mpetry912 

Kurt - that is a knife maker's tool !

as vintage centerpulls I go I think the Mafacs are the best. they are highly adjustable and thanks to Rene Herse cycles you can find parts.

The bronze bushings make a huge difference, as will the reinforcing plate. Rene Herse Brass Bushings for Centerpull Brakes – Rene Herse Cycles

The Weinmanns or Universals are just not very good brakes and I don't like the thought of using a 50 year old bridge wire. On the Racers you can use a derailleur cable for the cross wire and tune the length to suit the application.

/markp

cudak888 

They sell them as mini belt sanders these days. Would work perfect for knocking the burrs off these things. As much as I love the NOGA deburring tool that was recommended here, it can't handle the convex curve on top.

I've never done the bronze bushing modification on a Mafac brake, but I have installed Oilite bushings into Altenburger dual-pivots: https://www.bikeforums.net/classic-v...xperiment.html

I've found the Weinmann/Dia-Compe cables in a couple of different sizes, but there's just too much flex in these brakes for my liking, and unless you use modern pads that sit farther inboard than the old stuff, they require really wide rims to apply square against the rim's braking surface.

-Kurt

El Chaba

I have to compliment your impeccable taste, Mark….I have never had any complaints about the stiffness of Mafacs on brazed on mounts, but the easy availability of these stiffeners may still tempt me to experiment. Small parts are also available from Grand Bois in Japan, who offer two versions of Mafac reproductions. They also offer reproduction straddle cables for Competition/2000 brakes. I think it really speaks to the brilliance of the original designs that people are still spec’ing bikes with these brakes and that two companies have gone to the trouble of introducing reproductions.

madpogue 

That would be "Mes accoutrements font...." BTW (plural).

mpetry912 

yes the brazed on mounts put thing at a whole different level level, since you have two load paths for the braking forces, rather than the single bolt mount.

those look like some real nice bikes ! Let's see some overall pics. here's mine, "built for me" in 2003.

/markp

dddd

Great job on your sculpture!

Looks to me that you preserved all of the caliper's tire/fender clearance while mimiciking the sleekness of the caliper's original profile (mirroring the caliper's stationary arch so as to maximize strength-to-weight while maintaining the caliper's full clearance).

And you've got those tamper-proof bolt heads, to keep your art from being stolen!

Adjusting the pads in/out can get the caliper arms to sit perfectly in the plate's shadow while in their "rest" position.

bulgie 

I have a "real" 2x72" belt grinder, the style the knife-makers prefer, and I love it, but good ones are expensive. I made mine from a kit, bought a used motor etc, and it still was the better part of a grand. Overkill for a home-handyman, but one of the things I love about it is the array of belt types and accessories you can get, especially different platens and contact wheels. Specifically here, for deburring those stiffeners, you'd want the "small wheel adaptor" which has the belt jutting out towards you, going over a itty bitty contact wheel. Generally speaking you choose the largest contact wheel that fits in the tightest curve on your part. I have contact wheels from 1/4" to 12" diameter.

OK, I'm getting into the weeds, I'll leave it at that. But I will add, before I had my 2x72, I used a small 3x18" hand-held belt sander. Like this ($41), though mine is a bit fancier brand. Not meant to be used this way, but I typically would clamp the handle in my vise, platen facing up, switch locked On, so I could use both hands for manipulating the part. The safety guard on mine prevented much access to the belt where it goes over the wheel, so for grinding curves, I removed part of the guard. If you hurt yourself doing that, please don't say I didn't warn you! But honestly I never lost flesh or even had a close call.

Then there's a Dynafile, which is godlike for this kind of deburring. Real Dynabrade-brand Dynafiles are expensive, but there are low-cost clones or knockoffs suitable for a home mechanic. Again, meant to be hand-held, but you can hold it in a vise to allow both hands to hold the part. Here's one, probably weak and low-quality but only $36. I'm not recommending this brand, just one of the first hits I got in a brief search. That could be useful for grinding the cut ends of cable housing flat, removing hacksaw marks after shortening a bolt or steerer, that sort of bike-mechanic stuff that's typically short bursts of grinding, not all-day production use.

But if you ever get a chance to use a real Dynafile, like if it turns up used on Craigslist, those things are bulletproof, and all the spare parts are available. I favor the air-powered ones, but they need a fairly strong compressor, so for most people, the electric-powered ones make more sense.

Oh and if you have a bench grinder, consider a 3M Scotch-Brite EXL deburring wheel. They're a bit expensive but they last a long time, deburr fast, and put a beautiful finish on metal. In say 6" diameter 1" wide, they're usually $80 - $100. They come in different densities, grits, and aluminum-oxide versus silicon carbide. I prefer a fairly hard density, silicon carbide, fine grit, which in their schema would be something like "8s Fine", where 8 is the density, S for silicon. If you find a 6s, that would still be dense enough, still long-lasting but a bit more conforming to the work. I think the alumina ones are less expensive, but I was told to get SC by Gary Helfrich (of Merlin fame), and so I have never tried the AO. 3M EXL is a bit of a unicorn; as far as I know none of the competitors are anywhere near as good. Let me know if you know of another brand that's cheaper but still good. But I'm still on the original 3M wheel I bought some years ago and it hasn't gotten much smaller yet, so I won't be shopping for one any time soon.

