As promised, I thought I'd throw up a few detail pics and share some about each of the new fixture.
This fixture has been in the conceptual phase for many many years, and has been actively developing over the last year and half. The brain child of Bill Grove, I've been fortunate to have some input into it's development, while he's done all the hard work :)
The goals of the fixture were to provide full access to all joints for easy welding/joining, to have a precision set up system that allowed for accurate repeatability, simple smooth movement and articulation, rigid design to prevent flexion, maximum flexibility in desired sizing/specs, and it had to look cool ;)
While certainly not the complete laundry list of desired features, these listed filled many of the gaps that we've experienced with our previous fixtures, my design now going on 15 years old.
So let's take a quick tour...
You can see from the basic layout of the fixture that it allows for independant movement/adjustment of each of the critical dimensions. The fixture is set around the fixed bottom bracket point, with independant movement for the chainstay length, axel heights, fork offset, seat tube angle, head tube height and angle, and top tube length. The entire fixture shares the same bolt head sizing, allowing a 1/4" ball end T wrench to adjust each element. Rolling on a tripod stand with the ability to utilize adjustable fixed feet, the fixture is counter balanced and is able to rotate 360 degrees freely in the vertical position, 360 degrees in the horizontal direction (180 each way, fore and aft), and then 360 degrees swivel on the base with the most minimal effort.
From the side shot, you can see the counter weight arm that pivots around the main beam...
The base rotates on leather washers with adjustable tension and has two quick clip sprung knobs that can lock the fixture in place if desired...
The bottom bracket uses a unique adjustable post, allowing for bottom bracket shells from 68 to 80+ to fit on the centerline of the fixture...simply loosen the collar and rotate to change the dimension. The fixture plate is designed to allow for maximum accessibility for fitting and joining. An adjustable tool can affix to the plate to allow for symetrical positioning of the chainstays on the bb, equal centerline spacing of the wheel/tire position, and centering of the seat tube over the bottom bracket.
An acid etched plate will be secured to the main beam to show the dimensional measurements to achieve the desired geometry...
The entire fixture is purge ready, though I've not yet run the iridium blue tubing, and has two quarter turn valves to control the flow circuits.
Two frames down and I've made a list of small changes I'd like to make, most not necessary but fall into the "would be nice category". As this is the prototype, I'm sure there will be a number of revisions before we achieve the final version.
Anyhoo, I feel very fortunate to have the opportunity to work with the development of this piece, as I feel it will increase the efficiency and precision of frame fabrication. You rock Big Willy!