Over-engineering a hinge for a boom arm

 Everyone who uses power tools to sand wood and uses some form of hose attachment  for dust collection, knows what a pain it is dragging the hose and cable across the bench. It often catches and pulls off the tool or gets twisted up. Far better to have the power and use dropping from above.

There are lots of ways to do this. My solution was to build a boom arm that swings out across the work space. I thought this would be the easiest and neatest solution, but I didn't figure with the issues I'd face with the hinge system that allows the arm to swing. The weight of the arm and hose produces quite a force on the hinge, pulling it down and away. 

I tired an ordinary butt hinge and a gate hinge, but neither worked well. I then made my own from threaded rod and 18mm ply, but that too wasn't able to support the arm as well as I wanted.

So I went for this:

This is it clamped together for a test fit. It's made from 18mm ply and rotates on a 20mm Aluminium tube shaft. The boom arm (made from 12mm and 6mm MDF in the arm of an I-beam) fits into a couple of slots.

The hope is that the central shaft and the shape of the hinge will offer better support.

I made a wall plate from more 18mm ply along with with a base and top plate for the shaft.

I bolted the whole thing together with M6 bolts. 

In order to make sure everything lined up, I used double-sided tape to assemble the hinge block with a piece of scrap where the boom would be fixed in place. I then counter-bored a 10mm hole in one side before drilling all the way through with a 7mm bit.

The 10mm hole is just the right side to allow the head of an M6 bolt to be driven in and head tight without splitting the ply. It's neater if you line the head uo with the grain, but it doesn't seem to make a big difference.

Once all the holes were drilled I separated the parts and then reassembled it with the boom arm in place and carefully drilled through the arm.

You'll see in the pictures that there are grooves. These are to take top the shape of the beam. To make it easy I added shims to the inner part of the beam so that everything clamped together nice an tightly.

The wall plate and other part of the hinge was again made from 18mm ply. This is all scrap wood I had around the place by the way.

20mm holes bored out using a spade bit and than all screws together with the bottom section glued in place but the top only screwed in to make dismantling a little easier if I every need to do that.

And there it is. It seems to work okay, although I might need to shim the wall plate because the wall in a little uneven. The hose and power cable is simply cable-tied to the arm and I can make connections as I need them. It works really well for both routing and sanding, so I'm pleased with the eventual outcome.

The new thing I didn't take into account is that the roof slopes from to back which means that long ladder you can see is lower at the from of the photo than at the back. The arm just clears the front, but had I set it 5-10mm higher wouldn't have cleared the ladder and I would have had to take it off the wall and repositioned it. 

Thankfully I got away with it, but only just!