The steps whereby a collection of tubes, lugs and dropouts become a high-performance Torelli racing frame is fascinating.
It is our goal to make the finest possible frame for the lowest possible price. To do that, we must match building method with materials. Our "Private Reserve" frames have almost a man-day of time invested in them, exclusive of frame preparation and painting. We build our Express SLX, Express OSNeuron, and Nitro Express EL-OS frames in our Private Reserve shop. If we were to build our less expensive Corsa Strada Aelle frame in this shop, even though we had backed off the materials to reduce the price, the heavy investment in time would still leave us with a very expensive "economy" frame. We therefore use a shop that makes superb frames, yet does not devote quite so much time to each frame, to build our Corsa Strada, Super Strada, and Countach OS. In other words, as the cost and quality of the raw materials goes up, we also increase the amount of time invested in the frame. The effort and the materials match.
We believe that the new miracle steels like Columbus' Nivachrome and Cyclex deserve extreme care when fabricating frames of these materials. The payoff, by bringing out the hidden capabilities of these steels, is an extraordinary bicycle. It is an easy thing to put very little time and care into building a frame with expensive tubing. One can then advertise a Neuron frame, for example, for a very low price. This is not our way. It is not our goal to provide the cheapest box of parts. We want to provide high performance at the lowest possible cost.
With that in mind, we will occasionally hit a fork in the road. We use two basic techniques to build our frames. One method of building, which we call "pinning" will require one set of steps that ultimately produces our "Private Reserve" frames. The other method, which we call "custom" is the methodology used by the overwhelming majority of top-end builders that make limited production high-performance framesets. As we go along, we'll also point out some of the shortcuts used by shops that produce cheap frames. At Torelli we call these low-labor frames "industrial" frames. These are decent, usable frames. Our objection is that they often try to masquerade as custom quality frames. An educated and careful buyer can usually purchase a custom quality frame for the same price as an industrial frame. That is our goal. The more a rider knows about what goes into building a racing frame, the better the choice he will make in choosing a frame. Also, he will be inclined to appreciate what Torelli does in creating its bikes.
We will follow the whole process from start to finish, and when we come to one of these forks in our story, deal with both methods, pinning and custom, then move on. This way, a comparison of what is involved can be more clearly understood. Please be sure to understand that these designations (pinning, custom, and industrial) are not industry standard nomenclature. They are terms we at Torelli, in investigating frame shops in Europe and America, have come up with to deal with the basic differences in the way builders approach their craft.
Generalizations are always dangerous, but we will venture one here. There are two general areas in Italy that produce frames. The finest, the frames with the great reputations, come from the area around Milan. This area is called Lombardy. Masi, Mondonico, De Rosa, and Pogliaghi are Lombards. The area to the east, near the Adriatic around Venice is called Veneto. Venetians might be the most bike-crazed people in the world. These Venetian builders make very fine frames, yet they don't quite have that obsessive, perfect edge that the Lombard frames possess. Faggin, Battaglin, and Basso, are some of the builders from this region, respected fabricators all. The shops of this area generally lean towards value and produce frames we would call more economic. In this area there are some builders whose work quality can overlap some of the Lombards. These top Venetians are the builders we look for our "custom" frames. By astute selection of the builder, we can get Venetian pricing with near Lombard quality. We go to Lombardy for our "Private Reserve" frames.
The first step in building a frame is the inspection of the raw materials. This is crucial. While the tubes have undergone a careful hand inspection in the Columbus or Oria factory, a last look will make sure that a builder's long hard hours are not compromised by the use of a part that doesn't measure up. In addition to looking for little imperfections in the surface of the tube, the builder rolls the tube on a machined table to make sure that it is straight, not banana shaped. The lugs are inspected for any flaws that result from the casting process. Items that do not measure up are discarded.
The next step is to cut and miter the tubes. A builder likes to do a quantity of tubes for a particular size frame at one time. He will often do more of a particular size than he needs immediately for the few frames he will be building at the moment and save the extra cut and mitered tubes for later. Just getting the machinery set up to do this takes a while and the builder likes to be as efficient as he can.
