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A chisel is a type of hand tool used for carving or cutting hard materials such as wood, metal, stone, or masonry. There are a variety of chisels intended for different purposes, such as the rock chisel and the cold chisel. What’s the difference between the two? Can one be used in place of the other?
Rock chisels, a specialized version of masonry chisels, are designed to break rocks to extract mineral specimens, semi-precious gems, and fossils. Cold chisels are designed to cut any unheated metal that is softer than the metal the chisel is crafted from. A cold chisel can be used on rock; however, it will not work as well as a rock chisel and will eventually break the chisel.
Read on to learn more about the differences between standard cold chisels and rock chisels, as well as why they should be used for their intended purposes.
In case you are looking for advice about what chisel to buy, here is the link to the best chisels for rockhounding (Amazon link).
Rock Chisels Are For Breaking Rock
Multiple sources, like this one and this one, advise that there are two options for rock chisels:
- Specialty rock chisels – tend to be more expensive but are harder and better for geological work due to a carbide tip
- Cold chisels – are more economical but will break if used for rock.
Cold chisels will be discussed in more depth later. For this article, “rock chisel” will refer to the specialized chisels designed with rock breaking in mind.
First, let’s take a look at the composition of all chisels. Then we’ll look at each one more closely and compare the two.
Anatomy of a Chisel
It is important to know the anatomy of a chisel first. Here it is:
- Cutting edge
- Striking edge, or head
Cutting Edge – Cold Chisel
The cutting edge of a cold chisel is beveled. Roy Berendson of Popular Mechanics advises that a cold chisel’s edge should be maintained at a 60 to 70-degree bevel.
While this angle may not seem very sharp, harder, and stronger beats sharpness when it comes to cutting cold metal. A more acutely angled beveled edge would be more likely to chip and break when striking against hard surfaces.
The cutting edge of a cold chisel is tempered and hardened by heating the metal and then suddenly chilling it. Hence, the name. The flash cooling is done so that the chisels will be able to maintain their sharp edge.
- Cold chisels are available with varying widths of cutting edges. Berendson suggests always using a chisel that’s 25% wider than what you’re cutting.
- There are different types of cold chisel cutting edges, which will be addressed later.
Cutting Edge – Rock Chisel
The cutting edge of a rock chisel differs from that of a standard cold chisel in that there is a piece of tungsten carbide welded to the tip of a rock chisel.
- This carbide tip is what gives the rock chisel the advantage over the cold chisel, in terms of endurance and strength, when used on granite and hard stone.
- The bevel of the carbide tip varies from tool to tool. It is important to observe the shape of the carbide when the tool is new, and this shape must be maintained.
Striking Edge, or Head
There is little to no difference between the striking edge of a rock chisel and a cold chisel.
The striking edge, or head, of these chisels, is chamfered or cut at a 45-degree angle to remove the 90-degree edge. This is to prevent burring and mushrooming from repetitious strikes with a hammer.
The striking edge of a cold chisel is not hardened but left soft so as to absorb the impact of hammer blows. A chisel must be softer than the hammer used to prevent the chisel from shattering. Due to this, wear on the striking edge is to be expected after use.
The body is the portion of the chisel that will be held while in use. Chisels are available in varying sizes, lengths, and cutting edge widths.
|Cold Chisel||Rock Chisel|
|The body of a cold chisel will typically have a cross-section that is octagonal or hexagonal, depending on the metal composition of the chisel.||Rock chisels can be found with bodies that are octagonal, hexagonal, or even round.|
|Cold chisels are composed of either carbon tool steel or steel alloys.||An octagonal body is generally regarded as easier to grip.|
Cold chisels made with high carbon steel or steel alloys might be marketed for their hardness, but they can be softened by improper sharpening. They may also be softer than intended if the heating and tempering were done incorrectly.
Rock chisels are generally the same size as cold chisels, but they have a section of carbide welded to the tip.
“Carbide” refers to tungsten carbide. What is commonly referred to as tungsten carbide in the tool world is “a metal matrix composite of true tungsten carbide (WC) ceramic particles bonded together by a cobalt metal binder.“
This “true tungsten carbide” is a ceramic compound of tungsten and carbon.
In terms of hardness, tungsten carbide registers as a 9 on Moh’s scale of mineral hardness. By comparison, steel registers anywhere between 4 and 8 depending upon the amount of carbon in the steel and how the steel is treated.
Chisels and Their Recommended Usage
And what are chisels good for? Find a recommended usage for both, rock and cold chisel in the table below:
|Cold Chisel||Rock Chisel*|
*The list of rocks and minerals recommended for the rock chisel is incomplete. The list goes on to include any rock or mineral that has a Mohs hardness rating of 6 or greater.
How Hard Are Rocks Compared to Metal?
