Folding Bikes - folder DIY?

so here's a line of thinking that i can't seem to "let go" since i've become increasingly aware of various folders' mechanism, for, well, folding and also looking at older designs (raleigh twenty, vintage pugeot, et al)...

how hard would it be to cut an existing non-folding frame in half, and weld on locking hinges (a hinge with some sort of clasp) or plain hinges and then drill holes for a locking pin... ??

i imagine this is perhaps how the original folders were prototyped... well, i want to do this to my bmx! the frame is already small enough to be quite portable, if it were only folded in twain! obviously i'll have to use TWO hinges for both the top and bottom bar, but no biggie, really. and i already have become acquainted with a neighborhood welding expert who's adept at modifying bikes, to boot (he's made some really crazy looking tandems, recumbents, cruisers, off-roaders all from bits of other bikes).

so... am i nuts? is this possible? anyone here done it or seen it done?

and more specifically, where do i source the kind of hinge i'll need?
i don't even know what i'm looking for when i visit hinge/clasp manufacturers' websites...
the kind of hinge that has two flat bits and comes together with an integrated locking mechanism/lever...
what's that even called?

If I tried that, I'd only succeed in making it easier to take the two bits of bike to the dump.

how hard would it be to cut an existing non-folding frame in half, and weld on locking hinges (a hinge with some sort of clasp) or plain hinges and then drill holes for a locking pin... ??
It's rather difficult to do properly, even for an experienced framebuilder.

For example, you can retrofit S&S couplers onto a steel frame. However, S&S won't sell direct to the public; I don't think they sell them to a framebuilder until they meet specific criteria (presumably including signing waivers and having big insurance policies). Most of it is that if you don't do the procedure properly, the frame will split under load and the rider will end up eating pavement / dirt.

This is especially important if you want to continue to use this bike for BMX purposes (e.g. off-road, grinding, tricks etc). Not many folding bikes are made with those kinds of tolerances in mind.

Also, what's the frame material? Steel is fairly easy to weld, but aluminum is much trickier. Even the S&S guys won't do aluminum.

The hinges are proprietary; you'd have to design and build your own, or jack them off of other bikes.

I think you'd be much better off picking up a used folding bike, and upgrading parts as needed.

Yes, you are nuts.
I doubt that you would achieve a satisfactory result for the work invloved.
Most BMX bikes already have quite a small frame and both seat and handlebars can be lowered/twisted significantly, making the package even smaller, and with 20" wheels would probably fit in medium sized car.
Also they have a high bottom bracket which is not good for riding any distance.
My advice is to give up before you start and get yourself a folder which has been designed as such. Even a poor folder is likely to be better than anything you might achieve by carving up a BMX bike.

Well, if this is purely for experimental purposes, why not? But if you are actuay gonna use the bike I'd advise against it because of the abovesaid reasons.

I have a dahon cadenza which hinges on the top tube and seat tube. The alignment of the hinges, their position on the tubes and their orientation in relation to the whole bike is fairly critical. The biggest challenge will be building a jig that holds your bike so you can "cut and shut" with both hinges in alignment.
If you really want to do this you need to figure out the hinge position (suggest you use cardboard tubing/ductape scale model, then prototype the jig (using an junk frame) before taking a saw to your bike.
The hinge unit need not be super complex like the Lockjaw, check out some simple ones like the Raleight 20 shopper.

a 230mm grinder might cut both tubes at the same time :D

I think it would be best to take the frame you're thinking of doing this to, and throw it straight in the skip /dumpster, just so you save some time and money, not to mention raising your blood pressure through frustration.

:)


Waiver - I do realise that some people are immensely more skilled at metalworking than I am. I know this because if it were down to me, we'd all be chipping away at flints and we aren't.

If you've read all of the above and still want to have a go at it, why not? Even if it was a dismal failure all you will have lost is a BMX frame and some of your spare time.

So yes, you are nuts, but remember that's a social definition and it need not hinder you! If nothing else, you will learn a lot about mechanical problem-solving in a three dimensional universe (and that's always fun!).

