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Tips for Designing your Own SCUBA Backplate

The web page for my original H-Plate Single tank travel backplate went up in early 2004. The Aluminium Hplate Mk II was added in 2007, in 2008 a conventional Aluminium backplate, and most recently in 2009/10 full-size stainless steel twinset and single-tank H-Plate Mk III. Ever since the first page went online, I've received a steady trickle of emails from people interested in designing or making their own backplate - but only a handful of follow-ups from anyone that succeeded, hint hint - and 30,000+ hits from discussion forums around the world; so there is a lot of interest in DIY plate fabrication out there.

I've created a downloadable template for my basic backplate design; this page is an attempt to gather in one place some of the things I've learned during those processes to help anyone who wants to give it a go.


The original H-Plate (left), & H-Plate Mk II (right)

Note, this page is about designing your own plate, rather than actually making it yourself. I don't have access to the heavy machinery that would be necessary to physically make a backplate so I can't offer direct advice on how to go about that. This also isn't about setting up a commercial enterprise - or even a cottage industry - this is advice for hobbyists.

Why make your own plate?

Before talking about how, why is worth mentioning. For a start, the answer probably can't be "to save money". The manufacturers have economies of scale that you aren't going to be able to match - if cost is a serious factor, you'd be better off trying to pick up a second hand plate. (You probably could save money at the expense of time and work if you have access to the machinery for doing your own fabrication, and this would be very satisfying, but that isn't what this page is about.)

A better answer would be: I want some design features that aren't available off-the-peg. The original H-Plate was born from dissatisfaction with many of the details of my first purchased backplate, a Portland Oceaneering Mk 2. That was a large, heavy stainless plate: too flat against your back for comfort, much wider than it needed to be, the cam-band slots were too low, the harness slots were in strange places and at funny angles, and there were a whole bunch of superfluous (for my purposes) holes all over it. In addition, the webbing slots were so badly finished, it still needed hours of elbow grease to make it ready for use.

However, it did have a reversed curve to the spine which allowed a single tank to be banded directly and securely to the plate. None of the other plates available in the UK at the time had this feature - though they otherwise offered improvements against the opposing list of imperfections - and I didn't (and still don't) feel that a single tank adapter offers the truly optimum solution for single tank backplate and wing diving.

So I started to think about what features I would put into my dream backplate: a plate specifically and singlemindedly intended for single tank diving, as small as it could be (to make it easier to take on holiday) while still being comfortable. These thoughts led to sketches, which led to drawings, which led to cardboard mock-ups - and, ultimately, to the first batch of H-Plates, the one of which that I kept seeing five years of regular use. Ultimately, the decision to make the plate was because there wasn't anything commercially available that would do the job I wanted - single tank BPW diving - in as pure and precise a fashion.

The following generations of plate followed on from this: The H-Plate Mk II, an even lighter weight version in Aluminium for travel to tropical locations; a conventional Ali plate for twinset use, and most recently full size stainless steel twinset and H-Plate Mk III single tank plates. Cheap and well-designed commercial plates have become much more widely available available over the years, so the reasons for making these later plates are to do with really refining and perfecting the details, personal satisfaction and vanity rather than necessity, but hey, those are as good reasons as any. It can also become addictive seeing your ideas move from concept to regular diving use. :-)


The latest versions:
H-Plate Mk III (left), & Stainless Steel Backplate (right)


Choosing a Material.

Stainless Steel.

Commercial Backplates are nearly all Stainless Steel or Aluminium. Reasons for choosing SS are that the material is extremely hard, strong and corrosion resistant, and it is also dense, which can be both a plus and a minus. Hard is good, as it will look better for longer when battered about (as dive gear usually is); Strong is obviously good (though from an engineering standpoint 3mm SS is pretty overspecified for backplate use); corrosion resistance is important for anything that is going to come anywhere near saltwater. The extra density can be a good thing (adds weight in an ideal position to improve trim underwater and stability on the surface, reduces size of necessary weightbelt) or a bad thing (could make thin wetsuit divers overweighted, sucks for air travel).

The ideal choice of SS alloy for backplate use is marine grade 316. Expensive, but if you are going to all the hassle of making your own plate, why muck about with inferior materials? Grade 304 should also work OK.

Aluminium.

The reason for choosing Ali is basically that it is about a third of the density of stainless - a full size backplate in 3mm stainless will come in somewhere around 2.5 kg/5 pounds, while the same design in 3mm ali will be less than 1kg/2 lbs. This is a boon in the kit bag, and particularly for travel.

Ali is less hard than SS, so will scar more easily; weaker (though not so much as to really make a functional difference for backplate use), and unless anodised is less resistant to corrosion (though see below).