After the tube has been cut to length, it must receive a very precise bit of machining. Inside the lugs, the tubes must fit together perfectly. One tube is "fish mouthed" against the other. The quality of this miter, in which one tube fits against the other inside the joint largely determines the quality of the joint. This is one of those unseen aspects of the building of a bike where the best builders take extraordinary care, and the builders of "industrial" frames do perfunctorily. Some builders will have just one mitered angle for all the different sizes of frames. At one size of frame, the miter will be perfect, but as the frames get larger or smaller and the angle of the tube changes, the contact area of the mitered tube against the adjoining tube is reduced. This reduces the strength and integrity of the joint. Mitering is usually performed on a lathe with a mill.
When the miter is done correctly, the frame is an almost seamless whole, and the brass that forms the glue inside the lugs has a very small gap to bridge, making a stronger, longer-lasting, finer bike.
A good builder does not just use the lugs as they come from the castinghouse. Rough edges and cosmetic imperfections that pose no structural danger are touched up with a file and grinder. Also, there may be a bit of rust on the tubes or lugs. In addition, the very surface of an investment-cast part may have a little contamination that is a result of the casting process. A little steel wool, a flex hone, or even a slight bit of sand-blasting will remove whatever surface contamination that is there on the raw materials. There must be only bare, clean steel on all the surfaces that participate in the joint.
Torelli uses investment-cast lugs (sometimes referred to as "lost wax" castings) exclusively in its frames, except for the least expensive of our frames, the hand-made Corsa Strada. The high cost of these castings makes them impractical for use throughout this frame (the Corsa Strada does use an investment-cast seat lug and fork crown). Investment cast lugs can be made so that they follow the complex contours of the mitered joint almost perfectly. The greater precision of the cast lugs means that the optimum distance between the lugs and the tube is obtained for brazing. This results in the strongest possible joint. Our Corsa Strada uses "bulge-formed" lugs, which are a good way to build an economical frame. The surfaces inside the lugs that contact the tube are machined to the precise diameter needed to get a good joint. This results in a superb joint, only slightly less perfect than that given by the cast-lug joint.
With the materials prepared to his satisfaction, the builder starts to build the sub-assemblies of the bike. Once again, because the builder is looking for the greatest possible efficiency in the use of his time, he tries to break down his work into as many repetitive tasks as he can.
The rear triangle is done first. The finest builders (and all builders of Torelli frames) insert the rear dropout into slot cut in the back of a chainstay that has already been cut to length. The end with the dropout is filled with brass to join the dropout to the chainstay. Later, when the frame has been completely brazed, the end will receive a careful shaping with files and emery cloth. "Industrial" shops use pre-shaped chainstays that do not need the time-consuming filling in with brass and the later hand shaping. Even the least expensive of Torelli frames uses the finer, stronger, and more elegant method of hand forming the rear dropout joint.
At this point, builders can use one of two different methods. Custom builders also join the seatstay to the dropout on a jig that has the angle set to give the builder guidance. Each frame size has a different angle, with these at stay being more vertical in the largest sizes.
The finest builders don't join the seat stay until the frame is partially assembled to avoid even the slightest cold setting. Torelli frames use both methods, the second method is used on our Private Reserve frames (those frames of SLX quality and higher). To save weight, most Torelli frames have the seat stays brazed directly to the seat lug. In frames like the Express SLX, and some earlier Corsa Stradas, the seat stay has a cap or plug to finish off the top of the seat stay. This is brazed onto the cut seat stay and filed and polished before the seat stay is brazed to the dropout. In time, more and more builders will be finding ways to attach the seat stays to the seat lug without a plug or cap (the English call them "top eyes" the Italians refer to them as "pendine) in order to keep the weight down. The plugs are usually investment-cast, and a pair of them can weigh up to 1/4 pound, negating a lot of the benefit of an expensive, lightweight tubeset.
A new system to finish off seat stays has started to appear. A cast seat lug is made with two socket holes just under the seat binder ears. The seatstays are inserted into these sockets. This has the advantage of both lightweight and being marvelously cheap to do. The seat stay does not have to be cut to exactly the precise length, there being a bit of "fudge "allowance inside the seat lug, and it doesn't need the terribly precise miter needed to precisely fit to the side of the seat lug like on a Torelli. We have seen this system on both Faggin and Colnago frames. As yet, because we have not used frames with this system, we have not formed any opinion regarding this method. If, however, builders as diverse and knowledgeable as Colnago and Faggin think well of it, it is probably a good method of attaching the seat stays.
