How much do cranks expand by?

I'm trying to convince someone that cranks expand as they are fitted on
square tapered spindles.

How much does the hole enlarge by when the crank is correctly fitted, and
how can the amount be measured or calculated?

If a specific example is needed: Campagnolo Veloce.

Thanks.

~PB

"Pete Biggs" wrote: (clip) How much does the hole enlarge by when the crank
is correctly fitted, and how can the amount be measured or calculated?
^^^^^^^^^^^^^^
First, I would measure the taper. Then I would hand seat the crank on the
taper, and count the turns of the screw required to bring the crank to
appropriate tightness. From the thread pitch, you can calculate how far it
moved up the taper. Knowing that, you can figure how much the taper
expanded the crank. (Assume the tapered square shaft, being steel, does not
compress.

On Wed, 25 Aug 2004 21:22:19 +0100, Pete Biggs wrote:

I'm trying to convince someone that cranks expand as they are fitted on
square tapered spindles.

How much does the hole enlarge by when the crank is correctly fitted, and
how can the amount be measured or calculated?

The hole will expand, and the spindle will compress. Both aluminium and
steel (or titanium) are "elastic" materials and are placed under
"stress" by the bolt and the taper, and therefore experience "strain".
How much? Somewhere between "just a little" and "not a lot". It should
be calculable (with more effort than I'm prepared to put in ;-) If you
happen to have a class of mechanical engineering students handy this
would be an interesting question to set them.

You could try asking in rec.bicycles.tech where Jobst Brandt may have an
answer. (And a lot of fools will have wrong answers...)

As a wild guess, you probably couldn't measure it with a conventional
micrometer, or only just.



Mike

Mike Causer wrote:
The hole will expand, and the spindle will compress. Both aluminium
and steel (or titanium) are "elastic" materials and are placed under
"stress" by the bolt and the taper, and therefore experience "strain".
How much? Somewhere between "just a little" and "not a lot". It
should be calculable (with more effort than I'm prepared to put in
;-) If you happen to have a class of mechanical engineering
students handy this
would be an interesting question to set them.

You could try asking in rec.bicycles.tech where Jobst Brandt may have
an answer. (And a lot of fools will have wrong answers...)

As a wild guess, you probably couldn't measure it with a conventional
micrometer, or only just.

Thanks Mike. Enough expansion to make count as an interference fit,
would you say?

Buy the way, this *is* r.b.t! :-)

~PB

On Wed, 25 Aug 2004 23:56:34 +0100, Pete Biggs wrote:

Thanks Mike. Enough expansion to make count as an interference fit,
would you say?

It's an interference fit for sure, but not in the traditional
engineering sense. Tightening the bolt does it, whereas a "proper"
interference fit comes from the slight overlap of the unforced sizes of
the two components. I did have a quick look at Machinery's Handbook,
but it doesn't appear to cover bicycle tapers. For any real calculation
I'd have to dig out my college textbooks, which haven't been opened in
the last 35 years ;-(


Buy the way, this *is* r.b.t! :-)

Ahhh, yes. In traditional usenet fashion I noticed a split second after
sending the reply. I'm used to seeing your name on uk.rec.cycling, and
I assumed (silly boy!) that's what I was reading....


Mike

Pete Biggs writes:

I'm trying to convince someone that cranks expand as they are fitted
on square tapered spindles.

How much does the hole enlarge by when the crank is correctly
fitted, and how can the amount be measured or calculated?

If a specific example is needed: Campagnolo Veloce.

These use an ISO square taper seems to be 1:15 or so and the crank
bolt has a 1mm pitch. Assuming you push the crank on manually as far
as it will go, you'll get 0.0666mm expansion with every rotation of
the bolt. The reason for this approximation is that the steel spindle
cannot readily compress and must extrude elastically axially like a
rubber rod grasped in hand. Steel having a higher modulus:

Al = 68.95 GPa
Fe = 196.50 GPa

So count the turns of the crank bolt and divide by 15 roughly
speaking, if I got the ISO standard correctly for square tapered
spindles. Maybe someone can check on that. I don't have the value
handy.

