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My family was at a recent family reunion.   While there, one of the cousins had a an interesting looking contraption.  It was a swingbike?!!?!?  A bike that had two pivot joints in it.  I tried riding it while I was there, but didn't have much luck, as the terrain was rather hilly, and somewhat hard to learn on.  He told me that it was something that had been around for quite some time, and the design wasn't necessarily anything new, just fun.

Upon arriving back home, I decided to do a little bit of looking around on the internet, and see what I could find out about said bikes. There was a company that produced these bikes in the early 70's, but they never really caught on.  There is also a company making these today, called americasbikecompany.com.  The original swingbike, and the newer swingbike design, while the same are rather different in design.  The original swingbike design was almost more of a unicycle type thing where they pedals were in front of the pivot point by quite a bit.  The newer design bikes have the pedals kind of below the pedals.  I looked at both designs, and by luck I reckoned that it would be easier for me to build the latter type design, because it could essentially be built with one bike, and a donor bike that would provide the head tube.  (NOTE:  Look around on the internet for "swingbike", and you'll pretty quickly see the two types of designs that I'm talking about, and what the differences are)
 
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Step 1: Starting point...

Picture of Starting point...
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These are the things that are required to build this project:

Materials:
One complete bike.  Can be multiple geared, or single speed.  I suppose that any size bike would work for this. 
One donor bike to get the front forktube, headtube and all hardware from
Heavy walled tubing, or possibly solid round bar (I used 1.25" OD x .375W tubing)
Some plate steel for making the pivot mount (I used 11GA (.120 thick))

Tools:
Grinder
Cut off wheel, or way to cut tubing
Die grinder (helps with shaping fishmouths)
Welder (arc, MIG or TIG)
Variety of wrenches to dis-assemble and re-assemble bike
Sharpie or marking device

My cost to build this was more or less nothing, other than the cost of welding gas and wire.  I was able to scrounge for the main donor bike, and I've had the second donor bike laying around for several years.  At most, I would think that you should be out less than $50 for everything.

As for difficulty, I wouldn't say that this is really a hard project, but it does require a few metal working tools that not everyone might have, or have access to.  So, I put the difficulty level at the middle of the range because of that.  My total time to build the bike was about 16 hours in all.

Let's get this thing started.  This is the only pic that I have of the donor bike, and I don't have any pics of the second donor bike at all.  My main bike is a 26" run of the mill cheapo Murray MTB.  But, this isn't just any old MTB, this is an Ultra Terrain Extreme!  My donor bike was a gem as well.  It was a built-for-Kmart bike, and it was ALL PRO.  I actually kind of felt a little bad cutting up that bike because it was a brazed together frame, from back in the day, so it was probably a pretty decent bike as far as that goes. 

Psh... I got over that pretty quickly though.   ;)

My first step was to disassemble my main donor bike, and get to a bare frame.  After that, I cut the frame at the arrows indicated as close to the downtube as I could.  I wanted the remaining tubes to be as long as possible.  In this case, a slightly stretched out bike won't be a bad thing.

Before cutting it apart, I also measured the angle between the upper main tube, and the lower main tube.  I needed to know what this angle was, because I am going to cut the LOWER tube at some point, and make it parallel with the top tube.

After making all of the cuts to the main bike, the resultant pieces can be seen in the third photo.  Notice that the top and lower main frame tubes are now parallel to each other.  The lower tube ended up being mitered very close to the front headtube, and that was fine, since I knew from the measurement I took above what the angle was.  I did it this way, rather than cutting these off front head tube, because again, I wanted these tubes to be as long as possible, and this was a good way to recycle these tubes without needing to add more tubing into the project, which I didn't really have anyway.

Step 2: Cutting angled fishmouths for rear headtube...

Picture of Cutting angled fishmouths for rear headtube...
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I didn't take as many pics of this part as I thought that I did, but I thought that it was still worth sharing how I did this, in hopes that it will help someone else along the way.

Cutting fishmouths in tubes is not the easiest thing in the world.  Well, actually cutting them isn't all that hard, but figuring OUT where to cut them is whole other matter.  Add to that in this case, I have to cut those fishmouths on an ANGLE, and now there is another layer of complication in this whole matter.

