Bending the Lower Keel Tube

After a long summer break, the E-Hawk Team is back at it again.  Today we manufactured the lower keel tube from a length of 6061 T6 aluminum tubing (1.0″ OD x .058″ WT).  This part requires two bends with a 9″ radius.  We do have a hydraulic pipe bender however we don’t have a die that will make the 9″ radius bend.  Instead we decided to design specific tooling that would allow us to make the correct radius bends.  For that we used Onshape to create a bending die comprised of two halves of 3/4″ plywood cut on the CNC router (Shopbot).  The two halves were then glued and screwed together and mounted to a larger piece of plywood.  The assembled jig was then clamped to a sturdy table.  The straight length of tube was measured and marked with the bending parameters and then filled with sand (actually waterjet abrasive) to prevent it from collapsing during the bending process.  It was then placed in the jig and clamped down on one end of the fixture with an aluminum strap.  The team then proceeded to manually bend the tube around the die up to the correct angle.  Following the first successful bend the tube was readjusted within the fixture and the process repeated for the second bend.

Lower Keel test fit.
Bend specification drawing.
CAD of the bending die to be routed from two layers of 3/4" plywood.
Cutting the tube bending die halves on the CNC router.
Assembled tooling fastened to a work table.
Closeup of the die wall showing the radius to match the 1" OD tubing.
The bend in progress.
Verifying the angle of the bend.
Emptying the sand after a successful bend.
Triming the end of the lower keel.
Installing the keel by clamping in place prior to drilling.
Pilot fit check.

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