I was given an old broken bicycle today.
I've got the day off and I've had an idea in my head to make a unicycle recently so today is the day.
I've seen two other designs:
- one that uses the rear triangle and a chain drive
-one that uses the front fork with direct drive using purpose made bearings.
I absolutely stand to be corrected but I couldn't find one like this , that uses the front fork with a chain, on the internet.
The problems that I forsee are that there will not be sufficient chain adjustment and that getting the wheel off will involve splitting the chain . . . here we go . . . and I want this finished by today . . .
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Step 1: Parts and Tools.
- A bicycle.
-6mm allen ket, to remove handlebars.
-Adjustable spanner to remove the forks.
-15mm Spanner, for the wheels.
-A crank removing tool.
-A bar to spread the forks.
-A hacksaw to cut the frame.
-A half round file.
-A chain splitter.
-A welder of some sort.
Step 2: Cutting the BSO Up.
This is what is known by some as a BSO ( Bike shaped object); made to such a shoddy standard that they should never have been built.
I have no guilt in cutting this up, it was headed for the rubbish tip.
Ok, I took off the fork and used a strong lever to open it up to about 130mm.
This was to allow the rear wheel to fit in.
I then cut everything from around the bottom bracket, except the seat tube.
( I will tidy up all the sharp sticky out bits up later, if the project succeeds.)
With these two frame parts, I now will proceed to the welding preparation stage..
Step 3: Welding Preparation.
I had to join these two pieces.
I filed the bottom bracket free of paint.
Using a half round file I cut out a cradle shape in the top of the fork tube to allow the bottom bracket to sit in it nicely.
I wanted the bottom bracket axle to be in line with the wheel spindle so that the chain-line will be straight.
Step 4: Welding and a Bit More Welding.
I laid the two pieces out and held them in place with bricks and clamps; this was maddening.
I used an arc welder (stick welder); It's not ideal for bike frames as it tends to just burn holes in them.
I took it delicately.
When I finished I supported each end of the assemblage and then stood in the middle; it immediately snapped in two.
I nearly gave up; I was not prepared to file the welds off and make it seat nicely again.
Instead, I wedged it together and just forgot politeness altogether.
I tentatively tested it again, and it held.
Step 5: Optional Step - This Step Was a Failure- Feel Free to Skip It.
On a chain driven unicycle the front and rear sprockets must have the same number of teeth to give it a direct drive feel; otherwise it's just too weird to ride.
The biggest sprocket at the back has 28 teeth.
Unfortunately this bike only has two front chainrings.
Usually they have three chainrings and the smallest one would be have 28 teeth , which would be perfect.
I had to improvise.
I took the largest sprocket off another old set. by hitting the lockring with a chisel.
See diagram- i hit the lockring anticlockwise and it all separates.
Then I cut the chainrings off and welded the 28 tooth sprocket onto it.
The heat caused it to warp and I straightened it out using an adjustable spanner.
Step 6: Creating a Fixie Sprocket.
Unicycles need to be fixed wheel ; unlike most bicycles which have a freewheel.
There are finer ways to disable a freewheel so that it becomes fixed but this wheel is on its way home; I can feel how loose and worn it is despite tightening the cones, so . . .
I weld these parts together.
Step 7: Putting on the Chain.
I fitted the chain but it was half a link away from the ideal length. ( half a link too short or too long).
I was stumped.
I tried making a device using the de-railer and reflector bracket; it did not work.
I dug around in my toolbox and found a small length of half link chain left over from this project
It worked but the chain kept coming off .
I needed some kind of wheel adjustment that a front fork does not have . . .
Step 8: Adding Adjustable Dropouts.
I decided to add the dropouts from the rear of the frame.
I realised that I could, using the existing eyelets , bolt the two pieces together before welding.( See picture.)
This helped; I welded it thoroughly, bolts and all.
Step 9: The Same Problem.
The adjustment was good but the chain still came off.
How ever tight or loose I set the chain it came off.
This could be because:
- the sprocket was too warped( but I think that it was ok.)
-The up and down movement caused by it being slightly off-centre.
-It was a Hyperglide sprocket; which means that the teeth are not uniformly deep.
-The chainring was too much out of line with the rear sprocket.
I nearly gave up again . . . I had a cup of tea.
I vaguely remembered some bits in my loft . . could it be ?
Yes, very worn but useable.
The inner chain ring was 28 teeth and it worked instantly; why did I not remember this before ?
Step 10: Finished
Here it is, and it is a unicycle and it works.
It's half past four and I've just tried it and frankly, I was terrified.
I used to ride a normal unicycle years ago that was lots of fun.
I tried to get on this thing and after several attempts I've got to admit that my mortality came into focus.
On a normal unicyle the worst that seems to happen is you fall forward onto your feet but with this I could almost sense the back of my head cracking open like a DDT exposed egg.
It may be that I have to modify the seat into unicycle style but at the moment just getting on it would be nice.
I will have a go tomorrow and possibly post a video but until then it's time to eat.
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