Book review – Lugged Bicycle Frame Construction

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I have recently been considering getting some brazing equipment so that I could make repairs to frames that have minor failures, rather than sending out to a frame builder for this service.  Having taken UBI’s lugged frame building class a few years back, I had a general idea of what I might need, but didn’t want to go any further until I re-familiarized myself with the topic of brazing.

I found Marc-Andre Chimonas’ book, Lugged Bicycle Frame Construction, on the evil empire (Amazon) website, with what appeared to be some favorable and thoughtful reviews by actual readers.  When the book arrived, I immediately delved into it and have now read if not studied much of the book.

It is written with a dry, understated wit, with an emphasis on the science of frame building.  There are numerous zingers in the text, hidden amongst the tables and formulas.  Consequently, I thoroughly enjoyed reading it.  The author is a physician (which he describes as his “day job”), a writer (of both technical manuals and fiction), and a frame builder.

After reading just the first few chapters, I began to seriously question the idea that anyone can take a frame building class that lasts only two weeks, and from which an actual frame is produced.  Whether that frame is safe to ride may be another thing altogether.  My own frame has several flaws that can probably be corrected, but more on that later.

The book is logically organized and takes the reader through introductory concepts such as nomenclature, frame geometry, measurement and sizing protocols and includes helpful tables for determining angles and lengths for different sized riders.  He naturally recommends smaller wheels for smaller frames, and there is a good discussion of toe overlap and bottom bracket height.  He states his opinions about frame geometry as if they were facts, and that may irritate some readers, but I found it refreshing.  For instance, recommended BB height is 25 cm for pretty much all types of normal road riding.  This is a lot lower than you will find in production bikes.

Another interesting concept that I found both helpful and puzzling was the idea of controlling the variables in frame building.  He differentiates between “operator controlled” variables and “outcome” variables.  Outcome variables are the result of the frame builders operator controlled variables.  But, he describes outcome variables to include BB drop and toe overlap, which in my mind are operator controlled.  At any rate, what is clear is that frame design is a highly complex  undertaking, and one that is aided by software.  He recommends using excel and offers a link to a useful frame design spreadsheet, which is available on the author’s website.

There is a quick trigonometry and metallurgy review (which the author calls optional), and then the theory turns into fabrication as the author goes through chapters on frame parts, tools, mitering, torches, brazing technique, and lug modification.  Again, the author doesn’t hesitate to state his recommendations, even down to a specific brand or manufacturer of a particular tool.  For me, someone who didn’t take shop class in high school, the specific advice is extremely helpful.

After digesting many of the chapters, I decided to drag out the frame I completed 2 years ago but never finished filing or painting.

My frame with front-center at 59 cm - a little shorter than I wanted.

My frame with front-center at 59 cm – a little shorter than I wanted.

I built this frame for myself, designed around a 650b wheel size.  I wanted enough front-center distance to allow for fenders and decent sized tires.  The book uses a formula to determine an ideal length.  I plugged my numbers into his formula and found that I won’t have toe overlap with this frame, so that is a relief.  I did have to use a longer than usual (for me) top tube length to get this much front center distance (combined of course with all the other measurements).  That means I’ll use a short reach stem when I eventually build the bike up.

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One of the things that troubles me about my frame is that it was built so hastily and with so little actual knowledge.  Well, after reading the brazing chapter I think I have reason to be concerned.  I remember having a lot of trouble sanding enough material off the top of my fork blades, and off the inside of the fork crown so that the legs could be inserted without a lot of force.  After hours of filing, I still wasn’t happy, but ran out of time so just brazed the fork legs into the crown even though the fit was tight.  This is definitely a no-n0 – there needs to be enough room for the silver to flow into the joint.

Here are some other details of the frame I built.  Using this book as a resource, I will be able to correct the other two (known) mistakes on the frame.  I may decide, however to build a new fork.  And, I now know what kind of equipment to purchase and how to use it safely, so I am looking forward to being able to do my own small repairs.

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Nice looking BB

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Mistake on the seat stays – they are out of alignment

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Drive size DO not yet cleaned up and filed – you can see I got the tubes a bit hot.

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Aaack! Seriously out of whack shifter bosses – the jig probably got bumped when I turned away to get more silver.

Building a Bike Frame

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Last year, I enrolled in the frame building class offered by United Bicycle Institute (UBI).   I registered for the lugged/fillet brazing class (of course) but they also offer other courses in TIG welding and titanium frame building.

As it turned out I was the oldest member of the class and the only woman in the class (including the two instructors).  That wasn’t so daunting as was the quick pace of the class – and it caught all of us off guard!

