The web page for my original H-Plate Single tank travel backplate went up in early 2004. The Aluminium Hplate Mk II joined in 2007, and in 2008 a conventional Aluminium backplate. Since the start, I've received a steady trickle of emails from people interested in designing or making their own backplate - but no further follow-ups from anyone that succeeded, hint hint - and 10,000+ 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, and this page is an attempt to put down in one place some of the things I've learned during those processes to help anyone who wants to give it a go.

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. And this isn't about setting up a commercial enterprise, or even a cottage industry, making backplates, it is advice for hobbyists.

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. Though they were improvements against the above list of imperfections, none of the other plates available in the UK at the time had this feature, 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 intended for single tank diving, as small as it could be while still being comfortable to wear; to make it easier to take on holiday. These thoughts led to sketches, which led to drawings, which led to cardboard mock-ups - and ultimately to having the first stainless steel plate made up, and put into five years of regular use.

After a while, I started thinking that an Ali version at even lighter weight would be great for travel, and that I could incorporate some further refinements to the original design; this became the H-Plate Mk II. These plates were made because there wasn't anything commercially available that would do the job - single tank BPW diving - in as pure and precise a fashion.

Also about that time I also started diving a twinset regularly, so designing an Ali backplate for twinset use was an obvious step. With cheap conventional plates available everywhere, the reasons for making this plate were more to do with personal satisfaction and/or vanity than necessity, but, those are as good reasons as any. :-)

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 would 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, particularly for travel; in the tropics in a 3mm wetsuit with Ali 80 tank and Ali plate I need no additional weight - a steel plate would make me significantly overweighted.

Ali is less hard than SS, so will scar more easily; weaker (though not so much as to 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... I have tried to get prices (in Aus) for having a batch of Ti plates made, but it is hard to find a supplier (most places aren't interested in quoting for the kind of small quantities we are talking about here, other places advertise that they will work in Ti right up until the point of being asked for a 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.

As a general principle for marine use, smoother is better. For Stainless, the ideal for corrosion resistance would be a high-quality electropolished finish, followed by mirror polish, followed by the various levels of grained finish in order of increasing roughness - but practically for diving use, the finish achievable is likely to be dictated by the supplier, and if your gear gets a rinse every now and again, corrosion on 316 is unlikely to be a serious issue.

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.

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 OK. 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 ali underneath remains soft. When (not if) this layer gets compromised, the sacrificial corrosion effect becomes concentrated in the exposed bits of raw aluminium. I can see this happening on my hard anodised Ali plate - while the overall anodised surface remains untouched, several chips round the edges of the plate are becoming small pits. After a year and a half of regular use however, this is still a long way from becoming a functional issue, and on balance my feeling would be that anodizing is worthwhile.

If not anodised, then an Al plate should be as smooth as possible, as per the principle above. My batch of Al twinset plates came from the fabricators with a linished finish, which immediately tarnished terribly. After stripping this finish off with caustic soda, the plate fared better. (...before being anodised).

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, so it can be a significant time load on a batch.

My latest experiment in getting a decent edge is to specify a machine chamfer on all edges, we'll see how that goes. Depending on your supplier, they may be able to provide tumbling, machine chamfering or other finishes, but don't expect it to be cheap.

Minimum order sizes, and what to do with all those spare plates.

All content © Copyright Huw Porter 2009