Starting to Cut....

Now that the rear axle is in the general vicinity of where I want it, it is time to cut off the excess frame members and start laying out the hard tail sections that will be added to the frame to make it a hard tail. First, I am cutting away the "seat frame" section, away from the connection joints. I will then be able to do a more surgical removal of the smaller parts.

 

Removing the upper section.

Then cut of the attachment to the lower section.

 

Along with removing the "seat section" the brackets that held on the foot pegs needed to be removed so that the 1" mechanical tube could fit over the lower seen in the above pic. The small tubes that form the cradle around the engine are 3/4" O.D., which is convenient since a 1" O.D. tube with 1/8" wall has an I.D. very nearly 3/4". I can now create a slip joint that will attach my hard tail section to the lower tubes. Pretty slick :>). Next we will begin to mock up the lower hardtail tube with cheap EMT from Home Depot to make sure we like the look before committing to the more expensive 1" mechanical tubing..

Axle Plates

After establishing where I want the rear axle to be, I need to make some axle plates. These can be purchased from online sources like Low Brow Customs, but I have some 4" x 3/8" flat bar that I will use to make my axle plates with. First, I made a drawing of my design that would fit the flat bar...( I designed this with Alibre design.... it was free at one time)

I printed it out with a scale of 1:1 so I could cut it out for a pattern. I traced the outline on the steel flat bar giving myself some room to machine down the edges if they got too uneven. I cut the plates out with a 4" grinder with cutting wheels I purchased at Home Depot ( the cutting wheels are the handiest things I have found for custom metal fabrication!). After cutting the two axle plated out, I tack welded them together before machining the edges so they would match each other.

Then started the machining process....

As seen above, I am making both edges even before clamping the part flat in the vise to trim up the 90 degree corners. The arc was made by rough machining then using the cutting wheel to finish. The diameter of the wheel was the perfect radius to finish it with. I would take credit for having planned it that way in my original design, but it was actually an accident that worked out in my favor :).
The finished axle plates are now mounted to the axle jig.....

Now that we have axle plates and they are placed correctly in space, it is now time to start cutting and fitting tubes to mock up the hard tail section, but first we need to remove the existing tail section...

Getting Started

So the bike is now torn down to the frame. It once looked kind of like this...

And now looks more like this...

The first order of business is to decide how low the bike should be. This will in turn, determine how much angle and rise the hardtail section will have. Because the it would be a very large job to stretch the neck out to lower the frame rails, I am just shortening the forks to compensate. I will build the hardtail to match the front. As shown above, the rear wheel is in place to get an overall perspective of how much I want to stretch the wheel base. And the magic number is 4", or a total of 53" front axle to back axle.
Next, I want to build a jig to place the rear axle plates in their relative position, see below.

A piece of angle and a 1" square tube will serve as my jig for the rear axle. The plate it is welded to will have a center line scribed down the middle to ensure that a plumb bob and square can be used to align the frame to the jig. We will see how it works.... poor man's frame jig.

Where to start?

Well, this is the start of our chopping and bobbing motorcycle experience. I chose a Honda CL100 because I saw one previously done for the DirtBag Challenge. Then one conveniently came up for sale on craigslist for $300. I promptly forked over said three hundred and did nothing for 6 months. So now we ( my son and I) are starting the chop in earnest(sort of...).