Steffen Joergensen asked this chopper frame tubing question. Since it's a good question that many builders might be pondering regarding our bobber frame plans and motorcycle frame tubing, here are his answers. Thanks for asking Steffen...
Side Bar: Answers are below but many questions and answers on chopper frame tubing and bike building are here as Well.
Motorcycle Frame Tubing Answer 1:
Thanks for purchasing the bobber frame plans. The tubes are structural carbon steel tubes. You can obtain standard structural steel tubes from various suppliers. The carbon content should be between 0.15% to 0.3%. This is classified as mild carbon steel.
It's very common and is relatively low priced steel.
Chopper Frame Tubing Answer 1 Continued:
If you prefer something a little harder then you can also use medium carbon steel which has 0.30% - 0.60% carbon content. This has additional strength, ductility and good durability. This is usually what is used for automotive components. Getting above this content from 0.6% - 2.0% is classified as high carbon steel or ultra high carbon steel. These are extremely hard steels and may be a bit more difficult to work with. These are usually reserved for special purposes such as knives, punches, springs, etc.
Your frame should be fine if you use something between 0.30% to 0.60% carbon content.
Motorcycle Frame Tubing Answer 2:
The axle plates are welded directly to the down rails. The plate is not milled. The tube itself was milled so that it has a flat area that fits up against the axle plate. Take a look at the photos below. The axle plate is symmetric and the tubes were cut into so that they fit up correctly against the axle plate and then welded. Please let me know if you have any additional questions or concerns.
Question 2: From Steve: Is 1 1/4 inch tube the standard size for most chopper frames? Or are there other sizes?
Answer To Chopper Frame Tubing Question 2:
Motorcycle and Chopper frame tubing sizes are dependent on the style and aesthetic taste of the builder. Some prefer really small tubes so that the focus is on the components such as the engine, wheels, handle bars and fuel tank. Others prefer to have solid heavy lines showing the frame and even painting the frame so that it is very visible.
Frame tubes vary from as small as 1" all the way up to 1.5". Some of the frame drawings we sell use 1.5" tubes. The most important factor is that strength should be maintained. A smaller tube generally uses a thicker tube wall for added strength. A larger tube requires less wall thickness for the same strength. This helps to optimize weight of the frame. Another important factor is the type of tube as well. We always recommend using DOM tubing. Feel free to let us know with any additional questions or concerns.