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Throughout the course of your woodworking adventures the time may come when you need to cut a triangle.
While this job may seem more suited to a miter saw or circular saw, you may not have one available – so this guide is here to teach you how to cut a triangle on a table saw.
How to Make Miter Cuts with a Table Saw
Table saws are great for making accurate 90-degree cuts, but that isn’t going to help much when you need to cut a triangle.
Going back to geometry, a triangle is made of three different angles that all add up to 180 degrees. So, to make a triangle, first you need to know how to make miter cuts.
Many table saws come equipped with a miter gauge, but the problem is that they aren’t always the most accurate. For making precise angles you’re going to want to set the gauge yourself.
These are the materials you’re going to need:
- Framing square
- Straight piece of scrap wood
- Wood screws
As for how to cut a triangle on a table saw, first you need to know what angles you need for your project. Let’s say for example you want to make a 40-60-80 triangle, starting with the 60 degree angle. That’s where your framing square comes in.
You may already be a pro with a framing square, or all those numbers and charts may be meaningless. Either way, you can save yourself time calculating what numbers to use by referencing this chart.
Since you’re making a 60 degree cut, it may seem counterintuitive but you’ll need to set the miter gauge to 30 degrees.
Per the chart you’re going to use 16 and 9/16ths inches on the blade (long, thick side) of the framing square and 9 and 9/16ths inches on the tongue (short, thin side).
Now that you have what numbers to use, you can set the miter gauge angle by placing the tongue of the framing square flush against the gauge.
Adjust the miter gauge with the framing square until the 9 and 9/16ths mark on the inside edge of the tongue is on the outside edge of the miter slot on the table.
At the same time, you want the 16 and 9/16ths mark on the inside edge of the blade to line up with the outside edge of the miter slot as well.
Once both numbers are aligned with the miter slot, tighten down the gauge. It will now be slanted at the right angle for the cut.
Some miter gauges come with a fence built in, but depending on the size of the board you’re working with you may need to add an extension.
Most miter gauges have a place where you can use wood screws to secure a piece of scrap to the fence. If yours doesn’t have a fence piece built in, you should still be able to attach a piece of scrap to the gauge.
Just make sure whatever scrap wood you use is straight – this will help it keep good contact with your workpiece. You should now be all set to make the first miter cut.
How to Make Miter Cuts Less than 45 Degrees
Say you need a 40-40-100 triangle or a 20-40-120, but your miter gauge only goes up to 45 degrees. This is where you can put your geometry knowledge to good use to get the angles you need.
When you cut the hypothetical 60 degree angle above, the board that ended to the left of the table saw – your theoretical workpiece – was the one that came away with the correct angle. But what about the other part of the board?
The angle of the scrap will be 90 degrees minus the angle of the other piece because you cut the board at the corner. So in the case above, the scrap board would have a 30 degree angle.
This works for any angle you need, but the problem is you’re orienting the small angle with the short side of the board.
What if you want to make it lengthwise? In this case you’ll need to set the angle of the miter gauge to 60 degrees.
If your miter gauge only goes up to 45, you can achieve this by taking the measurements on the blade and tongue – 16 and 9/16ths inches and 9 and 9/16ths inches respectively – and swap them.
The long measurement will now be on the tongue, and your angle will be set to 60 degrees.
Now let’s take a 40-40-100 triangle. You’ll set the miter gauge to 50 degrees and follow the same process if you want the smaller angles aligned with the long side of the board.
For angles less than 10 degrees and other thin angles, you’ll probably want to use a taper guide.
These table saw jigs are commonly used to make the tapered legs of tables and chairs, but you can also make precise, small angles if you use a protractor with them.
How to Cut a Triangle on a Table Saw
Your first miter cut is finished, which means that one of your three angles is complete. To get the other two, the steps you’ll take depends on what kind of triangle you’re cutting.
Cutting a Right Triangle
A right triangle has one angle that is 90 degrees – and this makes these triangles the easiest to cut. Take a 30-60-90 triangle for example.
If you want the 30 degree angle on the short side of the board, you can make a right triangle with a single cut.
Set the miter gauge to 30 degrees, and cut through the bottom corner of the board. You now have a 30-60-90 right triangle on the cut piece.
On the other hand, if you need a 30 degree angle on the long side of the board, you’ll set the miter gauge to 60 degrees and make that cut first.
After that, you’ll just have to make a 90 degree cut using the saw’s rip fence.
You’ll want to position the miter cut you already made on the outside of the blade so that you can press the flat end of the board against the fence. From here you can adjust the size of your triangle if need be.
If you want a triangle with shorter sides than what is already on the angle you cut, just position the board so that the saw goes through closer to the end. You’ll still get the same angles no matter what size you cut it.
Cutting an Isosceles or Equilateral Triangle
An isosceles triangle has 2 of the same angle like a 50-50-80, so let’s say you already cut one of the 50 degree angles.
For your second cut you don’t need to do any adjusting to your miter gauge – leave it set at 40 degrees. Instead, you just need to flip your board over.
Make sure that either the short end of the edge is on top and the side you already cut is facing to the left of the blade, or the side you cut is facing to the right and the long side of the edge is on top.
Either way, you’ll get the same angle. Line up the cut so that you start or finish cutting right where the edge of the last miter stops, and you’ll be left with a 50-50-80 triangle after.
As for an equilateral triangle, all three of the angles are 60 degrees. To make it, you’re going to follow the exact same steps as above, just with your miter gauge set to 30 degrees.
Cutting a Scalene Triangle
This is by far the trickiest triangle because none of its angles are the same. Let’s say you’re making a 40-60-80 triangle, and you already cut the 60 degree angle.
For your second cut, you’ll need to adjust the miter gauge to 50 degrees using the framing square.
Remember to invert the measurements you would use for a 40 degree angle to set the gauge.
Make sure the angle you cut first is facing to the left of the blade, and the short side of the edge is on top. After the cut is complete, you’ll have a 40-60-80 triangle. In conclusion, it can be confusing to figure out how to cut a triangle on a table saw. However, with the right tools and a little bit of geometry, your DIY triangles will be on point.