The Sculpture Channel

How to Sharpen Flat Chisels for stone carving​

How to sharpen flat chisels for stone carving

What is a tooth chisel is? How does it look like? What traces does it leave behind? What is its use? And finally, how to use a tooth chisel? 

In this video, Athar is going to discuss the gradina, or tooth chisel. This video provides you with a detailed description of the various shapes in which it can be found and includes an explanation and demonstration of how to use the tooth chisel. 

If you’re making a sculpture and getting to the stage where you want to put in the finer details, or perhaps you’re carving letters, you will need to use a flat chisel and it’s very important that its cutting edge is crisp sharp. In this video, Athar will show you how to sharpen flat chisels

Stone carving flat chisel are finishing tools, they are used to remove the rough and uneven marks left by the tooth chisel and to achieve a smooth surface.

They are also used for letter carving, and when used for this purpose they need to be extremely well sharpened and kept that way. The degree of sharpness of the chisel will also affect the degree of smoothness of the stone surface.

That said it’s important to point out that in stone carving the term sharp is relative compared to wood carving tools. Stone carving chisels are far from being sharp. Wood carving chisels must be dangerously sharp, in fact you can even shave yourself with a well-sharpened wood chisel, but stone carving chisels don’t need to be as sharp.

Wood carving happens literally by means of cutting, shaving, or slicing through the material, whereas stone carving happens by means of breaking the stone. Therefore, a razor sharp stone carving chisel would immediately lose its edge. A clean straight cutting edge is good enough.

The shape of its cutting edge this can be shaped in two different ways: a rough shaping with a finer edge at a slightly different angle. This will make the cutting edge stronger. Or a perfectly straight surface

The choice between the two options will be determined by the kind of stone that you’re working on and the level of finish that you’re aiming at. Harder stones require a strong cutting edge with a wide angle whereas finer details and softer stones require a narrow angle.

Flat chisels, like any other stone carry chisels can be fully fashioned out of hardened steel or they can be fitted with a carbide tip. If you want to know what the difference is between hardened steel and carbide check out our episode on how to sharpen the point chisel or the episode specifically dedicated to carbide.

When sharpening chisels, what you must remember is that hardened steel is very sensitive to high temperatures and needs to be kept cool during the sharpening process, while carbide tipped chisels are very sensitive to temperature shocks so they must not be abruptly cooled down.

Flat chisels, have a very thin cutting edge and the ones in hardened steel are very easy to burn when sharpening then on the bench grinder. Therefore, it is better to sharpen them by hand on a flat sharpening stone. This method will grant you more control in the process, it will avoid you the stress of burning the chisel, and it will also avoid the formation of rust on the steel due to the constant contact with water. So, all in all, at the end a flat sharpening stone will give you better results than a bench grinder.

The basic principle of sharpening chisels on the flat stone is the same for all chisels: place the chisel on the stone, feel when the cutting edge has full contact with the flat surface and push the chisel back and forth. Count the number of times you go back and forth turn the chisel over and repeats counting the number of times you go back and forth, this is essential for keeping the cutting edge of the chisel cantered to its axis.

When sharpening flat chisels for letter carving, the corners of the cutting edge need to be perfectly square and perfectly sharp. This will ensure a clean entry into the stone surface resulting in a crisp letter.

Keep in mind that when used for cleaning and finishing a flat surface sharp corners might create tiny scratches on the stone, so the best way to resolve this problem is to lightly round off the corners of the flat chisel, the absence of sharp corners will not make it possible for them to scratch the stone. You can do this by lightly turning the chisel on its sides while going back and forth on the sharpening stone.

Carbide tips are much harder than hardened steel and they can withstand much higher temperatures. Therefore, you can easily sharpen them on the bench grinder. We still recommend sharpening them on the flat stone – in that case the process is exactly the same as I have just explained.

Let’s now look at how to sharpen flat chisels on the bench grinder. Bear in mind that on microscopical level, the sharpening wheel with a coarse grit will leave an irregular texture on the surface of the metal. It will also introduce tiny cracks on the cutting edge of the chisel, these are not visible to the naked eye, but they will affect the lifetime of the chisel as the tiny cracks will make the metal even more brittle than it already is. So, it is better to use the grinding wheel with a coarse grain for the rough shaping of the chisel and then switch to a fine grain wheel for cleaning up the edge.

The technique with which you hold and move the chisel on the grinding wheel is very important. Hold the chisel at its centre, with my left hand the hand is also resting on the platform and using it as a rail with my right hand I hold the chisel if it’s end to maintain stability once the wheel is at full speed I place the cutting edge of the chisel slant on the grinding wheel and go from left to right over the whole width of the wheel sliding the chisel on the grinding wheel from left to right is very important because if you keep the chisel on one place you will create a groove on the wheel and this will make sharpening on the chisels very difficult and annoying now the position of the chisel on the grinding wheel will affect the angle of its cutting edge if held higher the edge will be narrow and long while placing the chisel on the lower end of the wheel will result in a wider angle and a stronger edge one of the difficult things of sharpening a chisel on a grinding wheel is that you can’t see what’s happening on the side that it’s being sharpened in order to see what’s happening you will need to lift the chisel turn it over look at the cutting edge and after judging the surface placing him back on the grinding wheel and continue sharpening and it’s at this point that it will be very difficult to place the chisel exactly at the same position and a different position will affect the angle of the cutting edge so what do we do about this experience you will eventually develop a feeling after having spent quite some time sharpening chisels on the bench grinder but there is one method that can give you a clue on what part of the chisel is being sharpened and that is by looking at the sparks coming out of the grinding wheel if they come from under the chisel when you are shaping the rock surface while if they appear from above the edge of the chisel then you’re shaping the cutting edge okay it’s time to put my money where my mouth is so let me show you how the actual sharpening goes [Music] [Music]

If you sharpen the chisel on the bench grinder it’s good to finish the procedure with a quick sharpening on the flat stone this will remove the imperfections on the cutting edge of the chisel and will make the work more pleasurable.

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