Other sub-assemblies are done. This varies from builder to builder. It is common for builders to make head-tube and down-tube sub assemblies. Some builders will braze the seat tube to the bottom-bracket shell. In our private reserve shop, the seat tube is fitted inside the bottom bracket shell. Then, a small hole is drilled in the shell in the back of the seat tube. A tapered steel nail is driven with a brass mallet to fix the tube to the shell.
There is one method of making sub-assemblies that we have seen in only one shop. De Bernardi puts small sub-assemblies together, putting a ring of brass in the proper location and passes the tube and lug through an oven, heating the entire tube and lug. By placing the ring of brass in the proper place, the brass melts and flows exactly where desired. This is incredibly fast and inexpensive.
When the required number of sub-assemblies for a given frame size have been completed, the builder then assembles them on a fixture called a "jig". These vary from builder to builder. Some builders make their own jigs, others buy them from two of the largest suppliers of tooling to bike builders, "Marchetti and Lange", or "Bike Machinery" If you ever see pictures in magazines of frame building shops, you can instantly recognize each company's tools. Marchetti are always green and Bike Machinery tools are blue. Torelli has tooling from both companies in its frame preparation area.
A simple jig is a thick, flat steel plate mounted on a stand so that the vertical surface faces the builder. It has slots cut in it to mount fixtures for holding the tubes of the frame. These tube holding fixtures must be movable because each frame size has different angles and tube lengths.
There are very expensive, complex jigs that are pneumatic. The builder need only preset the dimensions of the frame and loosely put the tubes together on the jig. He hits a button and the tubes and lugs are all forced together and the frame is ready for brazing. Very quick. A shop must produce a huge number of frames very quickly in order to make this kind of expensive tooling pay.
The more ordinary jig used in Custom and better shops requires that the builder laboriously loosen and exactly set the tube holding fixtures to the exact dimensions. He will often have one of his completed frames of the size he is going to build right there and check his setting by bolting in this verified and checked frame. The jig, by the way, is very robust and strong.
Often, Americans will ask an Italian builder the angles he uses in his frames. He often responds that he doesn't know, or will come up with an approximate guess. That's because the builder is using linear measurements. 1/360thof a circle is a very difficult unit to use to build, especially when trying to set up something as short as the head tube of a 48 cm frame. For the seat tube angle, the builder will check the distance the center of the seattube at the seat lug is laid back from the vertical. He knows exactly what this should be on a given frame size.
As the builder slides the tubes into the lugs and assembles the frame on the jig, he coats each tube with what is usually a white paste. This is called "flux". When heated during brazing, this flux removes the very last of the oxides that are on the tubes and lugs, ensuring a good joint.
A Custom builder usually just assembles the fluxed tubes onto the jig. A "pinning" builder drills a small hole at each joint and drives in a tapered steel nail.
The fit of the tubes into the lugs is quite snug. As he assembles the tubes, the builder must often resort to a rubber mallet to get everything to come together.
At this point, the "custom" builder heats each lug just hot enough to melt the brass he uses to braze the frame. He touches each lug with bit of brass, "tacking" the joint in place. The "pinning" builder only tacks a couple of joints, some having been free-brazed in a sub-assembly, others having been left to be held by the pin.
Builders do not generally braze up the completed frame on the jig. It is used as a fixture to assemble the frame. It is almost impossible to get behind the frame and do a good job of brazing between the frame and the jig.
The pinned and/or tacked frame is removed from the jig and put on an alignment table and checked for straightness. It is then mounted in a holder a lot like the repair stand your local bicycle shop uses to repair bicycles. It can be turned, raised and lowered to gain complete and easy access to all parts of the frame. Now, the lugs are brazed up.
Brazing a lug is simple in theory, yet when we visit builders that are gifted, we are always fascinated by how quickly they work and how skillfully they perform their tasks, knowing where the brass is inside the joint.
