A cordless drill is a very versatile tool to have around, despite its low speed and torque. Its freedom from a cord makes my tool of choice for handyman types of repairs around the house and in my shop/laundry-room/garage.
My particular drill is a 9.6V Makita Model 6095D, which comes with a keyless chuck and an adjustable clutch that allows adjusting the fastening torque so that it will slip before damaging something.
Unfortunately, the clutch is too imprecise to reliably prevent sinking screw heads too deep in wood or plaster board, but I have found it useful when tapping threads; I set the torque low enough to avoid breaking the tap and repeatedly run it forwards until it slips, then back out a few turns, forward again until enough threads are cut. I find that I can hold the tap reasonably straight when I am just pulling a trigger and flipping a switch.
Although I own a lovely 1/2" Milwaukee corded drill that has enough torque to sprain a wrist, I succumbed to the temptation to use the cordless drill to try to drill some large holes in 1/4" steel when building the fence for my table saw. Instead of drilling the desired holes, I ended up damaging the drill's clutch. After that abusive day, my clutch slipped with the slightest torque, rendering the drill just about useless.
Normally, I would respond to the damage by taking the case apart and trying to determine what I broke. However, in this case the adjusting collar for the clutch fits over both halves of the case, and the collar can not be removed without first removing the chuck.
Most hand-held drills have chucks that screw onto the shaft with a right-hand thread. Reversible drills lock the chuck in place with a left-hand threaded screw inside the chuck. To remove this screw, open the jaws of the chuck all the way and use a screwdriver to back out the screw (turning it clockwise, of course, to loosen it).
The easiest way to get the chuck off, once the screw is out, is to chuck the short end of a large Allen wrench into the drill, run the drill backwards at low speed, and let the long end of the Allen wrench bang into a concrete floor or a 2x4 or something until you hear a pop and the chuck just screws off. The impacts seem to loosen stuck threads very well.
The problem with my drill was that my clutch was damaged and I couldn't get enough of an impact to loosen the threads. I had to get to the clutch before I could get to the chuck.
Fortunately, the plastic case is flexible enough to allow it to be pried apart enough to get access to some of the internals, even when it is held together in the front.
The first thing I tried was to jam a screwdriver into the reduction gears and attempt to whack the Allen wrench to break the stuck threads free. That didn't work, but it did mess up the reduction gears so that my drill now ticks every revolution.
While playing with the drill in its partially-disassembled state, I noticed the spring-loaded clutch mechanism just forward of the trigger. I have scanned in part of the exploded parts diagram for this drill and I have marked the relevant parts of the clutch assembly in red.
By pressing the slider (part 37) back towards the trigger with an appropriate tool, the clutch can be prevented from slipping, and the Allen-wrench-loosening technique can then be used.
A few seconds later I had the drill apart and I determined what was wrong; The clutch change ring (part 7) had turned past its normal range of motion and the cam plate (part 5) was no longer engaging the slider (part 37). I turned the ring back to its normal position, tested the drill, cleaned up some of the old grease, and had the drill back together in no time.
Before I attacked my drill's internals, I did contact my local Makita Service Center. It turns out that they had a fixed-price repair policy for that drill (and other products, I believe), and, for about $50 they would fix what ever was wrong with my drill. I didn't feel like spending half of what a new drill would cost to repair an old one, so I opted for the solution described above. You may want to, at least, check with a service center before risking real damage to your tool.
Makita also has an online site with lists of service centers, parts breakdowns, and online ordering of parts and tools at http://www.makitaparts.com.
Of course, I believe that you can't really learn how something works if you are afraid to break it. That means I have experienced that special, sick feeling in my belly and the remorseful "why did I ever do that?" while working on machine tools, hand tools, cameras, cars, operating systems, computer hardware, stereo equipment, dive gear, and a few other things so far, and I will probably experience it again more than once.
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Repairing a Makita Drill / email@example.com / revised 1999 June 25