Folding Bikes - BB replacement Q for Raleigh 20

I wonder about taking a regular 73mm Shimano BB, reducing the left cup length on the lathe or even saw it off, such that the thread would just fit before the 24TPI interfered with the 26TPI. For the right side, on the lathe and remove same amount of thread so it will just fit threadwise. Or do you have to remove too much thread that it becomes iffy? Any way to calculate the amount?

Anybody do this before? If it works, you basically throw open the entire repertoire of cranksets available to choose from.

I'd guess it was worth a try though going to all that trouble you'd probably end up spending more than on a couple of 26tpi Phil Wood retaining rings. Unless you have your own lathe of course.

I guess it could work but like you I'd have some doubts about running the thread 'on empty' in such a high load area.

How about filling and re-tapping the BB shell? I've heard of successes that way before. There's also an inexpensive option using a plastic-bodied BB made by ***. V1nce (where are you V1nce?!!!) has a good page explaining what's entailled here: www.rhizomes.nl/twenty.html

I have my "own" lathe at work, so no prob there.

I been thinking about it, and there are 2 threads diference over one inch, so 1 thread over 1/2", and 1/2 thread over 1/4". I suspect 1/4" will be the maximum usable amount before threads start wrecking themselves.

I have an old plastic cup BB which I intend to use for this caper.

I wonder how much thread a BB "needs"? I know it is a high load area, but the load is carried by the bearing while the threads are for retention. The fact that some BB have one or more plastic cups confirm for me that they are only for retention not strength. I figure on using a strong thread locker so I can undo them if necessary but still have high retention strength. As long as there is zero movement at the cups I should be OK.

Anybody think this is a realllllly dumb idea?

About 3 weeks ago I've noticed a Raleigh Twenty for sale on e-bay that uses the cup & cone option (See Shedlon Brown).
I asked him about it and he said that he used the '7' spindle along with new bearings (and old cups)

I would suggest trying this option before cutting the frame

I had my LBS rethread my Twenty's bottom bracket and I have had no problems whatsoever. I now also have the advantage of using any BB that I want.
juan