I built my first bike.
Some years earlier I had ‘built’ a bike in the sense that I bought a beaten up bike frame on Craigslist and set about modifying it to build a single speed belt drive bike, but having started with an already-built frame always felt like a cheat somehow. Sure, many people never so much as tighten a screw in their entire life but I couldn’t shake the feeling that the bike I would introduce to others as the one that I’d ‘built’ wasn’t entirely mine. After all, it used to belong to someone else.
There was another level of abstraction to grok — a level down from this one. I didn’t need to start smelting ore to feel legitimate but at the same time I didn’t want to be lumped in with those kids who claim to have ‘built their own computer’ by plugging a video card, a motherboard, and a power supply together in a pizza box. Sure, the questionable wheels that I custom-laced from rims, hubs, and spokes to ‘form this cool trillium pattern’ were the only thing keeping me from being ground up like pesto against unforgiving pavement should they catastrophically fail, but the frame itself was still full of mystery to me. I longed for a chance to screw that up too.
That’s when I learned about Framebuilding 101. Paul Brodie — a successful West Coast bike framebuilder — teaches a literal masterclass in bicycle design and framebuilding out near the airport of a small city with the most profitable agricultural land in the country (which, surely, has to do with the price of blueberries). It took me 7 years to find time to take two weeks off work but I finally did it.
Paul rents out a small corner of an airplane hangar to host his course. Normally, there’s an aircraft structures class being taught at the same time in that space but the University had cancelled it this time around so we had the entire hangar to ourselves — me, my two classmates, and Paul.
In the 1980s you couldn’t go on the internet and order a bicycle framebuilding starter kit like you can now. If you needed a tool to help you hold, bend, or align something you had to build it yourself. We got the opportunity to build our bike frames using some of the original homebrew tools that Paul had built when he was starting up, in all of their glorious jank and genius.
The first thing we did was to learn how to control a welding torch. Too cold and your weld might not stick. Too hot and you’ll have molten metal dribbling all over the place. Combine this with ‘too close,’ ‘too far,’ and ‘too angled.’ If you can properly manage all of your ‘toos’ without burning yourself (which you inevitably will do anyway) you should be able to build a little tower of brass like this. This control will prove important later on when you’re trying to shape a weld on your bike frame just so.
Melting brass droplets one on top of each other in free space is one thing, but melting a thin strip of brass into the most inaccessible corner of a bike frame is quite another. For this reason, among others, we build a mini frame to practice cutting and welding.
Building a mini frame teaches you to properly measure angles and lengths, to cut metal tubing accurately, and to align it in a jig to be welded.
Cutting bicycle tubing was a hybrid process that involved some numerical control, some tactile feedback, and some eyeballing. To angle the cutting blade you match the angle of the mill to some markings on the side of it. To center it you sandwich a little strip of metal between the side of the cutter and the side of the bicycle tube, feeling how tightly it was gripped between the two. Then you sandwich the same strip of metal between the cutter and the other side of the tube at whatever feels to you to produce the same grippiness. Look at the numerical readout for the distance between those two points, divide it in half, and call that the center. For everything else you use your eyes and cut when it seems about right.
Presuming that you cut all of your bicycle tubing at the correct angle and length it should come together nicely in a jig. This is the device that will hold the frame together for your while you weld its joints.
The first weld you make is the thinnest and strongest. You draw a thin line around the joint by melting a rod of nickel-silver into it.
Next, you goop up the joint with a liberal but even stripe of brass. How much control you exert over the application of the brass determines how much polishing work you will have afterward. If you apply too much brass you’ll be grinding it away for hours and if you apply too little your stripe will end up with holes in it where metal should be.
Believe it or not, it’s possible to transform that into this with a series of sandpaper-based tools and a lot of perseverance.
Looks ready to ride, doesn’t it?
