Hello My names is Michael.
Welcome to my Instructional on making a truck bike (butcher bike) from a vintage steel mountain bike the hack way. I'd say one in one hundred cycling enthusiasts is serious about owning a cargo bike, and one in 20 of those people are serious about making it themselves, and one in five of those people are going to have the bare bones metal fabrication experience it will take to follow these directions, so this post is for all ten of you people in all the world who are as excited about truck bikes as I was six years ago! Making a truck bike from an old mountain bike was my first project when I decided to have my own shop where I would make bicycles seven years ago.The main reason to do this project this way is that the tail end of the bicycle frame is the most complicated part and you save yourself a whole heck of a lot of hassle by just taking something that already exists and adding a cargo bike front end to it, and really there's something to be said for just taking something off the shelf. Nobody can do it all on their own, and people who think they can are generally just kidding themselves.
WHAT DO YOU NEED TO KNOW?
Seven years ago, when I undertook my first salvage truck bike, I already had a lot of heavy duty welding, precision machining, and bicycle maintenance experience but since this project requires neither of the first two and plenty of the third I was about where you hopefully are now. If you know the difference between a head tube and a steer tube that's a good start. You want to be able to do your own mechanical work for this project so that some poor mechanic in a bike shop won't have to tell you you screwed up. Also you want to have all the parts you're planning to use on the final build on hand when you start. That's always a good idea. In this lesson I planted a bunch of photos of my finished truck bikes, some of which have salvaged parts and some of which do not. My main reason for this was to show a couple different ways of doing things. I recommend you go with a square mid tube like I show in the Microsoft paint instructions, the most important Bike I included was the Surly steam roller truck bike made by Dirty Dave in San Francisco. His philosophy when it comes to utility bikes is something like this, "the easy way is hard enough", so be like Dave and get your bike done in a reasonable amount of time.
WHAT is a SALVAGE TRUCK BIKE?
The basic theory behind a truck bike is that they use a standard adult commuter sized frame and rear wheel that's typically a 700C or 26" and a 20" BMX wheel in the front. The utility is in that the small wheel allows you attach a front rack right to the frame and gets your load beneath the swing of the handlebar, and lower to the ground which improves handling and means the 120 pound box of sensitive laboratory instruments (or whatever) you're carrying won't have as far to fall once you get to wherever you were going. Attaching the rack to the frame rather than the front fork and handle bar also improves handling as your cargo doesn't have to swing back and forth when you turn.
WHY make it?
This value added custom bike project is cool because it's something you can make after work at the fab shop or in community college welding class, bikes and especially utility bikes are incredibly useful, it is an alternative transportation for yourself and others, it will be made at least partially from reclaimed materials, you will learn a lot about bikes, anger management, and welding in the process, a well done truck bike hack is hard enough to pull off that other geeks will think you're cool, and because truck bikes are hard to attain any other way. Even if you could find one for sale it would be more expensive than a small old car. Probably the coolest part about home made cargo bikes is that what you're building will be closer to the Corvette end of what's available than the 65 pound Maytag washing machine end of the spectrum. But keep in mind no matter how much your truck bike weighs you will have plenty of fun peddling your "friend" and their baggage to the airport at five am on a Saturday morning.
Things you'll need.
1 mountain bike frame
1x 1-1/8" head tube (2 feet long), source it from Henry James, or Nova. Buy the thickest piece they have unless you're a whiz with the welding/brazing process you're using. Remember the longer the material is hot and or the thinner the tubing is the more distortion you're gonna get, so for beginners who are slow welders, (I don't do anything quickly) that means you want the BMX or mountain bike, heavy duty head tube stock.
1 20" inch front wheel, preferably disk brake, but drum or rim brake would work. I recommend the Avid bb7- they're about the price of a low end hydraulic, but they are virtually maintenance free
Triple down tube cable stop, or three single stops, If you're cutty, you can just pull them from the main tubes of the "old mountain bike".
A park stand.
A piece of particle board or butcher paper to draw your frame on. If you use wood, you can bolt the bike to it later to help tack, just like when people make small airplanes or race car chassis.
A Bevel Gauge.
A half round file.
Welding hood or goggles.
Rubber chem gloves or a wire wheel.
A fire extinguisher.
Chromoly airplane tubes are choice. You can get them through wicksaircraft.com. Remember, you want wall thickness of .049" for main tubes and .058" for steer extension. You can go thicker but it won't make your bike any stronger, a little flex in the tubing takes the stress of the welds. I suppose you could use mild steel in .065" for main tubes. As far as main tubes go, I wouldn't go any smaller than 1-1/4 round, or any larger than 1-5/8. In-fact I recommend 1-1/4 OD for the top tube and 1-1/2 OD for the down tube. I believe you can use 1-1/2 .083 for head tube. I think using a square 1.5 inch mid tube is a good way to go, a great way to go!, just to make it easy to mount the rack. The easiest way I've attached a rack was by using two pieces of 1-3/4" angle to a square mid tube and letting the ends extend past the HT and form the rack portion.
Hole saws, one 1-1/8 and an a 1-1/2 will probably get you through the project if your brazing, if your tig welding buy holes saws after your tubes have shown up, tubing notched, and or printer for generating
Welding rod if your welding, brazing rod if your brazing, MIG set up if your Mig welding. For tig welding I use weld mold 880-t or 80s2 tig rod, I don't use chromolly tig rod anymore since I don't have my bikes normalized after welding. And you want your welds to be somewhat elastic. I like 035 and 049 diameter wire. I don't recommend Mig because its so difficult to obtain a high quality finished appearance with that method, but if your know what your doing it will hold. The nice thing about brazing if your ocd is that its easy to go back and fuss with your work afterwards with Tig less so, but with MIG each weld is a one shot deal. You can get your welding rod from wicks.
Brass Flux and brazing rod, and sorry to be a pain but not all brazing rod is equal, get the stuff through Henry James, but don't let them sell you lugs, if you use lugs you will need to make fixtures, or at least I did! Do not use harware store flux unless you want to chip it off with a hammer afterwards, the henery james flux will soke off overnight.
3'x4' piece of butcher paper, for 1/1 scale drawing
Regarding Fork, you may be able to find a recumbent fork that will do, but otherwise get a bmx fork.
Disk brake tab, I recommend a bb7 cable disk brake but since its hard to source twenty inch wheels with a disk tab you could also go with a drum brake front wheel. I usually use 32 spokes, 3x lace for front wheel, double wall rim for these, (plus they're easier to build) try to get this stuff for free, except for spokes, have a shop calculate length unless your a real masochist.
I use a little disk brake plate I made myself, it was one of the first tools I made, you can find ISO disk brake specks here, I have a photo of the disk brake plate and the rest further on.
Hand to have but nor required, angle finder, used copy of the Performance Welding by Ritchard Finch, Sink or Swim fabrication by Tom Lipton and for how to draw something that works Paterick Manual for frame builders by tim paterick.