Gryphonn's Bike Build Tutorial
So just how do you make your own frame anyhow?
Spring's here and time for many of us to think about a new ride. I'm working on my next bike which will have a fat 80mm wide rear rim, 3" Kendas front and back, Nexus Inter 4 coaster brake and a disc brake front fork.
After drawing designs on paper until you get one you like, draw it out full size on a flattened cardboard box to see what it really looks like. I stared at mine for days and changed it at least 2 times before I started to build.
Getting the curves I wanted actually created another project, a homebuilt tube roller. The main frame of it was made largely from scraps around the shop. The dies were made by cutting out circles from oak on the bandsaw, laminating them together and cutting the V-grooves on a table saw. It does a good job on tubing up to about one in diameter as the dies lose traction on larger material.
Because the pipe dies do not fit snugly on the tube, some flattening will occur. Not much can be done about this unless you have about $600 for a decent tube bender or use some alternative method like bending over a large wooden die. Another problem is there are no dies for the non-bend side so the rollers tend to make 'dimples' in the tube either side of the bend. As my frame is all curves I made sure to bend more length than I needed to ensure a consistantly flattened tube. You can also see the larger brass coloured tube I slipped over to stop the rollers from making dimples either side of my bend because as you can see, I made tiny bends every couple of cm along my tubes. Yes, many, many tiny bends...
Nothing high tech here: I just put my full sized drawing on top of the bench and nailed my pieces in place to hold them.
Just another shot of my no dollar clamping system. You can see how I changed the design a few times before I got to this stage. Double/triple check everything and move to the next stage...
Always firmly tack your projects together, flip over and tack the other side. There's nothing worse than things going out of shape or falling apart after you handle them a bit. I usually don't do all my final welding until the entire frame is fit together.
And there it is, the new front frame section tacked together on both sides and ready to go in the jig. I just use one of the inexpensive 110v mig welders, I recommend the welders with the small bottle of gas rather than the flux core ones which are more messy and use more costly wire. The bottles are cheap to purchase/refill and you can buy an adapter to run a 10lb spool instead of the little more costly ones.
Here is another really low tech item, my frame jig. I tend to like to build with what is on hand: I started with a really straight 4x4 fence post I had, using a couple of Canadian Tire workmates I levelled it front/back and side/side and dug out some 2"x2"x1/8" angle for the uprights. It's mainly about measuring everything at least 2x and drilling things together to ensure they are exact mirror images or each other.
There's a lot more to be concerned about when building with a fat tire/rim combination. The chainline is much more difficult to setup. In my case the hub will be offset to allow chainline clearance on the tire sidewall. The Kenda Kraze when mounted on an 80mm rim is actually almost 3.5" wide at the sidewall and because I'm using a Nexus Inter-4 I couldn't use an offset sprocket as it would have interfered with the shifting assembly.
Here you can see how offset the rim/tire are from the hub, they are about 1.6cm from the bike's centreline. This means once I've calculated the different driveside/hubside spoke lengths and laced up the wheel, it will have to be returned to the centreline. Likely the rear stays and bottom bracket will need to be offset 1.6cm, allowing the bike to track true with a straight chainline.
One more shot of the bike in the jig. Use a framer's square and several sizes of bubble level to check everything. Front/back/side to side all need to be square and level across the axles, bottom bracket and frame height.
Getting the vision in your head of the finished project is often part of the problem. I like to use a bit of photoshop work to help the process along. You can save a lot of time by drawing and dreaming of the finished product.
After shimming the tire/rim over to center and offsetting the hub to correct the chainline, I used a makeshift plumbob to measure the offset. I found the drive side holes in the rim are directly in line with the drive side hub holes and the other side is offset by 21mm. I use a spoke length calculator (and other info) you can find at Rockx site. Editor's note: You can find some spoke calculator info in the Vancruisers tech section too!
As you can see the rear wheel is laced up and it's time to finish the rear chain stays. The arcs of tubing I rolled had to be cut about 3/4 of the way along and rotated inward to clear the chain and join with the front section.
3/16" steel plate works well for dropouts and I decided to go with covered ones for a cleaner look. Rectangular tubing was used to make the shell, the slots were cut with my trusty 4.5" grinder and the cover itself will be polished aluminum.
All four chainstays are now done and you can see how the covered dropouts will clean things up at the back end. If you click to view the larger image, you can also see where I cut the lower stay to rotate it inward. A torch had be used to heat the upper stays in a few places to bend them out and back in to line up with the dropouts in order to create more chain clearance on the drive side.
Still a long way from finished, but at least it's looking like something now. I'm hoping to have it ridable for the Freak Bike Militia cruise May 4th here in Nanaimo.
Ready to roll with a few things left to do; shifter, different handlebars, mold and paint the frame, etc. I am thinking about a leather covered suspension seat too, but frills can wait. This bike feels very solid with minimal flexing and with calculated rake and trail, low speed stability is much improved over my last build.