It was at this point in the course that I discovered how woefully unprepared I was for the Real Thing™. I had a general idea of what I wanted to build: my current bike but from scratch and faster. I didn’t have any answers to the questions that came next, though. What head tube angle are you going for? What’s your ‘front center’ distance? What’s the rake of your fork? I didn’t know what front and what center we were talking about, and I didn’t even have a fork yet.
I went home that night and furiously Googled the relative merits of having no rake or lots of rake, of having long or short trail, of having a long or short chainline, and a myriad of other things that I’d never given a thought to — let alone knew existed. I tried to measure the angles in my existing bike’s frame using only photographs and the worst ever angle-measuring app on my phone, to ballpark dimensions for my new bike. I shopped for carbon front forks and Gates belt drive components, running the numbers until everything started to fit together. I regretted not doing this before I left my old bike behind in another country, unlike my classmates who arrived with fully wrought CAD drawings of what they wanted to build. Given a literal once-in-a-lifetime opportunity to build a bike with a master framebuilder I had literally showed up without a plan.
Never the less, I settled on a suite of dimensions, completed a full-scale drawing of the frame I was about to build, and cut all the tubing to the correct size and angle. Paul even sold me a fork that he had custom built for himself but ultimately never built a bike around.
The real frame begins much like the mini frame. First you weld the bottom bracket to the downtube then bend it as straight as you can. With that piece straight and solid you assemble the rest of the tubes around it in the jig.
A small tack of nickel silver rod applied in a specific order makes the frame solid enough to take out of the jig. If you’re lucky you’ll get to enjoy a smoking seat tube for a short while.
The idea is to weld and polish each joint around the frame in a specific order, letting the other joints remain free to flex around the small tack welds for now.
After each weld you return to the alignment table to make sure that the frame is staying nice and flat. If you find that it’s pulling one way or the other, you bend it.
Once the frame was straight and the welds were all polished it was time to add details like cable guides and a notch where you insert the seat post.
With brass dust in every crevice of my body from polishing the welds, I could say that the bike was starting to take shape.
What comes next is a whole lot of careful measurement and anglesmithing. The rear triangle has to be built so that:
- the tire will fit comfortably without rubbing,
- the gear sprocket won’t collide with the chainstays,
- the distance between the bottom bracket and the rear dropouts is correct to within millimetres, and
- the distance between the dropouts is exactly 130mm.
All of this was made strictly so in my case because I was building a belt drive bike. Chain driven bikes are less fussy because you can always add or remove a link in the chain if you need it longer or shorter. If you’re building a bike with gears then typically any slack or excess will be taken up by the derailleur. Belt drives demand that everything be perfect.
Oh, and there’s one more thing. In order to get the chain from the outside of the frame (pedal sprocket) to the inside of the rear triangle (hub cog) you typically split the chain, thread it through, and re-link it. A belt is one solid loop of carbon fiber and rubber so you can do no such thing. You have to split the frame.
On my last belt drive bike I built a splitter and welded it high up on the seatstay. Paul came up with a design for a splitter that sits at the point where the seatstay meets the dropout, and challenged me to build it out of scrap metal.
I started by rounding the end of a cylinder on the lathe, freehand. The only controls you have on a lathe are one wheel that moves the blade along the axis of rotation, and one that moves it toward the axis of rotation. I had to channel all of my math (and frankly, Etch A Sketch) skills to draw a hemisphere with the blade, in free space. I think it turned out pretty well.
Next, I needed a tab that was going act as an extension of the dropout that meets this hemisphere thing. We sketched it on a piece of scrap metal and I got cutting.
The next steps were to cut a step into the plug so that it fit into the seatstay tube, to slice the hemisphere in half to make a place for the tab to sit, to drill a hole straight through both, and to tap a screw hole through the whole assembly.
There were a few joints on the bike that I didn’t weld and the dropouts were one of them. Given enough time I would have enjoyed a lesson from Paul in an electricity-based welding technique called TIG. With enough practice I would have been able to do an acceptable job but time was short; I opted to let Paul apply his master TIG skills to the dropouts.