By all means, keep us informed on your progress and present us with any specific problems that you may not find immediately solveable. We may be able to help. Or we may not. But if you already know how it's going to turn out, where's the adventure in that?

Rick / OCRR

wow i wasn't expecting any reponse no less some of the more technically-minded sound-offs - thanks all!

yeah hinge position of the top relative to bottom tube is critical and the two cuts would have to be made perfectly in line with each other and exactly perpendicular to flat ground... not exactly that easily done with two seperate cuts even with careful measuring and proper equipment (mitre saw & a LARGE workbench w/ clamps).

i kinda figured the hinge/latch combination was proprietary as i haven't seen Anything similar from plain-vanilla hinge manufacturers' sites... it's probably an in-house custom job with a butt hinge machined onto or welded onto a clasp/latch to form the unified mechanism... if you look Really closely at the design of the pugeot folding bike's hinge it seems to be this case.

the s&s coupler is precisely in line with another line of thinking i've had on this topic, namely -- does it need to be a hinge? the other way i was thinking i could achieve the same result would be to cut the frame, find steel tubing that's smaller in diameter than my bike frame tubing, fit sections inside my top and bottom tube at the cut points, drill holes through both sets, and use locking pins, ubolts, or ulocks to join them whole again... it appears the s&s achieves the same result, albeit, in a far more elegant manner.

ironically the s&s site has a link to one of my oft-frequently local shops as one of their official framebuilders/partners - http://www.sandsmachine.com/bp_bil.htm -- though the place has been renamed 'bicycle stable', and montana norvell is Much older and more experienced now :)

the s&s doesn't seem to account for locking/security... which is kind of an issue... at least my idea of using a ubolt to join either the top or bottom tube would solve this problem.

as an alternative to a u-lock, a minimum of two hitch receiver locks could be used... these are straight pins meant to be used to secure a car/truck hitch:

http://www.masterlockcycle.com/images/product_receiver.jpg
http://www.masterlockcycle.com/product_receiver.shtml

there are many brands/diameters/material of these.

major upshot of ditching the notion of a hinge? NO WELDING.

What about avoiding interrupting the middle of a frame tube? You could create something like a rear triangle that bolts onto the main triangle, and it would be way easier. For example there are designs for recumbents and tandems that involve sticking two small frames together. You could have a folding tandem (not exactly solving your original problem, I know) if you stuck the two halves together non-permanently.

it's a possibility, but the main top and bottom tube are WAY long so you'd have a really short back section and a really lengthy front section rather than a bike nicely lobbed in half... also the chainring would be sticking out anyways, so you don't gain much by considering a 'cut point' further back on the frame.

chopping up and trying this on a used frame that Isn't in use by my current bike is a good idea... i'm keeping tabs on a few ebay auctions for some decent-condition gt, diamondback, redline frames that would all be suitable replacements to my current frame...

edit @ 5:54am - on a whim after being up late (insomia) i checked ebay buyitnow's for 'bmx frame fork' and found a Totally Sweet simple chrome unstickered solid-condition mongoose frame and fork, even including cranks, for < $100 (< $70 actually With shipping). i will NOT feel bad about experimenting on this one to work out a hypothesis.

you'd have been better with a painted frame as it would be easier to refinish.

*****-and-a-half finding a source of metal pipe that has inner/outer diameters that would serve as either an inner or outer 'sleeve' to the top and bottom tubes of my newly acquired mongoose frame, but at last i was able to find suitable diameters in short-order (don't need to buy in bulk) from SMALLPARTS.COM (http://%3Cb%3ESMALLPARTS.COM%3C/b%3E) (all caps because their site is Totally useful for project builders/prototype people).

going with a two-sleeve scheme where i'm slipping the original halves of the frame tubing between short segments of pipe with a bolt through them & secured with really nice hand knobs from JW Winco ... http://www.jwwinco.com/products/section8/krska/index.html
http://www.jwwinco.com/products/section8/krska/ttkrkp.gif

