Anthony A."
wrote:

Just to clear up something about Thomson stems - they are forged into a
rough aproximation of their final shape, and then are machined to the
final shape/finish. This is similar to what RaceFace did on their
Turbine cranks. RaceFace had to print "Forged" on the sie of their CNC
looking Turbine cranks because so many people got scared of CNC cranks
snapping back in the ultralight, multicolored MTB days of the early
90's.

But.. the strongest bit in a forging is the surface. Milling that away
seems to be pointless.

Jasper

AFAIK, forgings compress the whole member, so even the grains far from the
surface become aligned, etc. I like the idea of a shot-peened finish
though.

Sometimes manufs claim that their stuff has a shot-peened finish, which it
indeed does, but this could simply be due to the casting process, like those
little balls or ceramic bits in investment casting... I can't think of it
now. In that case, there's no residual compressive stress at the surface to
increase the fatigue life of the product.

--
Phil, Squid-in-Training

On Thu, 29 Sep 2005 20:20:41 -0400, "Phil, Squid-in-Training"
wrote:

Sometimes manufs claim that their stuff has a shot-peened finish, which it
indeed does, but this could simply be due to the casting process, like those
little balls or ceramic bits in investment casting... I can't think of it
now. In that case, there's no residual compressive stress at the surface to
increase the fatigue life of the product.

If you give the forging molds a shot-peened finish, the forged product
will have it as well. And they usually do have a non-smooth finish,
presumably because it helps the molds last longer or something.

Jasper

Chalo wrote:
Forging *can* make a stronger, more durable part than
machining. However, machining often allows the use of
a stronger material, better part geometry, or better
finish and tolerances than forging, at the same or lower
cost.

Phil, Squid-in-Training wrote:
This can't possibly be true across all economies of scale.
If you were to mill 10,000 stems versus forge 10,000 stems,
I'm sure that the forging process would save a whole heck
of a lot of material. Sure, you need molds and all that
stuff, but you can recoup initial investment after X number
of stems.

Chalo responds:
You are absolutely correct, but then we're not discussing
*all* economies of scale. For really cheap bike parts,
forged steel is hard to beat. And if cost is no object,
then you forge the highest-performance alloy possible, then
machine it to a precision size and finish-- or you use even
more exotic materials and techniques. But when the criterion
is maximum strength-to-weight, at a known acceptable cost, in
a comparatively low-volume item (e.g. a single manufacturer's
premium stem in a single size), then it's very likely that
machining will yield better results than forging.

I expect that the Thomson stem has higher strength,
stiffness, and longevity per unit weight than most if not
all forged stems in the same price range. And if that's
true, then it's because machining the stem allows the
manufacturer better control over more relevant features at
a given production cost than he would have with a forging
process.

Interesting. How do you think this applies in the case of hubs? I
admire both Chris King hubs and Shimano hubs, but they do take
dissimilar approaches to manufacturing the hubshell- machined versus
forged, like we're discussing here.

"Dan" wrote in message
...

"Ron Ruff" wrote in message
Some test data on stems can be found he
http://www.biketechreview.com/stems/summary.htm


I looked at the link but couldn't get past the fact that they have the
equation wrong. Cantilever beam deflection is PL^3/3EI not PL^3/16EI. I
assume the rest is also unreliable.


I decided to give this page a second look and read past the error at the
top. The next thing they say is the stiffness is proportional to
pi*(Ro-Ri)^4 which is wrong. It is proportional to pi*(Ro^4-Ri^4). Jeez,
somebody needs to talk to these bone heads.