How to sharpen an expansive bit?

29th February 2020


	How to sharpen an expansive bit?


	Shop for Expansive bits


			There are several different parts of an expansive bit that must be kept sharp for the tool to work efficiently: the guide screw, the lips and the cutters. Each requires a different approach.

			Guide screw
			When sharpening a guide screw, the best results can be achieved using grinding paste, a compound containing abrasive particles that are designed to wear down imperfections in metal surfaces that are difficult to reach.

			Step 1 – Create reservoir Using the screw of the bit you would like to sharpen, bore just far enough into a piece of softwood for the guide screw to fully enter the wood, then remove the bit.

			Step 2 – Apply grinding paste Apply some fine grain grinding paste into the screw hole with the implement of your choice (you might use a toothbrush, a scoop or even a lollipop stick).

			Step 3 – Grind screw sharp Reinsert the guide screw into the bore hole and twist it backwards and forwards. This will cause the abrasive particles in the grinding paste to remove any dirt and sharpen the edges of the thread.

			Step 4 – Clean off excess paste Remove the bit from the bore hole and clean off any paste left on the screw. Check the packaging for the grinding compound to see if it’s water soluble. If it is, you can rinse it with water.

			If not, you will need to spray water displacing oil onto the guide screw before wiping it with a cloth.

			Body
			Sharpening the tip and cutting edges of an expansive bit is a similar process to sharpening the tip of an auger bit. As such, you will need an auger bit file. These tools are specifically designed for sharpening right into the corners of the narrow lips and spurs of wood bits without wearing down any other part of the tool.

			Step 1 – Sharpen lip Sharpen the top of the primary lip with the file. A few passes should be enough to revitalise the edge. Be sure not to sharpen the bottom of the lip, or this will lift the cutting edge of the lip too high for it to be of any use.

			Step 2 – Sharpen spur Repeat this process on the inside of the primary spur. Be sure not to sharpen the outside of the spur, as this will change the profile of your tool and prevent it from boring even holes.

			Cutter
			The adjustable cutter is a little more complicated to sharpen than the rest of the tool, and requires a specially prepared wet stone.

			Step 1 – Prepare wet stone In order to sharpen your outrigger cutter properly, you will need to customise a wet stone by rounding off one of the edges.

			This can be done on a bench grinder, a machine that rotates abrasive wheels at high speed to shape and smooth down objects made from a wide range of different materials.

			Once you have rounded one of the edges of the stone, run it across the concave surface of the cutter to find any bumps. If there are, return them to the grinding wheel and grind them down.

			Repeat this process until there are no remaining bumps.

			Step 2 – Sharpen cutter With your wet stone secure on a solid surface, locate your cutter so that the concave surface is resting against its curved edge. Push your blade forwards and backwards against the stone, applying light pressure and wetting it occasionally by dipping it into a small container of water and shaking off the excess. The grit of the stone will grind the edge of your cutter sharp.

			After sliding your blade along the wet stone around twenty to thirty times, your blade should be sharp. Check it regularly during the sharpening process just in case you need to sharpen it a little more. Do not sharpen the bottom (flat surface) of the cutter, as this will impair its ability to evacuate waste wood by lifting the cutting blade out of contact with the material.

			Step 3 – Sharpen spur Just as you did for the primary spur on the body of the bit, sharpen the inside of the cutter spur using an auger bit file.