You have to weld the dropouts into the chainstays before cutting them so that you can use the dropouts themselves to align the chainstays in the mill.
Measurements willing, the chainstays should neatly meet the bottom bracket shell to form a morass of angles that are difficult to weld and three times as tricky to polish.
After welding the chainstays in place you have to bend them into alignment by hand. The tool of choice to help you do this was a little pointer that you’d hold against the frame and brush against one dropout then the other. The goal was to get them both 130mm apart from each other and centered with respect to the frame.
Building on top of the aligned chainstays, the final step in completing the rear triangle is to weld the seatstays into place.
And with a few extra steps such as chasing the bottom bracket threads so that they run straight and reaming out the head and seat tubes so that you can attach parts to them, we were done.
Of course no product would be complete without a maker’s mark. As we discussed before I was woefully unprepared so I had no such thing, but I did manage to find time to punch this cool serial number into the bottom of the frame. Thieves beware.
I described the process of building wheels in some detail last time. You can read that if you’re interested in the procedure but otherwise you can just enjoy these photos of the wheels I built for this bike.
Months passed between the completion of the frame and the final assembly. In between work days I made a billion Google searches in pursuit of the right parts in the perfect colors and sizes.
As the parts rolled in I bought a membership at my local bike workshop and started regular visits to build wheels, install the headset, route brake cables, and accessorize the thing for duty.
The Bike Kitchen in San Francisco is a fantastic place filled with nice folks and knowledgeable volunteers. If you’re interested in learning how to build or fix bikes I highly recommend buying a membership or volunteering your time.
I’ve been riding this bike for daily for a couple of months now and it hasn’t yet crumbled under load so I must have done something right. I plan on disassembling it one last time to have it clear coated; to leave all of the details of the process visible as a reminder of this once-in-a-lifetime experience.
Here is a dump of the extremely raw notes I took during the two week course, for anyone interested. Altogether these notes are surely wrong, but some might be useful.
Centering a downtube on a bottom bracket shell without a ruler
- Eyeball it and make a mark on one side
- Take a stick and hold it at the mark
- Flip the shell over and make another mark with the stick
- Repeat until your marks meet the downtube perfectly
Drawing a centerline on a tube without measuring
- Get the tube parallel to the ground
- Scratch the top with a sharp edge held parallel to the ground
Removing burrs from mitred tubes
- Use belt sander in vertical position
- Hold tube 5° off parallel from the belt pointing upward
- Rotate counterclockwise while grinding
How to mitre a tube
- Cut down halfway with the mill
- Pull out the sharp edge that was cut off
- Continue all the way through
How to mitre a tube at an angle
- Make small cuts and creeping up to your line little by little
- Follow regular instructions
How to mitre to precision length
- Measure the target
- Mitre one side of tube
- Mark other side 1cm too long
- Zero the digital readout and mitre the other side
- Measure how too-long the tube is
- Move over that much using the digital readout and cut
How to mitre two ends parallel to each other
- Mitre on side
- Flip the tube and put it back into the vice
- Insert a tube into the mitre and place flat on the table of the mill
How to notch a down tube
- Draw a centerline
- Use a disc sander to grind away the notch holding the tube against the platform at an angle. The angle will determine which end doesn’t fit your frame when you grind too much; the corner or the side of the tube.
How to start a torch
- Open the valve on the autofluxer
- Open tanks three half turns
- Open the acetylene valve very little
- Light with a striker
- Open acetylene until you can hear the flame
- Quickly open oxygen
- When you see a shadow outside the cone you have an carbonizing flame with too much acetylene. When you go too far past the point where the cone disappears the flame falls apart and you have an oxidizing flame
- Turn off the acetylene first when finished
How not to burn yourself
1. When you need to manipulate the piece or adjust your glasses or scratch your head put the brazing rod in your torch hand pointed toward the floor. Otherwise you will do something dumb like stick the rod up your nose or grab the hot end with your other hand.
