a few fixture details...

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...

The main fixture is made from K100 cast tool grade AL, annodized black.  Basically the same product as Mic 6, just made by a different manufacturer.  It is water jet cut to the required dimensions then gets some CNC time to chamfer the edges, place critical slots and holes, and make it dead sexy. 

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.

The head tube uses a machined puck for the bottom locator and a tapered cone at the top, all headtube sizes are available from 1.0 up to the new 44 headtube. The bolt that holds in the bottom puck utilizes an inset c-clip, so that once it is loose, it will not drop out and roll under the bench. This allows the puck to slide freely out with the frame for easy removal once the frame is joined. The top of the head tube cone has a tension adjuster, so that you can gently set the head tube plate/cone into place, then snug it up with the tension adjuster to prevent any cocking stress on the fixture during securing.

You'll notice there are no scales or other visual indicators to set up the fixture, this is because all the necessary adjustments are made with a digital caliper.  Each of the key elements utilize eccentric securing point and a machined post to hold the calipers.  Movements are driven by the 1/4" wrench on a lead screw to provide precise set up that has not been achievable before. All the major components roll on sealed bearings, providing ultra smooth, friction free movement.

With the caliper system setting the dimensions, there is no more sight guessing off of a scale or hoping to get it close enough to survive the critisism of the most anal customer.  The real magic of this precision system is that you have exact repeatability even years later, or you can cut multiple sets of tubes to the desired settings, come back weeks or months later, reset to the exact dimensions, and have all your miters be just as tight for welding.  Sweet.

On the rear tower, you can see the lead screw inside the fixture plate. The rear axel tower is designed to easily swap out axels for differing widths by a simple twist of the wrench and sliding the spring pressured top cap back.  Fast and smooth, especially when taking out a completed frame.

a peek inside the rear plate shows the ball bearing rollers that sit in a machined pathway to guide the movement...so smooth.

An acid etched plate will be secured to the main beam to show the dimensional measurements to achieve the desired geometry...

I've working with a vinyl sticker right now.

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!

cheers,

rody