UBI shop facilities in Portland, Oregon

I wanted to build a frame to my own specifications and size because I haven’t ever ridden a frame that is exactly to my liking.  Many shorter riders probably have never experienced the joy of riding a properly designed frame.  I have seen smaller riders with their arms straight out, riding frames with too long top tubes, inappropriate 700c wheels, and very bad front end geometry.

Having ridden hundreds of bikes over the last 10 years, I had a strong feeling about how to design a bike frame to fit my 5’4″ height and riding style. I wanted a frame built for 650b wheels, with steeper angles, plenty of fork rake to reduce wheel flop and trail to an acceptable level, long enough chain stays for good sized rear bags, and enough front/center distance to eliminate toe overlap – all in a frame small enough so that I could stand over it reasonably well.

I have often ridden bikes that were slightly tall for me, so I have never worried a great deal about standover height. The most important frame measurement is actually the top tube length.  And, I have come to learn that I like steep angles so that I can get more of my body weight on top of the cranks and closer to the front end of the bike.

Much is mysterious when it comes to bike frame geometry, and much is disputed, even among the experts.  My own personal experience tells me that, for the type of riding I do mostly (commuting in Portland, Oregon and longer weekend rides), I needed a frame with very stable slow speed handling, but decent cornering at high speeds.  This translates into a bike with low wheel flop and fairly mid range trail.  My frame geometry, noted at the bottom of this post, yields a wheel flop factor of 11 mm and trail of 39 mm.  Just about perfect.

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After spending the first day learning flame control and doing practice brazes with silver, we  began by brazing the head tube to the top tube.  Silver is used for the lugs because it can be brazed at a lower temperature so there is less risk of overheating the main tubes and weakening them.  In the midst of that we needed to begin our full sized drawings so that we could properly select, cut and miter our tubes.

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Doing the full sized drawing came very naturally to me, but was difficult for some of our fellow students.  Harder for me was the flame control and brazing process.  It took awhile to believe that not only was the shop not going to explode when I ignited my flame each morning, but that my fellow students were NOT going to burn the place down, either.  I was a bad and slow brazer initially, and it took quite a while to get the hang of it without destroying my hands with flux and lug filing (still, my hands were a mess at the end of the class).

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My favorite day was “fork bending” day – a process which proves that frame building is as much art as it is science (with a little luck thrown in).  Forks are bent on a mandrel, and mandrels can come in different shapes and sizes.  There was only one mandrel at our class, so our fork blades would only vary by the amount of rake we selected.  There is no gauge or  measurement to insure that you get the right fork rake when you bend it (or “wang” it, as I am fond of saying).  Fortunately, I managed to “wang” my fork blade to the exact amount of rake I was looking for – 60 mm – on the first try.  Whew!

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My fork dropouts are a mess – this was our first brass braze and the process on the dropouts is slightly different and with higher heat.  Fortunately, my skills improved on the chainstay dropouts, although I did get the tubes a bit hot.

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I’ve got the my chain stays in and I decided to use these “plugs” for my seat stays rather than hand making a seat stay attachment, as some of my fellow students did.  I was behind schedule, so had to proceed full steam ahead.

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Here are the plugs, which I have brazed to the seat lug and bent inward to wrap slightly around the tube.  Then, the brake bridges need to be measured for the proper wheel size, mitered and then brazed.

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Here is the completed frame.  It has several mistakes that need to be corrected – I brazed the downtube shifter bosses askew and the seat stays are not perfectly aligned.  The former can be corrected by re-heating the bosses and re brazing them, the latter is a small enough variance that I can fix it by doing some creative filing.  Then, all the joints and brazes need to be filed and cleaned up before the frame can be painted.

My frame varied only slightly from my original drawing:  my seat tube angle ended up slightly slacker than 74 degrees. Not a bad result for a first time effort!    Here are the specs (all measurements center to center):

ST 50 cm, TT 53 cm, BB drop 71 mm, ST degrees 73.5, HT degrees 73, Fork rake 60 mm, Fork length, 367 mm,  chainstays 441 mm, wheel size 650b.  Standard diameter tubes – Kaisei 4160 Cro-Mo double butted.

If you are interested in taking this class, and if you haven’t brazed before or used shop equipment, you might want to find a way to get some background first before enrolling.  While we all managed to complete our frames, we didn’t get to complete the final process of learning how to file, sand and prep our frames for painting because the class, as a whole, was too far behind.  The class proceeds at a very fast pace, so it’s best to be rested and have nothing else going on in your life while attending – you’ll be exhausted each day – but energized by the new knowledge and skills you are gaining.