How to Use a Combination Square

How to use combination square featured

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 the combination square is one versatile tool that can handle measurements, straight lines, and angles.

What is a combination square?

A basic combination square is a tool that looks like a metal ruler, and a speed square had a baby. It comprises 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: 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 toolsets.

How to check your square for accuracy

Like any measurement tool you buy, you want to ensure 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.

  • Line the anvil up to the material and mark a 90-degree line along the length of the blade.
  • 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.
  • 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

Checking for Square
Checking for square. Credit: Nathan Hamilton

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. It isn’t perfectly square if you see any daylight between the ruler or anvil edge and the box.

2. Mark 90-degree angles

Combination Square Marking 90 Degree Line
Marking 90-degree lines. Credit: Nathan Hamilton

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

Combination square marking 45 degree line
Marking 45-degree angles. Credit: Nathan Hamilton

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 the material edge (scribing)

Combo Square Scribing a Line
Scribing parallel lines. Credit: Nathan Hamilton

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 Combination Square as a Ruler
Using a combination square as a ruler. Credit: Nathan Hamilton

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

6. Setting miters on a saw

Set Miters with Combination Square
Setting a miter saw at 45 degrees with a combination square head. Credit: Nathan Hamilton

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

Combination Square Bubble Level
Using the head as a level. Credit: Nathan Hamilton

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

Setting router bit depth
Setting the router bit to a precise height. Credit: Nathan Hamilton

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

Combination Square Measuring Material Thickness
Measuring precise material depth. Credit: Nathan Hamilton

Place your workpiece on a flat surface, then put the anvil flat on the top material. 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 in your shop.

Nathan Hamilton
Nathan Hamilton
Nathan Hamilton is the founder of DIY Gear Reviews and a recognized expert in the home and DIY space. He has over 200 bylines covering topics such as power tools, hand tools, and woodworking. Nathan is the strategic director for DIY Gear Reviews, deciding everything from the content covered to designing the testing methodologies for lab-tested reviews. He can be emailed at nhamilton@diygearreviews.com.

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