Archive for September, 2012


Eight Tubes, Part 10: Getting My Head On Straight

I got to pull out a pretty cool tool this week: the good ol’ head tube reamer and facer. Not a tool that your average bike mechanic has in his or her tool box, but I have one.

Don’t know what a “head tube reamer and facer” does?

It is the tool that you use to prepare the frame to accept a good quality headset. It finishes off and squares up the top and bottom of the head tube and it opens up the inside of the tube to the proper size so that the headset fits inside with the appropriate level of drag.

But first, I had to trim off the bits of the head tube that were still standing proud of the top of the lugs. This was a few minutes’ work with a hacksaw. Be careful not to cut into the lug. It is okay if you don’t get it totally flush; you will fix that when you level up the tube with the facer.

Being a careful sort, i wanted to double check that the headset that I am going to install matched the fork and the cutter that I was going to use to ream the head tube. I got out the calipers to confirm that my headset (a new, in-the-box Shimano 600 cartridge-type unit…a modern classic)is in fact an “English” size and not the Japanese JIS standard. There are subtle but important differences dimensionally. No worries here; it is an “English” headset.

The facer/reamer is set up and ready to go…

It does a nice job. One key is to use “liberal” amounts of cutting oil. This keeps the cutter sharp and allows for nice, smooth finished surface. I used a hand file to put a slight chamfer on the inside lip to allow the headset to fit flush when it is pressed into place.

Press in the headset, throw on the fork, which we finished a while back, and it is starting to look like a bike.

It is enough to make a pretty girl smile…



Eight Tubes, Part 9: Finger Rippin’ Good

We’ve taken a few casualties here in the Bike Bunker. I will spare you the details – and pictures – but I think that the bench grinder is plotting something…big. I’ve currently got it set up with a wire brush so that I can clean up parts quickly. For example, it does a really good job on removing spent brazing flux from tubing.

And removing skin from fingers.

Let’s just say that this isn’t the first time that the bench grinder has tried something. Its favorite party trick is to snatch whatever you are cleaning up out of your hands and wing it across the shop.

Or, if the mood strikes, at your head.

Despite the repeated attempts by my power tools to maim me, and the constant interruptions to go and find band-aids, we’ve also made a lot of progress on the frame.

1. My Head(Tube) Is On Straight: If you recall from the last installment, I screwed up the braze job on the head tube. I had come up with a dandy little device out of an old brake cable and a hose clamp to hold the tubes together while I braze. I got excited and tightened things down a little too snug. The head tube angle was supposed to be 74 degrees. It was more like 76+ degrees when I measured my work. Oops. This was an easy fix: I just grabbed the torch and sweated the joint apart ( i.e., got it hot enough to melt the silver solder) and started over. This also let me check my work and see whether my brazing skills are up to snuff. Things looked good, apart from the fact that I screwed up the angle.

2. Getting’ Down With The Downtube: Having fixed my mistakes, it is now time to attach the last of the four tubes that make up the front half of the bike. To do this, we will be attaching the bottom bracket – and setting the seat tube length and head tube length in the process.

Our seat tube will be 55cm, measured center of the bottom bracket to the top of the top tube. The easiest way to sort this out so that, when I am finished, the axle of the crank is at the desired 55cm from the top tube is to start by trimming the seat tube to 55cm, measured from the top of the top tube to the bottom of the seat tube. You will be cutting off more later, but for right now start with your target length.

I still haven't cleaned off my workbench.

When you measure “center to center” or “center to top” or “center to whatever” one of the tricky things it to sort out exactly where the center of the bottom bracket is. It is located somewhere in that open space where the cranks usually reside.

This is a machinist's center.  A cool old tool.

You could just eyeball it when it is time to measure where to locate the bottom bracket, but I figured out a better way. To make it easier to figure out where the “center” of the bottom bracket is located, I used a ruler, some tape, and a used spoke to help line this up. It is easier to show than to explain…

Slip the bottom bracket onto the seat tube, and work it up to the point where it touches the spoke that (if you did it right) is located in the center of the bottom bracket. When the end of the tube touches the spoke, the center of the bottom bracket is located 55cm from the top of the top tube.

I'm pretty good at coming up with Rube Goldberg devices.
Easy, huh?

I used my electronic angle finder/level to make sure that the bottom bracket was oriented so that the axis of the cranks is 90 degrees to the direction of travel. Or, viewed differently, make sure that the faces or “cheeks” of the bottom bracket are parallel with the top tube.

Okay, this is a weird picture that doesn't really explain a lot.

Get out your Sharpie and make some “witness marks” noting where the bottom bracket sits on seat tube when everything is lined up so you can locate it again without a lot of rigmarole.

Kinda zen looking.

Don’t put away the Sharpie quite yet. Use it to mark where you need to trim the seat tube. The was way to do this is to use the marker to trace the shape onto the tubing by running the pen around the inside of the bottom bracket and the as well as the opening on the front of the BB for the down tube.

