Build A Motorcycle Frame!
Types Of Frames:
When you get into the discussion of motorcycle frames and what to build for your next bike building project you first need to decide what kind of motorcycle you want to build.
Whether you want to build a sport bike frame or a chopper frame, neither one is easy to accomplish for the home builder or even small motorcycle shop, but it is a rewarding experience. How many people do you know that have actually built a chopper frame from scratch? Even the 'famous' bike builders don't do it anymore. They just outsource it...
However, building a chopper frame is the easier route because there are many frame blueprints and designs available, and the design is easier to accomplish for a home or small motorcycle. The reason is because a sport bike frame is generally a lighter frame because it needs to be fast and nimble. As a result you'll be working with titanium, or aluminum, or even carbon-fibre or magnesium and the designs are not easy to put together and weld.
Conversely a chopper or bobber style frame is going to be made of steel because a heavier frame is not only needed to support the engine and stress loads, but a chopper is also a 'cruiser' which does not need to be light and nimble.
So the type of frame we are going to discuss here for a home or small motorcycle shop to build or design is going to be a chopper or bobber style frame because they are easier to build. But more fun and rewarding in my opinion.
So now that we narrowed down our frame building project to a chopper or bobber style frame lets discuss the frame types.
Rigid or Softail:
Basically it comes down to two types of frames: rigid or softail.
A rigid frame is exactly as it sounds; rigid. There is no suspension. It's a rigid or stiff ride other than having a springer seat and springer, hydraulic, or girder forks. The rigid frame is often considered by bikers to be for the 'tough' guy. But let me tell you, there's a ton of softail style frames because many bikers have bad backs, and a long ride on a rigid can be very hard on the body.
A softail frame is a frame that has a suspension system consisting of shock absorbers or springs so as to make the ride smoother. The main idea behind the softail is to not only give the bike a smoother, softer ride but to keep it hidden making it appear to be a rigid style bike.
The picture here is a softail design. The frame above that is a rigid chopper frame design.
Now that we have covered the basics of rigid and softail frames, it's time to decide what you want to build. Building a rigid frame is a bit easier only because there's less work involved. But don't let that stop you because a good softail is something you should consider.
A very important matter when it comes to building a chopper chassis is rake and stretch. A chopper is stretched and raked in comparison to regular cruisers or street bikes. In other words they are lengthened and the forks are raked forward giving the bike a more 'bad a**' look.
For a detailed description of rake and stretch read this article:
Conversely, a bobber motorcycle is considered a chopper as well but the forks are not raked very much, and the frames are not usually stretched. They are simply stripped down bikes and the fenders are removed and 'bobbed'.
Main Tools You'll Need:
Building a chopper frame requires tools, a little skill, and a lot of patience. But once you get the frame built right putting the bike together becomes easier. The main tools and bits you'll need are:
- Frame Jig
Frame Building Tips and Recommendations:
The size of tubing can vary from 1.25 to 1.5 inches in diameter, and use DOM or ERW tubing. Do not use pipe.
A frame jig is needed so that you can clamp the tubing into place for mock up and welding. Trying to build a frame without a jig is very difficult but it can be done.
A jig can be as medieval as a wooden formulation, or you can get or build a nice heavy duty jig that you can use over and over or sell it once you are done with it. They are very valuable to lots of bike builders, especially if you can show them the killer frame you made with it.
You can weld a frame using a MIG welder but by far a TIG welder is the best welding process to use on a chopper frame because you have more control of the weld. Using a MIG welder is manageable but it can be more difficult and the welds may not come out nearly as clean and potentially with less penetration which is not a good thing.
You'll also need a set of plans. You can hire someone to design a frame for you based upon you sketch which can be fun, or of course, design it yourself using CAD or Solidworks. Or, the easiest and cheapest way is to buy your own set of plans.
Putting your frame together can be a piece of cake with a good jig. But there are some pitfalls to avoid, and some time saving tips. I recommend you get this free frame building course (it's on the right hand side, or scroll to the very bottom of the page).
The only area you may have a little trouble with is where to place the mounts on each of your frames. However, this can be solved simply by using your math skills and lining the engine up.
The biggest problem you can experience, and a costly one is building a bent frame....
A Straight Frame:
Building a straight motorcycle frame is critical for the performance and safety of any custom chopper or motorcycle. The frame must be created in a perfectly straight line so that the tires will be in alignment when rolling down the road.
In order to build a straight motorcycle frame, you must begin with straight frame tubing. If the tubing is bent, you may not be able to bend it back to perfect straightness. It's better to start off with the best materials for the optimal end result.
How To Check:
To check whether tubing is straight, lay a piece of tubing on a flat piece of plywood or lumber. Using a carpenter's pencil, mark where the tubing touches the wood at the bottom of each end. Remove the tubing and measure the distance from the edge of the wood to each mark.
The distance should be perfectly equal. If it is not the same, your tubing is not straight. While tubing can be straightened, it is not really a task for a home frame builder.
You will need a welding jig to hold the pieces of frame tubing in position while welding joints. This welding fixture prevents the pieces from moving and helps ensure that each weld works toward building a straight frame.
A jig is basically any device used to hold material during welding. See the image above for a picture of a professional jig. However, a jig can be as simple as a C-clamp or a fixture you make from wood or metal. You may need more than one jig design for welding a straight frame since joining the neck is much different than joining to pieces of metal at 90 degree angles.
Welding Your Frame:
When welding frame tubing, be careful about applying too much heat. Use only the heat required to create a good bead. Too much heat can warp lightweight frame tubing and result in a frame that is not perfectly straight.
As you weld your frame tubing together, stop frequently and check the straightness of the partially completed frame. Repeatedly use a long t-square to extend from a point on the frame to the ground or jig and make a mark. Check that each mark is the same distance from a known-straight fixed point. If you find a weld throws the frame out of line, re-work the joint before continuing or you'll end up spending a lot of extra time later repairing the problem.
Continue to check alignment as you add pieces of frame tubing to your design. Even after completing the frame, check carefully yet again that the frame is aligned properly.
A Good Plan and Your Frame:
Building a straight motorcycle frame is not difficult if you begin with a good plan, use the proper tools and continually check accuracy and straightness.
A less-than-straight frame will rattle, shake, wear tires and parts unevenly, and cause nothing but problems, so start your custom motorcycle project with a straight frame to ensure you'll end up with a bike you'll truly enjoy and be proud of.