Here is how some of the rocks one might find compare to the metals that can be cut by cold chisels in terms of hardness.
|Metal||Mohs Hardness Rating||Rock||Mohs Hardness Rating|
TIP: The advantage of the hardness test is that it can be easily done at home or even in the field while rockhounding. Check out the complete DIY guide on testing mineral’s hardness in the article below:
DIY Guide: Testing Mineral’s Hardness (Explained by Expert)
Rock Chisels and Hand Points
Whereas your standard chisel narrows down into a straight, thin edge, the hand point is tapered at the cutting edge on all sides to a point. Similar to the shape of a carpenter’s pencil.
- The standard chisel is used to break rocks along a line; the force of the strike is spread over more area, which is less effective but more controlled.
- The hand point is, as the name suggests, pointed; the force of the strike is concentrated in one spot. A hand point may also be referred to as a punch.
Trow and Holden advise that their carbide-tipped chisels and points are “ideal for fast, aggressive material removal.”
Types of Cold Chisels
There are different cutting edges for cold chisel that perform different tasks:
- Flat chisel
- Cape chisel
- Round-nose chisel
- Diamond-point chisel
A flat chisel is the most commonly used cold chisel as it is the most versatile. The cutting edge is flat and perpendicular to the body. A flat chisel can:
- Cut sheet or plate metal
- Cut rods
- Cut chain links
- Shear off rivets
- Shear off bolts
- Split bolt heads
If want to buy a flat chisel, I recommend buying this one (Amazon link).
A cape chisel has a long taper on the top and bottom of the cutting end and a narrow cutting edge.
Cape chisels are ideal for:
- Cutting narrow grooves
- Making keyways
- Making slots
- Locking nuts and bolts so they won’t loosen
You can check my pick for the cape chisel here (Amazon link). Different sizes of this cap chisel are available.
A round-nose chisel is similar to the cape chisel, except that it has a semi-circular cutting edge. This chisel is primarily used for cutting round grooves, such as for oil channels in a bearing.
This chisel can also be used to cut a small groove to redirect a drifting drill bit while starting a hole in thick metal.
You can check my pick for the round-nose chisel here (Amazon link).
The diamond-point chisel has a tapered, four-sided cutting edge. This chisel, again, is similar to the cape chisel, but its cutting edge is used to cut v-shaped grooves.
Other uses for the diamond-point chisel include:
- Prepare metal parts for welding
- Chip out welding
- Squaring and clearing debris out of corners
Check out my pick for diamond-point chisel here (Amazon link). Different sizes are available.
TIP: You need to cut bigger rocks from time to time. It seems to be an easy task but it is always good to know how to do it properly. Read more in this article:
Step-by-Step: How to Cut Rocks with Hammer and Chisel
Mushrooming and Burring
A chisel should not be used if it has signs of mushrooming or burring.
- Burring – refers to the forming of rough edges or ridges on a piece of metal.
- Mushrooming – refers to deformation where a flat metal surface is compacted and distorted, causing the flattened edge to hang over the edge, flaring out.
In these situations, edges are jagged and sharp and can cut the user while handling them. Also, when striking with a hammer, these edges can break off and cause damage. Important note: always wear eye protection when using chisels.
Maintaining the Carbide Tip of a Rock Chisel
Whereas the cutting edge of a cold chisel has a fairly standard 60 to 70-degree bevel, the shape of the carbide tip varies from tool to tool.
- Shape. It is important to observe the shape of the carbide when the tool is new, so this can be maintained.
- Sharpness. A bench grinder with a silicon carbide wheel of 80 grit or finer or diamond pads can be used to sharpen a carbide. The carbide needs to be returned to its original shape. Sharp edges need to be beveled or chamfered as they were before the carbide was used. A carbide that is too sharp is more likely to chip or crack.
- Heads. Keep in mind that Tungsten Carbide is a very hard metal; special equipment will be necessary to redress a carbide tip.
Allow the carbide to cool slowly; never dip a carbide in water or oil to cool it. This rapid change of temperature can result in thermal cracking, a network of fine cracks that “normally result in catastrophic failure.“
Sharpening a Cold Chisel
If the cutting edge of a cold chisel becomes dull, it can be sharpened using a medium or fine grit file. File away from the cutting edge, which will direct heat away from the cutting edge.
- Don’t let it overheat. Occasionally dip the chisel in water if necessary while sharpening to keep the metal cool.
- A grinder should never be used to sharpen a cold chisel. The excess heat can cause the cutting edge to lose hardness, strength, and durability.
Redressing Deformed Heads
One source advises that if a chisel shows signs of mushrooming or burring, a bench grinder can be used to remove these deformities.
Avoid overheating the chisel and softening the metal. Dip the head in water often while grinding to keep the metal cool. Use a finer grit to smooth the surface of the head once it is reshaped.
