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Christian, ..250 is thousandths of an inch or less than a 1/4 inch or less than 6.350 mm, depending on where you reside on this planet ;-) The scientific community here is more likely to use the metric system, while the machinists and the like still use imperial but that is changing. Clear polycarbonate is no problem, however thicker walls will be needed versus glass fiber filled. You mentioned the wall thickness being greater, but the depth rating being less, so that is a good example anyway. The Gavin scooters are made of PVC and nylon, both with different characteristics. PVC is cheap and readily available, but emits an acid when heated up beyond a certain temperature, so cooling and tool speed is very important when machined. Certain types can also be affected by UV light when exposed for long periods. It is the perfect plastic for how it is being used in that application. Highly impact resistant, very strong solvent welds are easily obtained (when the joint and surface area are designed properly) and relatively easy to work with. Nylon is on the expensive side, easily machined and can absorb water and swell to a certain degree, but is most likely not even noticeable. I believe the nose cones are made of this. The Ikelite camera housings you mentioned have quite a bit of large flat surface areas, which will also be a factor in its' strength. A cylinder or sphere is stronger,(same wall thickness) unless the appropriate measures are taken. Bulkheads, fins or other structural members come into play here. Dell Motes Dive Rite 117 W.Washington St. Lake City, Fla. 32055 www.Dive-Rite.com -----Original Message----- From: Christian Gerzner <christiang@pi*.co*.au*> To: Dell Motes <dell@di*.co*> Cc: techdiver@aquanaut.com <techdiver@aquanaut.com> Date: Wednesday, April 14, 1999 7:54 AM Subject: Re: Yet another Canister light Question >Dell, > >Thanks for your informative response. > >Dell Motes wrote: >(a couple of snips) > >> Straight polycarbonate is very impact resistant but much too flexible. The >> glass fill allows for thinner walls,yet greater strength. Walls of less than >> .250 that will go to 500 ft. repeatedly. > >What do you mean by .250? Of an inch? A centimetre? Here in Oz as in almost >all of the rest of the world we now deal in metrics. Not so, sadly, the US of >A (except in scientific circles). > >It's interesting to note that my Nikonos SB104 Speedlights (camera strobes for >our photographically disinterested colleagues) _seem_ (I have no idea) to be >made of an _entirely clear_ as in eminently see through, close to glasslike, >"plastic" which is (roughly measured) 7mm, or 2.5 eights of an inch, thick. >They are rated to 100 metres (328ft) and I've taken mine to 73 metres (240ft) >without managing to drown them. Now, having had a quick look at the manuals >confirms that Nikon (typically, why am I unsurprised?) makes no mention of >build materials. > >Did I mention that the Speedlights' "armour" is a clear plastic? Gee, can >anyone tell me why Nikon chose to cover it with that red "overcoat"? Is it >that they don't want us to see when that water is rock, rock, rolling along? > >I point out that when these Speedlights came out they were, just like the RS >AF camera which they were intended to complement, hugely expensive. As I >recall, they cost some $Oz2,000 _each_ at that time (over six years ago). With >hindsight (ain't that thing just wonderful?) I know I made a mistake. This is >not the list to go into that. > >This, though, is actually the reason for my interest and I do note that the >Gavin scooters (I wish, I wish) are also housed in some type of plastic. > >George Irvine? Any input please? > >> Molded plastics are inherently >> stronger than machined, which creates unseen stress. Annealing (heat >> treating) can take care of some of the stress, but this is an additional >> process. Molded plastic is not without its' undesirable traits either. >> Shrinkage and warpage are some of the first things to come to mind. Glass >> fibers, bubbles, plastic temperature, mold temperature, gate location, etc >> are all factors that must be determined before the mold is produced. Then >> you still have to shoot parts to see if you got it right. Accurate >> prototyping is very difficult. Plastics is a very interesting and diverse >> field. There are many parts made of plastic that just aren't possible with >> other materials, including metals. > >Again, thanks for the response Dell, very useful, > >Christian > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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