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Old 01-24-07, 04:05 PM   #1
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tubing question.

I'm experimenting with an old steel frame to see if I can turn it into a colapsible bike. BAsically I want to cut the top tube and down tube near the seat tube and either slip a collar around the outside or a narrower diameter tube inside, drill through, and bolt together.
What I need to know is if there are standard diameters that will fit, ie, can I get a diameter tube that will fit over a standard top and down tube?
I'm assuming it must be a standard size, because lugs must be made out of it, right?
If I'm right, can someone tell me the diameters.
Also, can anyone tell me if drilling and bolting will weaken the frame any? I'm assuming it's safe, as there are places on a frame that are already drilled (cage bosses).
I know it's not an ideal solution, but like I said, it's more an experiment than anything.
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Old 01-24-07, 09:32 PM   #2
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I strongly suggest you check out and pony up the money to get some proper couplers if you really want to make a travel bike. Regarding the diameters, get some calipers and measure. To measure is to know.
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Old 01-25-07, 02:54 AM   #3
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I think there is pretty much zero chance S&S will sell to you. In theory they sell only to pros, though I have heard speculation they will sell to amateurs for personal use, whether they filter amateurs or not I don't know but they might want to know whether a person had the machinery to do the job. Anyone who knows, please tell me.

There are versions of your plan that work, but what I understand you to be asking probably won't. There are aircraft tube sizes that go up by the 1/16" or the 1/8", so if you want to make a insert or a sleeve you just dial in the right piece. You probably would have to make a sleeve since there are IDs of 1 1/8" for instnace, but getting something to fit inside that tube would probably require machining. Once you find the right tubing you would still need to find a way of making it fit tightly more like the fit of the stem over the stearing post or bars. Using bolts through the tubing would crush the fragile wall in this kind of application. Attached is an example of something with a similar purpose:

Also Check some velonomad posts he has posted another bolt together option. One problem with bolting together the triangle with sleeves is that they are at converging angles and won't pull appart. One tube has to be secured by means other than a simple fixed sleeve.
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Old 01-25-07, 06:16 AM   #4
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Thanks for the help, chaps. I'd not seen the desparadocycles page before. I think I've seen Velonomad's posts, but I'll check them out again.

I have an Idea that it can be done. I just need to work it out. I'm wondering if a long sleve with bolted grips (a bit like the part of a stem that the handlebars go into) would work. I'm trying to figure out in my head if the pressure was all around and the sleve was long enough, it would hold fast. If it were a two piece affair, then there would be no difficulty in taking the frame apart. I'll have to look around and see if there's anything on the market that would do the job; some sort of longish tubing clamp. I have a mind there is.

I'll let you know if I'm successful.
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Old 01-26-07, 07:25 AM   #5
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I started a similar project a couple of months ago,unfortunately I have been busy with with other things and it is just sitting there right now.

It is much easier to put a slip joint over an existing tube. If your top tube is 1" OD get a 1.125 tube with a .058 wall thickness, similarly if the down tube is 1.125 OD you need a 1.250 tube with a .058 wall thickness. Companies like sell .058 wall tubing in short lengths. If the bike you cut has double butted tubing and you cut in the thin part of the tube. you might want to braze a 1" long reinforcement ring inside the male tube to prevent possible damage to the end of the male tubes when the bike is apart.

Because the main frame is a triangle there is interference when taking the bike apart or putting it together. you will have to squeeze the front triangle together almost 1/2 "when taking apart or putting together which is pretty near impossible to do on a regular basis without damaging the tubes.
Herse used a baloney cut and a sliding collar with a lock pin on the down tube to compensate for the interference of the tubes. It undoubtedly works, but it looks bit scary . I would be more inclined to put the sliding collar on the top tube where the loading of the frame would have that joint under compression and you could also use a square cut on the mating tubes. IMO it would give a greater margin of safety and be far simpler to make in a home workshop.

The other option is to make a step-through(mixte frame) where the top and down tubes are parallel. This is what I'm likely going to do if I continue with the project.

I recently came across a folding bike cheap, I may just strip that down to the "J" tube and add new stays, new fork, integrated racks etc.
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