Clutches, torque and you.

Many of us have drills, either corded or cordless that we use often.  In fact, it’s the number one answer on the DIY Stack Exchange ‘What are the tools that every Do-It-Yourselfer must own’ question .  They can be used both as screwdrivers, to put fasteners in things, or actual drills, to make holes in things.  However, these two actions are actually a little bit different from each other.  So, let’s take a look at the drill clutch and figure out how it helps us accomplish these tasks best.

First, let’s review exactly what a clutch (in the mechanical sense) is.  According to Wikipedia, “A clutch is a mechanical device that provides for the transmission of power (and therefore usually motion) from one component (the driving member) to another (the driven member). ”  It is most often used when one wants to control the amount of power being transmitted.  Most of us are most familiar with a manual car’s transmission clutch.  With the clutch pedal all the way in, no power goes from the engine to the wheels.  With it all the way up, they are mechanically linked 100%. Anything in between, and they slip past each other and transmit some power.

On a power drill, the clutch setting is the amount of torque that the motor will pass through to the bit.  With the setting at 1, it will pass very little power, and at the maximum setting, it will pass the most.  Some have a numerical scale, 1-5 and then a symbol for a drill bit.  In this case, the drill bit completely disengages the clutch, it will always pass the maximum amount of power.

So, you’re asking yourself, why would I ever want to use less power than I have available to me?  Didn’t I buy this awesome drill for all the power it has?  Well, the answer is “sometimes”.  A common time you would want to dial this down is when driving Phillips-head screws into wood.

Let’s say you put your drill on maximum torque and drive that screw all the way in.  When the screw reaches the depth you want, a couple of things might happen – 1) You might over-drive the screw.  Remember, you’re on maximum torque and wood is generally soft.  So you might put that screw in a bit more than you wanted, especially if it’s soft wood.  2)  You might start stripping the head if it’s hard wood as the bit cams out of the head.  Phillips-head screws are made to cam out, but this was in the days before there were torque limiting tools.  The bit will rise up and out of the screw to avoid shearing the head off of the fastener.  However, nowadays you’re most likely to just strip the screw slots and make it impossible to remove.

However, if you put it on one of the lower settings, the clutch will not transmit any more power to the bit once the power needed to turn the bit is more than the setting.  More than likely, when driving our screw into wood, you want to set the clutch number at the number that will cause it to stop when the screw head reaches the surface.  You’ll probably want to start low and maybe turn up a notch or two if it stalls out before the job is done.  But when you have it right, you’ll have the best of both worlds – getting your fasteners all the way where you want them without having to worry about stripping the head because you didn’t let go of the trigger soon enough.

Another great place the clutch works for you is when driving in hex bolts into knockdown furniture.  Typically a hex-head wrench is supplied with the furniture, but if one has a power tool, spinning that around by hand just gets tiresome after the tenth or fifteenth bolt.  Luckily, since you have learned about the clutch, all you need to get is a hex-head bit for your drill, bring down the clutch to almost its lowest setting, and let ‘er rip!  You’ll drive that bolt completely home and when it is full into the hole, the motor clutch will just disengage and you won’t damage the bolt, the piece of furniture, or anything else!

On the other hand, when using a drill bit or spade bit to make a hole in something (the “drill” part of drill./driver), you always want this on the drill setting so that you have the maximum amount of power available to  you.  Putting it on a smaller setting will just make your life difficult.  For example, you might start OK, but if you run into a knot in the wood, this would require more power to get through it, and you wouldn’t be able to transmit that power – the motor would continue to spin, but the clutch would disengage and no power would get transmitted to the drill bit.

So now you know how to most effectively use your drill/driver for the two purposes it was designed – to put holes in things and also to put fasteners in things.  Use it correctly, and you’ll get much more bang for your buck, and your proejcts will go smoother.  Next time we’ll cover impact wrenches and what purposes they are used for.