Drafting Tutorial: How to Draw a Traditional Bicycle Frame. Step Three.

Now is the time your sketch will start looking like a bike. We'll be drawing the tube outlines, so you need to know what diameter tubes you'll be using. Also, if you're using any tapered tubes-- like chainstays, seatstays, and fork blades-- you should know where the taper starts. The process you'll use is the same as you used in step #5 above in the prior section. This process will be further detailed in step #1 here.

Note that I start with the TT, then move on to the HT and fork, then DT, and finally the ST. Lastly I'll finish off with the rear stays.

  1. To make sure you're making an outline of the correct width for your tubes you have to be quite accurate in measuring from the center tube lines. I use my protractor as pictured because it has a nice center line marked at 0 (serving as a perpendicular) and I can easily mark either side of the center line the same distance. For example, if the tube you're using is 1.25" (31.8mm) you can make a marking on either side of the center line at 16mm. The extra one-tenth of a millimeter you're adding to each side of the tube is much smaller than the width of the line you're going to draw so don't worry too much. If I don't have something that starts at 0 like my protractor I'll use just a clear plastic ruler. With the ruler you would put it on the center line at 14mm (or whatever the radius of the tube is), try to get it as close as possible to perpendicular to the center tube line, and mark at the 0 mm and 32 mm points.

    Now along the length of the tube I'll generally make 3 or 4 markings on either side of the center line and then connect them using a long straight-edge. This should give you enough points of reference to make an accurate line. Once you have drawn the tube outline you can check it with your ruler.
  2. The next step is to finish off the top of the HT. Now that you know where the top of the TT is you can measure out the extension of the HT above the TT. In my case it's 15 mm. Once you mark this and draw your line perpendicular to the steering axis you're done with the HT.
  3. The line for the fork blades are a bit more difficult. If you know what blades you're going to use then you can draw them in just as you do for any tube with your start lines at the marking for the crown-race seat. If you know where the taper in the blades start mark that also. The difficulty part is figuring out what the curve/rake should look like. Personally, I just draw in the rake by hand in the finishing steps of the design. If you have an outline of the curve you want to have you can lay this over the drawing and copy it. This is the easiest way and gives the best idea of what the finished frame will look like.
  4. Just as you did with the TT in step #1 repeat for the DT and then the ST. Remember that the tubing diameters are different in most cases.
  5. Ideally you would have the actual dropouts you're going to use on the frame. At this point you'd want to lay them on top of the drawing and make sure the centerlines of your chain- and seatstays are correct. If they're not, you can easily correct them at this point. You should also outline the front fork dropouts, too, if you have them, though if you don't it's not as critical to the design as it could be in the rear.

    Some people say that you should do this step right when you're ready to draw the chain and seatstay centerlines, but since this is such a simple thing to correct if need be, I don't worry about it until now.
  6. Now that everything is where it should be, it's time to draw in the seat and chainstays. As with the fork blades' treatment, you should mark where the taper begins so you can draw that into your plan. In my case the seatstays start at 12mm and taper down to 10 mm at the dropout. You can see a little mark next to the #6 indicating the start of the taper. Once you've done this step your frame drawing is far enough along that you should be able to give it to a builder to build. Personally I don't think it's anywhere done which leads us to the final step in this process.

Forward to step four of the tutorial!