How to Easily Find Angles for Carpentry and DIY Jobs

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How to Find a Cutting Angle

Before we can actually cut anything, the first job is work out the exact angle that you need to cut to.

In almost all situations, the surface you are working with will not be square, although it may appear to be. For example, if you are mitreing two pieces of skirting board together in the corner of a room, chances are that the corner you working in will not be at a perfect 90°

We get hundreds of questions from people about how they can fill big gaps between skirting boards caused because the walls of the room are not exactly at right angles.

With this in mind, it’s essential to firstly work out the exact angle you’re working with.

There are several ways and tools that you can use to do this:

Use Good Old Mathematics

If you are a dab hand with the old maths then it should be easy enough to calculate the internal angles of a triangle that you can create from eth area you are working in.

For example, you can measure equally each side of a triangle and then also the longer hypotenuse line that joins the 2 other lines together and then from that, work out all the internal angles.



Measuring and marking the corner of a room to cr

Measuring and marking the corner of a room to create a triangle to work out angles

We won’t go into the exact calculation required her, but a great explanation on how solving sss triangles (side, side, side) can be found on the Maths is Fun website here.

Use Specific Angle-Finding Tools

As good and accurate as the above maths solution is, sometimes it’s just not practical to spend precious minutes performing a calculation, especially if you are out on site, where time is money.

To this end, there are plenty of manual and digital angle finders available that can very quickly and accurately find any given angle for you, here are some common ones:

  • Standard protractor
  • 

Standard protractor used to find and mark angles

    Standard protractor used to find and mark angles

  • Digital angle ruler or digital angle finder
  • 

Digital angle rule used to quickly calculate and

    Digital angle rule used to quickly calculate and find angles

  • Site protractor
  • 

Starrett large site protractor used for quickly

    Starrett large site protractor used for quickly finding and marking angles

  • Angle measurer
  • 

Angle measurers feature both a protractor and ru

    Angle measurers feature both a protractor and ruler for quick and easy angle finding and marking

  • Angled bevel
  • 

Angled bevels can be used to quickly find and ma

    Angled bevels can be used to quickly find and mark cutting angles

Each of the above tools can be used to accurately mark a given angle on pretty much any surface. However, if you also want to know what the angle you are dealing with is, some tools may be better than others.

For example the angled bevel will allow you to set and mark and angle, but does not feature any form of visual gauge to tell you what the angle is.

Likewise, a standard protractor is a great tool for marking an angled cutting line onto a given object, but trying to use one to find out what the exact angle of the corner of a room is would be pretty much impossible.

With the above in mind, if you are looking to purchase angle finding tools, make sure you invest in the correct tool that will fulfill all of your requirements.

Method 2: Using a Miter Box

This gives improved accuracy when cutting. A miter box has slots in its vertical sides which act as guides and prevent the blade of a saw from sloping from the vertical. Metal, wood and plastic versions are available. Some need to be held in a vise while others have a "hook" or raised edge on the underside which can be butted up against the edge of a bench.

A miter box enables you to make 90-degree cuts in timber and usually 45-degree cuts also.

Note: When cutting timber, cut on the waste side of the line rather than the center line.

Various types of miter boxes

© Eugene Brennan

This miter box has a "lip" or hook on the underside which allows it to be pushed tightly against the edge of a bench

© Eugene Brennan

Using a Tenon Saw

A tenon saw is shorter than a "normal" hand saw and is less cumbersome to cut with. It also has smaller teeth (the pitch is greater), which reduces the tendency of the blade to tear or chip the ends of wood fibers whilst cutting. Thirdly the rigid spine of the saw stops the blade from curving and warping too much while cutting. All this helps to give better results, which is important if you are making furniture or other stuff where accuracy and finish are important.

Kerf of a Saw

When cutting, position the blade and teeth of the saw so that you cut on the waste side of the pencil line rather than cutting along the center of the line. The kerf or width of the saw cut can produce "gaps" if you are cutting joints or doing other fine work. The slight error in length due to the kerf of the saw when cutting on the center of the pencil line, can accumulate and cause a greater error (e.g. if several pieces are cut to size and placed side by side).

Kerf of a saw. The diverging teeth cut a slot in timber, wider than the thickness of the blade, so the blade doesn't bind.

Ludraman, public domain image via Wiktionary

The slots in metal miter boxes don't wear away as quick from contact with the teeth of a saw

© Eugene Brennan

A miter box and tenon saw produced these results

© Eugene Brennan

Making and Using a Marking Knife

A pencil is fine for rough work, however, a marking knife never gets blunt and produces a fine line, allowing you to produce more accurate results when cutting joints. You can make one by cutting a 45-degree angle on an old dinner knife with an angle grinder and then sharpening it. You could use a Stanley knife, however, the advantage of a long-bladed, flexible knife is that it can reach into tight spaces. (This knife also comes in handy for spreading silicone sealant and putty!)

