Modifying a crank spider to fit Praxis 48/32 rings?

[Look585]

Has anyone modified (filed, machined, dremeled, etc.) a standard 110mm BCD crank spider to fit the new Praxis 48/32 gravel rings?

Praxis machines a small shelf into the inboard ends of the spider arms such that its 32t chainring doesn’t cause the chain to skate on the ends of the spider arms.

I’d like to do this for a non-praxis crankset. Am I crazy? Would you answer the “crazy question” differently if I told you the spider was an expensive-ish SRM 110 compact?

[hollowgram5]

I would think it's probably not terribly difficult, assuming one had access to a mill and the dims of the praxis shelf. I've considered it myself with a less expensive sram spider!

[staggerwing]

Could you first mount the ring, then lay a length of chain around, to see if there is even a problem that needs to be addressed?

If the amount of material that would need to be removed is quite small, as shown in the image, I don't see a problem. On the outside of the mounting hole, it would be in a low stress zone.

And, for that small amount of material removal, I would hand file. Would also clamp a bar of plastic to the inside to act as a dam/barrier to file against.

[Look585]

I decided to give this a go on a test crank (Shimano CX70) before attacking the SRM.

Mounted the rings before making any mods to test things out. You definitely need to file down the spider arms. Very clunky / creaky / crunchy when I took it around the block.

I started with a Dremel burr bit. That quickly broke. Swapped to a Dremel diamond grinder bit and it was taking ages. Finally tried the Dremel grinder disk and that was great. Very quick removing material and a smoother finish.

I went slowly, only taking off enough to get the spider arm below the valleys between chainring teeth. Reassembled everything and it is perfect. A bit unsightly where things slipped in the grinding process, but functionally excellent.

I haven't decided whether to attack the SRM yet. I found a silly deal on a Stages left arm ($120 shipped for Shimano 105!) so I'll start with that. Not matchy, but close. I'll probably learn to live with it and not risk damaging the SRM.

Overall it was a fair bit of work for just 2 fewer chainring teeth. :rolleyes: The matched/timed rings do shift better than the mismatched 48/34 I was running before.

[R3awak3n]

might as well sell the SRM and buy a praxis crank with 4iiii power for $500, you probably come out ahead.

i have a set of these rings on a praxis crank and it indeed shifts very well, just like all the other praxis rings I have.

[hollowgram5]

might as well sell the SRM and buy a praxis crank with 4iiii power for $500, you probably come out ahead.

i have a set of these rings on a praxis crank and it indeed shifts very well, just like all the other praxis rings I have.Paulo brings up a good point. The praxis guys will sell you a crankset with your choice of rings ($530) + a bb (~$45 for English threaded) and you get the install tool with the purchase.

I picked up one of these 4iiii/Praxis setups from the forum and am liking it pretty well so far.