Don Boose builds an EconBent

The idea to construct an EconBent came from an article that appeared in the 1994 Buyer's Guide issue of RCN. I was quite certain that I could accomplish this task as I have had experience in the metal working area. After purchasing an Oxygen-Acetylene welding/brazing unit, all the tools and equipment needed were on hand.

I ordered plans and parts catalogs from Cyclopedia in early January this year. For those who are not familiar with the specifics of the Econ Bent let me say it is a SWB design primarily using a 1-3/4" automobile tailpipe and the back end of an upright bicycle frame. Additional bicycle frame parts are also required such as a BB shell, steering tube, fork, etc. These parts can be scrounged and/or purchased. For the frame I was ready to sacrifice one of my "still-good" wedgies. Before I put the hacksaw to the old Raleigh, a friend of mine donated a Reynolds 531 Trek frame that had been damaged in the front end. This frame was perfect for my needs.

After receiving the plans, the first item of business was to visit a local Muffler Masters here in Pensacola Florida and have the main frame manufactured. The proper length of a 1-3/4" tailpipe with the required three bends and a couple short pieces required cost a total of $19.80, including tax.

The bicycle frame is separated at the down tube and seat tube six inches or so from the bottom bracket. The seat stays are separated from the top part of the seat tune. This action renders the usable part of the frame. The down and seat tube stubs are subsequently cut, mitered and trimmed for brazing to the the main frame (tailpipe). Note that the bicycle's bottom bracket shell is still intact and is a necessary part of the structure.

I used a 3/4" sheet of composition board, because I think it surpasses plywood for thickness consistency. I placed this board on a table and shimmed it to provide the flattest surface I could manage. The size of the composition board was cut large enough to support the entire frame at the extremities of length and height.

One of the first steps is to cut a hole in the tailpipe in which the headtube is mounted and brazed. A hole saw would have facilitated this task. I used the drill and file technique. The importance of proper alignment can not be over stressed for this evolution. A friend's help was required as I did not have a large enough drilling surface to properly mount and secure the work.

Another critical task is to connect the bicycle to the tailpipe. To so this properly, it is necessary to provide a means to hold the parts in a rather precise position.

I procured a length of PVC (any material will suffice) with an outside diameter value that provided a snug fit when inserted into a BB shell.

The PVC was securely attached to the work surface in a vertical position. With this setup, the bicycle frame can be held in a precise and steady position by inserting the BB over the vertically mounted PVC. A shim is used to keep the BB at the proper height. The tailpipe is placed in position on the surface using shims to level it in the horizontal plane at the proper height. Reference points drawn on the work surface are used to align the two parts (frame and tailpipe) in the "x" and "y" planes. It is at this point when one must decide the desired rear wheel size (26, 27, 700C).

 

	Completing the above steps while maintaining the proper frame alignment is, in my viewpoint, the most difficult part. It's downhill from here. As I mentioned above, one can scrounge or purchase parts. Gaylord Hill at Cyclopedia, and other suppliers have all the parts necessary to complete the Econ Bent. In addition to the plans and catalogs, I ordered a 16-inch front wheel, non-lugged BB shell and a 16-inch fork from Gaylord Hill.
My Econ Bent deviates from the plans because I modified the construction to provide for USS. I tried the linkage style like the Ryan Vanguard and the tiller style like the ATP Vision. I settled on the linkage style and it is not adjustable to accommodate rider size. It is, however, adjustable to align the steering. The seat can slide, but the handlebar pivot point is fixed. Having a fixed pivot saves weight and complexity. The boom is not adjustable.
	The seat frame is made from 3/4-inch EMT (electrical conduit). I will use 1/2-inch EMT when and if I make another Econ Bent. The seat material is cotton macrame cord. I was doing macrame years ago and I had much cord left over. The cord works fine, but I thought it would stretch. So far, it has not.
There was a lot of trial and error involved in getting the machine not to be ultra twitchy. I finally settled on a fork rake around 1/4-inch. The handling is still more "nervous" than my Vanguard, but more-or-less on a par with a newly acquired V-Rex with a 700C wheel.
	I am going to experiment with a 20-inch wheel setup. My goal is to make it easier to ride. Perhaps I should say easy to ride. I have one friend who just could not balance it. After crashing twice he gave up (I was glad). It was the best Arte Johnson imitation I ever saw and he has ridden uprights for years. On the other hand, one young-lady-first-time-bent rider jumped on, and down the street she went. After that she rode the Vanguard and the V-Rex like a champ. I was impressed. The total cost of the project was less than $200.00 excluding the Oxygen-Acetylene equipment. The only parts I purchased are mentioned above. Other parts such as cranksets, derailleurs, tires, etc. I had on hand. I almost forgot, I did purchase a cyclocomputer or two. Let me stress the job can be done without a lot of exotic tools. However, since I altered the plans, and I am an experienced metal worker, the job would have been easier for me had I a metal lathe. For example, I could have designed a better USS steering mechanism using a lathe. As long as I am dreaming I'll stand vertical a milling machine next to this mythical lathe and have the ultimate frame-building luxury. Additionally, owning a MIG or TIG unit would have allowed me to fabricate some parts from aluminum. All parts were fabricated from steel except for the teflon bushings in the steering mechanism. This Econ Bent weighs 34# with everything on it except water bottles and tools.
If anyone has questions, please feel free to email me. Don Boose Pensacola FL bluerocket@gulf.net