A sharpened dinner knife used for marking timber

© Eugene Brennan

Using a marking knife to mark a section of timber.

© Eugene Brennan

Video

Mmmmmmm Square!

A miter saw gives an accurate cut if it's setup properly

© Eugene Brennan

If you plan to cut a lot of lumber, one of these miter saws is practically essential. This 12" Dewalt Sliding Compound Miter Saw (model DWS779) from Amazon will do everything you need. It's a corded power saw with a 120 volt, 15 amp motor and is suitable for cutting rough or planed lumber up 2 x 14 at 90 degrees and 2 x 12 at 45 degrees. Another option is the cheaper Metabo HPT C10FCG 10 inch Compound Miter Saw. (This is a cordless, battery-powered, non-sliding saw, limited to cutting approximately 2 x 5 or 3 x 3 at 90 degrees).

Mitre saw

Amazon

A miter saw is virtually essential for rapidly producing accurate square cuts when framing (building timber frame walls)

© Eugene Brennan

I used a miter saw to cut all this timber to size.

© Eugene Brennan

Section 3: How to cut angles on table saw

The following are the three major steps for cutting angles on the table saw:

Prepare the wood and saw blade:

Fetch the wood and make sure all your tools are close-by to avoid clumsiness. You will come close to the saw blade as you prepare, so you should always keep the saw turned off and unplugged.

Measure and mark out the beginning and end of the cut:

Determine the nature of the angle you intend to cut. It involves knowing the exact dimension needed for your project. Marking the target spot in pencil, measure along the wood’s sides using a measuring tape or ruler. Verify that your angle is correct before you proceed.

Outline the Cut:

Indicate the cut’s start and end by linking the points you have marked. Double-check the sketched outline on the board before placing a ruler on the board to draw across it with a thick, dark line. Then measure the angle again.

Adjust the saw’s height:

The recommended blade height is about 0.64 cm. With this height in mind, you can then use the adjustment crank to adjust to the height.You can make adjustments byplacing a ruler on a piece of broken wood. Label the 0.64cm mark on the broken wood and position it beside the saw. Adjust the saw until it coincides with the marked point. Raising the saw’s height allows more contact between the blade’s teeth and the wood which translates into a smooth cut. However, if you are not sure of the best height to keep the saw at, use your discretion to judge. 

Figure 4: Saw blade at a particular height. 

Prepare a drafting triangle for crosscut: 

Clear the table before using a drafting triangle. You can create crosscuts across a board’s width or perpendicular to the grain of the wood. However, if you are trying to stay conscious of the wood’s length or edges then a taper jig is best. In a case where the drafting triangle is not available, you can use a simple framing square

Set a miter gauge for cutting angles: 

A miter gauge is a portable holding device that enables you to cut angles on wood boards. To use this gauge, place it firmly against the edge of the drafting triangle. Pay attention to the calibration of the gauge as it is necessary to place the wood at your preferred angle.  

Open the taper jig to set an angle for the wood: 

Standard taper jigs are long pieces of wood used to brace a board’s side. It is particularly useful when making bevel cuts to keep your fingers away from the blade. Hold the jig against the side of the board opposite the cut. To make the process less complicated, use a sled-style jig instead of the triangular-shaped jigs. 

Secure a Fence: 

Take advantage of the table saw’s fence, which serves as an integral safety feature. Slide the fence around the table to brace the miter or taper jig gauge. You can also slide a piece of scrap wood into the clamp at the back of the taper jig or front of the miter gauge. 

Figure 5: Miter gauge on the table saw.

Put on safety gear: 

You must put on safety glasses while cutting angles on the table saw to protect your eyes against wood debris.

Make a couple of test cuts:

Make samples to ensure that your saw and miter gauge is in order. Get pieces of scrap wood, cut them as you would cut the wood for your project. Make the necessary adjustments and make sure the cut is clean. 

Hold the scrap wood tightly against the fence

Furthermore, at the edge of the table, put the fence in front of your dominant side. Set the wood in between the fence and the saw, then align the saw with the sketch for cutting. Before you start cutting, make sure the miter gauge is out of the saw’s way.

Stand behind the wood: 

Take a few moves to the side in the direction of your dominant hand. Place yourself instead of the saw blade right behind the miter gauge. Standing in this place prevents you from something called a kickback. It’s uncommon, but when you least expect it, it can happen.

Push the board and the fence: 

Place your opposite hand on the miter gauge’s handle while holding the fence and board together with your dominant hand. Then, start at a slow, constant pace to drive things forward. Go slowly to get a clean cut to avoid a kickback. Stop when the saw slices through the wood.

Pull the wood back after cutting: 

Pull all back towards you when the saw has sliced through the surface, including the fence and miter gauge. Carry it around to the table’s edge. You can easily cut the wood and disconnect it from the miter gauge after deactivating the saw.

Types of Cuts

Crosscut

A crosscut is made across the grain of the wood or across the width of the board. A crosscut changes the length of the board or makes the board shorter. A crosscut is often referred to as simply a cut or cuts.

