Archive for June, 2004

Steering setup

On to the steering setup. This was an area of much work (and rework). As you can see from the illustration, I have tried several different steering setups. The one that seems to work the best is similar to the ones that appear on most commercial recumbents. (Hmmm, I wonder why that is…)

I will only go into detail on the system that is currently in place on the bike. As it seems to be working well. Starting from the front of the bike and working back. The first thing I added was a front pivot for the steering linkage. This is simply just a all-thread coupler (a nut that is 1” long) brazed to the crown of the front fork. For the steering rod, I brazed a nut onto the end of a short length of steel tubing. The aluminum tubing that makes up the length of the steering rod is friction fit on the outside of the steel end piece and both are held together by roll pins. Both ends of the steering rod are made in the same way.

The final part of the puzzle is the seat mount/remote steering head. After rebuilding the steering, I found that I could combine the handlebar mount with the seat mount and bolt both of them together. I salvaged about 5 inches of the original down tube from the donor bike for the body of this part. Onto this tube, I brazed four one inch lengths of 3/8 inch tubing to serve as bolt guides to complete the clamp portion. At the top center of this assembly, I brazed a short (1 1/2 inches) piece of 1 inch tubing to serve as the “seat post” for the seat base.

Next, I “salvaged” some parts from a second donor bike. All I needed was part of the head tube (with hardware) and part of the steerer tube. First, I cut the steerer tube at 5 inches from the top. (keeping the threaded end). I brazed this in place on the clamp I made (above) directly opposite the seat post. Then, I cut a 2 1/2 inch section of the top tube from this bike. This section was the bottom half of the top tube with a 3 inch section of the down tube attached. This down tube section serves as the stem of my new handlebar mount. On the end of the salvaged down tube (now a stem) I brazed a 1 1/2 inch section of leftover down tube to serve as a handlebar clamp. On the left side of the head tube (looking down from the top) I brazed a piece of 1/8×1 steel strap that had been bent into a “relaxed Z” shape to serve as a attachment point for the steering linkage.

Once all of the brazing was complete, I (re)assembled the new steering head. To the new steering head, I attached the steering linkage. Re-checked the chainline clearance (in all gears) and tightened everything up. By the way, the handle bar was given to me by a friend and comes from a early 70’s era motorcycle. A person with longer arms could probably get by fine using a “standard ten-speed” style handlebar that was flipped over.

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Seatworks

Seat Post?  With the three main tubes in place, it is time to add the seat tube (accurate but misleading name) and a false brake bridge to complete the basic frame. First I cut and shaped a piece of the tubing left over from the new chainstay tubes to fit between the chainstays about 3 inches forward of the end of the top tube. This will help maintain the proper spacing of the chainstays and provide a support for the new seat tube. I selected the position of of this tube to allow me to slope the seat tube to match the “old seat tube”.

To complete the basic frame, I replaced the seatstays, rotated to match the location of the new top tube and brazed them in place at each drop out and on the top tube.

The seat base is a “standard” industrial trike seat from the local bike shop. I paid about $25 for the seat and clamps. This seat has three mount points. The front point is a compression clamp that clamps to a single vertical tube (think department store kids bike seat clamp). The other two are simple single bolt pipe clamps for holding on a upside-down “U” shaped tube like the old banana seats.

The seat back is made of 1/2” EMT bent into a closed rectangle. The ends of the tube are brazed together and a brace is brazed about 1/3 of the way down from the top. A “U” shaped tube was then brazed in the bottom of the seat back to connect to the two remaining clamps on the seat base.

From the local canvas shop, I purchased several yards of “outdoor furniture mesh” fabric. I cut the fabric 2 inches wider then the seat back. Then I folded the ends of the fabric over twice and sewed the seams with dental floss. I then inserted a thin metal rod in each seam. Approximately every two inches around the perimeter of the seat fabric (inside of the rods) I melted lacing holes using a soldiering iron. Through the holes I passed loops of “parachute cord” to lace the seat fabric to the seat frame. The construction of the seat back only took one evening (after I had finally decide on a design).

