Rhys worked very hard to get sponsorship from Makita. We'd heard that they had sponsored the Mulu caves expedition in 2011, so we were hopeful that Makita would be interested in supporting our expedition. We asked for two BHR 162 of the type Jarv and I wrote about earlier but these have been discontinued and replaced with the DHR164, which also uses 14.4V Lithium Ion batteries. Having more drills is incredibly useful for expedition, as we will be able to bolt multiple pitches in parallels as opposed to waiting for drills to be moved around, and we will have backup drills in case of damage or loss. We're very grateful to Makita for providing us with two of these excellent drills. We know from experience that Makita makes drills that can withstand the harsh conditions in caves, and the lightweight nature of the their cordless drills makes them easy to transport and use in the remote and tight spots.

Makita DHR164 Rotary Hammer Drill

Modifying the drill

On the outside, the DHR164 looks very similar to its predecessor, aside from minor cosmetic changes. This guide also quite similar to the previous one I wrote, which in turn was derived from Jarv's instructions. However, there are enough differences to warrant rehashing the material with the necessary alterations. Rhys was inexplicably busy when I offered to let him help with taking apart this drill, so I passed another solitary weekend huffing solder fumes.

Copper plate of the carbon brush

Firstly, it's still necessary to prise back the rubber covers over the carbon brushes on either side of the body, and then remove the carbon brushes by gently prying them out with a flat head screwdriver.

Carbon brush, new and unworn!

Once these have been removed, the four long screws that hold on the front half of the drill can be removed. These have slots for both flat and cross head screwdrivers, which is very useful when you have limited tools for a repair, like up a mountain in New Zealand.

The drill, partially disassembled, showing the motor coils.

The permanent magnet at the back can provide a bit of force, but with a quick yank you can separate the drill into two halves - the front half that contains the pneumatic chuck, and motor, and the back half with the permanent magnet and the electronics to drive the motor via the carbon brushes.

The back half of the drill contains lots of wires and transistors.

The electronics are a little different here - the high voltage rectifier chip that was mounted on the permanent magnet (presumably as a heatsink) has been moved to behind the magnet. I wonder if this is to provide active cooling from the air currents driven by the co-axial fan on the motor shaft. The third contact on the battery is still there, having been added some time between BHR162 model 2006 and model 2013. But most importantly, the contacts for attaching external fly leads have been removed.

The new trigger unit has no contacts for external fly leads

This is not a disaster - I desoldered the leads that would connect to the standard battery, and soldered my own leads in their place. Then I noticed that quite a few wires branch off from just where the standard battery attaches, including the rather nice LED that illuminates whatever the drill is pointing at.

Big blobs of solder are your friends

It would be a shame to lose this functionality, so I attached the internal leads to the external with generous amounts of solder, the last resort of a bodger. Not entirely satisfactory - if there had been space in the moulded case I would have tried something more elegant with chocolate block, but I think it should hold. As with my previous blog post, I cut the yellow wire that goes to the third contact on the standard battery and soldered it to the positive terminal to bypass this unused safety system.

Cable tie glued on with Araldite

I used a soldering iron and file to melt and cut a hole in the case for the external leads to leave. I placed a cable tie just inside the case, got it tight as possible with pliers and then glued it in place with Araldite, a two part epoxy resin. This should mean that if there is any external force on the leads it is transferred to the case and not to the weaker soldering points. On the other end of the cables I crimped and soldered 30A Anderson powerpoles, which are reassuringly chunky connectors.

Reassembling the drill is easy - just follow the reverse steps. The permanent magnet can rotate a bit and prevent the case closing properly, so watch out for that. The external leads became noticeably warmer when the drill was under load, so it's advisable to not run the drill at full power and not to run the drill for a long time - this is easy in a cave, where placing a bolt may take five minutes, giving plenty of time for the drill to cool down.

Jack Hare