1 1/4" outer diameter [outside bike frame tube]
http://www.smallparts.com/dp/B000FMUR9M?ie=UTF8&pf_rd_r=1S35Z92HXMNVNN12YHYM&pf_rd_p=358014801&pf_rd_i=3000&pf_rd_s=right-3&pf_rd_m=AIUBT5HP6PMAF&pf_rd_t=2901

1" outer diameter [inside bike frame tube]
http://www.smallparts.com/dp/B00137PNWY?ie=UTF8&pf_rd_r=1S35Z92HXMNVNN12YHYM&pf_rd_p=358014801&pf_rd_i=3000&pf_rd_s=right-3&pf_rd_m=AIUBT5HP6PMAF&pf_rd_t=2901

the slight discrepency in diameters will be met with 1 1/2" diameter heat shrink tubing, also providing the bonus effect of keeping metal from rubbing on metal
http://www.smallparts.com/dp/B0013HR35O?ie=UTF8&pf_rd_r=1S35Z92HXMNVNN12YHYM&pf_rd_p=358014801&pf_rd_i=3000&pf_rd_s=right-3&pf_rd_m=AIUBT5HP6PMAF&pf_rd_t=2901

already sawed my mongoose frame in half with a hacksaw... which was effort, but not as much as i might have guessed.

pictures to follow once things start to take shape.

I have done this with a BMX frame. I cut the top tube and down tube. I put the bike back together using two sleeves. Each sleeve was a piece of tubing that just fit over the frame tubes, and had a slit at each end
I used hose clamps (aka "jubilee clips") to tighten the sleeves onto the frame. It worked, but the hose clamps had to be very tight to keep things from slipping.

So I ended up with a heavy, single speed bike that could be disassembled/reassembled in about 10 minutes time.

It was an experiment to see if it could be done. With a little bit of welding I could have made proper clamps rather than using the hose clamps.

One thing I learned is that you can not get by just attaching the down tube and leaving the top tube free - the two halves of the bike quickly rotate in opposite directions around the clamp.

I then stuck a wooden dowel in the top tube to keep that from happening. It worked, but I found that during riding the top tube is not only compressed (front and back pushed together) but also tensioned (opposite motion).

So, i wouldn't say you were any crazier than I am. :)

glad i overengineered and using four bolts and two sections of tube...

as i'd mentioned previously, i was going to Really overengineer this and do both an inner and outer 'sleeve' but as it turns out that's easier said than done... you'd have to come up with some way of retracting the inner sleeve into the frame completely while you line up your bike halves, then slip them into position inside the frame -- some kind of 'slit' cut into the frame and a little 'catch' sticking out of slit bolted or welded onto the sleeve would be needed to provide you with a sort of 'sliding door' device...

so i'll continue as planned with just the outer sleeves and i'll reevaluate after a few test rides to see how it holds up; if it's strong/stable etc.

as for locking considerations i decided to just invest in a longer chain to use with my new york fugghetaboutit mini u-lock... i can think of a bunch of times i wish i had a longer chain than my current 3'3" length, so this upgrade was on its way anyway... i got the trimax t-hex 5' which is a bit longer than the kryptonite noose (4'-something) which will allow me to cinch a loop around the back tire & rear brake frame, around to the front tire, onto a bike rack or street post, and completing the loop with the u-lock on the vertical frame tube beneath the seat post... this way even if someone takes the time to undo all four of my bolts and removes the tube sleeves, they're still looking at two bike halves very much attached to each other and the rack/sign/post/tree... which is good enough protection for only the times i'm too lazy to disassemble the bike and lock the two halves to each other doubled-over.

at some point in the future, however, i may upgrade to these:
http://www.urbanbiketech.com/product-p/m10dual.htm

intended for 10mm rohloff axles, but there's nothing stopping me from substituting two of my 3/8" bolts for 10mm bolts and attach them with these special locking nuts -- then there'd be no removing them without the special 'pit' and bolt turning tool.

i'd like to add that cutting metal, especially stainless steel, with a miter saw and metal blade is FRIGGEN FUN!! sparks galore, man-with-power-tools-grunt-tastic.