As I was watching videos on the internet planning how I was going to do this, I saw a video of a guy who used a template to cut his fishmouths with.  I thought, "Hummm.  That would sure make the process of at least marking them a ton simpler."  So, what I did was to accurately measure the headtube diameter, the top tube diameter and the lower tube diameter.  I'm fortunate to have access to solid modeling at work, so I modeled all of these tubes in the appropriate diameters, also placing them at the appropriate angles that I measured earlier.  Then, I could copy off the OUTSIDE surfaces of ALL these solid models, and I what I ended up with was surfaces that were intersecting, and the fishmouths were created automatically at the intersections of all of these surfaces.  Then, I used a command that allowed me to unfold the resultant surfaces into a flat file, and I printed these flat files, which were EXACTLY the OD of the tubing.

After marking the centerline of the tubing, I used that centerline to line up the fishmouth on, and I wrapped it around the tube, and taped it on there like you see in picture 1.  I did this for both the upper and lower tubes, lining them up at a predetermined spot that would also up the rake angle for the rear head tube.

After getting them both taped on there, I used a 4 1/2" grinder and  air die grinder to grind out these notches until I was right on the paper.  Then I would test fit the head tube and grind some more.  This way, I was able to slowly sneak up on the fishmouths, and make them very tight fitting.  You can see a finished fishmouth in pic 2.

My ultimate goal here was to cut these accurately enough so that I could TIG weld the joints, but my TIG welding skills are just not there yet, and after having issues with that, I resorted back to MIG, and welded all around the top and bottom to the headtube.  I also added some gussets in the corners just for good measure.  You can see the finished "swingarm" part of the bike in pic 3.  The part to right side of the pic is the REAR half of the swingarm.

All-in-all, this method worked out very well, and it was very easy to get tight joints that were easy to MIG weld.

Step 3: Rear pivot joint...

In doing research for this bike, one of the things that I ran into several times was that this particular design is "weak" in the rear headtube area, and often times bends at the joint where the headtube mount attaches to the rear bike frame.  The way that most people solve this problem is that they put something across the top of the rear headtube, tying it back into the rear frame.  But, I had seen the commercial designs that were available out there, and they were doing it somehow without adding any extra support on the top.  I liked the look of that, so I decided that there needed to be a way to accomplish that.  The red arrow in pic 1 is where this joint is historically weak, and the green arrow indicates where it is historically "bridged" to the rear frame at the seat post area.

My way to accomplish that was to use a thick walled piece of tubing.  I had a buddy turn that tubing down to an OD that would fit inside of the ID of the forktube that I got from my second donor bike.  In pic 2, you can see the tube before we started turning on it.  That is 1.25OD x .375W tubing! It IS thick walled!

Pic 3 shows the OD of the tube after turning it down.

Pic 4 shows the donor bike forktube slid over the turned down part.

Pic 5 shows some slots that I cut in the forktube so that I could weld it to the thick walled tube.

Pic 6 shows the washer that I put on the ledge that we turned in the tubing.  This "ledge" will hold up the bottom bearing cup.  It eventually got turned down to the same OD of the bearing cup used on the rear headtube.

Pic 7 shows some of the poor TIG welding that I was able to cobble onto the washer to get it welded onto the down tube.

Pic 8 shows the TIG welds that I added to the slots that I cut into the forktube, welding it to the downtube.  This was all then carefully ground off flat with the OD of the forktube so that I could slide over the bottom bearing cup.  The turned down section was up in the headtube about 5" or so, so it's all tied together pretty well.

Pic 9 is a bad shot of the inside of the forktube, after welding to the downtube.  As you can see, there's still quite a bit of meat in that area as well.  I think that the resultant wall thickness that was in the downtube was around .180.  The joint that normally has issues should be pretty stout on this bike.  In the riding that I've done so far on the bike, it shows no signs of fatiguing or bending.

Step 4: Finishing the rear frame assembly...

Picture of Finishing the rear frame assembly...
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I didn't take a lot of pics of this part, but I think that it's pretty self explanatory.

I just made some plates that I welded to the downtube, and then onto the downtube of the rear clip.  For aesthetics, I added some holes, and also added a cap to the plates so that it looked a little more finished.

Pic 2 is a pic of the fully finished rear clip.  You can also see in this picture how the rear headtube assembly looks when it's all put together.  Notice that there is NO support on the top of this area back to the rear frame or seat post.  However, if for some reason I was ever to find that the frame was bending in this location, it would be very easy to add a brace back to the seat post area.