Rip Cut

A rip cut is made with the grain of the wood or along the length of the board. A rip cut changes the width of the board or makes the board narrower.

Miter Cut

A miter cut is made diagonally across the grain of the wood or across the width of the board. A miter cut changes the length of the board or makes the board shorter.

Bevel Cut

A bevel cut is an angled cut made on the edge of a piece of wood. A bevel cut changes the profile of the wood. Bevel cuts can change the length of the board or the width of the board.

Compound Miter Cut

A compound miter cut combines a miter cut and a bevel cut. Compound miter cuts are needed to install crown molding. A compound miter cut changes the length of the board or makes the board shorter. Back to Table of Contents

Miter Saw

  • Crosscuts
  • Miter Cuts
  • Bevel Cuts
  • Compound Miter Cuts
  • Best for cuts on narrow boards usually up to 12 inches
Crosscuts

Crosscuts

The saw we’ll use most often to make crosscuts on narrow boards like a 1×4, 1×6 or 2×4 is a miter saw.

Related: Why is a 2×4 Not 2 Inches by 4 Inches?

Miter saws are typically available with a 10-inch blade or 12-inch blade. Many compound miter saws with a 10-inch blade can make crosscuts on boards up to about 5-½ inches wide by 3-½ inches thick.

Many compound miter saws with a 12-inch blade can make crosscuts on boards up to about 7-½ inches wide by 3-½ inches thick.

A sliding miter saw that slides front to back can increase the length of these cuts.

For boards wider than the cutting capacity of our miter saw we could make two cuts. In other words, we could place one edge of the board against the fence and cut partially through the width of the board. Then we could flip the board placing the opposite edge against the fence and make a second cut. This second pass would complete the cut.

I have used this method in a pinch. It works, but it’s often not accurate. If the edge of the board has a curve or bow it can push the board away from the fence. This means the cut won’t be straight from edge to edge.

To make cuts on wider boards I think it’s better for us to use a different saw like a circular saw, or table saw.

Related: How to Adjust a Miter Saw for Accurate Cuts

Miter Cuts

We’ll also use our miter saw to cut angles. A miter saw is a great tool to make miter cuts on workpieces for projects like picture frames and more.

We’ll use the miter adjustment to change the angle or the degree of the cut. The miter adjustment is usually a knob or lever at the front of the saw.

Related: How to Make Wood Picture Frames (Without Miter Cuts)

Bevel Cuts

A miter saw is a great tool for cutting bevels on the ends of narrow boards. We’ll often need to cut a bevel on trim boards or molding like baseboards.

We’ll use the bevel adjustment to change the bevel or degree of the cut. The bevel adjustment is usually a knob or lever at the back of the saw.

Related: 7 Miter Saw Tricks Every DIYer Should Know

Compound Miter Cuts

A miter saw is also great for making compound miter cuts. Compound miter cuts are needed to install crown molding.

To make compound miter cuts we’ll use the miter adjustment and the bevel adjustment to change the angle or degree of the cut. Back to Table of Contents

Cutting Mire Joints to Fit an Angled Surface

As we now know exactly how to find or measure an angle and then accurately mark on to a given object ready for cutting so that it will fit perfectly against an angled surface, there’s one more point concerning cutting angles that you should be aware of.

To explain this in full we need to look again at the humble mitre joint. As we have mentioned, one of the most common jobs in carpentry and also the building trade as a whole is making sure that where two items meet at a corner, they are finished nicely, e.g. are mitred.

To ensure that this happens, knowing the angle they are fitting into as a whole is only one part. As the two objects meeting will form the whole angle, each object will need to be cut at half the angle of the whole angle.

To explain a little more, the image below shows 3 walls along which you can imagine placing skirting. On the first wall, if you had to join the skirting on the dotted line, you would need to make two cuts at 90° to get a tidy joint.

On the middle piece, two mitre cuts of 72.5° would need to be made to get a perfect joint and on the last piece, two mitre cuts of 45°.



3 different shape walls and what angle each mitr

3 different shape walls and what angle each mitre needs to be cut at for a perfect joint

So, with this in mind, to work out the angle for your mitre joint, simply divide the angle as a whole by 2!



90 Degree mitre joint

90 Degree mitre joint



45 Degree angle

45 Degree angle



45 Degree cut

45 Degree cut



70 Degree angle = 35 degree angle cut

70 Degree angle = 35 degree angle cut

Finally you can see from the image below how the principle can be applied to a staircase dado rail.

First mark the height and position you want the dado. You can do this with a pencil and spirit level or ping the lines with a chalk line.



Dado rail angle diagram

Dado rail angle diagram

After reading through the above, you should now be able to see how important and common angles are in the building trade as a whole and how common the need to work out an angle is.

All project content written and produced by Mike Edwards, founder of DIY Doctor and industry expert in building technology.

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