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There are various ways that have been used in the past. In the early '70s, a couple of Italian builders I'm aware of and at least a couple British bikes I saw had Campy brake centerbolts brazed on. This bothered me slightly as it made brake-centering adjustment impossible, other than by bending the spring, which is do-able but seemed inelegant to me. Also the heat of brazing almost certainly weakens the centerbolt. Still strong enough for anything short of crashing, but I wanted mine to not have any weakened HAZ (heat-affected zone).

So on my one and only frame I made with "brazed on" brakes in 1977, I solved those two quibbles. The braze-on is a sort of hockey-puck-shaped piece of steel with an M6 internal thread. The actual centerbolt was a piece of an M6 high-strength "aircraft" bolt, with threads on both ends. It threaded into the hockey puck and was secured with a setscrew, so no heat. Then for the piece with the slot for the spring, I made that from aluminum, with a recess in back that fit over the hockey puck, so the spring holder can rotate to center the brake. Then the alu part was slotted on both sides, with small screws that went through the slots into the puck, to lock down the centering adjustment.


That's the only pic I have of it, a scan from a print from a bad snapshot camera. You can just make out the top of one of the slots where the alu piece is secured to the puck.
Although I was too poor then to afford a decent camera, still I rode on Clement Del Mondo Seta tubulars — priorities! (Actually the tubs were hand-me-downs from club members who flatted and didn't want to repair them. I got good at sewing.)

All that work resulted in a brake that worked exactly the same as any other Campy brake, whoopee! Just with the dubious bragging rights of not having a nut on the other side of the bridge and crown.

In my defense, I was 19 years old when I made that frame. It had other goofy stuff on it that I later regretted, like a "seat mast" — the seat tube continued past the seat lug all the way to the saddle clamping mechanism. It was a dumb idea then, and still dumb when that idea was resurrected decades later.

On the subject of who made the "best" fillets (however that is defined):

Even back then in the '70s I was a fillet specialist, making tandems all day at Santana. In my subsequent jobs at other frame shops I was "the tandem guy", plus with all the lugless MTBs and funnybikes and such, I laid miles of fillet over a couple decades, got pretty good. One thing that all those years of looking at fillets does is it trains your eye to see the subtlest signs of improper or over-done filing. I can say with complete confidence, there are probably a dozen guys in the US who did finer work than this Mercet guy. I see signs of undercutting, where the tube wall has been thinned from over-filing, and some edges that weren't completely smoothed. Nice work for sure (if you like gagantuan fillets, which I do not), but nowhere near the best I have seen.

The overly large fillets on these Mercet frames are grotesque to me, but my aesthetics are largely based on function, so maybe they aren't so bad from a purely sculptural point of view, that is, as wall art. If you're going to actually ride it though, there's no getting around the fact that these ridiculously large fillets are just extra weight that does nothing for you. In fact they weaken the steel, due to the extra time taken to lay them down, the extra heat that entailed, and the slower cooling rate due to all that added thermal mass. Bigger, weaker HAZ. The frames are obviously strong enough, for the amount they got ridden (looks like not much...), since they haven't buckled or cracked (yet), but they are definitely weaker than those same tubes would have been if they'd been brazed quickly with minimal-sized fillets. Add to that the fact that there's also some undercutting evident in these pictures, and thin-wall tubes such as EL being used, where even a little undercutting is a more significant fraction of the total wall thickness.

Early Santana tandems had large fillets (not Mercet-large, but still too big IMHO), but as soon as I moved on to my next posting, making Rodriguez tandems, I downsized the fillet size considerably. Still bigger than they need to be, confirmed with destructive testing, maybe twice as large as the minimum needed for strength. Bicycling magazine tested a Rodriguez I built in about 1980 and said "Is there a tandem more advanced than the Rodriguez? We haven't seen one." The testers were John Schubert and Gary Fisher (yes, that Gary Fisher!) Soon the Rod tandems had a 3-year waiting list. The frame Phil Wood used at the trade shows to show off their disk brakes was a Rod that I built, with no canti studs or any other place to mount a brake (against my advice!) I mention this just to point out that my frames were being seen and appreciated by a fairly wide audience.

Then a few years later when I was making tandems and other lugless frames at Davidson, I grew tired of finishing the fillets, plus I'd gotten so good at laying them down that they didn't need it. We decided to charge extra for smoothed fillets, and since customers couldn't see the difference in a painted frame, none of them opted to pay extra for smoothing, so I didn't have to do it anymore! I actively pursued techniques to braze faster, with the goal of minimizing the weakening of the HAZ and the size of it. Though it may sound self-serving to say it, the fact is the faster I brazed them, the better they came out. I was also making the fillets smaller during this time, with continuing destructive testing to show that the minimum fillet size for strength was still smaller than I was making them. Smaller fillets laid down faster also made for less heat-distortion. (How to spot a charlatan framebuilder: if he says "I don't get any heat distortion, they just come out perfectly straight." Uh huh and you knocked out Chuck Norris with one punch too I bet.)

Smaller fillets made the frames lighter too of course, though that wasn't the main goal. One small Prestige .6/.3 frame came out just under 2 lb, lighter than any lugged or TIG welded frame I ever made in steel. I only mention this because I've heard some people say fillet brazing is heavy. It can be <coughMercet<coughRitcheycough> but not necessarily!

Mark B