YFBS: Day 6 - Stem Saturday

I'm continuing to document my adventures at the Yamaguchi Frame Building School.  The first day can be found here

The Saturday in between the two weeks spent here is an optional stem building class, though why anyone would opt out of this class is beyond me.  Today our focus was entirely on building a stem from start to finish, and custom made to fit each of our frames, to boot.

Everything you need to make a stem!
Coming in to the shop the morning, the first thing that I noticed was the amazing (and probably blazing fast) stayer bike that was sitting next to one of the work tables.  With 120 gear inches, it looked like a force to be reckoned with, but what I later learned was that it was an example for how *not* to build a stem.  

Stayer, or motorpace bikes, are designed to reach high speeds while following a motor.
Speaking of what to do and what not to do, the class began with a discussion on the various types of stems, starting with the older quill style stems and moving to more modern styles.  Mr. Yamaguchi talked about what worked well, and what didn't.  "This stem was poorly designed, because the force of a rider sprinting from the start would cause the bolt to shoot out," he explained, holding up an older quill stem with a vertical bolt.  "This happened once - it sounded like a gunshot as the rider sprinted off the starting line, and shot out with such a force it dented the concrete track surface." The stayer bike, as it turned out, used an old Sakae stem that looked nice but lacked strength.  In Keirin, NJS must test and approve everything.  If a component fails on the track, you get a warning and a temporary ban.  If a component fails twice, all components are banned for life.  The stayer bike stem had some of its steel removed so that it looked sleek, and as a result had failed (twice).  This is why Sakae never became a major component supplier for NJS bikes.

These stems have horizontal stem bolts - a tried and true method as opposed to the vertical design that failed.
We measured out our stems - Mr. Yamaguchi recommends 110mm stems for road bikes, and 100mm for CX bikes.  Track depends on many factors, but that's a different story.  I chose to do a newer style stem that bolts to the steer tube and uses a 31.8 clamp for the handlebars.  Quill stems are difficult to make in the US, since the bottom parts are no longer supplied.  In Japan, Keirin frames still use quill stems, so parts are easier to get there, but since many frames in the US are aluminum or carbon, that's no longer the case here.  

The two lower stems are the newer style - what I am making.  The quill stem, shown above, is not a style commonly used anymore on newer bikes.  
I started my stem with a miter cut to match the angle of my head tube (at this point I'm getting pretty okay at mitering by hand!), and checked to make sure everything was straight and my stem was the right length - 110mm center to center.  All good.  Then a hole had to be drilled in the steer tube clamp to allow for internal brazing to work nicely.  Stems don't require too many components, or at least the ones we made don't, so that was all of the tube prep that was needed.  I sanded my bolt clamps for later, and cleaned everything with acetone.

There's a stem here, waiting to be born.
We were then surprised with a birthday treat - a strawberry cake and the girliest balloon I've ever seen was delivered, and we all enjoyed a slice of cake during a quick break.  It was by no means a random cake - I'm taking this class as a birthday gift to myself, but I have to thank my mom for orchestrating a cake delivery out in this tiny little town near the middle of nowhere.  Thanks Mom!

I didn't get a photo of the cake before we dug in, so here are stom stem blueprints instead. 
Mr. Yamaguchi set up the stem jig, and I set to work tacking the handlebar and steer tube clamps to the stem.  The same tacking method as before was used, first tacking one side, then the other.  If the temperature of the torch is too high and the bronze or flux burn, the area must be cleaned up and flux reapplied, which I had to do after my tacking was done and the stem cooled down.

Starting to tack on a special stem jig.  
Internal brazing the stem was one of the more musical experiences I've had so far - the little tubes made quite the racket as the bronze was pulled inside.  It sounded like something in between a whistle and a puppy whining, and with three of us brazing at the same time was quite the symphony.  This too had to be cleaned after it was cooled down before the final outer brazing can begin, so it was back to filing and sanding.

Just the drill press, used for drilling holes in the tubes.  
Mr. Yamaguchi then demonstrated the external brazing process, and how to get a nice fillet around the outside.  Of course, he made it look easy, moving the torch and the bronze around with precise calculations to shape the fillet into a perfect band.  Then it was my turn.

External brazing was easier than internal, and I did a decent job (for my first time, at least).  My stem was actually starting to look like a stem, but it still needed to be finished.  The stems were given a bath of hot water to remove the flux, and that was all for the day.  

Stem bath.  The hooks are used to fish them out of the hot water.
Monday is the beginning of crunch week, so tomorrow I'll rest up and prepare to really work hard to finish my frame.

No comments:

Post a Comment

Tell me your bike related thoughts!

Template developed by Confluent Forms LLC; more resources at BlogXpertise