Bucchi Step Drill Bit for 1000L Tank Bulkhead Fitting - 1/2, 3/4, 1 inch

Drill a 1000-litre tank without splitting it. This step drill bit opens the three most common bulkhead fitting holes — 29, 35 and 43 millimetres — with a single tool, centring itself and without chattering like a hole saw.

The real difficulty is not the fitting, it is the hole

Fitting a bulkhead fitting on a 1000L tank calls for neither strength nor special skill : you engage the body, tighten the clamp, and it is done in two minutes. What stops people, and what they tell us, is the step before : drilling the wall. A container or a cistern is expensive, the wall is thin, and a botched hole cannot be recovered. You cannot plug an oval hole in polyethylene.

The reflex is to reach for a hole saw, and that is precisely where the trouble starts. A hole saw attacks the material around its whole circumference at once. On a plastic wall two to three millimetres thick, often curved, the teeth catch, the tool starts to vibrate, the saw jams and tears out a chip instead of cutting it. You get an irregular hole, sometimes the start of a crack that runs several centimetres — and it is then the seal that has to make up for all that.

A step drill bit works in exactly the opposite way. It enters by the tip, centres itself, then opens the hole step by step. At every moment only a thin ring of material is being cut : the effort stays low, the tool does not chatter, and the edge comes out clean, with no burr to remove. It is the tool of sheet-metal workers and electricians for cable passages, and it is exactly the same problem here.

Three holes, one tool

The steps are engraved on the body of the bit and carry the fitting sizes : 3/8", 1/2", 3/4" and 1". You drill down to the step you want and stop. Three of the four steps match the holes of our Quick Joint bulkhead fitting range.

What it does not do, and you might as well know before ordering. It stops at 1 inch. The three large sizes in the range — 1 1/4", 1 1/2" and 2", that is 52, 59 and 70 millimetres — still have to be drilled another way, with a hole saw or a bi-metal hole saw. No ordinary step drill bit goes up to 70 millimetres, and this one is no exception. If your project is in 2 inch, this tool will be of no use to you and we would rather tell you so here.

The shank is hexagonal : it sits in the chuck of an ordinary drill without turning in the jaws, which is the weakness of round shanks as soon as the tool is under a little load. No drill press needed, no stand : the tank stays where it is.

How to use it without damaging the tank

A few simple actions are enough, and they matter more than the tool itself. Plastic melts before it burns : the whole point is to clear the chip instead of heating it.

• Slow speed and steady pressure. Plastic cuts at low revs ; at high speed it melts, sticks to the tool and the hole closes up behind it.
• Drill when empty, with the tank drained below the level of the future hole. A wall under pressure deforms and the hole goes off centre.
• Choose an even area of wall, away from ribs, corners and welds, and check that no frame bar runs behind.
• Clear the chip every two or three steps rather than forcing through in one go.
• On a tank that has held a fuel or a solvent, empty, rinse and let it gas off before drilling : drilling generates heat.

One last piece of advice that costs nothing : try it on an offcut of plastic or on a can you no longer need, to feel at what speed the tool cuts best. Two minutes of testing are worth more than a cistern drilled crooked.

Who this tool is worth its price for

Let us be direct, because the price is visible. If you are fitting a single bulkhead fitting in your life, an entry-level hole saw will do the job : less well, with more attention on your part, but it will do it. This tool is not justified for a one-off fitting, and we are not trying to make you believe otherwise.

It becomes worthwhile as soon as you are in one of these cases : you are equipping several 1000L tanks, for example a rainwater harvesting battery ; you install for third parties and cannot afford a botched hole at a customer's ; you drill different diameters and do not want to buy three hole saws ; or the tank you are drilling is too valuable for you to take a chance.

It is a tool you keep, and it will serve well beyond tanks : thin sheet metal, electrical boxes, plywood panels, cable passages. It hardly wears at all on plastic.

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