Thompson Choppers, located in Nixa Missouri, builds frames for rigid, softail or swingarm style bikes, along with the components to go with them including Springer forks, Gas tanks, oil tanks and fenders. All our frames are built to order based on the customer's specs and riding style.
So this gives our customers a lot of options for the finished bike and how they want to ride, which is the first question we ask when we start a new project. Are you looking for a bar hopper, do you want a chopper, or are you planning on doing 500 miles a day on the bike? All of these riding styles make a difference in how we build the frame and set-up the geometry and trail for the finished bike. As follows is a step-by-step overview of what goes into building a bobber frame for one of our customers.
STEP #1 - Material Selection
All of the frames and components that are built at Thompson Choppers use high quality materials including thick wall DOM tubing and cold-rolled steel flat stock. The DOM (Drawn Over Mandrel) tubing is drawn through a die and over a mandrel to create dimensional accuracy and to improve surface finish. Different tubing sizes are used based on which part of the frame it will be fitted to.
STEP #2 - Material Cutting
All material is cut to length based on the type of frame being built. We keep a master cut list for the lengths of tubing and flat stock needed for each part of the frame. Each piece of material cut has extra length added to allow for exact fitment and coping during the build process.
STEP #3 - Frame Table & Fixture Set-Up
After all materials have been cut, our frame jigs and fixtures are set-up based on the customer order. Our frame building tables are designed to hold parts and tubing during the build process. The table as well as the fixtures are leveled and trued to produce a straight frame.All fixtures are checked for squareness before the build starts, as well as multiple times during the welding process.
STEP #4 - Parts Fixturing
It is critical that all the parts that go into the frame be anchored and bolted to the table and fixtures during the welding process. This ensures that no parts move or torque from the heat of the welding. The frame neck is set-up on the table based on the customers order and desired dimensions. The rake angle of the steering neck is set and all motor mounts and components are bolted to the frame table.
STEP #5 - Wheel Hoop Fabrication
Wheel hoops are the 2 pieces of tubing that wrap around the rear wheel and hold the axle blocks in place. Our wheel hoops are bolted into a jig based on the rear wheel size. We have different size jigs based on the rear wheel size, which range from a stock width wheel all the way up to a 360mm wheel. The axle blocks are trued and squared in the jig and the hoops are clamped into place for welding.
STEP #6 - CNC Machining and Cutting
Most of our frame parts and components are CNC machined in-house, which enables us to machine an accurate part time after time. All of our parts are designed in a CAD program, and the programming code to machine the parts are stored on the computer. Those part files can then be loaded on to our CNC mill or CNC Plasma cutter depending on which part is needed during the frame build.
STEP #7 - Tube Bending & Forming
All of the DOM tubing used on our frames are bent on a hydraulic bending machine. Our tubing bender allows us to do accurate and repeatable bends time after time. Several of the bends that go into the frame are common to our brand of frame, while other bends are specific to the customers order and stretch of the frame being built.
STEP #8 - Tube Coping & Milling
Once all the tubing that goes into the frame has been bent, it is then notched and coped to fit together. Joining tubing members together is referred to as a cope, or sometimes a "fish mouth joint". The tighter we can make these tubing copes fit together, the stronger the final frame joint will be. Depending on which of the frame parts we need to cope, we use several different methods. One of which is a dedicated tubing notcher that uses bi-metal hole saws of different sizes. Another common method is to use our manual milling machine to create copes, which works best for compound angles.
STEP #9 - Chamfering & Weld Prep
After all the tubing has been cut, bent, and coped, a chamfer is beveled on the edge of the surfaces to be welded together. The edges are typically chamfered at a 45 degree angle. This allows for deeper and better weld penetration.
STEP #10 - Downtube and Backbone Fitting
This is the step in the project where this project starts looking like a real motorcycle frame. All of our frames are built from the neck back.
Here we are fitting the downtube to the steering neck and tack welding it in place for one of our Hitman Bobber frames, which is an old school goose neck style set up. All parts and tubing are tack welded together before any final welding is done. This also helps in keeping the frame true and square.
STEP #11 - Bottom Frame Rail Fitting
As we work backwards from the steering neck during the fabrication process, the next step is to fit the bottom frame rails. The frame rails tie together the downtube to the rear wheel hoops and is also the structure that supports all the motor mounts for the engine and transmission.
STEP #12 - Refining Tubing Copes
As we go through the process of fitting the frame tubing together, some fittings and notches are refined by hand. This is especially true when the joint has extreme compound angles.
STEP #13 - Adding The Seat
After the backbone is tack welded in place and clamped to the frame table, it's time to fit the seat rails. The seat rails tie the backbone to the wheel hoop on the top of the frame. Our seat rails can be custom fitted to the customer based on their preference on the seat height off the ground. All of our frames are offered in a drop seat or straight seat configuration.
STEP #14 - Final Welding
During the last stage of the process, and after all the tubing and components have been tack welded together, it's time for the final welding. All of our frames are TIG (Tungsten Inert Gas) welded together, which uses a shielding gas around the weld area to keep oxygen out of the weld. The TIG welding process is the only process we use on our frames and allows for a stronger weld. As the welding progresses, a filler material or rod is added at the welding arc to fill in the joint.
STEP #15 - TIG Weld Examples
As shown are some close up shots of the final TIG welds with filler material added.
STEP #16 - Completed Frame
After all fitting and final welding is finished, the frame is left bolted to the frame table and fixtures overnight. This allows all the welds to cool slowly and is critical to keep the frame straight and true once it is removed from the table. As shown, is one of our Hitman Goose Neck Bobber frames, which is going to one of our customers, Kyle Service. Kyle is currently serving in Afghanistan, and we're sure he'll have a smile on his face when he returns home to his new project.