- Flux the joint
- Heat very close and tack using nickel silver brazing rod
- Flip over and do the same
- Always keep the surface normal of the joint pointing up
- Heat a little further back (1.5cm) and insert the rod when you see the tack starting to melt
- Drag the rod along the joint as it melts
How to change a mill bit
- While applying brake loosen the nut on the top
- Bang the nut with a hard object; bit drops out
- Heat the joint always keeping the surface normal of the joint facing up
- Melt a drop of brass on one side of the joint then the other dragging the rod in the direction of your weld’s progression each time
- Refine until smooth, no low spots, and no holes
- Use grinder to draw a centerline that conforms to the contour of the joint. Use the middle section of the cone as much as possible.
- ‘Edge out’ from the centerline using the grinder, feathering the brass to the steel surface. Grind to reveal a smooth arc. Make sure not to stop at the base of the fillet lest you grind a groove into the steel.
- Use belt sander to finish. Wrap belt around much of the joint. Ease in and out of the joint using a diving and scooping motion to start sanding from the center of the joint to the edge, then reversing to dive and scoop in the other direction.
- Finish with emery cloth
How to face a tube
- Insert the tube into the lathe
- Touch the tube with the cutting tool. Back off
- Turn on lathe. Advance 1/1000” at a time and cut until no chatter can be heard
- Back off cutter and file burrs with flat file, first at 45° then hit it briefly at 5° and 85°
- Use inner burring tool on inside edge with constant pressure. Hit the edge with the armpit of the tool and point your elbow at the ‘x’ on the floor
Alignment (Force and Finesse)
- Use tool to feel for side of tube then flip over and compare
- Mark what direction you have to bend it
- Put bottom bracket cups in and out bottom bracket in the vice
- Repeat from #1
- Axle to crown (A>C) is measured from the center of the axle to the center of the top of the fork tines
- Front center is measured from the center of the front axle to the center of the bottom bracket
- Drop is measured from the axle center line to the center of the bottom bracket
- Bottom stack height is the height of the bottom piece of the headset
Weld order and alignment process
- Head tube at top tube
- Front half of bottom bracket
- Perform alignment on seat tube then downtube (alternate until within 1mm)
- Bring the frame to the alignment table and affix a rod to the head tube with cones
- Lay the frame on the table and aim for the seat tube nearest the bottom bracket to sit 2–3mm above the seat tube nearest the top tube. Measure using equal sized blocks slipped underneath the non-butted portion of the tube. Bend by pressing on the point where the top tube meets the seat tube being careful not to snap the tack.
- Tack the bottom of where the downtube meets the head tube and weld
- Check for alignment again this time aiming for no gap
- Weld last remaining joint where the top tube meets the seat tube
- Check for alignment again and aim for no gap
How to cut a slot in the seat tube
- Mark where you want the slot to end
- Clamp the frame into the mill with the rear of the seat tube facing the wall
- Using a level, alternate between the seat tube and the top tube until the frame is parallel to the floor
- Center a saw bit and start to cut partway down the tube, moving the blade in until the radius meets your target length line
- Punch a depression just below the cut while holding the frame in a vice
- Drill a hole
- Using a hacksaw blade, cut upward until the slot meets the hole. Be sure to press the blade against the side of the slot so that it cuts straight.
How to attach dropouts
- Measure the wall thickness of the chainstay and the outer diameter of the dropout plug
- Double the wall thin ones and add it to the plug diameter. Find the point on the seatstay where the outer diameter is this quantity
- Mark 2mm shy of that point and hacksaw it off
- File the end straight
- Using a round file, remove material from the inside of the seatstay tube until the dropout fits tight when lightly hammered. If you file too much then punch holes along the circumference of the dropout plug to rough up the surface
- TIG weld them in place
How to mitre chainstays
- Attach a jig to the dropout
- Mitre it to the correct length making sure that the dropout is fully bottomed out in the jig
- Repeat with the second one making sure not to reset the x-axis
How to attach chainstays
- Place frame in jig and adjust to the desired chainstay length
- Please mark 1/4 inch from the edge of bottom bracket
- Insert chainstays into jig
- If chainstays do not meet the line marked on the bottom bracket then remove them and bend them until they do
- Tack chainstays in place using TIG welder. Braze.
