Because each and every bike is designed and made for an individual, each one is different. Even small changes in the geometry of the frame can result in significant changes in performance, so each cut has to be spot on to the calculated geometry. Also, because the geometry, tube diameters and tube shapes vary from bicycle to bicycle, the jigs used to cut the tubes must be adjustable and accommodating, There are some jigs available out there for purchase, but in the spirit of Firefly, we wanted to make as many of them as we could…
Based on the thousands of front triangles that Jamie has made over the years he had a good idea as to the the kind of front triangle tube cutting jig we need. He has also pushed the limits of the tooling he has used in the past giving him the knowledge needed to create tooling that will cater to the needs of Firefly in the future.
The main tube blocks were designed with flexibility in mind and were precision machined on the same machine that will cut the tubes.
Pictured above is the jig, mounted to the precision rotary table which is mounted to the bed of the Bridgeport milling machine. We used a right angle attachment on our machine so that we could cut the tubes horizontally, instead of the usual way this machine cuts, which is vertically.
The blocks supported the test tube securely and the first cut came out perfect. With our new jig all we need to do is set the calculated angle and length and cut the tube once. No filing needed, first cut = only cut.
The double miter pictured above is where the seat tube matches up with the down tube. This makes for an efficient and sturdy weld joint around the bottom bracket, this is also one of the hardest miters to get right with just one cut. Your math and tooling have to be spot on and calibrated perfectly in order for this to happen this easily.
On the back end of the jig extends a long arm, this arm supports a sliding stop that ensure accurate and consistent cuts for the different tubes. For example, when you cut a top tube/head tube joint you need to register the cut at the other end so that it is parallel to the first cut you made. Pictured above are the various fixtures that get mounted to the arm to register each cut.
Jamie made each one to match up to the specific diameters of the tubes we are using.
There is also a flat device (attached to the arm above) used for registering the top of the seat tube relative to the desired length.
For all of the test cuts the jig was mounted to the machine all by itself.
But now it is sharing the Bridgeport’s bed with the chain stay mitering jig, (pictured above on the right).
Stay tuned for chain stays :: slotting and mitering jigs.