Lockdown Challenge: Making holes without using a drill
Image credit: Neil Downie
In this week’s Lockdown Challenge, Neil Downie shows how friction alone can create a neat hole, and even be used in circumstances where a normal drill doesn’t work.
Lockdown Challenge #35 – Drill-less drilling: the power of friction
You can use rods and tubes with friction to create heat to make a hole without a drill-bit. Cutting holes with friction can even give better holes.
Take a battery-operated, portable electric drill or a small stand drill and put a piece of dowel rod of 4-8mm in diameter into the chuck. Narrow the dowel tip down to 2-3mm. Also, particularly if using a hand-held machine, put a dimple on the surface of the wood that you are piercing to stop the dowel from sliding around as you start. Now select a high speed on the drill machine and push it into the wood. Keep water handy in case of fire, although this isn’t likely, and open a window so you don’t have to worry about a little smoke. You shouldn’t be surprised about the smoke: this is, after all, rather like the ancient way of lighting a fire by twirling a stick against a piece of flammable wood.
The dowel rotates, and as you push on it, it rubs against the wood workpiece and friction creates heat. The heat is proportional to the rotation speed, how hard you press, and the coefficient of friction. The temperature rises to hundreds of °C, at least in the fraction of a millimetre between dowel and workpiece, to the point that dowel and workpiece are both carbonised.
Now here is a curious thing: with the workpiece flat, try adding a little puddle of water around the dowel as you go. You might expect hole creation to stop since the water cools. But you can make a hole at a similar rate with water – and the hole ends up neater and less burnt looking!
There’s another curious thing: the hole-making dowel ends up with a neat conical tip with a 90° cone angle. Maybe with the work-piece harder than the dowel you will get a flatter angle like 120°. And would a hole in softer wood give a sharper cone?
For bigger holes, it pays to remove a ring, rather than the whole bore of a hole. This reduces the volume that needs to be melted to make the hole. The volume that needs to be melted is 2πR.T.W rather than πR2.T, where R, T, and W are the hole radius, the workpiece thickness, and the tube wall thickness. Try this using a short piece of steel tube in the chuck of the drill machine to make a hole. Use steel (better, stainless steel) because it will conduct less heat away from the cutting edge. It will easily cut through plastic and wood, leaving a good finish. Don’t touch the tube just after making a hole, though: it can be very hot.
For holes larger than the chuck size, you can put a steel tube in the rotating mount used for the cylindrical hacksaw type of hole cutter (shown in the picture above). File slots in the tube to engage with the drive bar on the tank cutter mount and glue it on, for example using a block of glue around the central alignment drill (or rod). You can get a remarkably smooth bore and accurate hole. In plastics, the melting caused may avoid the weakening caused by small cracks around holes made with a standard drill-bit.
You can also put holes in pottery. Pottery usually cracks if you use a drill-bit in the usual way. But a tube with sand and water makes it easy. Surround the hole area with a ring of Blutack to contain a little puddle of sand and water. Go gently with the rotating tube to avoid cracking the pottery. The tube doesn’t produce much heat in this case, and the melting point of pottery is over 1,200°C, so probably the cutting action is sharp-edged sand particles being dragged over the pottery surface. You can use a central pilot drill or rod to start the hole from one side, and then finish it from the other side. This avoids chipping on the backside, the well-known ‘bullet-exit-hole-is-bigger-than-the-entrance-hole’ effect.
If you liked this, you will find lots more fun science stuff in Neil Downie’s books like ‘The Ultimate Book of Saturday Science’ from Princeton University, and for lots of other things (and a free copy of the ‘Exploding Disk Cannons’ book), visit www.saturdayscience.org
There is also the back catalogue of Lockdown Challenges from 2020 to choose from if you are looking for more options. The IET also has a host of resources that adults can use to engage children with the world of STEM.
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