The seat back is held in place by adjustable aluminum supports that run from the brace on the seat back down to the rear dropouts. These are simply a fitted rod and tube that have a number of holes drilled along the length that a hitch pin is pressed into. This feels quite solid, but there is some side to side play. The ends are made in the same way the steering linkage rod (below) using a steel sleeve and roll pins (omitting the “rod ends: fittings)…

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Chainstays

Next, I worked on the chainstays. This was the most difficult part of the building process and is something I will avoid on the next bike. The first step in this part of the construction was removing the stubs of the chainstay tubes from the bottom bracket. The plan was to simply heat the bottom bracket lugs and remove the tubes. In the process, I managed to tear the tubes into several pieces and crack the bottom bracket lug. I had to resort to cutting each tube lengthwise inside the lug and heating and removing each piece. On several really stubborn pieces, I had to grind them out and shape the lug. What a pain!

Next, I turned my attention to the rear end of the chainstays. Because I liked the taper of the chainstays on the donor bike, I decided to braze them onto the ends of the new chainstay tubes. Now that I have done this once, I can say that I probably will not do it again! The first step here was to unbraze the chainstay tubes from the rear dropouts. Then I cut both of the chainstays from the donor bike to the same length. Then I brazed the lugs back in place tilted upwards 45 degrees. This tilting of the lug was to provide clearance on the seatstays when they are placed in their new position.

On the open end of each modified chainstay tube, I attached a 4 foot length of tubing to create the new long chainstays required. To strengthen the butt joint, I inserted a simple split sleeve made from a piece of spare tubing before brazing. Once the tubes are brazed together and everything looks straight and correct, then cut both chainstays to the same length. Were I building a second bike of the same design, I would extend the new tubes all of the way from the bottom bracket to the rear dropouts.

Now that I have two extra long chainstays created, it’s time to put them in place. I set up my jig so both tubes were seated in the bottom bracket lugs and the dropouts were straight up and down. By the way, at this point, the chainstays are about a foot apart and 6-8 inches to high. This is ok because I will be bending them into place after they have been brazed in place in the bottom bracket. Once I was happy with the alignment of the chainstays and dropouts, I brazed them into the bottom bracket.

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Cutting the frame

First, I needed to cut off the front part of the bike. To do this, I cut the seat tube about 1/2” above where the top tube joined. Then I cut each chainstay approximately 2 inches from the bottom bracket. The plan was to “unbraze” the remaining chainstay pieces from the bottom bracket shell later. I used the chainstays and seatstays in the next part of the construction. Also, I kept the remaining part of the seat tube for making various clamps and fittings. The Top Tube

The first new tube I added to the frame was the top tube. The plan was to keep this parallel to the ground to maintain a consistent seat height throughout it range of adjustment. I created a hole in the original seat tube (now part of the front triangle) and mitered the end of the new top tube to fit the seat tube opposite the hole I had made. I determined the length of the new top tube by determining where the back of the seat would be and adding a few inches. This gave me some room to adjust the seat for taller riders.

Next, I worked on the chainstays. This was the most difficult part of the building process and is something I will avoid on the next bike. The first step in this part of the construction was removing the stubs of the chainstay tubes from the bottom bracket. The plan was to simply heat the bottom bracket lugs and remove the tubes. In the process, I managed to tear the tubes into several pieces and crack the bottom bracket lug. I had to resort to cutting each tube lengthwise inside the lug and heating and removing each piece. On several really stubborn pieces, I had to grind them out and shape the lug. What a pain!

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The Donor Bike

I found a well used mixte frame upright bike at the local Goodwill store for about $10. This was the basis for the bike. It had a lugged frame and department store components – the *perfect donor bike for the project. On second thought, I wish I would have looked a little longer and got a bike with better components!

To keep things as simple as possible, I wanted to keep the same head tube angle, trail, and fork rake as the donor. To do this, I needed to take two measurements BEFORE disassembling it. With the bike standing straight up with tires inflated, I measured the height of the bottom bracket(BB) and the front axle. By keeping these measurements the same in the final bike, I kept the front geometry from the donor bike (because I did not alter the “front triangle”).

The next step was removing components from the frame. I removed all every thing except the front fork and one of the bearing cups that was stuck in the bottom bracket. I should have taken the time to remove the cup before I started working! It took a lot of effort after I had applied heat to the bottom bracket!

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