What is the Difference Between an Mortise and a Firmer Chisel?

A chisel is one of the oldest tools around. The firmer and mortise chisels are two different styles, with a thick blade designed to be used in combination with a mallet.

The difference between a firmer and a mortise chisel is the cutting edge angle, among other details. In addition, each tool is designed to be used in a certain way. Therefore, the biggest difference in a firmer or mortise chisel is how you will use it.

So, what is the difference between a firmer and a mortise chisel? Let's take a look at each tool and its features.

What is a Firmer Chisel

A firmer chisel is probably the first type of chisel. Originally it was used to roughly form pieces of wood into useful objects and thus was a “former” chisel. Over the years, this sturdy, reliable chisel’s name developed into the current “firmer”.

The firmer chisel is a sturdy tool with a somewhat thick handle. The blade itself has a flat rectangular design with straight sides. It does not have beveled edges, nor does it taper to a point. This makes it less than ideal for fine detailed work and such normal cuts such as a dovetail joint.

While it may be a little more work to use, a firmer chisel has been in use for thousands of years and is a great general-use tool for both lightweight as well as heavy work. The downside is that while you can use a firmer chisel for most basic woodworking, it may take more patience, and the result may not be as good as if another, more modern type chisel was used.

What is a Mortise Chisel

A mortise chisel is almost as old as a firmer chisel. It also is used in a large number of applications.

A mortise chisel has three main features that differentiate it from the firmer chisel.

A Mortise Chisel has a Thicker Blade Than a Firmer Chisel

The thick blade of a mortise chisel means it can take some abuse. A mortise chisel is made to be used with a mallet. The handle design of a mortise chisel usually has a cap or a hoop around the end of the handle to help provide strength.

The best technique to work a mortise with a mortise chisel is to gradually pound it in at increasing angles. This gives you increased accuracy and the ability to keep the cut clean as you go.

A Mortise Chisel has an Extended, Trapezoidal Blade

This blade design allows for more control of the cut than a firmer chisel provides. The blade of a mortise chisel is anywhere from a 35-40 degree angle. This means you can get a straighter, more precise cut. This is essential when you are cutting a mortise, and you need that tight fit.

A Mortise Chisel Can Provide a Cleaner Mortise

The design of the mortise chisel additionally allows you to use it to flick out the bits and pieces of wood that accumulate in the mortise as you cut. Using the blade as a sort of pry bar against the bevel of the cut allows you to get a cleaner, more exact cut. Again, this is essential when you need a tight-fitting joint.

What are a Mortise and Tenon Joint

The mortise chisel is used to create one of half of one of the most common woodworking methods: the mortise and tenon joint.

This type of joint combines two pieces of wood that fit tightly together without glue or adhesive. This explains why it has been used for ancient woodworking as far back as the Neolithic period. You can find examples of this ancient technique in Leipzig, Germany, home of the world’s oldest intact wooden architecture. Mortise and tenon joints have also been found in the Khufu ship buried near the Giza pyramid in Egypt.

The word mortise may come from the Old French word meaning hole or groove. It may also have come from the Arabic word "murtazz," meaning "fastened". Either origin works to describe a mortise.

  • A mortise is cut that forms a recess, slot, or opening in the wood.
  • A tenon is the wooden part or “tongue” that is carved to fit perfectly into that hole.

Types of Chisels and their Uses Including Firmer and Mortise Chisels

While Mortise chisels and firmer chisels may be the oldest known chisels, they are by no means the only ones. The type of chisel you need depends on the type of project you are working on.

Type of Chisel Description
Firmer Chisel A firmer chisel is general used to form or shape out a design. The blade is not quite a thick as a mortise chisel, and it does not have a beveled edge.
Butt Chisel A butt chisel is a firmer chisel that can be used in small, compact spaces. A butt chisel has the same square blade design as a traditional firmer chisel, but the blade itself is shorter and broader. This makes it perfect for when you need to remove or waste out a large area. A butt chisel is used for the mortises in a butt hinge.
Mortise Chisel A mortise chisel is made to be used with a mallet. It has a thicker, sturdy design that some find clunky and hard to maneuver. This is a good general purpose chisel for the right project.
Sash Mortise Chisel A sash mortise chisel is a lighter, thinner version of a traditional mortise chisel. This more lightweight version is designed to get into the nooks and crannies of the wood surrounding windows.
Japanese or "Nomi" Chisel This type of chisel is slightly thicker than a beveled edge chisel. It has a very sharp cutting edge made of tough carbon steel. The middle of the chisel is made of a second type of metal, usually slightly softer. Their sharp edge makes keeps softwood from crumbling.
Beveled Edge Chisel A beveled edge chisel is the most common type of chisel. A versatile tool that is not too short nor too long, you can find this chisel in almost any woodworker’s toolbox.
Paring Chisel A paring chisel is longer and thinner. They are more flexible than most chisels and never used with a mallet. Their primary use is shaving off very thin slices of wood to make a joint fit that much tighter.

Recommendations for Firmer and Mortise Chisels

Whether you are a seasoned pro or just starting, having the right tools makes a difference in the success of your project.

Stanley Sweetheart Socket Chisel Set, 4 piece- Stanley is known for quality tools, and this set is no exception. High-carbon blades with sturdy socket handles mean this set will last you a long time. Worth the investment if you are serious about your woodworking projects.

Narex Woodworking Chisel Set- A favorite with woodworkers both new and experienced, this set is made by a small Czech company and has four different sizes with a 25-degree blade angle.

VonHaus 10 pc Premium Chisel Set for Woodworking A versatile set, you should be able to complete most projects with this one set. Comes with a sharpening stone and a wooden storage case.

Choosing the Right Chisel For Your Project

Chisels used today have progressed far beyond the firmer and mortise chisels used in the past to construct everything from furniture to roofing beams. These days it doesn't matter whether you are a hobbyist building a bookshelf in your garage or a professional carpenter making a cabinet in your company's shop; there is a wide selection of chisels to meet your need. Knowing the difference between a firmer and a mortise chisel is the first step to choosing the best tool to match your purpose.

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