Red Diagonal Lines: the univeral symbol for "trim this off"
After you trim it up, the end of the seat tube looks like this:

That discoloration on the tube is blood.  My blood.  The grinder claimed another victim.
Now it’s time to trim up the down tube. This is fairly straightforward. Like the top tube, the down tube is butted, so you want to trim it to length by taking an equal amount of metal from either end. Eyeballing it, I estimated the miter to miter distance along the bottom of the tube to be around 56cm. I found the center, marked it, and then printed one of those handy computer-generated patterns to miter the downtube/headtube joint. Using my 56cm estimate, I slapped the pattern on one using the same technique for cutting the top tube to length (take equal, smaller amounts from both ends, not one big cut from one end) and mitered the headtube/downtube joint.

To "eyeball" this I stuck the down tube in the bottom bracket before I cut anything.
At this point I located and drilled the holes for the bottle cage – it is much easier to do this before the tube is permanently attached to the bike. Because we’ve done both mitering and bottle mounts before, I will skip all the gory details here.

At this point, we need to figure out just how tall the head tube is going to be. On Old Number One, as on is bike, the length of the head tube is simply a function of where the angle of the lug on the bottom bracket and the angle of the lower head tube lug cause the down tube to intersect the head tube. It is easier to show you rather than to explain it with a bunch of words. As with Old Number One, the head tube worked out to 160mm. The fork that I built has a compatible steering tube length, so no worries. I knew to make it long…

This is not an optical illusion, the down tube is behind the head tube.

Her clothes are not OSHA approved for workers employed in light industry.Are you tired yet? The pretty girl isn’t.

Like the seat tube, you have to trim off the excess on the end of the downtube that intrudes into the bottom bracket. Get out the Sharpie, mark it off, and let the metal fly. When you do it right, it all looks like this:

Peering into the abyss....

Do a final fit, check all the angles, clean it up, and braze.

I need to find a better place to store my Christmas Tree stand.This picture looks like it was taken by a chimp.

The finished product:

Starting to look like a bike frame.

That toilet bowl cleaner sure makes things shiny....

A little trick: cleaning off spent flux from a brazed joint it not my idea of fun. The wire brush on the bench grinder (when it isn’t trying to kill me) is good for getting the big stuff, but it won’t reach into the nooks and crannies. The solution: toilet bowl cleaner. Yes, this is actually pretty nasty stuff. The Lysol brand that I bought contains hydrochloric acid. It can make a gnarly commode look like new, and strip baked-on slag from steel tubing. It will also remove skin and dissolve eyeballs, so be careful. I use a small steel brush to scrub the deposits. When I am done I rinse the the tube with lots of cold water, warm the frame with the torch to evaporate any trapped water, and then liberally spray the whole shootin’ match with WD 40 to ward off rust.

Checking my work, things turned out as planned. The head tube angle is smack on 74 degrees (74.05 according to the angle finder), seat tube is 73.4 degrees, and the joints all look like they have good penetration.

Next up: chain stays…


Eight Tubes, Part 8: Cutting, Brazing, And Screwing Up

My buddy Jon stopped by today; he was finishing up a ride and he saw the garage door open. Luckily, I was able to give the impression that I was actually working on stuff.

Well, I was working on stuff.

Jon also reminded me that I had not updated this blog in a little while. Thanks, buddy!

Seriously, I’ve made progress. Metal chips have started to fly, and the torch has been busy. Oh, and I have to redo a chunk of what I did because of some, well, innovative production techniques.

Take a look:

You start building a frame by putting together the front triangle first. And you start building the front triangle with the top tube. You need to figure out how long you want it, and the angles of the seat tube and the head tube so you can miter the ends.

The bike will have a 55cm top tube (measured center to center), and the angles are 74 degrees (head tube) and 73 degrees (seat tube). The key measurement to figure out is the length of the top tube “miter to miter” along the top of the tube – the distance between the miters for the head and the seat tubes. This becomes important when you miter the tube ends.

For this frameset, the “miter to miter” measurement along the top of the top tube is 52mm.  How did I figure this out?  I cheated.  I have a 55cm frame that fits me perfectly, so I just measured the “miter to miter” distance on that one.  The other way to do it is to subtract half of the diamter of the head tube and the top tube from your target center-to-center length.  This gives you a rough approximation – it isn’t totally accurate given that the tubes are not at 90 degree angles to each other.  It is close enough, however.

Speaking of mitering tubes, it is now time to run off the paper patterns that will help you miter the tube accurately.  I mentioned these patterns a couple of installments back.   Nova Cycle Supply has a miter program that is pretty slick; you give it the the size of the tubes that are being joined and the angle, any it spits out a paper pattern that you cut out and tape on to the end of the tube.Get out the scissors! Art project!

