Monday, August 30, 2010

Next Step

It's time to move onto the next step with this carbon frame (feel free to click pictures to enlarge).

First I bonded the threaded Ti shell into the CF BB sleeve.  To keep epoxy off the threads, I coated them with heave anti-seize grease.  Then I cleaned the outside of the shell with acetone.  After applying epoxy to the sleeve and the shell, the two get pressed together, sliding the non-drive side of the shell into the drive side of the sleeve.  When the drive side of the shell is even with the drive side of the sleeve, we're good.  Then I wipe off the excess epoxy from either end, and clean off the outside of the sleeve with a paper towel and acetone.  Once this has set up, I trim the non-drive side of the sleeve, and sand it down even with the non-drive side of the shell.  The last step is to clean the grease out of the threads and try fitting a BB - like this:

You can see that I've clearly marked the drive-side, so that I don't mount it backwards into the frame.  Don't laugh, it's easy to do.

From here, I work from the Bible for this frame, which is the printouts from BikeCad for the design.  This includes a picture with the measurements that are key for me to setup (and double check) the jig, and pages of details ranging from measurements to colors.  It looks something like this:

Next it's time to start setting up the jig.  The BB drop is the same as the last frame I did, but I double check this to make sure.  Then I make sure that the BB is the correct width:

Looking good, so I center it on the jig:

215mm is the center-line on my jig, indicating that everything is fine.

The next step is checking to make sure that the jig is level so that tube angles can be set accurately:

The seat-tube comes first:
This will be fine tuned with a machinists protractor - in this case at 73 degrees.  

Then the head-tube gets set - which is a little fussier on this jig - so I go right to the protractor.

Part of the fussiness here is that we have to simultaneously set the angle and top-tube length. And changing one changes the other.  Getting the head-tube right is the hardest part - because it's height above the BB must also be set, but that's a separate operation.

Here's an example of the fit between the seat-tube and BB.
And here's the same joint with the down-tube in place:
That's all for tonight - hope you're enjoying the pix.

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