Archive for August, 2012

14
Aug
12

Eight Tubes, Part 7: Where’s My Sharpie?

My favorite Sharpie marker has bitten the dust.

This particular Sharpie was a veteran of building Old Number One, and I had gotten rather attached to it. Granted, Sharpie has probably pumped out literally millions of blue permanent ink markers, but I rather liked my particular pen. I used my trusty blue Sharpie to mark off where to cut the tubes, where to locate things like the brake bridge and bottle bosses, and most importantly to help orient the lugs so that everything lined up square. By the time I had finished building Old Number One, it was a chewed up mess with a cracked top that I had “fixed” with electrical tape. It also had a nasty habit of turning my fingers blue every time that I used it. No matter; my blue pen became a small good luck charm and whenever i was out in the shop I would make sure that I knew where my Sharpie had gotten off to.

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The reason why I was reaching for my blue Sharpie is that it is time to begin sorting out all the “stuff” and identify what my friends at Nova Cycle Supply have sent me. And by “sorting out” I mean literally that – sorting which tubes are which and getting the relevant measurements. You need the measurements (specifically, the tubing diameter) to feed into a neat little computer program that will generate a paper pattern that you cut out and use to miter the ends of the tubes. You also have to identify which of the main tubes go where, which sometimes isn’t self evident.

"In Praise Of The Small Queen"

I bought is a “standard” sized (as opposed to “oversized”) tube set that is “double butted”, meaning that the tubes are drawn in such a way that the metal on the ends of the tubes is thicker than in the middle. This saves some weight without sacrificing much in the way of strength. I used a simple caliper to measure the tubing diameter. This is another of those “must have” tools for the shop – the non-fancy ones are dirt cheap.

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Poking through all of the stuff in the box from Nova, the head tube is the easiest to spot – It is the shortest of the lot. The top tube is also easy to spot because of the three main tubes (top tube, seat tube, down tube), it is the skinniest, with a diameter of 25.5mm.

It is the down tube and the seat tube that have the greatest potential for getting mixed up. Both have a diameter of 28.6mm. The seat tube, however, is butted only on one end ( ie. the internal diameter of the tube is greater on one end of the tube than the other) while the down tube is double butted (ie. the internal diameter of the tube is the same on both ends, and skinny in the middle). You stick the beefy end of the seat tube into the bottom bracket, where the thicker metal makes for a stronger, stiffer joint while you can get away with less metal up top because the seat cluster is reinforced by the presence of the seat post.

The easiest way to figure out which is the down tube and which is the seat tube – and which is the thick end and which is the skinny end of the seat tube – is to take a seat post of the appropriate size and see if it fits easily into one of the likely suspects. The skinny end of a seat tube with a 28.6mm diameter will usually have an internal diameter that will take a standard 27.2mm seat post. The thick end of the tube won’t accept the seat post without a lot of bashing and cussing, and the seat post won’t fit into either end of the down tube.

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The other sure-fire way to figure this out is, of course, to get out the caliper and to measure the thickness of the metal on each end of the tubes. If you bought straight gauge tubing without butting, then you don’t have to worry about finding the “thick” end of the seat tube because the tube will have a consistent internal diameter the entire length of the tube.

Bored? Look at the all of the pretty French women on bikes.

So having sorted the sheep from the goats, I got out my NEW, pristine blue Sharpie marker and made notes right on the tube that identifies which one is which and, for the seat tube, which end is up. That way, it will be tough to screw it up later.

Totally Tubular

Next: Metal Starts To Fly….

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09
Aug
12

Eight Tubes, Part 6: Put A Fork In It…

Check “build fork” off the list. It’s done.

And the damn thing looks pretty good.

Last time out, I had finished brazing up the crown and steering tube and had just finished trimming the fork legs to length. What has left to do was to set up the tubes in the jig and to braze it up, Easy, right?

It was a little trickier than that.

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The thing that took the most care was the set up. I had built a fairly simple jig out of angle iron and an old front hub. It is a fairly rudimentary piece of equipment but, with some patience and my kick-ass angle finder, it got the job done.

First, I had to double check to make sure that the jig that I had built was actually square. Turns out that it wasn’t – it had a small twist in it. I found that out by putting the level/angle finder across each end of the jig and comparing the angles. If things are parallel, the angles should match. They didn’t. A couple of shims under one end fixed that problem.

