BUILDING A STEEL FRAME

Real classical steel frames are built with lugs (brazing parts).  The oldfashioned clunckerbike was made with thick tubes and heavy sandcast lugs. The tubes could be cut off straight and needed no mitering or filing (see FIG.1a). Using thin tubing would lead to cracks at the edge of the lug, so they started to make thin lugs out of steel sheets, that would be cut, pressed and welded . Often the fitting was not great, but you could use light tubes and lugs (see FIG.1b). Now mitering was important to create a strong joint; it is even more important in lugless construction (see FIG.1c) ! Modern cast lugs are made with the lost-wax-procedure (Italian: microfusione, in English: investmentcasting); this is an expensive production process. If the fitting is very thight the builder should use a high silvercontent brazing material; this should also be used with stainless steel and lugs. Using pressed steel lugs had the advantage the builder could alter the angles 3 to 4 degrees; for cast lugs this is only one degree. The craftsmanship of the builder is partly altering of the lugs!  In factories the building of a lugged frame is often done this way:

The tubes are cleaned, cut to size and mitered. The tubes and lugs mounted together in an iron jig.. A small  hole is drilled through the lugs and tubes and a small steel pin is pushed in. Some builders use more fixation and braze or TIG-weld the tip of the lugs. Next each joint is heated with an oxy-acetylene torch  and brazed lug by lug . The big jig might transport the heat of the frame so it cools rather quickly. We don't like this, because the fast cooling might harden the steel. Small builders often use simple jigs or even none....

A steel tube will go into a bath of preservation oil as the last step in the production process. So the tube must be cleaned before building the frame. Take a cleaning rag with some degreaser and clean the tube inside and outside.

A quality tube is butted. From the outside you can't see this; the seat tube will only have a greater wall thickness between the bracket and the frontderailleur. As supplied the tube is ± 620 mm long; if we built a 50cm, and cut the wrong end to size , we cut the whole butted part off !. Well that won't happen to you (?). Reynolds frames one short butt (marked !) and a long one. The short side may only be filed fitting! So the long side should be cut to size.

  Tubes used to be round. Nowadays there a many profiled tubes, some flat (less airresistance), others multiform (more frame stiffness). The framebuilder needs to work carefully then; stiff frames are hard to align. A frame of Reynolds 753 tubing can't be aligned at all, because the tube has no yielding point. The frame needs to be perfectly brazed with a 55% silver brazing rod, because the temperature while brazing, should not exceed  700 °C. The frame can't be welded . The frontfork can't be bent too. By cutting a part of the rake off, that was made in the factory before hardning, the builder can alter the trail. Reynolds frontforks are often raked at the factory; this can be specified when ordering. Columbus forks are usually straight and are bent by the builder.

To build a frame you need: 1 bracket and forkcrown, 2 headlugs , 1 seatlug, 2 front and rear dropouts, 1 small bridge, one large bridge several smalll braze-ons (for guiding cabels, bosses,  etc.) and the tubing.

  The steerer colomn needs to be longer than the headtube; this depends on your headset. “A-headset”-design needs a steeringcolomn without treading. Needlebearing headsets like Stronglight use a lot of space (up to 44 mm). Choose the threads 50mm longer then the headtube measured from the forkcrown; cut to size later. Check the rake and braze the forkends.

  You must make a design: a drawing at full size.  All angles and dimensions are known now. Make a simple jig to braze frontfork (see FIG.3). On the base plate we draw a central line. On the dropout side we use 100 mm wide spacer on the middle of the line. The steerertube often has a dimension of 25,4 mm. So the axis of the fork 12,7 mm above the base plate. Check if the rake you chose, is met by this set-up. In FIG.3 it is 12.7 + S mm; hold the steerertube with a C-clamp. Make a venthole in the forkparts befor brazing (2 mm), so the air can get out while heating. Clean and flux while setting up the jig; for brazing I use it vertical and the fork upside down. Protrude the steerertube a few mm's through the crown. This is where we will add most heat. Start adding braze at the protruding steerertube until it is coming out on the other side, so we are sure the joint is filled. Then we braze the forkparts.

   If the fork needs bending after brazing , you should build a special jig.  I welded a frontwheel axle on a base-plate and made a lever of 500 mm tube 30X2mm. Clamp the dropouts and bend the fork over a wooden or metal curved surface, radius about 200-300mm; don't bend too far.

    For the main frame we can make a jig as well (see FIG.4). At first I braze the headtube/ downtube joint. Headtube should be protruding a few mm's so the flux can be pushed out of the joint. Check the angle after brazing on your drawing. Next I am going to do the bracket seattube joint. Check with a straight edge if it is perfectly perpendicular. I clamp it on a flat surface, measure its height flip it over and measure the other side; if correct both sizes are the same. Then unite the downtube and the bracket. Align the headtube and seattube; be carefull you don't spill too much flux and braze in the bracket. Then I clamp the frame on the flat surface again and flip it around. Align if there are any differences. The toptube joints are last joints we make; check if the mitered tube is perfectly fitting. As you know by now , the headtube and seattube should protrude a few mm's.

