Sunday, April 11, 2010

Bender's Head - head & neck

To build Bender's head....
As mentioned previously, the head was made from the top of a NuSwift 9Kg (20lb) DCP fire extinguisher. In the photo below, you can see Bender's head (incomplete) and one of the stripped extinguishers immediately behind him, and several more sitting on the low shed.

To make the head I simply stripped the extinguisher of it's valve, pressure gauge, and cut away the carry handle. I marked the head at the desired height (370mm = 14 1/2") and cut around the extinguisher. I marked up and cut out the opening for Bender's mouth, and marked on the upper and lower limits of the eye shroud. I also cut out the boss from the pressure gauge, and welded a patch in place cut from another extinguisher top (similar to what was done with the foot cups)
A closer view of the above photo shows the marks above the eye plate where the handle was cut away, and how the original valve boss was retained and used to secure Bender's antenna to his head.

With the upper and lower limits of the eye shroud marked on Bender's head, the eye-plate securing holes (bolt and prong) were spotted through, drilled and tested. For the progress photo I dropped a scrap of Colourbond inside his head to simulate his teeth, and start ironing out the details of how that would work.

I'll cover the eye shroud as a separate page (next I promise) and now discuss how his neck joint was built.

The neck joint needed to permit rotation of the head, and provide positive retention of the head. These objectives were both met with the design I used. I started with some scrap pipe which was 165mm (6 1/2") across the outside diameter. The interior diameter of the extinguisher was just under 180mm so there was a gap of approx 6-7mm (around 1/4") all around the smaller pipe. This gap was used to house the retaining ring.
The retaining ring was a 1/4" ring cut from the same pipe as the neck joint. I then cut the ring and added a piece of steel, and re-welded it in so the ring was a larger diameter, and an loose fit over the neck joint, and a slip fit inside the head.
The retaining ring was plug welded at several locations around the head through 1/4" diameter holes.
The retaining ring rides on a number of support bolts which have been tapped through the neck ring, and the head is retained by a number of retaining bolts which are held in nuts welded on top of the neck ring. A sketch of the joint is shown below...

And the photo below shows how it looks in real life, plug welds, retaining bolts, neck ring and gap containing the retaining ring all clearly visible. The neck ring is only 25mm (1") high, and the gap under the head edge, compared to the bottom of the neck ring is 1/4".

The bottom of the neck ring is welded to the top of Bender's body to attache his head. Since I made two heads, I made two neck joints, the spare neck joint being used to keep the spare head from scratching up the book shelf.

The hole in the top of the 44Kg (100 lb) propane cylinder where the valve boss used to be was oxy cut out by one of my friends from work. (Thanks Vince!!) I was originally going to chain drill it out, but oxy cutting was quicker, and easier. The same workshop where Vince works also has the bandsaw I used to cut the neck rings, and retaining rings. The guys at the workshop are always happy to see what nutty things I'm building at home, and got quite a giggle out of the arbor press I built using an old door closer. I don't know if they see value in what I make, but they're always willing to offer advice on techniques, and when I get some spare time, I'll be learning how to oxy cut from them. All I need is some spare time...

Next installment - building the shroud for the eyes.

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