While impressed by the fantastic quality of this pack, I have always wondered why the internal support is so flimsy. Compared to the harness, the pack can’t really carry lots of weight comfortably.
The commercial Endo-frame supports the main compartment just fine, but it doesn’t really add anything to the overall rigidity.
So, I got my hands on some cheap round aluminum bar. It’s quite soft, just to make prototyping easier. Diameter is 8mm and if you go by this rough example, two meters of it will be plenty.
First, you want to bend the right angles to top corners. Except they are not actually 90 degrees, because I wanted to have the upper arc slightly convex for additional rigidity. So about two inches from the corners, there are smaller bends to create that convex shape.
Then you need to bend a smooth curve starting at the level of your shoulderblades. The ends should meet just below the hip belt.
This is roughly where you finally decide the height of the frame. I was shooting for about 10cm longer than the pack, and bent the free ends so that the bendy will tuck inside the hip support, ends pointing straight down. The hip belt is kept in by a patch of velcro, and the frame will sit right by the patch on both sides, under the hip support.
Now you REALLY get to decide the frame height, as you need to make a 90 degree bend so that the frame rests against the bottom of the hip support, below the hip belt.
Another angle of the final bends. As you can see, the ends don’t really line up. Should have been more mindful when doing the bends as I went, but this can be fixed later on.
I’m quite pleased with the overall shape, since this is my first try on this sort of thing.
I made some webbing for securing the pack to the frame. This was not the first idea I had, but seemed like a simple solution while not putting too much strain onto the load lifters.
I first planned to use the original load lifter tension locks for attaching the pack and adding extra locks to the frame for load lifter straps.
This may still happen, as it looks like the prototype aluminum is too soft to carry substancial loads without buckling.
The vertical shape needs to be bent according to the owner’s back articulation. I’m not too sure if the frame will hold with this much curvature, but I’m planning to use sturdier material for the final thing.