Probably laser cut sheets of 15mm-20mm tick steel then assemble with welding. Jig needs to withstand banding of frame because heat stress in metal while welding.
I think I’d approach that differently. If you’re welding steel, the jig need not be 15-20mm thick. In fact, rigidly restricting the steel forces too much stress while cooling. As soon as you release the jig, the steel will expand and likely crack. Welding up a frame is ALL about heat control and distortion. The metal MUST move, and knowing how much it will move as you weld it, is the hard part.
Now aluminum is a bit different (Egli) if that’s what’s used. Aluminum will move a great deal in any direction against its restricted force. Then as it cools, it will shrink and that’s when the welds crack. You can’t restrain aluminum in a jig too tightly while cooling, else you will have a taco with weld cracks everywhere.
There are ample plans for quality jigs available, and even professional jigs that are easily copied with inexpensive steel. The trickiest part is to get the engine hoops bent equally and symmetrically side-to-side. Placement of the mounting lugs and brackets comes with other fixture plates, where a CNC machined fixture would be handy.
All-in, probably $500 for steel and ally for fixtures and jig. Steel tubing for a 750 frame, here in the States, 4130 x0.063 would run about $125 for raw tubes. Figure another $50 for brackets and bungs. Bending and notching and welding, $1500 per frame. So for someone here, $2,000 gets you a professionally built frame of highest quality material.
Mirko, if you have the geometry for the stock/custom frame, it’s easy to have numerous frame components CNC bent and shipped back to EU. Deal with VIN and Neck issues locally, but send unassembled parts back is super easy. And much cheaper.
Just some friendly input.
