Presentation on theme: "Here is the bare 953 tubeset as it arrives from Reynolds. The main tubes, chainstays and dropouts are 953 material. The seatstays, brake bridge and headtube."— Presentation transcript:
Here is the bare 953 tubeset as it arrives from Reynolds. The main tubes, chainstays and dropouts are 953 material. The seatstays, brake bridge and headtube are 316 stainless. Reynolds is now offering actual 953 seatstays for 2007, all my future frames will have those. The tubes come in a nice brushed finish, the chainstays are darker as they’re not brushed after heat- treatment (presumable because they’re not round and would be more difficult to finish).
Here are the bare lugs. For this frame I used Kirk Pacenti’s slant six stainless lugs. I start by drawing a rough outline of the shape I want on the lugs with a marker. Then I begin the process of cutting/filling/sanding to shape the lugs
I start shaping the lugs by removing the larger amounts of material with a dynafile and hacksaw as shown below on the left. Then I create the finished shape with hand files and emery cloth. The marker lines are just a rough guideline, I create the final shape simply by look and feel. I like to keep what I feel is a smoothness and flowiness to the shoreline of my lugs.
I check all thicknesses with a caliper as I’m carving to ensure that the lugs are perfectly symmetric. Once the shape is created, then the lugs are thinned a bit and sanded smooth with 80 grit cloth. Once the outsides are done, the interiors are also sanded up to clean them in preparation for brazing.
Next I miter all of the main triangle on my horizontal mill. This is probably the biggest obstacle to working with 953. The material itself is extremely strong and hard, and using the tubing used for lugged frames comes aged from Reynolds which makes it even stronger and harder. The key to cutting it cleanly and efficiently is to have an exceptionally rigid mitering arrangement. I use a 2200 lb nichold horizontal mill with a 50lb tube vise mounted on a 12” rotary table. The cutter is just a standard holesaw, but with fine pitch teeth. As long as the tube is held securely and has all the mass of the machine behind it, I get a very clean and precise miter every time. It still takes about 3 times longer to cut a 953 tube than a 4130 tube, even with this tooling.
Next I need to machine the headtube. Initially Reynold did not offer an stainless headtube in 36mm diameter (which is the required size for the slant six lugs). So I took to making my own from 316 tubing stock. I have to turn down 38mm tubing on my lathe, then bore the ID of the tube. For this frame I also turned down the center section of the headtube to 35mm to shave some weight. Think of it as an externally butted headtube! After turning, I ream and face the tube (shown below right). I have a fixture which allows me to mount my headtube reamer right onto my lathe simplifying the operation. Reynolds now offers a stainless headtube in 36mm OD, which I will proably use in the future as this is a time consuming process.
Now I fixture up the front triangle and check the fit of all the tubes. If it looks good, I sand off the ends of each tube to clean them and flux up the whole thing and reassemble it in my jig. I tack braze the fron triangle in the jig. My jig rotates 360 degrees, so I can easily access all around the lugs and let gravity help me if needed. I tack to top and bottom of each lug, along the frame’s centerline so the heating and cooling don’t pull things out of alignment. Once it cools, I remove it from the jig, check the alignment on my table, and fully braze up the lugs freely in a workstand.
Once the front triangle is brazed up and cooled off, I soak it in a water tank to dissolve the flux. While that soaks I move on to working on the chainstays and dropouts. The 953 dropouts are shaped a little differently than most forged dropouts. The tabs are the exact size of the ends of the chain and seat stays. So rather than slot the stays as if traditionally done, I choose to file the tabs on the dropouts slightly to fit inside the stays. The pictures to the left below shows the chainstay tab filed and ready to go. Once they’re flied and sanded up, I sand the inside and out of the chainstays and flux everything up (center below). With the chainstay held vertically in the vise, I braze the joint with 50N silver to fill up the gaps. Shown below to the right is the finished braze ready to be filed and sanded.
After brazing both dropouts to the chainstays, I soak off the flux and then sand in the scallops. These are a little tricky as one slip and really ruin the look. Once the scallops are in both sides, I sand aroudn the diameter of the stays to clean up an residual silver.
Once the dropouts are all cleaned up and the flux is all soaked off the front triangle it’s time to attach the chainstay. Another problematic aspect of 953 is the shape of the chainstays. They’re ovalized, but not consistently and not that smoothly (compared to most 4130 stays). They have a fairly sharp point at the top and bottom and don’t fit the sockets on the BB shell very well. I have to do quite a bit of filing and sanding to the sockets to make them work and I still end up with gaps at the corners (as shown below left). For this reason I have to braze these with 50N silver to help fill those gaps as there isn’t much I can do to reshape the sockets that much. Once those are brazed in place I move onto the seatstays. They’re fitted up to the dropouts in the same manner as the chainstays, but the seat- lug end is a bit different. On this particular frame I decided to do a fastback style stay with a hidden binder. To do this I turn a solid section of 316 stainless steel rod down to fit exactly inside the top end of the seat-stay, then I braze that into the stay. From there, I miter up the stays as I would any other fastback.
Once both seatstays are mitered perfectly symmetric, I clean and flux them up and braze them to the seatlug. This is tricky as the seatlug is brazed with the same silver as the stays, so I need to be very careful not to melt out any of the silver filler between the lug and the main tubes while attaching the stays. In the picture to the left, I have marked where the stainless rod is brazed inside the tube, so I know where to bore the binder bolt hole. Also note, the stays overlap the seatpost slot opening. I plan on beveling the inside of both stays when I cut the slot.
Now that the seatstays are attached, I soak them off and give them a quick blast with the sandblaster and move the frame back to the mill. I cut the seatpost slot and the bevel on the inside of the seatstays at the same time on my horizontal mill with an abrasive wheel (below left). After that I hand file the bottom of the slot to make it round and prevent any future cracking. Than I move the frame to the vertical mill to machine the binder bolt hole. I start by drilling a 13/64” hole all the way through both stays perfectly perpendicular to the plane of the main triangle. Then I go and bore the driveside seatstay hole to ¼” and finally counterbore that hole to recess the bolt head. Finally I tap the threads on the non-driveside seatstay hole.