I also use smaller thinner EXL wheels mounted in an arbor that I spin in my hand held die-grinder, but you can also mount it in an electric drill. 1/4" wide by 3" or 4" diameter (up to 6" can still be useful for hand-held, but smaller is safer). Great for getting into tighter spaces where the bench grinder can't go. I like a softer density (2s) in those. The softer wheel doesn't last as long, but it soon gets rounded off at the business end, making it follow curves and fillets in a really handy way. As they wear down and get smaller, they fit in ever-smaller spaces, so I keep a few worn-down ones around for when I need the smaller size. The 1/4" arbor to mount them on is a generic item. They make them as thin as 1/8" — imagine polishing those places on a Campy Record crank arm where they tend to develop fatigue cracks, normally a slow painstaking job, but having it done (perfectly!) in something like 3 seconds per side. You would pre-grind the EXL wheel to a knife edge before using them to smooth that web of the Campy crank.

I own all the tools I mentioned above including a real Dynafile, but I would go for the EXL wheel if I had a stack of those stiffeners to deburr. You could use the EXL to refine the finish on the flat surfaces too, not just deburring the edges. The finish it leaves is not quite polished, but you could go right from there to your buffing wheel if you wanted a bright polish. The EXL would also be a good choice for rapidly removing the forging marks from your Racer, Raid or Competition brake arms, if you're fancy. It doesn't cut so fast that you'll do damage before you notice, you won't thin the arm making it unsafe, it'll just refine the surfaces.

Mark B

cudak888 

I've never had the privilege of owning anything with brazed-on mounts for centerpulls - would you say a stiffener becomes unnecessary with these?

I knew that fender clearance is a significant consideration with many users of Mafac Racers, so I tried to keep as much clearance around under the arms while still keeping enough meat around the mounting points and maintaining a pleasing shape.

The bridge is just slightly lower than the arms in a typical "at-rest" position, while still under tension by the cable yoke. I tried various alternatives including increasing the arch height, but that made it difficult to get both arches to look elegant.



Those tamper-proof bolts are from retired Spin rideshare bicycles; I have a bin full of M5 and M6 bolts that were removed when the lock mechanisms were taken off the bikes. They're the easiest stainless metric bolts to reach for in the shop! I think they look good too, so there's that .

Mark, I promise to read through this in depth tonight when I have a free moment so I can let it all sink in properly. Thank you for sharing all of that.

-Kurt

bulgie 

Well some might say a stiffener is never necessary. Like all the pros who won all the big races with Racers, and no stiffener. But yes, less stiffening needed with brazed pivots. You can still see the flex when squeezing hard, bike in the stand, but it's not very noticeable out on the road. There's more flex in the rear (seatstays are wimpy compared to forkblades) but also rear brakes matter so much less, flex isn't such a problem.
Well you sure nailed it for the pleasing shape IMHO. Perfection.

Mark B

cudak888 

I find this fascinating, for most of the weakness I've personally witnessed (note - witnessed = bending enough for me to see) from centerpulls has been either due to the elasticity of the mounting bolt or pressure it can exert on the rear bridge (something solved by brazed pivots, of course) or slop in the pivots themselves. I really can't recall a time when I've seen the studs on a center bolt configuration bend in a way to warrant a stiffening bridge; I've always seen arms bend first over the stud.

Honestly, I've always thought a stiffening bridge for single-bolt centerpulls is a bit overkill on the wrong thing, but I figure they probably help by pressing down on the bushings more evenly than an oversized hex head bolt.

I find the drillum does a lot to hide the actual edge of the bridge with the ideal edge.

I promised a reply to this once I read through: I'm currently running an old Craftsman (? haven't really looked at it recently) 4x36" bench belt sander. Prior to owning it I did the "inverted hand-held tool in the vise" approach, but bought the bench tool to avoid that. It's still too much of a tool for it though, which is why I like the idea of the tiny sander with the exposed contact wheels that allow me to do more precise edge work getting the burrs off.

I also have an cheap, but decent enough Wen hand-held Dynafile knockoff that I use for cleaning up surfaces (usually brass after having a repair done w/o finishing work), but it's location in the toolbox is almost always obstructed by some project disaster, and I like to avoid vise-mounting tools when I can avoid it.

Now a drill-mounted deburring wheel sounds just about right if I stick the finished side down on some masking tape. I think I have a few and never used them. Will give it a try; might be just the ticket for this small run.



-Kurt

mpetry912 

Kurt I would say the stiffener is redundant with the brazed on studs yes.

/markp

El Chaba

I will echo the sentiment that Mafac brakes do not need additional stiffening when mounted on brazed on fittings. Whoever the first person was to take that approach - likely Rene Herse or Alex Singer- they are to be commended. Since they were already brazing on fittings for everything that attached to the bike, it makes me wonder if they were just doing the same for the brakes and if they had any idea how transformative a step it was…I would guess that they did. I find it interesting that Spence Wolf was behind the design of the external stiffener since he was ordering frames from Singer and he had to be well aware that brazed on fittings were a recommended option. Such was the dominance of Campagnolo in the US market at that time that any high end frame had to be compatible with those parts to be attractive to buyers. I will be in Paris in a few weeks time and if I get the chance will ask Olivier Csuka his thoughts on the subject.

chain_whipped

Nice work. Who knows, but years from now and future collectors, MAFAC aficionado's might be scratching their heads.

Anyways, more mods; JP Weigle and René Herse had offered titanium eye bolts for the brake shoe studs.

Lastly, a modernized / variance copy of this brake in a more compact size was made by Tektro model Quartz R725. High quality, stout and no flex. They substitute the straddle cable with a noodle lead sheath. Clever and with really nice feel, modulation. Not the lightest but acceptable having approx. weight 167gm with pads.