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Drillium and Bottom Bracket Cutouts

Most vintage bike enthusiasts know about cutouts in frame bottom brackets, but some, especially newbies don’t know the reason. Someone recently asked me why I didn’t put drain holes in my bottom brackets? I was baffled and asked, “Who does that?” He listed frames that had “Drain holes,” and I realized he was talking about bottom bracket cutouts.

It was a fashion gimmick of its time, that’s all. There was no logical reason. Think about it, it is a poor drainage system. The bottom bracket is in direct line of fire from water spraying up from the front wheel. These large holes let in more water than they let out again.

For those who don’t know, here is a history lesson. In the 1970s a craze started amongst cyclists all over Europe, later referred to as “Drillium.” (Picture left.)

Drilling holes in component parts to reduce weight. The fad was huge in the UK, especially amongst time-trialists, who were forever looking for ways to save weight. And of course removing metal reduces weight.

The amount of weight saved by drilling holes in aluminum components was miniscule, but it didn’t matter.

It was a way to customize a bike and a few more holes than your competitor was a psychological boost if nothing else.

If your bike had so many holes, it had no shadow, you were a winner, in style anyway.

Component manufactures were quick to follow this trend, and for example, a seat post that was previously round and smooth, now had flutes machined in them. Frame builders too got on the band wagon. A large hole cut out of a bottom bracket shell, was a considerable chunk of steel that was no longer there.

Of course all these holes and flutes created more aerodynamic drag, but no one thought of that at the time. Aero bikes would be a future craze.

Frame builders used a special die and a press to stamp out these cutouts in seconds. Holes were similarly stamped in lugs before the frame was assembled. It also gave framebuilders an opportunity to individualize frames with cutouts in the form of their logo. It was done for brand recognition.

My newbie inquisitor was still not satisfied. “If these are not drain holes in the BB, then why weren’t they engraved?” I’ll tell you why. Holes can be stamped out in seconds, but engraving takes time, and is super expensive. Especially engraving on a curved surface.

I know this because I had my name engraved in the top of the BB shell.

It had to be done with a special fixture that rotated the shell as the engraving progressed, so the router bit that does the cutting is always at right angles to the curved surface of the BB shell. (Picture right.)


It is a highly skilled operation and is one of the reasons my custom frames cost so much. If you see what appears to be engraving on the bottom bracket of a production bike. Things like lettering, a logo or grooves. It was most likely cast that way. The design was in the mold.

Just as my custom frames had my logo engraved in the crown, whereas my production Fuso frame had the name cast in it. (See above.)  I had to buy 1,000 crowns to get that feature. So why did my Fuso not have a cutout BB? By 1984 when production on the Fuso started, the fashion had run its course.

Some Italian framebuilders continued doing cutouts, but remember they had dies to stamp the holes. I was not about to invest that kind of money for the tooling and a press, for fad that had run its course, and was dying out anyway.


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Reader Comments (7)

I remember drilling the hell out of a pair of chain rings in the early 70's.
You drilled small holes and used large chamfers, that way the holes looked bigger but you didn't take too much metal out.
The first cut out BB that I saw was a Raleigh Pro Mk IV with the interlocking CC for Carlton. I have to admit, I thought that it was cool (I was also 15 at the time).

August 15, 2017 | Unregistered Commenteredstainless

Alf Engers famous for doing this his times show the reason WHOS ALF ENGERS???

August 15, 2017 | Unregistered Commenterjohn crump

With or without the cutouts, you still used one of those plastic sleeves to prevent grease contamination.

August 15, 2017 | Unregistered CommenterBill K

When I was going through my 'fixed gear' phase, I was avidly looking for an Italian frame with cutouts. When I finally found one (a Colnago), I backed out because of the price and the fear that the cutouts would lead to more corrosion. I lived in Boston at the time and commuted by bike year-round (snow + salt + sand + cutouts in a steel frame = serious corrosion).

We all do strange things to try and be cool, I guess. :)

I still ride fixed gear most of the time, if my ride is less than 30 miles. I never did get a bike with cutouts, though.

I would certainly buy a Dave Moulton frame if I could fond one in my size that I could afford. Knowing something about the framebuilder makes it that much more attractive.

August 15, 2017 | Unregistered CommenterYohannM

It must have been interesting, perhaps frustrating, to be a framebuilder and have to deal with bullshit ideas like this.

And to whoever came up with "drillium," that is a great term.

August 17, 2017 | Unregistered CommenterTBR

We used to call the drilled & milled components "suicide gear." In addition to chainwheels, some folks cut out spider arms and hollowed out the back of crankarms. One would see drilled-out handlebars, stems, brakes, and even rims. People would show up to races with gear that would be questionable for a even solo time trial, let alone a mass start event over rough roads.

i once read that anyone considering taking a drill to things had best first put a note over the workbench listing the replacement costs of those components before proceeding.

August 17, 2017 | Unregistered Commentermike w.

I hadn't ever heard of drilled-out bottom bracket shells. That just seems like an inviting road grime, dirty, sand, and other "crud" into the shell to gum up the works prematurely. Bottom brackets aren't waterproof, I know, but cutting a hole in the shell is just leaving the door wide open for water and dirt to get in there.

August 21, 2017 | Unregistered CommenterMike

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