Help, bent spider arm on crank

[Sheer11111]

Does anyone know how to unbend a bent spider arm on a crank. I bent a
spider arm on my nice dura ace crank, only slightly, but enough to cause
the chain rings to wobble, which messes up my shifting.

Is it advisable to attempt staightening?

[Sheldon Brown]

First, you need to make sure that the problem is in the spider, not the
axle. Note which spider arm is out of position, and which way. Remove
the crank, then re-install it 180 degrees from it's normal position.

If the same arm is bent the same direction, you know the problem is in
the spider, not the axle. Here's my method for straightening spider
arms:

Remove the chainrings from the spider. Clip a spring-type clothespin to
the cage of your front derailer cage so that the handle end of the
clothespin approaches toward the spider arms from the side. Slowly rotate
the crank, and use your shift lever to move the clothespin until it is
almost touching the sides of the spider arms as they go by. This will
give you avery accurate indication of which one is bent, and how much.

The actual straightening can be done with an adjustable wrench closed
tightly on the part of the spider arm that goes between the chain rings.

This seems like a crude technique, but it is really quite accurate, and
easy to do. It might be a bit more difficult if you have indexed front
shifting, you might have to play games with the adjusting barrel for
fine tuning the indicator.

Sheldon "Clothespins Are Almost As Useful As Toast Wraps!" Brown
Newtonville, Massachusetts