The joint is heated with a torch. The builder dips a rod of low-temperature brass in a bucket of flux and touches the rod to the edge of the lug. The brass melts and flows inside the lugs, between the lug and the tube. The melted brass flows inside the lug through capillary action. As the builder moves the torch around the lug, the brass follows the heat of the torch. With this simple technology, the builder can create a strong, beautiful joint. A good builder usually introduces the brass at one point and dances the melted brass all around the lug.
"Industrial" builders employ carousels and pre-heaters. The tacked frames are mounted on a round conveyor. The workmen each have a station along the line. As the builder works on one frame, another frame is behind him on the assembly line, sitting with one of its lugs having several torches directed at it, bringing the whole area of the lug to brazing temperature. Then, when the builder is finished with the frame he is working on, the frame with the pre-heated lugs arrives. He can then, with great speed braze up the joint, gaining enormous productivity at serious cost to the quality of the frame.
The statistics given for the tensile strength of steel used in making frames are strengths before brazing. The tubes as they come from the factory are in the ideal condition. Heating them during brazing reduces their strength. Columbus' Nivachrom steel is special in that it is designed to have a very small reduction in strength when heated to brazing temperatures. With this in mind, one can see why carouseled, preheated-frames are unacceptable for serious riders. It is not that the resulting frames are bad. It is that the person who has decided to spend a large sum of money to acquire a high performance bike can get a custom or better quality frame for the same price, or for very little more. One can also see that pinning instead of tack-brazing all the joints has its advantages. Not only is the amount of heat used reduced, there is less chance that the tube should move inside the lug during re-heating to braze up the frame. Remember, the tack brass melts along with the brass of the full joint.
We are often asked why we don't us silver to build our frames (it is used on the braze-ons, but more on this later). It is true that silver melts at a lower temperature. The builders we talk to say that there are four reasons why they prefer brass.
In visiting different builders, it is interesting to see that there can be curious differences. When brazing the tubes in the bottom bracket, most builders bring the rod to the outside of the shell and draw the brass in. Yet we have seen some put the rod in the shell and draw the brass out. Both make fine joints and we, as yet, have no particular explanation for the difference. When you look inside the shell of a brazed frame, you can seethe brass that has flowed into the shell during the brazing. It is a more golden color than the steel of the tubes or shell.
After the joints have been brazed up, the various braze-ons must be attached. Here is a place, once again, where different builders each has his own method. Many builders will attach some braze-ons to the tubes while making sub assemblies, before the frame is built, others are done when the frame is completed. The builders either have home-made tooling, or have purchased tooling to hold the braze-ons exactly in place. The location of the front derailleur braze-on, for example, is critical. Also, it is important that the tool to hold the part in place not put any pressure on the tube, just hold it exactly in place so that the tube is not deformed during brazing.
Since the various braze-ons (chain-hanger, water-bottle mounts, shifterbosses, front derailleur boss, rear-brake cable mounts) are often put on parts of the tube that are not butted, special care must be exercised in mounting them. With the exception of the seat tube at the seat lug, the tubes are thicker at the joints than in the center of the tube. This is called "butting" For example, an EL-OS top tube is 0.7 mm at the ends of the tubes and only 0.4 mm in the center of the tube. That thicker end gives greater strength at the joint, where the greatest stress is placed. Also, because there is some strength reduction from the brazing process, this gives a large measure of security to the builder and the rider. The tubing manufacturers have had 100 years to work this out so that the bike is safe and strong.
In the unbutted sections, however, special care must be taken. This is where a good builder will use silver solder. Silver requires extra care to get a good, strong joint, but it's lower temperature requirement makes this care worthwhile.
When all the brazing has been completed, the frame must be cleaned up. Even the finest workman must remove little bits of brass residue from various parts of the frame. At this point, the "pinning" builder must file down his exposed pins flush with the steel tube. The rear dropout joint is carefully shaped with files. Sometimes a lugline must need a bit of cleaning up. Many shops do what used to be done with hand files and emery cloth with a hand-held emery-sander. A few passes, and in seconds, the joint is shaped and cleaned up. A little hand-polishing is still always needed. This cleanup process is crucial to giving a frame a good appearance. No amount of paint can make a frame that has not been carefully brazed, filed and polished look good. Good brazing reduces the amount of cleanup needed.
