Archive for October, 2012

31
Oct
12

Eight Tubes, Part 12: Oh Won’t You Stay, Just A Little Bit Longer…

Next up – seat stays. Not much to blather on about here; this is pretty simple. The top of the stay fits into a remarkably clever little socket on the back of the seat tube collar, and the bottom end is notched and then attached to the rear drop out just like the chain stay was.

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As I say, easy. What could go wrong?

We had a slight “moment” when it appeared that the seat stays were not going to be long enough. Slide the top into the remarkably clever little socket…offer up the stay to the rear drop out…and it barely reaches.

Time to get out the measuring tape.

Turns out that when I was making “adjustments” to the chain stays (i.e bending or, more euphemistically, “cold setting” them) in order to center the wheel in the frame, I managed to shove them downward, toward the floor. Whoops. Re-attach the fork, get out the measuring tape to locate where the rear dropout should be located, and reset the chain stays.

That fixed the problem, allowing me to breathe again.

The rest of it is straightforward. Double check to make sure that the dropouts are aligned both laterally and vertically – I did this by putting an old wheel (but true) in the dropouts when I brazed the top of the stay to the seat collar. I could visually check to make sure that everything lined up laterally and horizontally and that the wheel was located properly between the stays.

The results:

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The next bit to fabricate is the brake bridge. I opted for a nice Cinelli style bridge, and some fancy do dads that dress it up a bit. Figuring out where to locate the brake bridge is a bit of trial and error. The main thing is that it is really helpful if you know what type of brakes you are using and their “reach” – usually the distance from the mounting stud to the lowest adjustment for the brake shoes. Am using a set of short reach brakes that I have laying around the shop, so I attached a rear wheel and offered up he brake caliper to the frame to figure out where the bridge should go.

Get out the die grinder, and trim the bridge to fit. Add fancy doo dads. Here it is, ready to braze:

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I stopped here because I was on the verge of screwing up. Plus, the pretty girls wanted to go for a ride…

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15
Oct
12

Eight Tubes, Part 11: Chain(stay) Of Fools

Okay, it has been a little bit since I last updated the ol’ blog. I was going great guns there for a while and then I came down with some sort of respiratory deal that had me coughing and hacking. I was swilling cough syrup and, well, it left me a little loopy. I certainly didn’t want to be cutting metal or picking up a torch.

I am still swilling cough syrup with reckless abandon, but since I’ve apparently built up a tolerance to it over the past two weeks I went ahead and picked up the tools to tackle the chains stays.

Chain stays are…tricky.

Here’s what I am working with; some old school drops outs and some shapely, uncut chain stays. The stays are manipulated so that the middle is squashed flat to give tire/crank clearance and to add vertical stiffness.

Tres' shapely...
The dropouts are supposed to fit into the skinny end of the chain stay. The first order of business is to cut a notch into the end of the chain stay so that the dropout slides in.

You aren't going blind...it IS out of focus
That shiny thing sitting on the vice is the beginnings of a plug that will fit inside the chain stay and fill in/beef up the joint between the drop out and the stay. It too will be notched. The idea is to provide come up with the maximum amount of surface area to support the dropout. You need a good strong joint.

Yup, the dropout fits.

Okay, that's better.  In focus.
The plug was pretty easy to make. I took a 5/16th bolt (which fit inside the chain stay very nicely) and trimmed it to the length that I wanted. Pulling out the ol’ black Sharpie pen, I marked where the slot in the chain stay hit the plug. Using a hacksaw, I then cut a notch. Get out the torch, braze the plug into the chain stay. hacksaw off the end, clean it up with a file, and voila!

Again, photograpic evidence that I have feet.  Thank goodness I was wearing pants.

Clever, huh?

And we were doing so good with that "in focus" thing.

This is the bench outisde of my workshop.

Dress up the end of the chain stay with the bench grinder, and it starts to look nice…

Swanky!
When it comes time to get out the torch, you want to make sure that the dropouts end up parallel to each other. I did this by sticking a piece of aluminum stock that I had lying around into both axle ways. They brazed up perfectly.

Day 156: My Workbench Is Still A Mess.
And now for the tricky part…putting the chain stays into the bottom bracket and getting everything all squared up and oriented.

I cheated: I built a simple jig out of some angled steel and some bolts. This is what it looks like.

Most of that crap is my son's.  Except for the mini bike.  That's mine.

I bought that mini-bike when I was a kid.  $169.95.
What this jig does is help locate where the rear dropouts are supposed to go, and then hold them in place while you braze it up. Works pretty good.

How do you figure out where the dropouts are supposed to go? Easy. We have already covered it.

Anyway, the next job is to trim the chain stays to the desired length. Given that we have just done a lot of work on the skinny end of the stay, we will be trimming off a hunk of the fat end that goes into the bottom bracket. This is okay: before I started this process I determined that the metal would come off of the fat end next to the bottom bracket by measuring the chain stay against a back wheel that I had lying around. Laying the uncut stay against the wheel, it was clear that the “squashed” part of the stay matched up with the tire without cutting anything off the skinny end. In other words, if metal was going to come off, it would be from the fat end of the stay.

Just use the Sharpie to trace the shape on the chainstay.  Easy.
Trimming things up, the ends of the stays should conform to the curve of the inside of the bottom bracket. This is what they look like when you are done.

It looks like I caught some sort of metallic space fish.
So….nothing left to do but get out the torch and braze it up. Things turned out okay. With a little bit of tugging and tweaking, the alignment ended up dead on…

What a crappy picture.

I stil have to fiddle with it to make sure it all lines up correctly.
Not a bad day’s work for the pretty girl.

This happens in welding shops ALL THE TIME.




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