Step 5: Final assembly...

Picture of Final assembly...
The final assembly is basically a bike with two pivots.  ;)

One thing that I did encounter while I was building it though, is that it's kind of an unruly thing to assemble, with everything all wanting to move all over all the time.  I finally got tired of fighting it, and I just laid the whole thing on the ground, and built it "flat" on the ground.  That made things a lot easier.

I also have not hooked up the derailleur at this point.  I basically picked a range that was comfortable to ride in, and fixed the chain at that length.  I haven't decided if I'm going to add that back on there or not at this point.  Might be more complication than it's worth.

Final thoughts...

One thing that I commented on in my first slide was that I got lucky with my design.  The luck part of my design is that it is VERY easy to ride, which might come as a shock to some people.  I have let numerous people ride it, and to date no one has fallen over on it.  The reason that it's so easy to ride is that the riders weight is directly over the rear pivot point.   Also, when you pivot the rear, the pedals come UP off of the ground, ever be it slightly.  So, since you're weight is all over the pivot point, and the pivot point is naturally wanting to go down to a static point, when you ride the bike, it is always trying to seek this "home" position, more or less automatically, and that's where it wants to stay.

But the downside of this is that it does make it a little bit harder to actually "swing" the bike.  it CAN be done, and with just a little bit of practice, I've gotten to the point that I can swing the back / front pretty easily.  Sometimes holding it there takes a little bit of work, since it's always trying to find "home", but it can be overcome.  I'm thinking about changing the handlebars so that they are a little bit wider.  I think that this would help "push" out the front wheel.

All-in-all, I'm very happy with where this bike came out for my first attempt at building one of these.  I'm now considering making the original version, which I KNOW will ride completely different than this version. 

By popular demand, I've added a video of me riding on my FIRST voyage.  This is a crappy cell phone video, and at this point, I was "swining" out very far, because it was only minutes old.  But as I ride up the driveway, you can see that the rear wheel is not inline with the front wheel.
i simply must know; what is the benefit of this modification? or is it just one of those "look what i can do" moments?
swather (author)  golddigger15592 years ago
I don't know if you saw one of my earlier comments, but you're right, there really is not a "benefit" to making a bike like this, other than the fun of riding it. And, like I said in my instructable, I don't think that I would have ever tried to make one of these if I had not had the opportunity to try and ride one. While my first ride was not totally successful, I saw that it could be fun to ride.

If you really stop and think about it, what would be the benefit of unicycle? I'd have to say that there's not a lot "benefit" there, BUT people do some enjoy riding, as crazy as that is to me.

So, the real fun in this bike is actually riding it, and while it may be hard to believe, it IS actually fun to ride.

I posted some links to good riders riding them in an early post. Give those links a look if you'd like to see what's possible with this bike...
K4nyix swather2 years ago
Well, another reason would be, although pretty much as golddigger said... For the show. Just the plain show. As for unicycles, grand-bi and so on, swingbikes are uncommon, and unsettling, which makes them a good spectacle prop, especially for circus purposes. I myself am a unicycler, and although I never heard of any swingbike things, we have here in France several big unicycling associations, meetings, and even cups (including sporty stuff)... So yeah. Just throwing the info out there : swingbikes are a talent, and sometimes, just sometimes, showing off isn't a bad thing especially when it's about having people enjoy discovering or laughing or being amazed ;)
And, also, a swingbike can be way more flexible, for example in cities, and with your design, it can even be rode pretty much for cruising, so yeah, here's another use for it !
swather (author)  K4nyix2 years ago
Sorry, my post was NOT to slam unicyclists! I was simply using that as an example of what some people might consider WHY?

I personally OWN a unicycle that I picked up a garage sale, and I have never been able to ride the thing, but I have not spent a lot of time trying either. It is NOT easy to do, and I admire anyone that can.