So this gives our customers a lot of options for the finished bike and how they want to ride, which is the first question we ask when we start a new project. Are you looking for a bar hopper, do you want a chopper, or are you planning on doing 500 miles a day on the bike? All of these riding styles make a difference in how we build the frame and set-up the geometry and trail for the finished bike. As follows is a step-by-step overview of what goes into building a bobber frame for one of our customers.
STEP #1 - Material Selection
All of the frames and components that are built at Thompson Choppers use high quality materials including thick wall DOM tubing and cold-rolled steel flat stock. The DOM (Drawn Over Mandrel) tubing is drawn through a die and over a mandrel to create dimensional accuracy and to improve surface finish. Different tubing sizes are used based on which part of the frame it will be fitted to.
STEP #2 - Material Cutting
All material is cut to length based on the type of frame being built. We keep a master cut list for the lengths of tubing and flat stock needed for each part of the frame. Each piece of material cut has extra length added to allow for exact fitment and coping during the build process.
STEP #3 - Frame Table & Fixture Set-Up
After all materials have been cut, our frame jigs and fixtures are set-up based on the customer order. Our frame building tables are designed to hold parts and tubing during the build process. The table as well as the fixtures are leveled and trued to produce a straight frame.All fixtures are checked for squareness before the build starts, as well as multiple times during the welding process.
STEP #4 - Parts Fixturing
It is critical that all the parts that go into the frame be anchored and bolted to the table and fixtures during the welding process. This ensures that no parts move or torque from the heat of the welding. The frame neck is set-up on the table based on the customers order and desired dimensions. The rake angle of the steering neck is set and all motor mounts and components are bolted to the frame table.
STEP #5 - Wheel Hoop Fabrication
Wheel hoops are the 2 pieces of tubing that wrap around the rear wheel and hold the axle blocks in place. Our wheel hoops are bolted into a jig based on the rear wheel size. We have different size jigs based on the rear wheel size, which range from a stock width wheel all the way up to a 360mm wheel. The axle blocks are trued and squared in the jig and the hoops are clamped into place for welding.
STEP #6 - CNC Machining and Cutting
Most of our frame parts and components are CNC machined in-house, which enables us to machine an accurate part time after time. All of our parts are designed in a CAD program, and the programming code to machine the parts are stored on the computer. Those part files can then be loaded on to our CNC mill or CNC Plasma cutter depending on which part is needed during the frame build.
STEP #7 - Tube Bending & Forming
All of the DOM tubing used on our frames are bent on a hydraulic bending machine. Our tubing bender allows us to do accurate and repeatable bends time after time. Several of the bends that go into the frame are common to our brand of frame, while other bends are specific to the customers order and stretch of the frame being built.
STEP #8 - Tube Coping & Milling
Once all the tubing that goes into the frame has been bent, it is then notched and coped to fit together. Joining tubing members together is referred to as a cope, or sometimes a "fish mouth joint". The tighter we can make these tubing copes fit together, the stronger the final frame joint will be. Depending on which of the frame parts we need to cope, we use several different methods. One of which is a dedicated tubing notcher that uses bi-metal hole saws of different sizes. Another common method is to use our manual milling machine to create copes, which works best for compound angles.
STEP #9 - Chamfering & Weld Prep
After all the tubing has been cut, bent, and coped, a chamfer is beveled on the edge of the surfaces to be welded together. The edges are typically chamfered at a 45 degree angle. This allows for deeper and better weld penetration.
STEP #10 - Downtube and Backbone Fitting
This is the step in the project where this project starts looking like a real motorcycle frame. All of our frames are built from the neck back.
Here we are fitting the downtube to the steering neck and tack welding it in place for one of our Hitman Bobber frames, which is an old school goose neck style set up. All parts and tubing are tack welded together before any final welding is done. This also helps in keeping the frame true and square.
STEP #11 - Bottom Frame Rail Fitting
As we work backwards from the steering neck during the fabrication process, the next step is to fit the bottom frame rails. The frame rails tie together the downtube to the rear wheel hoops and is also the structure that supports all the motor mounts for the engine and transmission.
STEP #12 - Refining Tubing Copes
As we go through the process of fitting the frame tubing together, some fittings and notches are refined by hand. This is especially true when the joint has extreme compound angles.
STEP #13 - Adding The Seat
After the backbone is tack welded in place and clamped to the frame table, it's time to fit the seat rails. The seat rails tie the backbone to the wheel hoop on the top of the frame. Our seat rails can be custom fitted to the customer based on their preference on the seat height off the ground. All of our frames are offered in a drop seat or straight seat configuration.
STEP #14 - Final Welding
During the last stage of the process, and after all the tubing and components have been tack welded together, it's time for the final welding. All of our frames are TIG (Tungsten Inert Gas) welded together, which uses a shielding gas around the weld area to keep oxygen out of the weld. The TIG welding process is the only process we use on our frames and allows for a stronger weld. As the welding progresses, a filler material or rod is added at the welding arc to fill in the joint.
STEP #15 - TIG Weld Examples
As shown are some close up shots of the final TIG welds with filler material added.
STEP #16 - Completed Frame
After all fitting and final welding is finished, the frame is left bolted to the frame table and fixtures overnight. This allows all the welds to cool slowly and is critical to keep the frame straight and true once it is removed from the table. As shown, is one of our Hitman Goose Neck Bobber frames, which is going to one of our customers, Kyle Service. Kyle is currently serving in Afghanistan, and we're sure he'll have a smile on his face when he returns home to his new project.
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