By James Morikawa
5 January 2007
Pictured above, is a H20 boss drill-jig made by "Bicycle Engineering", and purchased from "United Bicycle Tools" many years ago. That rod attached at the jig's top-center is for center-aligning the jig — it came with the jig when I purchased it.. That other "rod" next to it, is just one of the drill-bits I will be using — don't pay any attention to it.
I once gave the jig to a really cool frame-builder in California, but he's so cool he gave it back to me, when he found out I had started building again. He builds these really cool looking bikes with curved top and down tubes — now ain't that, "top shape, first class, California styling", or what?
Enough jiving, back to the main-lining.
Notice the two lengths of wood — that's a tool to aid in center-aligning the drill-jig. In the above picture I've adjusted "that rod attached at the jig's top-center" so that it's centered between the two wooden lengths.
Once I have the jig aligned, and secured; I drill the H20 boss holes. I got two drills for the task — a small pilot drill that has upper shank that fits the drill guides, and final size drill. Without drilling a pilot hole first, the final size drill could drift "off-center", even with the drill jig. I've had this happen once too many times.
There are times I'm not able to use the drill jig. The following pictures are a brief summary, of drilling without the jig.
Locating linear "center plane" of the tube, and frame. I'm using a metric-rule to aid me in locating the center between the two wood lengths, and scribing (marking) this center on the tube.
Scribing (marking) a linear center line down the tube. Notice the aluminum anlge bar I'm using as a "straight-edge" guide.
Scribing (marking) the location of a H20 boss hole, and from there, I measure and mark the location of the second hole.
The reason I couldn't use the drill jig here, is because of the front derailleur boss. I should have brazed the derailleur boss after installing the H20 Bosses.
Center-punching and drilling — first, with a pilot drill, then with the final size drill.
After dilling the boss holes, I braze on the H20 bosses.
I don't show the brazing process, but I do use that "brazing thingamajig" tool to help hold the bosses in position during brazing..
Since I later seal, and fill the down tube with argon-gas, I use sealed bottom H20 bosses on the downtube. These I purchase from Nova Cycles.
Sealing, and filling tubes with an insert gas like argon, I've been doing it on most of my steel frames. I believe I'm going to stop doing it as a standard procedure. My reason being, it's a lot of extra work, and I think an internal coat of "Frame Saver" is good alternative. I'll write about sealing tubes later — how I go about doing it.
That's it for this page. Have a good day.