1515 double clamp for Kossel XL

Clamp to strengthen 1515 verticals on Kossel XL

This double clamp is designed to slot into 1515 extrusion, allowing a second vertical 1515 extrusion to be tightly clamped to it. This effectively gives you 15x40 verticals, with very good radial stiffness. An essential point is that you can fix to a 1515 beam without having access to the end of the slot to put a nut in - so you can add the extra verticals without dismantling your printer. I have used 3 clamps per vertical on my Kossel XL. You n