Festool PN561287 User Manual

As was mentioned previously, the slope of a crown 

moulding is the compliment of its ”Spring Angle” (the 
spring angle is measured relative to the wall, and the slope 

is measured relative to the ceiling). The two common 

spring/slope angles of crown moulding are 38/52 and 

45/45. The reason why these angles are represented by 
dual numbers is because the actual angle depends on 

which direction the moulding is oriented. For example, 

turned one way, the slope is 38 degrees, but turned the 
other way, the slope is 52 degrees. Note that the sum of 

these two angles is always 90 degrees. 

For mouldings that are not the standard 38/52 or 45/45, 
you will need to measure the moulding to determine its 

slope. This is very similar to measuring the Drop and 

Projection of a pyramid, but more care needs to be taken 

to ensure the measurements are taken from the correct 
locations. Important: The slope of a moulding does not 

necessarily coincide with the “points” or “Tails” of the 

moulding. The slope is measured from the back-side of 
the moulding, regardless how long the tails of the 

moulding may extend (see image below). 

 

There are two separate equations for calculating a 

compound angle. One equation is for calculating the miter 

setting of the saw, and the other equation is for calculating 
the bevel setting of the saw. 

(

)

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

Cos

2

Tan

ArcTan

 

(

)

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

Sin

2

Sin

ArcSin

 

If you don’t know the slope angle, but you know the Drop 

and Projection, then use the following to calculate the 

slope: 

⎥

⎦

⎤

⎢

⎣

⎡

=

ArcTan

 

 

The most common error in calculating compound 

angles is using the wrong Corner Angle. As a 
double-check to your calculations, for nearly all 

cases, the Corner Angle should be less than 100°. 

The only time the angle should be significantly 

larger than 90° is either for a 3-sided box, or a 
wall corner with a sharp edge. 

A compound angle calculator has been built into this Adobe

®

 Acrobat

®

 PDF file. If you do not have an original electronic 

version of this manual, visit the 

 website to download a copy. 

Note: If you are unsure 

about the corner angle 
you have entered, check 

the calculated “MiterFast 

Tool Angle” value. This 
number should be no 

more than 60 degrees for 

sharp corners, but 
otherwise, it should 

always be less than 45 

degrees for most corners. 

If it is significantly 
greater than 45 degrees, 

then you probably have 

the wrong “Corner 

Angle.” 

Supplemental User’s Manual 

21