You can see the left, right and middle spindles are lighter than the others. These are the ones I replaced. The originals broke where they were pinned into the top comb.
None of the other spindles broke because they're not pinned into the comb. They're loose in their holes.
I had 6 spindles to replace for my four chairs. Making the spindles was the challenge. I bought the straightest-grained ash I could find and roughed out octagonal blanks with the Shopsmith's table saw function. I chucked them into the Oneway lathe chuck, but, as many of you would predict, the spindle quickly got too whippy to turn without chattering. I made a quick attempt at a steady rest. The less said about that the better.
Then I found this one online. http://www.novawoodturnersguild.com/docs/steadyrest.pdf. I mostly kept to the instructions, except instead of using rollerblade wheels, I used roller skate wheels, because that's what I already had in the back of the closet. The rollerblade wheels would've been better.
The steady rest worked as well enough to get the entire spindle down the largest finished diameter. But, I still got chatter while thinning out the upper half of the spindle. At that point, I finished up with a spokeshave using the Shopsmith as my shaving horse, turning the spindle by handle as needed. The lathe rest served as a backer to keep the spindle from bending away from the spokeshave.
Perhaps there were other solutions. I'm finished now, but I'm interested in what else I could've done.