Mark III Underwater Video Housing - construction details

I've had a lot of requests for more details on how to build the Mark III housing so here are some further details.

Click here for a set of scale drawings. These are full size and can be printed out on multiple sheets and stuck together.
Sizes are in mm.

This housing is completely made from Perspex (acrylic). I have made a canister dive light for a friend and the battery holder
for this is almost identical to the housing tube - he has taken the light to a massive 84 metres without any leaks.

This is a picture of the end plate retaining clips showing the position they are in when open. Note the O ring compared to the Mark II as it is exposed on one side rather than being in a slot also note the position of the clip prior to closing. This is about the optimum angle for a nice tight fit without overloading the clip. The clip is screwed into a plastic block which is glued onto the side of the housing. You need special glue for perspex - talk to your plastics supplier. The screws also penetrate the side wall of the housing slightly so there is less chance of the glued block being pulled off.
A shot of the removable rear end plate (the front of the housing is fixed). From here you can see the shape of the O ring groove - the end is basically a top hat shape and the O ring sits around the rim like so.

You can also see the tapped hole for the screws that holds the clip on.

Another clip photo. You can see that the inside edge of the block was machined to the same shape as the outside diameter of the tube so the glue has good contact on both sides. This was done roughly on a machine and then the final shaping was done by wrapping some emery paper round the tube and rubbing the block against it to get the final accurate contour.
End retaining clip mounting screws. Also shown is the metal clamping plate that holds the velcro handle in place. The ring at the bottom is attached to a lanyard that I clip to my BCD for safety in case I have to let go of the housing.
The clamping plate at the other end. The plastic loop is where the velcro strap goes through before folding back and sticking to itself. The ring at the bottom connects to a wrist lanyard. Lots of attachments to my body I know, but I've actually had a ring like the one shown come apart on me in a strong current. I looked down and saw that my MotorMarine II and strobe was no longer attached to my wrist - there was just a piece of string there - I nearly had a heart attack ! Luckily the lanyard on my BCD was still holding on and the camera was waving about like a flag behind me. After that all my cameras have two lanyards !
Clip closed - look just above the clip at the O ring and you can see the centre has a extra black line - this is the contact point for the O ring the tighter the seal the thicker the line gets. Make sure there are no hairs or sand particles on this line - if there are it will leak. A thin smear of silicone grease helps lubricate the O ring if you want but is not required.

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