Second, slipping the tubes into the jig, the fork legs and crown have to be parallel with each other fore and aft. (Fork legs, of course, aren’t parallel with each other when viewed head on). Resting the level/angle finder across both legs, the angles (if the work table isn’t dead level) should match when measured at the fork crown, the fork ends, the middle of the leg, and on each end of the jig itself. In other words, you are checking to see if there is a twist your set up,

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Third, you have to orient the legs fore and aft so that the you get the appropriate amount of rake. This is measured by the angle formed by the steering tube and the fork legs. Again, I used the level/angle finder to measure this. The tricky part was taking into account the fact that the fork legs are tapered, meaning that I had to put a small shim under the angle finder to correct for the taper. The rake on this particular fork is supposed to be 7 degrees.

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Confused? Bored? Look at the pretty girl; that’s what she’s there for.

Anyway, after about an hour of futzing with the set up, I lit the torch and had at it.

It turned out pretty good. Getting good strong joints with no gaps or voids and solid penetration is important on a fork; the joints are highly stressed and if they fail the resulting accident can kill you. I think that I did the deed. Put it this way; I’ll be happy to ride on it.

Putting the dropout gauges on the fork shows that the dropouts are parallel and that he fork legs are the same length. Sliding a wheel into place shows that the lateral alignment is good.

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Most importantly, it looks cool.

Big thanks to bike guru Slippery Pete Czapiewski for cutting the crown race. The dude has skills (and tools).

05
Aug
12

Eight Tubes, Part 5: Get Forked

Now we’re getting down to business….

To recap: blah blah blah…I got a bunch of tubes and lugs that, when assembled, will hopefully form a lugged steel frame and fork…blah blah blah…Plans!? I don’t need no stinking plans….blah blah blah…because I am not working from a blueprint I need to build the fork first...blah blah blah…oh, I’ve never built a fork before….blah blah blah…so HOW do I do this?

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One step at a time works best. First things first: braze up the steering tube to the fork crown. Basic stuff here.

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The first photo shows a couple of things here. First, I wanted gravity to work with me when I started brazing this assembly (to help draw the metal all the way through the crown, from top to bottom) so I decided that I was going to position the piece with the steering tube in a vertical position. The fit between the fork crown and the steering tube was loose enough that it would not stay put so I pinned the two together using my special Ernesto Colnago Frame Building Pins (i.e a small finishing nail cut to length). The second picture shows the pin, a nice peek at the hollow crown on the fork, as well as photographic evidence that I possess feet.

These shots also show that I have a bit of the steering tube standing proud from the bottom of the crown. You need little bit of tube sticking out when you silver braze – it gives the molten metal a start as it wicks down into the joint.

So I got out the torch – a simple Bernz-o-matic MAPP gas torch (about $65 at Home Depot), cleaned the joints so things were all nice and shiny, slathered them up with flux, and did the deed.

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What you want to have happen is for the molten silver brazing rod to completely penetrate the joint. In a perfect world, you would feed the rod in from the top of the piece and it would eventually flow out the bottom of the joint as you worked it though with the torch. I must have had a good day, because that’s exactly what happened here.

I cleaned up the spent flux that was glopped all over the piece with Lysol Toilet Bowl Cleaner – it contains hydrochloric acid and really gets bare metal CLEAN. Be careful with skin and eyes, and rinse the piece with water. I then usually get out the torch and gently heat the piece to evaporate the water.

Next, I drilled the holes in the crown for the front brake. Because this particular crown is for a straight legged fork, the hole for the brake had to be drilled at an angle to match the fork legs. Luckily, the crown has little cast-in dimples to guide you. I set my drill press to drill at the necessary angle using a really cool tool that I just bought – a “digital inclinometer”. This thing kicks each of the 23 possible types of ass presently known to science, both actual and theoretical. It’s a little aluminum box with a digital readout that tells you (1) the angle of the piece from absolute level, or (2) the angle of the piece relative to a reference that you set. Mine is made by Beall Tools, and is made right here in the good ol’ USA.

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A little work with the die grinder and a file removed the portion of the steering tube that was sticking out of the bottom of the crown.

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Now it was time to trim the legs of the fork to length. As the come from the supplier, the legs are waaaaay too long. I was shooting for an axle to crown measurement of around 365 mm. I also wanted to trim the legs so that it positioned the wheel where the brake track would match up with the brake pads at about the middle of their range if adjustment in the caliper. (If that makes your head hurt, just look a the pretty girl. That’s what she’s there for.) I have the brake caliper that I am going to use, and a wheel, so I clamped the fork in the vice and did a trial fit. Uncut, this is what things looked like – off by about 4 inches.

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So I measured, got out the hack saw, held my breath, and trimmed it up. Against all odds, I hit the mark that I was shooting for.

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At this point I decided that I had used up all my good bike-builder mojo for the day and stopped while I was ahead of the game. All that needs to be done is to drill vent holes in the fork legs, clean up the fork ends, do a test fit in the jig that I built, and then braze it up.

NEXT WEEK: Get Forked, Part 2




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