Getting Bikey

Braze-ons

The braze-ons went on pretty quickly this time, except for one brake stop that kept moving around.  Ended up with about a metric ton of silver on there.  I'll have to get some little magnets.  The one I used to hold things still for a couple of other bits worked well, but I managed to ruin it with the flame. 

Head Tube/Down Tube Sub-assembly 

I didn't get a lot of photos of my first joint on this attempt, as my phone ran out of batteries pretty early on.  Luckily, it was pretty simple.  I checked the angles, fluxed it up, and brazed it.  I did burn some flux on the head tube side of the joint, right at the bottom.  Thankfully, after I chipped off the burnt flux and spread around some fresh, I was able to channel enough silver through to feel pretty confident about the joint.

Despite being pretty careful, it seems that the joint pulled back to the original 60 degree angle of the lug, not to the 59.3 that I'd thought I'd filed things to.  It only took a few minutes with a cheater bar through the head tube to make the adjustment, and I managed to finish it out within .1 degrees of correct.  

The above picture was taken after some sanding and filing.

Seat Tube/Bottom Bracket Sub-Assembly

I was worried going into brazing the bottom bracket shell on to the seat tube.  The BB is a big heavy piece of steel, and that makes it a lot harder to get up to temperature without going over.  I did a test joint right before doing the actual work, just to get myself calibrated.  

The test piece came out pretty well, a nice clean ring of silver in each of the cross sections.

When it was time to do the joint itself, I got everything aligned and fluxed, then tacked the front and back of the BB lug to keep it in place, then aligned everything again.  When I started brazing, it worked flawlessly.  I was able to draw the silver exactly where I wanted it.  Best braze I've done to date... until I got half way and  the BB fell right off.  It was comic, and frustrating.  

Basically, I'd had about half the shell up to temperature, so all of the silver was soft at the same time.  On my second try (after soaking and sanding each surface clean), I tacked the piece on four sides.  

This time it worked almost as well, but with less falling.  I used WAY too much silver, in my paranoia about gaps or voids, but that's easily fixed with emery cloth and patience.  I didn't even overheat things much!

I did find that the points were a bit far from the lug, as I'd widened the socket to get the angles right (this tube needed to tilt about 1 degree further in the direction of the down tube than the lug is set up for).  If I'd been thinking more, I'd have clamped the points back into place before proceeding.  As it is, I'll just have to dribble a bit more filler on the point when I do the other joints and sand until it doesn't look dumb.  Internally, it should be fine.

Just for fun, I slotted the two sub-assemblies together and was overjoyed to find out that, if I don't let stuff slip when I braze the last few joints, the vertical tubes should both end up at the required 73 degrees.

Funny story: 

I had to cold set (fancy term for "bend") the BB's angle, after tacking but before brazing.  When I cranked the tube to the side a degree or two, one of the little tacks popped free.  I must have jumped a few feet into the air, and was sure that I'd wrecked the whole thing.

Blueprints

Today I put together the blueprints for the new design.  I use Rattlecad, an awesome free open source program that does a lot of the calculations for you.  You give it important information, like the slope of the seat tube and the drop of the bottom bracket, and it calculates the less exciting stuff.

I started with the geometry of a bike that I knew I liked, then lengthened the head tube about 4mm, bringing the imaginary bars up and back a little.  I entered the sloping top tube (6 degrees to match the lugs), and the offsets for where the tubes enter the lugs (how far one tube extends beyond the intersection with another).  I also tweaked the water bottle locations.

I'll print this full scale so that I can line the tubes up against it.  It'll let me quickly double check pieces and dimensions without TOO much measuring.

Center-lines

A few operations in the construction of a bicycle require you to have a clear center-line for the tubes.  The top tube, for instance, needs to be cut on both sides so that it will mate up with the head tube and down tube.  If those cuts aren't lined up with each other, you'll end up with a very twisty frame.  If you have a center-line, you just match it up to your templates (more on that when I post about mitering).  If you don't, it gets more complicated.

Before drawing on the tubes, I needed to figure out which way they bent, since it was pretty unlikely that they'd be perfectly straight. To do that I used an alignment table.  An alignment table is a big slab of stone or metal that is ground carefully until it's perfectly flat across the top.  It seems like any table would work, but it has to be pretty damned precise to make this work.  I rolled the tubes on the table, looking at the gaps underneath, until I found the flattest axis... then marked those as the "sides" of the tubes.  The center-line would be 90 degrees around the tubes from the "sides", because the tubes being slightly curved towards the front or back of the bike wouldn't make as much of a difference as having them lean slightly to the right or left.

Actually making that line is one of those things that seems easy, but ends up being really hard.  Lining up a straight edge with the tube is difficult.  Keeping it there while you mark things is pretty impossible without designing some kind of a fixture to hold everything.  I basically held two tubes together, with the point that I wanted the lines to start from deep in the "V" between them and dragged a marker down the center... again and again until the line started where I wanted it to. 

I then used the alignment table to check if they were straight with a specially made caliper.  If both ends of the line were the same distance off of the table, then I was good.  Otherwise, back to the drawingboard.  

When finished, I taped over them so that I wouldn't accidentally rub them off when working with the tubes. EDIT: NEVER DO THIS.  Taking off the tape is a full time job.  Next time I do this, I'll just get the miter templates and bottle cage mounts aligned right away.  

That's it for today, next time I'll share the diagram that I'll be working off of.

A Bicycle is a Slightly Different Series of Tubes

The new tubes, lugs, and small parts have come in!  

Here's the entire bicycle, laid out.  The two tubes with an obvious taper are the chain stays (they connect the rear wheel to the bottom bracket.  The four thicker tubes make up the front "triangle" of the bicycle.  We call it a triangle because people get confused when scruffy bike guys use words like "quadrilateral".  

These tubes, with the exception of the head tube, are butted.  They get significantly thinner at the center to save on weight.  Since most of the strain on the tubes is near the joints, you don't lose a lot of strength.  

The small tube near the center with a drilling in the middle will hold the rear brake.

A lot of my favorite goodies are in that little plastic bag.  Reinforcement plates, classy adjustment barrels, and rack mounts.  I'm looking forward to dressing them up a bit this time around.  

This set of lugs are a little smoother than the last set.  They cover more of the tubes and sweep pretty gradually between them.  Unfortunately, this eliminates some of the elegance of the lugs I was originally using, which have a crease that better defines the tubes.  The flip side of that is that there's a fair amount of material to play with.  I might grind some detail work into the shorelines.

Tomorrow I'm going to prep a bunch of tubes (and the spare, cheap set of lugs I included in the order) for practice brazing.