wow dude, i think you lite a fire under me arse, cuz here i am now with a wonderfully re-assembled bmx frame... they say a picture's a worth a thousand words, and here's four!

http://farm4.static.flickr.com/3293/3085099374_59901fb6e2.jpg

http://farm4.static.flickr.com/3127/3085099930_bf22e749e8.jpg

http://farm4.static.flickr.com/3278/3085100464_c4f6827c65.jpg

http://farm4.static.flickr.com/3274/3085101036_a84c2c4082.jpg

i had to mark the two tube sections with 'B' and 'T', and directional arrows, on account of eyeballing the drilling of the holes -- there's only ONE way this baby comes back together, but at least it does, and in quite a Sturdy fashion, i might add.

anyone wondering about the black 'something' towards the front of the frame, that's heat-shrink that i applied up there so that i won't scuff up the frame with my chain lock as i did on my other bike (i like to wrap it around there & lock it instead of wearing it or throwing it in a bag)... i figured as long as i had access to slip 2" heat shrink on there, i might as well :)

I've been thinking a bit about this mod. the open tubes are obviously not as strong now that they have been chopped - aside from the compression and tension that they get, they will also be subjected to crush forces exerted by the sleeves. Maybe some wooden dowels inside the open tubes will help?

At any rate - Please update us on what happens with this experiment.

Cheers!

your point is valid but my educated guess is that lateral forces (sideways i.e. turning) aren't as much of a concern as distal (up/down, vertical) on account of sidewalk bumps and potholes... in either case it won't be clear if i need to upgrade to a different/stronger metal (314/304 stainless or hardened brass) until i've ridden it and seen the result. just holding the finished frame now, though, i'm pretty confident i won't see significant stressing for a while.

here we go! all built (it was a LONG day yesterday)

in two halves for travel...
http://farm4.static.flickr.com/3094/3122745165_0dcc229e91.jpg

let's go for a ride!
http://farm4.static.flickr.com/3260/3122745669_051fce642d.jpg

just took it on a test spin and i didn't notice any chatter/clatter/etc.
good to go!

Wow, you really did it you got determination - and it looks good too :thumb:
I keep my fingers cross that is does not break down under you.
(only time I did something similar, I ended up on the ocean with a surfboard in two parts which was not intended)

Hey, cool setup! I see two cables toward the rear triangle - so I guess you are running an internal gear hub?

you have a good eye - i sure am! sturmey archer SRF3 (freewheel 3spd).
it isn't super-amazing in terms of performance gain but 1st gear makes hills a Breeze,
which is all i wanted of it; i'm quite pleased.

my coupler section doesn't rattle during rides but it does require that i tighten it before the next ride... not that huge a hassle, really. just add it to the list before you go riding... brakes? check; headset? check; seat height? check; coupler? check!

the chainline suggested the absence of a derailleur and since there were two cables, i figured that the second one should go to some sort of internal hub.

I guess another way to go was with singlespeed + coaster brakes, that way you can split the frame and not have any cables in the way!

coaster brakes

have really bad memories of wiping out due to coaster brakes on my childhood huffy.
caliper brakes for me forever now.

found a good travel bag to wrap up this project and make it 100% travel friendly (and annoy bus drivers and train conductors a lot less, who would otherwise see me lugging a lashed together pile of bike on board)...

http://www.niagaracycle.com/product_info.php?products_id=31760
made by sunlite... works perfectly with room to spare.

Rekall, you did a great job. I'd love to seemore pics of the finished bike. The 2 halves are completely seperated when folded, right? There's no hinge keeping them together when folded?

Do you think that this is how Dahon or Downtube, or (insert favorite folder here) started?
I do. Go for it, but remember to sell when the first multi-million dollar bid comes.

yeah i seriously doubt i'm the first to look at a frame and a hacksaw and ask 'what if?' and if you look at the welds and hinge fabrication on vintage folders it's plausible, if not certain, that the first set of folding bikes were prototype knockups much like mine.

i found a pierce arrow folder (maybe rebranded from a bianchi or other make) and swapped the parts over from this bike to that one on saturday, and it makes for a much easier fold... however, now that i've stripped my modified frame away from its parts i'm going to consult with a local welder about maybe putting some hinges on there.

well done i wold like to try something similar.what things would you do differently? hinges, i'd consider something along the lines of a brompton

I posted a question about a do it yourself breakdown-type travel bike a couple weeks ago and someone mentioned this thread but no-one could find this link to it. I feel so fortunate to have finally found the link!

Anyway, the BMX conversion looks great. Sounds like the original poster has subsequently moved the parts off this frame and onto a "real" folding bike. My question- is that because of issues with the frame (like bolt holes elongating) or because you needed more of a folding type bike?

I travel several times a year internationally and would like a small bike that I could pack into an airline-legal 62" suitcase (samsonite oyster or similar). It looks like this bike would fit the bill? I like that the entire drivetrain would be unaffected when packing.

I have an old "Kent" BMX frame in the workshop that is awaiting the saw.

much thanks

So, can I clarify. Did you simply cut the tubes, add sleeves over the cut frame, drill through sleeve and frame, and insert bolts to keep it together?
I've been thinking much the same about cutting an old frame to see if I can make a separable bike. I was also thinking about inserting a dowel to give some strength - the main problem I found was that with dowels, the frame will not come apart, as one is not the same angle as the other. You would need some way of sliding one of the dowels, which would need a parallel cut down the tube's length, which would weaken it further. I suppose you could go for a single dowel on one tube.

BTW - well done. You look like you've done an excellent job.

Last night I pulled out the cheapo Kent BMX frame a started to build the bike up. I decided I will build the bike first without any frame mods to see if I really like the ride and feel. I must say it is a small package (this coming from a person with extensive long wheelbase recumbent experience). I still have to get an adapter to convert the bottom bracket and a new freewheel. No pics yet, but it looks very close to this one except I created a riser for the handlebars to elevate them more:

http://www.fixedgeargallery.com/2004/g/skid10.htm

It seemed most people were not too enthusiastic about this buildup on that thread, but I think it's pretty cool.

Of course, after riding it I may have a different impression. If I decide that I like it, I will cut the frame in a fashion similar to the original poster and create 2 outer sleeves that will be secured by pinch bolts (brazing is not an issue for me, so I won't have to use hose clamps or the like).

This will easily fit into a standard 29" suitcase by splitting the frame in two parts, removing the seatpost and handlebar riser, and stuffing everything into the suitcase.

Somebody in CV made a great detatchable from old frames.

CV??? I can't think of what that means. Help me out.

Classic & Vintage

http://www.bikeforums.net/showthread.php?t=523095&highlight=s%26amp%3Bs+couplers

i think its this thread :)

I've been following that thread for ages. I really like the way people tackle such a difficult task, and love reading the n'ersayers predincting doom and destruction.
Perhaps we should have a board called the Mothers of Invention for all those out of box thinkers.

So, can I clarify. Did you simply cut the tubes, add sleeves over the cut frame, drill through sleeve and frame, and insert bolts to keep it together?

100% correct.
i used 3/8" bolts... the largest diameter high-speed/metal drill bit i could find and also manage to man-handle through the frame was 3/8"

atom: i ride the folder as my main bike on account of it being easier to set up before getting on trains and into friends' cars. if i hadn't found that bike so cheaply ($50) i'd still be traveling with the cut-down bmx :) i do plan on traveling it down to my parents' retirement place as my 'home away from home bike'

rekall,

Good to hear the joints are not failing in any way. I"m taking your lead and creating my own bike very similar to yours. I have a BMX frame with a 19" top tube that I built up last week into this:

http://www.bikeforums.net/showthread.php?t=539610

With hopes to eventually preform surgery on the frame much like you did. It seems that it would easily pack into a standard 29" suitcase for travel (my ultimate goal). I will have quick-releases on both the handlebar riser and the seatpost, so it will be very easy to remove those two, the wheels, and then split the frame in two parts.

Nice built!

Another way is to just use a regular size full suspension frame. Almost any 4 link frame does work. Put a quick release on the rear suspension element. To fold it, you need to take off wheels of course. The rear folds towards the main triangle. This will fit into the trunk of a car. To get it smaller you can have 24" wheels (needs disk brakes). If you take off the fork as well you can get it into a suitcase for travel. Overall this is the lightest, strongest, and cheapest way to get to a non-compromise folder for off-road use.

that's a seriously sweet mutant Kent bmx, man. i myself am not a fan of race handlebars but it suits that bike strangely fine.

i recommend Not using a hacksaw, it'll take you a good 20-30 minutes of choppin' to get through the top and bottom tube... if you've got a table saw buy a metal blade for it, should run you about $10 - well worth it! not to mention you'll get much straighter cuts.

fitting the bike into a carry-on is a good goal; haven't tried mine in a carry-on-size suitcase but i Am happy to report that with the handlebar taken out of the headset and the seat out of the seatpost and things laid as flat against each other as possible, that my modified mongoose fits nicely with room to spare in this generic bag made for 20" folding bikes:
http://www.niagaracycle.com/product_info.php?products_id=31760

fitting the bike into a carry-on is a good goal; haven't tried mine in a carry-on-size suitcase but i Am happy to report that with the handlebar taken out of the headset and the seat out of the seatpost and things laid as flat against each other as possible, that my modified mongoose fits nicely with room to spare in this generic bag made for 20" folding bikes:
http://www.niagaracycle.com/product_info.php?products_id=31760

That's a good point; do the airlines even ALLOW something like a bicycle to be carried aboard a plane these days? I was planning on checking mine...

i recommend Not using a hacksaw, it'll take you a good 20-30 minutes of choppin' to get through the top and bottom tube... if you've got a table saw buy a metal blade for it, should run you about $10 - well worth it! not to mention you'll get much straighter cuts.http://www.niagaracycle.com/product_info.php?products_id=31760

I have a tubing cutter that is made for plumbing. I use it all the time to make square cuts in bike tubing, works great! But you're right, a chop saw would work just as well.

Here you are:


S&S Torque Couplers

Retrofit solution for disassembleable bicycles (quoted):

"For *touring* foldup bikes, people can retrofit their existing full-size steel or titanium bikes with S&S torque couplers (or buy new frames made with the torque couplers). These are easily competitive with the Bike Fridays for (a) time to completely pack the bike into a traveling case and unpack and set it up, and (b) size when completely collapsed. Cost can also be competitive with Bike Friday, since in all other respects, these are just ordinary full-sized bikes. True, these are not intended for frequent dis/assembly, but you get to use them on conventional full-size frames (steel and titanium currently, with aluminum-compatible supposedly in the works). When disassembled, a bike with normal 700C wheels fits into a case 26x26x10, which easily goes as ordinary baggage on a airline or train."

You can contact S&S Machine at: 800-763-5564, FAX: 916/771-0397. They can send you a current list of frame builders/manufacturers using their torque couplers.

Here is an e-mail I got from them on 5/3/96:

Thank you for including the S and S Machine Bicycle Torque Coupling (BTC) in the Folding Bike FAQ. We now have a web page which includes a list of 30 builders that use our system to produce road , mountain and tandem bikes that travel as regular airline luggage and links to those builders that have web sites. Co-Motion Cycles and Salsa Cycles stock bicycles built with the BTC ready for immediate delivery. I am not sure how familiar you are with our system but I would like to invite you to visit our site and review some of the comments and magazine articles as well as the builder list and profiles. Since S and S Machine doesn't actually build or retrofit bikes with the BTCs, I can't give you pricing but I have estimated prices and included them in my site. I also encourage you to visit Co-Motion's web site since they have a nice review of their travel bike line. If can be of any assistance in gathering or compiling information or in answering any questions, please don't hesitate to contact me by phone or e-mail. My web site address is: http://www.sandsmachine.com. TOP

from http://www.nordicgroup.us/fold/