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How to Use a Combination Square

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In a woodworking shop, precise measurements, straight lines, and accurate angles can make or break a project. The list of tools a person can use for measuring, marking, and creating angles is long. But one versatile tool that can handle measurements, straight lines, and angles is the combination square.

What is a combination square?

Parts of a combination square with labels and arrows pointing to each part.

The basic combination square is a tool that looks like a metal ruler and a speed square had a baby. It is made of two major components, a blade and a handle.

The blade is a flat ruler with a channel running down the center of one side.

The handle consists of a few parts. But the most important are the two surfaces for placing the combination square, which are the shoulder and the anvil

The shoulder places the square at a 45-degree angle to the material and is used for marking miters.

The anvil is used for aligning the square at a 90-degree angle to materials.

The other parts of the handle worth mentioning are the bubble vial, the adjustable knob, and a scratch awl. 

Warning: The scratch awl in your combination square, if not properly watched, has a tendency to disappear. Chances are, it runs off to the same place as the missing 10mm sockets in all your tool sets.

Choosing a combination square

A basic combination square is a great hand tool for beginners and that is because even a basic one has many capabilities.

Here are some factors to consider when picking the right combination square:f

  • Price: It is important to remember that this is a measurement tool and economic options aren’t always the best for precision. While some of the best combination squares can be found in the bargain bin for under $10, it’s important to ensure they’re square out of the box. Moving outside of that price range, nearly all squares costing $20 or more are accurate.
  • Material: Choosing a square made from higher-grade or engineered materials affects three things. Better materials will reduce warping, maintain a tight fitting between the handle & the blade, and ensures longer-term visibility of the measurements on the blade. It’s best to avoid squares with plastic handles.
  • Units of measurement: If you live in the United States, most squares will use inches on the blade. Finding a blade with both inches and metric will allow for flexibility in measuring. 
  • Size: Most combination squares come with either a 12-inch blade or a 6-inch blade, but there are longer and shorter-blade models.
  • Etched marking: A combination square with etched ruler markings will last longer than one with the markings stamped onto the blade with ink.

How to check your square for accuracy

Like any measurement tool you buy, you want to make sure it is accurate and free from defects. Checking the accuracy of your combination square is fairly simple and essential for woodworking. You will need a piece of material (at least two inches wide) that is already perfectly square and a pencil. 

  1. Line the anvil up to the material and mark a 90-degree line along the length of the blade.
  2. Flip the square over, line up the ruler to the line you just marked, and mark another 90-degree line along the length of the blade.
  3. Check to see if the lines overlap. If so, then your square is accurate. If not, get a new square.

How to use a combination square

There are many ways to use a combination square. Here are several of the most common uses:

1. Check boxes for square

Combination square checking for square
Checking for square

Adjust the ruler so it is slightly inset from the anvil and tighten the knob. Then hold the square in the corner of a box to see if the box edges are aligned at 90 degrees. If you see any daylight between the ruler or anvil edge and the box, then it isn’t perfectly square.

2. Mark 90-degree angles

Combination square marking a 90 degree line
Marking 90-degree lines

For a 90-degree angle, place the anvil against the material. Use a pencil to draw a line along the blade and back to the anvil.

3. Mark 45-degree angles

How to use a combination square
Marking 45-degree angles

For a 45-degree angle, place the shoulder against the material. Use a pencil to draw a line along the blade and back to the shoulder.

4. Draw a parallel line to material edge (scribing)

Combination square scribing a line
Scribing parallel lines

Extend the blade to the desired length past the anvil. Place the anvil against the material edge. Using a pencil at the end of the blade, slide the combination square along the material edge.

5. As a ruler

Using a combination square as a ruler
Using a combinations square as a ruler

Simply loosen the knob to remove the handle and you have a ruler and straight edge.

6. Setting miters on a saw

Using a combination square to set miters on a saw
Setting a miter saw at 45 degrees with a combination square head

Loosen the adjustment knob to remove the blade and use the anvil or shoulder to check the angle of your blade against your deck or fence on a miter saw.

7. Use the head as a level

Using a combination square to measure level
Using the head as a level

With the blade removed, place the anvil on the surface to be measured for level. Use the bubble level to gauge the level of the surface.

8. Table saw or router height setup

Combination square setting router bit height
Setting the router bit to a precise height

If you don’t have calipers, you can use the square in a pinch to set up a table saw or router for single cuts, dados, or rabbits. Place the anvil on the material and extend the blade to the desired depth. Remember to tighten the adjustment knob to lock in the measurement. Use that measurement as a reference for setting blade or router bit heights.

9. Measuring cut depth or material thickness

Measuring precise material depth

Place your workpiece on a flat surface and then put the anvil flat on the material top. Extend the blade into the cut (the thin blade will fit into most blade cuts) or to the flat surface and lock in the measurement with the knob.

More tips

The obvious don’ts

It really shouldn’t have to be mentioned, but don’t use your combination square as a blunt object to hammer or pry with. Doing so can loosen fittings, chip or warp the blade, and negate the measuring accuracy of your tool.

Faded Ruler Marks

Over time you might notice it is hard to read the ruler marks on the blade. After cleaning the ruler, use a fine-tipped permanent marker to fill in the marks and make them more visible. 

Another method is to apply a thin coat of your wife’s black nail polish (from her goth days) to the blade surface above the ruler marks. Then use a very fine grit sandpaper (400+ grit) to remove the paint from the blade surface, making sure not to remove the paint from within the marks.

Multiple combination squares

Apart from having different sizes of squares, having many woodworking squares of the same size isn’t a bad idea. Having a square at each workstation can save you from hunting for the tool within your whole shop. 

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