Additional discussion follows, basically in response to questions...

Handling: It is very responsive. I did quite a bit of experimenting with fork rake before I was satisfied. I ended up with about 1/4" inch positive rake. I am not sure of the head angle, but I think it is 68.5 degrees. The result is a neutral steering. That is neither understeer or oversteer. (The bottom bracket neither raises or lowers when I turn the wheel with the bike upright.)

The seat mesh is cotton macrame made from the large supply of cord I have left over from my macrame days eighteen years ago. As you can see the design is not symmetrical as the weave got too tight for me to add any more cords. I thought it would subsequently stretch and I could finish the weaving. So far it has not stretched at all.
 

The freewheel has seven cogs. There are three shiftable positions at the intermediate drive. A ordinary front derailleur is used here. These cogs are mounted onto a freewheel body with the pawls removed. The three driving (shiftable) cogs are mounted the smallest inboard and must be the splined type. The outer (driven) cog is screwed on with the necessary spacers to prevent interference with the driving cogs. The freewheel body is mounted into the BB by means of an adjustable cup. I rethreaded the right side of the BB to RH threads.

The drawback with this arrangement is the limitations on the size cogs that can be used. For example. the outside cog has fifteen teeth. All this make it somewhat difficult to get the gearing low enough. The chainring should be no larger than 36/38 teeth.
 

The bent now has a micro triple chain ring on it for test purposes. I have not installed a derailleur up front, but you can see such an arrangement would render 63 speeds. It is also possible to install a rear derailleur at the intermediate drive it add more gear combinations. I would like to braze/weld a larger cog to the 15-tooth outer cog to help remedy the gearing problem. So far, I have not figured out a way to align/center the two cogs on the same axis to be able to weld them. If I had a lathe...

I have no adjustment for rider height except for the seat position which, in this case, can be moved about four inches. I chose not to make the boom adjustable. I set the crank distance for me and brazed the boom in place.

The plans called for ASS, consequently the steering design is my own and is not adjustable. I started out with an adjustable system, but it became too cumbersome.

There is no steering rod flex. The rod is only twelve inches between pivot points and solid 1/4 steel. In contrast, my Ryan Vanguard, has over three feet of steering rod of 1/2" aluminum tubing. I notice no flex here either.

I did have trouble calibrating the front-wheel driven Cateye Astral computer. The settings from the book did not work. My solution was to install a Vetta C-15 driven by the rear wheel, calibrate it, and use it as a standard. I just kept changing (reducing in value) the Astral setting until the mileage and speed readings between the tow computers agreed.

I used a surface made of 3/4 inch composite board large enough to be as big as the frame. In the proper place I mounted a piece of PVC pipe. I think it was one inch. The pipe fit snugly inside the bottom bracket (intermediate drive location) of the frame and gave me a reference point in the horizontal and vertical plane. From there it was just a matter of following the plans, measuring, leveling, and shimming as I went along.

The main tube is 1-3/4" and the wall thickness is .0625. I do not know if this is a standard tailpipe thickness for this size tubing. I don't know if it could be any thinner or smaller in diameter.

The pictures