Another source recommends discarding any chisel that is mushrooming, chipped, dented, or cracked. While some might find it over-cautious to throw away your mushrooming chisels, chipped and cracked chisels could potentially be dangerous should the chisel shatter mid-use.
TIP: If you are planning on installing any pavers to make a pathway or simply decorate your yard, then you’ll need to know how to cut pavers with a hammer and chisel. Find out more in the article below:
5 Simple Steps on How to Cut Pavers with Hammer & Chisel
What Is a Hot Chisel?
The name cold chisel implies there must also be a hot chisel; there is.
- Cold chisels are designed to work on metals that have not been heated.
- Hot chisels are just the opposite; they are used on red-hot metal.
When metal is heated to this degree, it becomes softer. As such, hot chisels don’t need to be hardened or tempered. Also, the cutting edge of a hot chisel sports a 30-degree bevel.
This cutting edge is sharper than that of cold chisels. As the heated metal is soft, a sharper edge is both necessary and less likely to chip.
Hot chisels should not be used for any other purpose than blacksmithing and cutting hot metal. They are practically useless for other cutting purposes.
As mentioned earlier, the “rock chisels” discussed here are specialized, carbide-tipped chisels ideal for geological use. The carbide’s hardness allows it to stand up to heavy-duty jobs.
Steel masonry chisels can be used on some of the less hard rocks you might find, such as marble and limestone. When out on a dig, however, you can’t be sure what minerals and rocks you will come across.
There are more specialized masonry chisels, as the intended purpose of masonry chisels is to shape and refine stones rather than simply break them.
Types of Masonry Chisels
Just as there are different cutting edges for cold chisels intended to cut metal, there are different cutting edges for masonry chisels.
- Hand Point, or Punch
- Tooth Chisel
- Bushing Chisel
- Flat Chisel
- Rondel, or Bullnose Chisel
- Hand Tracer
- Hand Set, or Pitching Tool
Find the best masonry chisels I recommend here (Amazon link).
Hand Point, or Punch
As mentioned before, the hand point delivers the most impact. It is for roughing out and clearing material quickly.
A “stone bruise” can be left on a softer stone when the point has gone deeper than the intended surface. A stone bruise is a white mark on the surface of the stone that can only be removed by carving deeper than the intended surface.
The cutting edge of a tooth chisel has a row of sharp teeth. The number of teeth varies by tool.
After the hand point has roughed out a shape, the tooth chisel is generally used to clear away rough marks and high points left by the hand point.
As tooth chisels will leave behind sets of parallel lines, it is not a chisel typically used for finishing work.
Tooth chisels are not to be used on harder stones such as granite, as the teeth will break.
Bushing chisels are similar to tooth chisels in that they have teeth. Whereas the tooth chisel’s cutting edge is flat with one row of teeth, the bushing chisel has multiple rows of teeth.
The bushing chisel has multiple purposes.
- Roughing out granite or other hard stone
- Leveling the surface of the stone
- Creating an evenly textured finish on softer stone
Just as with the cold chisels, this cutting surface is flat. It can be used for roughing out a shape with a little more control than a punch, or for smoothing out the roughness left by a tooth chisel.
Rondel, or Bullnose Chisel
Similar to the round-nose chisel, the rondel chisel has a rounded cutting edge. It may be used as a flat chisel to smooth out rough surfaces, but it is particularly useful for cutting curved planes and hollows.
The tracer looks like a thicker, oversized flat chisel. It is used to score and split large sections of stone.
Hand Set, or Pitching Tool
The handset, or pitching tool, is primarily used for trimming, squaring, or “rock-facing” stone when the surface is relatively flat.
Rock-facing is a process where the top and bottom of a stone face or edge is chiseled to create a textured, rough appearance. This is meant to enhance the natural beauty of the stone being used.
A smaller variation of the handset is the chipper. Using different sizes allows more control over the amount of material removed.
Safety is always the most important. Follow these few recommendations and stay safe while using your chisel:
- Always wear eye protection when using a chisel
- When using any type of chisel, inspect it before use. Do not use a chisel if it is chipped, cracked, or has some other flaw.
- Never use a chisel with a mushroomed head.
- Be sure to use the correct chisel for the task at hand.
- Use the appropriate hammer
- Do not chip toward yourself.
- Strike lightly at first to test the relative hardness of the material being chiseled.
Rock chisels are meant for breaking and clearing rock. Cold chisels are meant for cutting metal.
There are sources that advise to never use cold chisels for cutting or splitting stone. This is likely due to the chance that the chisel will break against harder rocks.
Carbide-tipped chisels are the best option for geological work and rock breaking even if they do tend to be more expensive. When you account for replacing broken cold chisels, the carbide-tipped tools may save money in the long run.
TIP: If you are looking for the best safety gear for rockhounding, check out this article and find all the gears you need:
Recommended Safety Equipment for Rockhounding: Stay Safe!