This is not a good joint and that's why people are looking for a
better way. See ISIS or Shimano's latest answer. It's not change for
change's sake but because cranks and spindles fail. I can swear by
that!

Jobst Brandt

In article ,
wrote:

Pete Biggs writes:

How much does the hole enlarge by when the crank is correctly
fitted, and how can the amount be measured or calculated?

These use an ISO square taper seems to be 1:15 or so and the crank
bolt has a 1mm pitch. Assuming you push the crank on manually as far
as it will go, you'll get 0.0666mm expansion with every rotation of
the bolt.

This is not a good joint and that's why people are looking for a
better way. See ISIS or Shimano's latest answer. It's not change for
change's sake but because cranks and spindles fail. I can swear by
that!

I know you have mentioned that you get around this by inspecting your
cranks assiduously, and that you have mentioned specific
_implementations_ of ISIS with design flaws.

So, the question is, when you get your bike upgraded to a threadless
stem, will you also add an ISIS or Hollowtech II crank and BB?

--
Ryan Cousineau, http://www.wiredcola.com
Verus de parvis; verus de magnis.

i have two sets, one steel one aluminum
of l980's metallurgy-the aluminum set is a fancy SR,(rumour has it
that this one is worth $250 today-no more standing around the lathe
for $1/hr) the steel a lesser variety but still in today's $100-76 'no
stinking ramps' range.
each CR appears to last maybe 10,000 miles with two-three rebuilds a
year and maybe 6 or 7 reasins to pull the cranks off.
Ima no,well almost,gaulling mechanic.
the cranks, as JB maths, do expand even with a light touch-i see more
than a 32nd" up to an 8th" on the steel crank that works loose: one of
four!?
that's over two-three years. I was surprised to see this happen.
we use anti-seize!

Ryan Cousineau writes:

How much does the hole enlarge by when the crank is correctly
fitted, and how can the amount be measured or calculated?

These use an ISO square taper seems to be 1:15 or so and the crank
bolt has a 1mm pitch. Assuming you push the crank on manually as
far as it will go, you'll get 0.0666mm expansion with every
rotation of the bolt.

This is not a good joint and that's why people are looking for a
better way. See ISIS or Shimano's latest answer. It's not change
for change's sake but because cranks and spindles fail. I can
swear by that!

I know you have mentioned that you get around this by inspecting
your cranks assiduously, and that you have mentioned specific
_implementations_ of ISIS with design flaws.

My crank failures WERE at the pedal eye. The Square tapers had all
been detected as cracks beginning at the corners but never an advanced
one that could cause failure soon. I've fixed the pedal eye problem
but I'll have to defer to MFr's for the spindle.

So, the question is, when you get your bike upgraded to a threadless
stem, will you also add an ISIS or Hollowtech II crank and BB?

I've been using a threadless stem for some time now but that doesn't
do anything for the BB.

Jobst Brandt

Ryan Cousineau writes:

How much does the hole enlarge by when the crank is correctly
fitted, and how can the amount be measured or calculated?

These use an ISO square taper seems to be 1:15 or so and the crank
bolt has a 1mm pitch. Assuming you push the crank on manually as
far as it will go, you'll get 0.0666mm expansion with every
rotation of the bolt.

This is not a good joint and that's why people are looking for a
better way. See ISIS or Shimano's latest answer. It's not change
for change's sake but because cranks and spindles fail. I can
swear by that!

I know you have mentioned that you get around this by inspecting
your cranks assiduously, and that you have mentioned specific
_implementations_ of ISIS with design flaws.

My crank failures WERE at the pedal eye. The Square tapers had all
been detected as cracks beginning at the corners but never an advanced
one that could cause failure soon. I've fixed the pedal eye problem
but I'll have to defer to MFr's for the spindle.

So, the question is, when you get your bike upgraded to a threadless
stem, will you also add an ISIS or Hollowtech II crank and BB?

I've been using a threadless stem for some time now but that doesn't
do anything for the BB.

Jobst Brandt