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Build your own drill

A recycled electric power drill for nearly nothing

by Julian Edgar

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Want a high quality mains-powered drill that will cost nothing and last for nearly ever? You can – just assemble one good power drill from a bunch of old and broken Black & Decker drills.

But first, why would you bother?

Black & Decker must have sold tens of thousands of their ‘orange’ drills in Australia in the 1970s and 1980s. In those days, well before cheap Chinese-made drills flooded the market, these power drills were relatively expensive – and well made. They were also designed to be repaired as required, rather than just thrown away.

And they were tough. Drop one on concrete and it just bounced. Overload it by driving a 50mm hole-saw through chipboard and you could make the windings smoke. But if you then stopped drilling and free-ran the motor for a minute to cool it, you’d have likely done no damage.

So unlike the vast majority of modern-day drills, these drills are durable and easy to repair.

Furthermore, while the drills were produced in different models over the years, many parts are interchangeable. If you have (say) three broken B&D orange drills, the chances are that you can easily make one working drill – and it will then last you another decade or two.

Collecting

It’s worth picking up every old orange B&D power drill that you can find.

At rubbish tip shops you’ll often find drills with the cord cut off (so they don’t have to test and tag it) – buy them for a dollar anyway. Some drills have chucks that are old and worn – grab them. Others will be covered in paint splatters or abrasions – pick them up and take them home.

And a surprising number of these old drills will be fully operational – and still be available free or for only a few dollars.

Testing

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The first step after collecting a drill is to test it.

Make sure that the chuck rotates smoothly and grips drill bits correctly. There shouldn’t be any lateral movement in the chuck and when you rotate the unpowered drill by turning the chuck, the motor should spin smoothly.

If the cable and plug are still intact, power-up the drill and check it works correctly without odd noises, or sparks from the commutator.

Disassembly

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If you have a defective drill, the first step is to pull apart the handle, revealing the speed control (integrated into the trigger switch), wiring and brush holders. Older drills have normal Philips head fasteners in the handle, but later model ones use tamperproof fittings. Screwdriver bits are available for these tamperproof fittings, or you can remove the screws by drilling-out their heads – although note that the metal of the screws is quite hard.

The gearbox on the front of the drill – alloy-cased in older models and plastic-cased on later models – is held on with normal Philips head screws, so these can be easily removed. While you are looking at the gearbox, check to see if it’s a single speed gearbox or the rarer mechanical two-speed gearbox, with the speeds selecting by a side-mount lever. (On later drills with the single speed gearbox, often two speeds are provided via an electronic controller.)

With the handle disassembled and the gearbox removed, the armature (complete with its rear bearing) can be pushed out the front. Be careful not to damage the carbon brushes – these can be removed first if required.

Inspection and repair

With the drill apart, inspect the:

  • commutator for glazed or worn surfaces

  • bearings for play

  • carbon brushes for wear (often one is much more worn than the other)

  • gearbox teeth for wear or a lack of lubrication (the grease tends to get flung off)

  • power cable where it enters the drill handle (look for splits in the insulation)

If you find anything badly worn, see what’s inside your other donor drills! For example, the single badly worn brush can be replaced with the lesser worn brush from the other drill, the gearbox can be swapped, or even the whole armature changed for another.

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If the cord has been cut off short or is damaged, the safest approach is to cut the cables inside the handle. Remove the cable remnant from the rubber stress relief at the handle end. Place a drill bit in a vice and then screw the rubber stress relief grommet over the drill, enlarging its internal passage. You can then feed a new cable down the grommet, making the connections inside the handle. To make these joins I use screw connectors of the sort used in 240V house wiring – older drills use screw terminals on the switch, so that’s even easier. Ensure that the new cable is firmly anchored as that it cannot pull on the wiring connections.

(Of course if you don’t know what you are doing with mains wiring, get someone more experienced to do this step.)

Note that all these drills are double insulted – no earth lead is required. Replacement cables can be sourced from discarded vacuum cleaners – these cables are long, supple and have appropriate power ratings.

If the chuck is damaged it can be removed and another substituted – although note it’s often quicker and easier to swap the whole gearbox assembly, chuck included.

Cosmetics

To make your drill look nice again, marks can be removed from the plastic housing by wiping it over with paint thinners. Polish the plastic with a car paint cutting compound. The aluminium gearbox housing can be wire-brushed to remove marks and corrosion.

Conclusion

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To produce one good drill from some old discards is satisfying and fun. You need to have some experience with mains power and know your way around electric motors a little, but the drills are surprisingly simple inside and very straightforward to repair – especially if you have a source of free spare parts available!

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