One major disadvantage for Ali in use with a twinset - tank bands are usually Stainless, and as a dissimilar metal with lower resistance immersed in an electolyte (...sea water), an Ali plate becomes the sacrificial anode in a galvanic corrosion system. This means it may corrode faster, but the upside is that it will be actually protecting your twinset bands at the same time...

An Ideal alloy choice is 5052, though there are other Marine grade alloys that would also work well.

Other Materials.

Other plausible materials for backplate use are Naval Brass and grade 5 (or 2) Titanium. Brass is slightly denser than stainless, though is relatively soft, and should tarnish attractively.

Titanium has in some ways ideal properties for a backplate - similar strength etc properties to Stainless, at slightly over half the weight. However, Ti would cost a motza, and has a potential disadvantage for twinset use in that Ti is more corrosion resistant than stainless, so your tank bands would then become a sacrificial anode protecting the plate... Out of curiosity, I have tried to get prices (in Aus) for having a batch of Ti plates made, but it is hard to find a supplier (many fabricators aren't interested in quoting for the kind of small quantities we are talking about here, others advertise that they will work in Ti until they are actually asked to quote).

Platinum has a good set of properties for making a seriously heavyweight plate at about three times the density of SS, but if you find yourself seriously considering making a platinum backplate, I have this really nice bridge I could cut you an excellent deal on.

You can also find backplates made from plastics, which seems to work for some people - and would make corrosion worries irrelevant - but any plastic is going to be (significantly) more brittle than Ali, with marginal weight benefits. To my mind, quite a lot of the point of a backplate is that you can effectively eliminate any sudden failure of your harness system, and having a risk, even a small risk, of having your backplate snap kind of invalidates that.

Surface Finishes.

As a general principle for marine use, smoother is better. For Stainless, the very best finish for corrosion resistance would be a mirror polish followed by electropolishing - but from a practical point of view, mirror polishing is time consuming, expensive and creates lots of nasty side-product grime; mirror finishes look fantastic when new, but scuff and scar quickly and visibly. Textured finishes such as linishing aren't ideal as they tend to leave non-stainless materials ground into the grooves, which then create rust spots. A smooth matt finish is a good economical compromise. Electropolishing any finish is beneficial as it will clean, microscopically smooth and passivate the surface.

During fabrication, the surface of stainless can become contaminated by other metals, which can then appear to be spots of corrosion. The finishing process should aim to remove as much of this as possible, at least for cosmetic reasons. Practically, for diving use, and particularly if your gear gets a rinse every now and again, corrosion on 316 is unlikely to become a serious issue, it depends how perfectionist you want to be.

Aluminium backplates are often (usually?) anodised for protection, and the an anodised layer is indeed both very hard and very resistant. If you were to do this, the optimum would be hardcoat anodizing to the greatest thickness available - my first ali plates I had hardcoat anodised to a quoted 50 microns - but standard anodising to 20+ microns would be fine. Anodizing also offers the opportunity to put a colour on your plate. Like a kewl stealth black for example. ;-)

There is a bit of debate about the benefits of anodising for Ali plates - while an unbroken anodised layer indeed offers excellent protection, the metal underneath remains soft. When (not if) this layer gets compromised, the sacrificial corrosion effect becomes concentrated in the exposed bits of raw aluminium. You can see this on any used anodised Ali plate - while the overall anodised surface remains untouched, any chips round the edge or on the face of the plate will become small pits. After a couple of years of regular use of my anodised plates this is, however, still a long way from becoming a functional issue; on balance my feeling would be that anodizing is worthwhile if not essential.

If not anodised, then an Al plate should be as smooth as possible, as per the principle with stainless above. My first batch of Al twinset plates came from the fabricators with a linished finish, which looked terrible after just a couple of dives. After stripping and cleaning the surface with caustic soda, the plate fared better.

Edge Finishing

Achieving really smooth edges seems to be a challenge for most small fabricators, and even my first purchased plate had such sharp edges on the webbing slots that it ate webbing at an alarming rate. The first batch of H-Plates came from the workshop with similar sharp edges, and it took me by hand roughly 4 hours per plate to knock the edges off and polish the critical load-bearing slots to a really webbing-friendly level; this can be a significant time load on a batch.

My latest batch of steel plates were specified with a machine chamfer on all edges, which got most of the way to an optimum finish. The mechanical polishing of the mirror finish plates left all edges silky smooth. Depending on your supplier, they may be able to provide tumbling, machine chamfering or other finishes, but, evaluate the cost against your time.

All content © Copyright Huw Porter 2009-13