New Frame For My Rebreather

pictures and text by Kerry McKenzie


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It all started when John Dalla-Zuanna offered me an alloy shell for my rebreather.
I asked both Frank and Barry Gill if they were also interested and they both jumped at the opportunity.
So 3 aluminium shells arrived several weeks later but it has taken several months to get mine to where it can now be dived.
After cleaning up the shells and filing slots where needed I decided to change the frame design also.


                         

You can see the shell in its bare state as I was still in the process of cleaning up the casting when I took these shots. My original set up was an "A" frame which slotted into a cross member mounted to the shell. See picture below left and middle is the new one piece design, finally is a shot of the tanks mounts welded directly to the alloy shell.

            

                    

You can see the tank mounts now welded to the side of the shell, this actually helped strengthen the shell even more. Above you can see the stainless steel frame beginning to take shape clipping in from the front utilising the two slots originally used for the harness. However with the extra strength of the alloy shell a frame could be constructed which could be easily removed and allow complete access to the shell without bars or permanent fixtures to get in the way. I think I have achieved this now.

                      

All materials were 316 grade stainless steel and you can see the folded front ends of the frame used to clip into the shell.

                                                      

I used polyethylene plastic sheet to cover the frame to provide some protection for the breathing bags. While below the shell has now been painted "fridge white"

          

          

You can now see the frame mounted on the BC and here is a close-up shot of the bends and how they slot into the shell.

And finally here is the finished shell and frame mounted up ready to assemble and dive. Pictured below is Frank Feather testing the stability of the shell and weight testing the rebreather to see how the balance is.

Frank was doing  slow rolls through 360 degrees and was very pleased to find that no matter where he put the unit it would stay. Not like scuba where if you turn over you have a tendency to rollover onto your back and of course there is the UP/Down breathing thing you also get with scuba. After the rebreather that is very hard to get used to again. Three pounds of lead can be removed  from the unit as a direct result of the negative bouncy of the new shell. Pictured below you can see the trapped air in his BC escaping and breaking the surface as he rotates through 360 degrees.  

               

               

 Dimensions I used for my frame 

Listed are the materials and the dimensions in both metric and imperial that I used to construct the frame for myself.

* All materials were 316 grade stainless steel

* To keep construction simple I used the same sized material throughout except for the arches used to bolt the frame to the BC.

* These were 25mm X 3mm flat(1"X 3/16"), each being 160mm long X 25mm wide ( 6 1/4") X (1")

* length 1.75 metres (5' 8"ft) long X 50mm (2" inch) wide X 3mm (3/16" inch) thick.

* the two vertical struts are 405mm (1' 3 1/2" ft) to the first bend at 12mm 

   (1/2" inch) followed by the second bend at 16mm ( 5/8" inches)

* cross member top 300mm (12" inches)

* cross member bottom 335mm (1' 1 1/4" ft)

Fastenings

* only 3mm X 25mm Philips head screws (3/16 X 1"

* 6 only 3mm Nylock nuts ( 3/16")

* 6 only 3mm flat washers ( 3/16")

* 2 only 8mm X 25mm coach bolts ( 3/16"X 1")

* 2 only 8mm wing nuts ( 3/16")

* 4 only 8mm flat washers ( 3/16")

* 2 only 8mm X 25mm bolts ( 3/16"X 1")

* 2 only 8mm standard nuts ( 3/16")

The arches were bent around a scuba tank 8mm holes (5/16")drilled to the centres and the 8mm nuts (5/16")were welded on the inside of the arch, this way I only had two bolts to tighten from the inside of the BC. However this only needed to be done once as the frame seldom requires removal from the BC.

This concludes my latest project, as usual if you have any questions I am easily contacted on email tubby@vk4tub.org

John Dalla-Zuanna can be contacted for information about the Alloy shell.

jdz@paintandcustom.com.au

And Chris Law can be contacted about the frame.    chrislaw@pipeline.com.au

 

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