Remember that “miter to miter” measurement that you figured out a couple of paragraphs earlier? Use that measurement to locate the paper patterns on the ends of the tube. The “miter to miter” distance will be the length between the “scallops” on the pattern. Take your time lining up these patterns on the tube so that when you finish the miters and you attach the head and seat tubes the top tube turns out to be (1) the proper length and (2) properly oriented to each other.  What I mean with #2 is that the head tube and the seat tube line up with each other when viewed from the front (0r back).  No twists.  Yes, this is a gross oversimplification of what goes on with this step, but you really don’t want to read about it in gory detail.

Confused? Look at the pretty girl until it starts to make sense.

she doesn't look nearly as insane as the pin up a couple of posts back, does she?

One last thing before you start cutting metal; you have to know which end of the tubing to trim when cutting it to length.  This can make a difference.  Some tubing makers (I’m looking at you, Columbus) design their butted top tubes and down tubes with a longer butted area on one end, with the intention that you cut on this end of the tubing.  Seat tubes are the same way.  If you cut on the wrong end, you can end up trimming away most of the thick part of the tubing that is supposed to go into your lug, ending up with a weak joint.  Most tubing makers will put a splash of paint on one end of the tubing to mark this out….so you have to know whether the splash of paint means “cut here” or “don’t cut here.”  The tubing maker will have this information on their website.  For Columbus tubes, for example, the paint generally means “don’t cut on this end.”

If the tube doesn’t have paint on either end, and you can’t get guidance from the folks who sold you the tubes, what do you do?  Me, I ended up taking metal off of both ends. Why? Simple.  I presume that the tube is butted the same amount on each end.

I really need to clean up my workbench

After trimming the tubes, I used a pneumatic die grinder ( aka “the dentist drill from hell”) to shape the ends of the tubes. You want the tubes that you are joining to fit together tightly, with no gaps.

See! No gaps!

You can double check your work by fitting the the lugs onto the tubes and seeing how well the contours match.

Damn I'm good...

I'd say those contours match...

Before we fire up the torch, there are a few other things that we have to do. First, and easiest, is that we have to drill a vent hole in the head tube. The reason for this is that when you heat up the tube – any tube – the air inside the tube will also heat up and expand. Unless you provide an escape hatch for that expanding air, it will try to make its exit through the joint that you are attempting to braze. That causes problems; the molten filler rod won’t flow into the joint when the expanding air is heading in the opposite direction out of the joint. I just drilled a 1/4 inch hole in the head tube, centering it in the joint with the top tube.

The second bit of preparation is to drill the holes for the bottle cage mount in the seat tube. You could probably do this later, but I found that it is much easier to set it all up on my drill press before the seat tube is irrevocably joined to the rest of the frame. I made a simple jig out of an old bottle cage to locate the bottle mounts. After measuring all of the bottle mounts on all of the bikes in my shop and finding a happy mean, I drilled the top boss about 24 cm from the bottom of the top tube joint.

Re-purposing useless crap that was cluttering up my workbench

After checking one last time to see if everything fitted together correctly, it was time to fire up the torch.

I brazed the seat tube/top tube joint first. The seat tube fit into the lug just loose enough that it would not stay in place by itself. So, I devised a rather Rube Goldberg-looking device involving a hose clamp and an old brake cable to hold it in place. That worked like a champ.

In fact it worked so well that I used my little invention to hold the head tube in place. And to make sure that things were nice and snug, I gave the cable a extra tug to make sure that everything stayed put.

Big mistake.

After I put away the torch, I broke out the angle finder to check my work. I did a great job lining up the head tube and the seat tube so that that the frame doesn’t have a twist to it (as viewed directly from the front). And the seat tube was close enough to my target of 73 degrees that I won’t worry about it being a little steeper than planned. I can tweak that with a little muscle.

The other good thing is that the lugs look pretty sweet. They are fairly thin, which means that they heat up quickly. Best of all, they have “windows” in the design that make them easy to braze. Just heat the joint, touch the rod inside the window, and direct the flow of the filler material by aiming your torch where you want the silver to go. Easy as pie. Once you remove the spent flux, very little clean up is necessary.

Black tassled loafers.  Tres' chic.

The place where I screwed up was on the head tube, thanks to my handy tube holding miracle device. When I put the cable low on the head tube and cinched it down that extra bit I ended up tweaking the angle; instead of the target of 74 degrees, the head tube ended up a rather sketchy 76+ degrees. Whoops. I should have checked things before I fired up the torch. Lesson learned.

Near-genius in action.

As for fixing the head tube angle, I’ll just have to get the torch out, sweat the joint apart, and try again. No big deal.

The other bit of collateral damage was to my long-suffering bike stand. I got the tubing hot enough to melt the rubber pads that line the jaws. They were torched anyway (THEY WERE “TORCHED”!! HAHAHAHA! I CRACK MYSELF UP!) so I’ll have to spend seven bucks to replace it.

Starting to look like...random tubes stuck together.

%d bloggers like this: