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.


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.


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.


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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