As you stated, one thing about my design is that it IS easy to ride, and in fact, I have ridden it just like a bike, and it does a decent job of that. With that being said, I wouldn't want to ride it 20 miles. :)

People do enjoy laughing at you when you ride it as well, and at the end of the day, realistically, it's more of a clown bike than anything. That's a pretty good description of it...
K4nyix swather2 years ago
erhh... I just found out about this reply.
I'm sorry you felt like I had been defending unicycles and stuff : I wasn't. Was just completing your answer to Golddigger actually, which ended up being part of your answer too ! I wish I had the necessary skills/tools/materials/time (that makes a lot of stuff to get haha) to make one of those : seems pretty amazing.
How is it, as of maneuverability ?
Bikebudy2 years ago
Merry X-Mas , just a small update.
 Front fork is done, Rear fork/frame is done.

Still working on the Center frame.

Click for larger view

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Bikebudy2 years ago
Great job of this Swingbike, Your welding skill is well above mine.
Welds shown on the pivot are so clean and professional.

The placement of the pivot, is the reason the frame wants to return to center.
I have a Swingbike from the 70's, and they are very much like a uni-cycle.
Having the pivot just under the seat, it needs springs to help it return to center.

click on photo for a larger view.



I am also building a Swingbike. I will need two and a half bikes to do this.
It is  going to be a "Mini" version of the original 20" x 16"  bike!
A 16" rear wheel and a 12" front wheel.

I might do an instructional on the build.

click on photo for a larger view.




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swather (author)  Bikebudy2 years ago
Thanks for the props on the welding. That the weld that you're referring to is a TIG weld, and that particular one was a LUCKY day! They don't typically look like that when I do them either! My original plan was to TIG all of the tubes as well, but that didn't go good for me at all, so I ended up MIGing the rest of it.

I actually have the donor bikes to build a conventional/original swingbike like the one in your pics. I would like to build that version at some point, just to see how that works. Like I said in the posting, mine is very easy to ride, and for me, not knowing how to ride one, that's definitely a benefit...
Aaaarrrrgh!,  I can't fit another bike in my front room but you've got me all interested in making one . . must resist. . . must resist. . . .

I randomly searched for swing bike and got this demonstration.
http://www.youtube.com/watch?v=Q5IgBNYUFsc
k.aderer2 years ago
Here's a link to an online calculator which allows you to print templates for cutting angled fishmouths in tubing.

http://metalgeek.com/static/cope.pcgi
K.aderer, Nice link: Thank You.
racoontnn2 years ago
Great idea! Rigidity increases many times with this swivel.
posteljooni2 years ago
TY!

ps: Video for proof,
or it's photoshopped!)
swather (author)  posteljooni2 years ago
Hummm...

I just tried posting a video of the maiden voyage and it failed upload for some reason.

I'll work on it some more...
BobBuckner2 years ago
I have been looking for an affordable folding bike. Would this bike fold in half if your bracket that holds your swivel was mounted to the rear frame with a sleeve around the vertical rather than welding directly?
rimar20003 years ago
A video, may be?
A video for sure!
swather (author) 3 years ago
Unfortunately, I don't have any video of the build. I could probably take some video of the close up points or something, or would you like to see a video of me attempting to ride the thing the first time? I have one of those. ;)
I'd definitely like to see you riding it. This is a great, well documented build, but I guess I don't understand why you would want a bike that pivots like that.
swather (author)  depotdevoid2 years ago
And, thanks for the comment on the well documented!

This was literally my first rodeo in instructables. I looked around and saw what others had done, and I know that I like to have as much information as possible when I'm trying to do something, so I tried to be as thorough as I could when explaining how I did it...
swather (author)  depotdevoid2 years ago
The only video that I have at the moment is of the very first ride, and as you can imagine, that's a little bit shaky!

As for the why, it sounded like something fun to try, and like I said on my first page, I had access to try and ride one, and somewhat failed at that attempt because of the conditions, and I thought, "I should build one of those for myself, and give it a shot", so I did.

Have you looked on line for any videos of people riding these things? I am NOT good at it, so my video riding it would be somewhat terrible.

While I could take some new video of me riding it, since I have a "little" more time on it now, I think that these links of someone riding that KNOWS what they're doing probably give you a better idea of what is possible with one of these bikes.

This bike is built like mine (or more like, mine is built like his):

http://www.youtube.com/watch?v=ktyRiTv9qsI

Here's a video of someone riding the "other" typical design of a swingbike:

http://www.youtube.com/watch?v=R5P70XtI4zQ

At the end of the day, it's just really for fun. I don't ride it very far when I do ride it. Let's just say that...