When putting the tubes together, the head tube is not cut to the precise length. The builder usually slides the lugs onto a slightly overlong headtube. The seat tube is usually left to protrude through the seat lug. Now the head tube is cut flush with the head lugs. The seat tube is cut along the contours of the top of the seat lug.
When the builder is satisfied, he then gives it a rinse to remove the easily removed flux that has stuck to the frame. He then gives it a light sandblast, to remove any remaining flux and stray brazing material.
At this time, there are two general ways to build a road bicycle fork. One is to weld large-diameter, curved tubes to the steering tube to make "unicrown" forks. This style is a spinoff from mountain bike technology. It is very inexpensive and strong. In our judgement, it is an unacceptable method to build a road-bike fork. While we are the very strongest proponents of robust, stable forks, unicrown forks, as they have been made to date, make a very harsh riding bike. A fork functions as an important spring on the bike, giving with the undulations of the road, keeping the tire on the ground and saving the rider much discomfort.
The generally accepted method of building a good road fork is to insert fork blades into a fork crown. Fork crowns come in a plethora of styles. By designing the fork crown into different shapes, a gifted builder can give subtle character to the way his bike rides. Masi and De Rosa use a flat fork crown. The crown itself is very rigid, but has a longer unsupported fork blade. Serious riders say that forks made with this crown have a firm, stable feel. Most builders of track frames use some version of this design because of its strength.
Cinelli has two different designs. His most famous crown that has fallen into general disuse actually fits inside the fork blades, making the fork look like a seamless piece. Cino Cinelli was dissatisfied with fork design as it existed after World War 2. This solid piece of cast steel was his solution. His design was a success, and forks made with an internal Cinelli crown are extremely strong. Because it slopes downward from the steering tube and then fits inside the fork blade, it makes for a short hollow portion of the fork blade. It has fallen into disuse because it is heavy in the weight-conscious age. Also, because it is a big sink, builders must pour a lot of heat into the crown before it can be brazed, slowing production and raising expenses. Forks built with this crown have a firm, solid road feel, and in my opinion, are still the most beautiful of all forks.
The Cinelli external sloping fork crown has the advantage of keeping the flexible, hollow portion of the fork blade short while keeping the weight of the crown in line. This is probably the most popular fork crown in use in racing bikes today. The crown imparts a lively, comfortable feel to the bike without compromising the bike's stability by being too soft. Torelli uses this crown for the bikes using thicker, stouter fork blades.
There is a new design of fork crown that makes a fork look like a unicrown at first glance. It slopes far down and shortens the flexible portion of the blade by over two centimeters compared to a flat fork crown and by a centimeter when compared to a Cinelli external sloping crown. We think this extra support is needed when using the new lighter fork blades.
The builder generally inserts the flat fork tips into cut, slotted fork blades. He then fills in the ends with brass as he did when putting in the rear dropouts. Some builders now use a fork tip that is a cast plug that fits into the end of the blade that does not requires the filling and shaping of the traditional method. At Torelli, we have had extensive experience with this system and find it strong and reliable. Most builders purchase their fork blades straight and build a straight fork.
The fork-blades subassemblies are assembled into the crown that has had the steering tube brazed into the fork crown on the fork jig. The fork is then brazed up. The fork then receives the same cleanup that the frame received. Then the fork is raked. The fork is placed on a mandrel and the fork is bent cold. Each builder has his own fork rake. This includes not only the amount of bend, but also the shape of the bend. Some builders start their bend high up the fork and have a large radius bend. Other will have the fork rake start lower and have a smaller radius. A fork with a small radius bend is thought to be more supple. The large radius is used to make a stiffer fork. Over the years, as roads have improved, the radius of fork rakes has grown. Some builders like Colnago have all the fork rake designed into the fork crown in order to leave the fork blades straight. While this makes a distinctive and characteristic looking design, most of the cycling world have abandoned their short-term infatuation with this design and returned to the traditional bent blades.
Good builders exercise extreme care in building the fork. Because of its importance in handling and steering, errors show up as unacceptable handling characteristics.
The frameset is now built and ready for chrome-plating, painting, tapping, facing, alignment and assembly. For more information on this process, see Frame Preparation: What's Involved?