How to face bottom bracket after brazing
- First chase the threads using a thread chaser
- Screw in bottom bracket cups to produce a centered channel guide you can use to mount it to the lathe
- Mount a cutter on the lathe and mount the frame to the cutter
- Advance the plunger until the cutter just grabs the frame then advance 0.005”
- Repeat with other side or until you can see evidence that the bottom bracket face has been cut all the way around
How to face a top tube after brazing
- Mount cutter on lathe
- Mount head tube into cutter until the is just a little play
- Turn on lathe and advance until cutter just starts to grab
- Advance 0.015”
How to lathe a radius
- Starting from the center grab both wheels
- Move the cutter into the piece at a constant speed but the cutter away from the piece quickly at first then progressively slower
How to mitre seat stays
- Place them in a jig
- If you want the stays to perfectly meet the frame then space them at the diameter of the seat tube. If you want to leave a flat notch for welding rod to flow into, add 3mm total.
- Take a cut!
How to drill a bolt hole
- Drill the guide side to the width of the bolt so that it just slips through. Use a center drill to get the hole started.
- Use a 4.3mm drill (for an M5 thread) and drill a hole in the threaded side of what you’re trying to join. Use a center drill to get the hole started.
- Instead of manually tapping (which can lead to misaligned threads) put the tap in the mill and start it up. Then, cut power and let the bit slow down. Once it’s just a little bit faster than you would normally hand thread it, plunge it into the hole.
- When it stops leave the bit in the hole but retract the mill.
- Finish the tap by hand
How to spread the dropouts
- Use a straight stick with a pointer. It’s like a dishing tool for dropouts.
- Hold the stick against the head tube and seat tube then manipulate the pointer until it touches the dropout
- Move to the other side and test whether the other dropout is closer or further away from the centerline.
- Measure the spacing
- Bend whichever stay needs bending and repeat from step 2 until you have 1mm more than your target dropout spacing and the stays are centred.
How to get the dropouts parallel
- Affix cups to the dropouts
- Use leverage to bend the dropouts until the cups align
How to punch in a serial number
- Draw a baseline for the type
- Hold the punch with your thumb on the notch so as to hold the glyph right side up
- Hold the punch against the metal and rock it until you can feel it contact the surface tangentially
- Hit the punch once with a 2lb hammer once. Don’t bounce it. Letters with fewer strokes require less force.
How to mount a brake hanger
- Measure your seatstay angle
- Affix the hanger jig to your dropouts
- Approximate how much of the hanger needs to be cut until the bolt hole will meet the jig’s bolt hole
- Mitre the hanger at the seatstay angle taking off an equal amount on each side. Repeat until it fits
- With the hanger in the jig tack one side with nickel silver rod
- Nickel-silver braze the other side completely then finish the side opposite that
How to ream a seat tube
- Oil inside the tube and oil the reaming tool
- Only ever turn the tool counterclockwise and advance it a very little bit at a time
- When you jam give it a wiggle side to side and pull verily lightly. Continue reaming.
- When finished remove the tool by turning it clockwise while retracting it.
- Blow the chips off into the disposal
How to level the seatstays
- Mount the mitred seatstays to the dropouts
- Place both stays tight against the frame
- Put a ruler across the stays parallel to the ground
- Grind the longer seat stay until the ruler sits level
- Tack the stays and begin to nickel-silver braze opposite the tack from bottom to top
- When it comes to the tip of the ear point the torch toward the back of the bike so as to avoid heating the ear too much. Push the brazing rod toward the torch until you hit the corner of the ear.
- Finish it off by filling in the gap under the ear if one exists