   Check the sizes and angles on the drawing before brazing. There must be a venthole in the headtube toward the toptube. After brazing, grind off the protruding parts.  Drill a 2-3 mm hole on the back of the seattube about 40mm's from the top. Carefully cut the seattube with the grinder till you reach the hole. File and sand it inside, so it is smooth and won't scratch the seatpillar.

Now we going to fit in the rearforks. Watch out that the spaces for tires and chainring are in the right spot. Cut the forkblades to size. Short blades are only possible if you use vertical dropouts.  Now braze the dropouts and use an old hub as spacer; carefully align and braze the forkblades. Check the height of the dropouts as this influences your groundclearence. Stick a ruler in the bracket and lay one on the rearforks; are they parallel? Are the droputs in the middle of the plane through the mainframe? If not, align ! Then we braze the bridge behind the bracket. Now the rearstays can be brazed; you can use plugs or plates (FIG.5a), mount it directly to the tube (FIG.5b) or seatclamp (FIG.5c). Don't forget the ventholes. The last important brazing is the brakebridge. Before finishing  we fit the braze-on's. 

 For finishing we need a lot of special tools. A good relationship with the mechanic of your bike-shop might help.

1. With the headtube reamer/ race the cut the inside diameter of the headtube to 30,0 mm, and the top of the headtube is cut perfectly perpendicular to the axis. The same procedure is used at the bottom.

2. With the crownrace cutter we cut the diameter of the forkcrown to 26,4 mm and we face the top of the crown, so headset can be installed perfectly.

3. With the thread cuttingtool we align and clean the threads of the bracket.

4. Next we turn a guidesleeve in the bracket. This will help the bracket facing tool to make the outside surface of the bracket perpendicular and flat for fitting axle bearings.

     If you use a high quality bracket you might not need tools 3 and 4.  Finishing the frame before spraying, will take a lot of time. Use fine sandingpaper and productioncloth. Be carefull with files; you can easily damage the thin walled tubing especially when removing residue of the flux. These can be as hard as glass. Small imperfections can be filled with tinsolder or filler. Once the frame is ready for spraying, you could built it up to see if everything is in the right place and it rides well. Changes can be made before we spray the frame; after that it will mean a new sprayjob

    The era of the classical steel racers has come to an end in the nineties .......

   Progress takes its toll. Thus ended the use of a reliable production method for bicycleframes. The weight of the new generation of carbon frames, is half that of the classical steel racers with lugs; lighter and stiffer: technically a great progress. But we love nostalgia. People who started their cycling carreers with tubulars and steel, often dream about the good old days. Being old fashioned, I have built those but nice, lugged steel bikes too.

We are lucky we forgot about the repairing of the tubulars, and re-trueing the wheels after breaking the chromed spokes......

In FIG.10a. we see the frame tubes of choice ; the fork-blades are made from Reynolds '531' (the old default profile). The head-tube of the frame has been significantly altered ; it was the intention of Columbus to use a round profile head-tube. Originally there was a normal round head-tube in the Columbus tube-set ; but I chose a wing profile head-tube instead. The seat-tube and down-tube are both identical ; I will therefore have to make a seat post that can fit the oval profile of the seat-tube. The seat-stays start at around 12 mm in diameter round section, and then change into an aero profile shape. For the chain-stays I consciously chose a heavy tubing ; this provides a larger brazing surface contact area, and thus a better adhesion to the bottom-bracket shell. Moreover, this heavy tube choice improves the lateral stiffness of the frame,  which can be a weak point on these types of bikes. I will also add some additional reinforcement at the junction of the frame tubes with the bottom-bracket shell.

  The frame will weigh 2.3 kg, without fork (0.7 kg), (2.3 + 0.7 = 3 kg).

  The design specifications in general are : normal head-tube rake of 72.5 ˚ ; seat-tube angle of 73 ˚ ; the top-tube and the seat-stays join together just below the saddle. The seat post only has a length of about 6 cm ; the horizontal top-tube length is 55 cm, and the seat-tube is 67cm long.

The main brazing parts are : the bottom-bracket sleeve, the front and rear drop-outs, and the fork-crown (see FIG.10b.). In particular, the fork-crown (made by Davis) is far too heavy; I ground a lot of it away. After all the grinding and polishing, I weighed the crown again. The whole process delivered 53 grams of weight saving ; the lightened fork-crown weighs only 192 grams instead of 245 grams (saving 22 %).

  After the main part of the grinding work is done, the steerer-tube is brazed into the fork-crown. You can see in FIG. 11b. the steerer-tube protrudes slightly below from the base of the fork-crown ; this excess material is then ground down, to be smooth and flush with the surface of the fork-crown.

  There will be a normal round head-tube, fitted inside the wing profile outer aero section head-tube FIG.11a; the holes in the inner head-tube serve to allow hot air to escape from the workpiece, during the heating of the hot brazing process.

  On the drawing board FIG.11c, I laid-out the angles and the dimensions of the frame. The full length of the seat-tube is used ; I have shortened an old aero seat post, and adapted it to the shape of the profile of the seat-tube.