Originally Posted by
thook
member merziac posted some pics of his merz mtb with a modified dura ace crank making it a triple. seems like a neat idea. certainly looks nice! but, it got me to thinkin'
i've got two early 80's SR super custom cranksets with a 118bcd and the smallest ring you can run is 36t. even with a larger cog of 34t, that's still not real low for big hills around here. so, since i have two, it occurred to me i could try modifying the spider of one to fit a 74bcd inner to make a triple
i have a drill press, tapping tools, good bits, a vice, metric measuring tools, ring spacers and bolts.....basically everything i would think i'd need to try it. thing is, i believe there's a probably a good efficient way to go about doing this since it's obviously been done. no need to reinvent, and i could hopefully avoid mistakes. for example, what's an effective way to secure the part and make sure the holes are drilled evenly/straight and properly centered? and, of course, if there's design considerations of the part that might lead to failure, i'll have to reconsider this attempt
as always, thanks!!!
ps. i know...it'd be much easier to use a same period triple crank to achieve desired gearing, and for now i'm doing that. but, it think it'd be swell to run the original SR. i've got several 118 rings for it, too
The guys who do this are master craftsmen, Merz being at the top of the list, he did all of his own and may still. I'm no expert but I think its done on a milling machine or drill press with a rotating table so they are done in a perfect circle. I have seen it done by one offs but they were expert machinists to begin with. I have always thought you could use a BB setup of some sort on a press for the rotational portion, if you could get it clamped down solid and square it would be a matter of drilling the holes right in the middle of the arms.
