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Old 11-19-2008, 02:47 PM
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Frame Build



The backbone assembly represents the major part of the frame build so far. The next critical joint is the down legs to the steering neck. After the steering neck height is determined the top of the down tubes are rough trimmed to length. By this point, you need a frame jig or at least a platform where the bottom rails can be spaced and anchored. The down tubes need to have a bit of the center section removed so they move inward toward the centerline of the frame. In this case, was removed. This was done by plumbing up one down tube, measuring in at the top and using a square with a built in level to draw a vertical line. The same process is done for the opposite side. Drawing a flat file between the rough-cut tubes can produce a nice tight fit. The cope was rough-cut with a die grinder and carbide double cut bur. As a few trial fits are done with the neck, the cope is further refined until all gaps are eliminated. Note how the tube ends are squared off and not sharp knife-edges. The square edge along with a bit of a chamfer allows for a full thickness weld between the tube and steering neck.




The next picture shows how the down tube to neck joint looks. A little more chamfer needs to be added for weld penetration and the dark coat from the tubing will be sanded off to keep the weld clean. Although it is possible to build a frame without a jig, it makes fabrication of a frame much easier. Here you can see one of the neck centering cones holding the neck in place. If the centering cone rod is replaced with a shorter rod that has been center drilled on one end, a 2 hole saw can be used to cut the down tube cope for the neck.




Here is the connection at the bottom rail to the bottom rear wishbone. This is going to be a spot requiring an exceptional weld. Adding a gusset for reinforcement is also a good idea. On a typical frame build, the tube that acts as a crossbar just forward of the rear fender under the seat tends to pull the axle plates together making it impossible to get the wheel and spacers installed until the width is corrected. This weld will have an opposite effect and tend to widen the axle plates. The jig or a threaded rod keeps the dimension while this weld is done, reducing the problem. Short welds can help reduce shrinkage on various parts of the frame.



Here are the rest of the parts that need to go into the frame for a HD type engine. (Left to right) Steering neck, front engine mount with quarter round shaped gussets and bosses for forward controls, a rear engine mount, front transmission mount, seat post crossbar, 2 pieces to fabricate a rear transmission mount and the axle plates. Fitting an tacking in these parts will take about as long as setting up the basic frame. Cutting these parts out also takes considerable time since they are cut from to thick plate depending on the part.



The placement of the remaining parts is done after the frame is completely welded. Obviously some sort of plans will be required to ensure part fitment. Skip sections of weld in stragic locations to minimize distortion by playing welds against each other until all are completed. Install driveline mounts last. It is always best to use some sort of rigid fixture to maintain mount alignment. There will also be a number of other miscellanous parts to add to the frame like kickstand, light, tank, fender and electrics mounts.

Building frames is a path to total control of a project. It is not a path to a cheap motorcycle. Although anyone can learn the skills of metal working and welding, these are skills to bring to the project and not things to learn with the project. Your safety and the safety of anyone within sight of your creation rely on your skill and knowledge. There are a number of fabrication shops that cater to the bike building public at the fabrication level. You can purchase the parts you can't make. You can outsource the operations you can't handle. Some things can be learned on the way.

There is little that has the satisfaction or personality of a project to which you collectively applied your own skill and knowledge.

Steve Spencer
www.mechwerks.com

 

 

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Old 03-09-2009, 05:24 AM
Club Chopper Member
great article i hope to be able to use it some day thank you
 
 

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