OK to file a crankarm

Hi

Is it ok to file about 3mm off an old 6/7 speed 110 pcd triple crank arm?
I've fitted TA 9/10 speed chainrings but a 10 speed chorus front mech hits
the inside of the R/H side crank arm. I propose to file out a 3 mm deep
groove with a half-round file. Will I significantly weaken the crank arm?

Bin

bin wrote:

Is it ok to file about 3mm off an old 6/7 speed 110 pcd triple crank arm?
I've fitted TA 9/10 speed chainrings but a 10 speed chorus front mech hits
the inside of the R/H side crank arm. I propose to file out a 3 mm deep
groove with a half-round file. Will I significantly weaken the crank arm?

Yes. The groove will form a stress riser that will concentrate the
stresses at that one (weakest) point. I'd never ride a crank like
that, personally.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Mark Hickey wrote:
bin wrote:

Is it ok to file about 3mm off an old 6/7 speed 110 pcd triple crank arm?
I've fitted TA 9/10 speed chainrings but a 10 speed chorus front mech hits
the inside of the R/H side crank arm. I propose to file out a 3 mm deep
groove with a half-round file. Will I significantly weaken the crank arm?

Yes. The groove will form a stress riser that will concentrate the
stresses at that one (weakest) point. I'd never ride a crank like
that, personally.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

I agree. Find another solution. The last thing you need is your crank
failing 'while rinding'. You're begging for dental surgery if you go
that route.

bin wrote:
Hi

Is it ok to file about 3mm off an old 6/7 speed 110 pcd triple crank arm?
I've fitted TA 9/10 speed chainrings but a 10 speed chorus front mech hits
the inside of the R/H side crank arm. I propose to file out a 3 mm deep
groove with a half-round file. Will I significantly weaken the crank arm?

Bin

i wouldn't recommend it. but that said, if you're just pottering about
town /and/ you carefully inspect for cracks after every ride, you can
get away with it for a while. but it will be a stress riser and the arm
has a significantly increased probability of fatigue at that point, so
if you're a high mileage guy, invest in safety and get a new campy or
shimano crank. last thing, if you do file, when you're finished with
the crank, destroy it, don't let it get onto the used parts market.

1.)I'm not saying it is okay to do this, but if you do, it is safer if you
taper the crank, rather than notch it.
B.) The correct term is stress *raiser.*

On Mon, 20 Feb 2006 16:21:36 GMT, "Leo Lichtman"
wrote:

1.)I'm not saying it is okay to do this, but if you do, it is safer if you
taper the crank, rather than notch it.
B.) The correct term is stress *raiser.*

Just for laughs I did a google search for "stress raiser"; 685 hits.
"Stress riser"; 9,160. :-|


jeverett3ATearthlinkDOTnet http://home.earthlink.net/~jeverett3

"John Everett" wrote: Just for laughs I did a google search for "stress
raiser"; 685 hits.
"Stress riser"; 9,160. :-|
^^^^^^^^^^^^^^^^^^^^^^^
What does a notch do? It *raises* the stress, so it is a stress raiser.
What would a stress *riser * be? Something that rises with the
stress?...over the stress?...beyond the stress? Maybe a stress riser would
be a psychiatrist's income, which goes up when people feel stressed. :-)

I did that on a Stronglight 99 tandem driveside rear crankarm in about 1983,
for exactly the same reason. The crank is still going strong and still in
use. I figure the manufacturers engravings in the crank are more of a stress
riser than my carefully smoothed out scallop from the back of the crank.

Nick

"bin" wrote in message
news
Hi

Is it ok to file about 3mm off an old 6/7 speed 110 pcd triple crank arm?
I've fitted TA 9/10 speed chainrings but a 10 speed chorus front mech hits
the inside of the R/H side crank arm. I propose to file out a 3 mm deep
groove with a half-round file. Will I significantly weaken the crank arm?

Leo Lichtman wrote:
1.)I'm not saying it is okay to do this, but if you do, it is safer if you
taper the crank, rather than notch it.
B.) The correct term is stress *raiser.*



From http://www.sheldonbrown.com/gloss_st-z.html

Stress Riser
A stress riser is a notch, crack or other irregularity in the
surface of a part which creates a starting part for a crack or tear. A
familiar household example of stress risers is cellophane: It is fairly
difficult to start a tear in a straight edge of a piece of cellophane,
but once a tear has started it is almost impossible to stop.

A similar effect occurs with other materials, including those used
to build bicycle frames. Good design avoids placing stress risers in
heavily loaded areas of the frame.

Peter Cole wrote:
Leo Lichtman wrote:
1.)I'm not saying it is okay to do this, but if you do, it is safer
if you taper the crank, rather than notch it.
B.) The correct term is stress *raiser.*



From http://www.sheldonbrown.com/gloss_st-z.html

Stress Riser
A stress riser is a notch, crack or other irregularity in the
surface of a part which creates a starting part for a crack or tear. A
familiar household example of stress risers is cellophane: It is
fairly difficult to start a tear in a straight edge of a piece of
cellophane, but once a tear has started it is almost impossible to
stop.
A similar effect occurs with other materials, including those used
to build bicycle frames. Good design avoids placing stress risers in
heavily loaded areas of the frame.

The definition should be appended with the correct name. You rise out of
bed, and you raise a bike to put it on a car rack. It's a misnomer, even
more so than clipless pedals. We should say that we "click into" our
clipless pedals.

--
Phil, Squid-in-Training