Coming up are a number of tasks that need sheet aluminium bent accurately - the fuel tank, the cockpit floor, the door panels. In order to do this I needed a bending brake and as the starting price for a 36" brake seems to be around £450 it seemed prudent to make one. A bending brake has three parts: the apron, the clamp, and the table.The sheet of metal is placed on the table, and the clamp is tightened to hold the sheet in place. The apron is then lifted to bend the metal. The starting point was the plans available on the
Miller welding machines website http://www.millerwelds.com/interests/projects/bending-brake/But I needed something longer and stronger so the materials were significantly scaled up. The apron and the table are made from 40" lengths of mild steel angle iron 120mm x 75mm x 10mm. The clamp is made from a length of mild steel angle iron 80mm x 80mm x 10mm. The hinges were cut out from 1/2" thick steel plate and the hinge pins were cut from a length of 3/4" steel rod, 3/4" *0.058" tubing provides the sockets for
the handles which are 5/8" steel rod - it's heavy!! The difficult bit was cutting and shaping the hinges from the 1/2" steel plate. The bandsaw was used to do the cutting but the feed rate had to be incredibly slow. The holes were drilled using a 18.5mm drill which was also slow and generated untold amounts of messy swarf mixed with cutting oil. They were then reamed out to 3/4" - a tight fit in the outer part of the hinge and a turning fit in the inner.The outer part of the hinges which attach to the table were final welded together as per the Miller approach. The hinge pins were pushed into place using the vice and assembled with the inner part of the hinge which attaches to the apron. A section of the edge of the table around the hinge pivot was ground down slightly (about 1/50") to provide clearance and the apron itself reduced in length by about 1/100" to allow the two halves of the hinges to turn without binding. Then the table and apron were then clamped together in alignment and the hinges positioned and tack welded. Then it was a case of final welding the hinges into position. This is the first time I've had to turn the welding machine up but 150amps worked well getting good penetration into the thick metal.
I decided to use the angle iron for the clamp sitting on it's open edges so the bottom of the two sides were ground flat to provide a good contact area with the material to be bent. The edges of the clamp were then shaped to provide two different bending radius. Sections of box steel sawn in half were then welded to the top and into the ends to provide horizontal clamping positions. Finally, some scrap angle iron was welded to the bottom of the table to space it off the bench and provide space for the G clamps used to fasten the clamp onto the table and the tubing used to make sockets for the handles welded into place.
As a test, a 12" length of 0.071" steel was bent to make a blank for one of the spar attach brackets - works well, if it can handle 0.071" steel then 0.050" aluminium should be OK.
