Festool Kapex KS 120 User Manual download pdf (Page 20)

20 Kapex KS120 Miter Saw

Compound Miter Cuts

Compound miter cuts are where the saw is both in a miter

position and a bevel position at the same time. There are

several applications for compound miter cuts, but cutting

crown moulding and sloped miters are common examples.

The example below shows a very simple birdfeeder roof.

The greatest challenge with compound miters is

determining the proper saw settings to achieve the desired

miter angle. These saw settings can be found in look-up

tables for standard mouldings, but for non-standard

angles, determining the proper saw settings requires

mathematical calculation.

Note that there are several methods for

accurately cutting crown moulding depending on

the circumstances. Make sure to review the

methods described in the applicable section on

page 21.

Calculating compound miter settings requires two

parameters from the desired joint: the corner angle and

the slope.

Corner Angle

The corner angle is the angle between the two pieces,

when viewed looking straight down on the joint. The

corner angle is relatively easy to determine, but it is also

the value that can cause the greatest amount of confusion

for many woodworkers. That’s because most woodworkers

view angles differently than a mathematician will. A

woodworker typically considers both inside and outside

corners as 90 degrees (with a 45 degree miter) even

though a mathematician would make the distinction that

one corner is 90 degrees and the other is 270 degrees. To

be consistent with miter saw settings, the corner angle is

measured from a straight line between the two pieces, as

shown above.

Slope

The Slope angle is the angle that each piece makes with

respect to the base of the corner, such as the ceiling or

floor in the examples provided here. For a roof-like

structure, this would be the pitch of the roof.

For crown moulding, this would be the

compliment of the “Spring Angle” of the

moulding. Common spring angles for

mouldings are 38/52 and 45/45.

Determining the Corner Angle of Polygons

The corner angle for standard polygons is

shown in the table on page 18.

Using the MiterFast Tool to Find a Corner Angle

For non-standard corner angles, such as a

room that is slightly out of square, the

MiterFast tool can be used to determine the

corner angle. To use the MiterFast tool to measure

the corner angle, follow the “Using the MiterFast Tool

”

procedure on page 15, but instead of making the cut,

record the saw’s miter setting angle. This angle is ½ the

corner angle, so multiplying by 2 will give you the corner

angle. (The compound angle calculator on page 21 also

has an option for letting you enter this angle directly

without needing to double it.)

Determining the Slope of a Pyramid (Polyhedron)

A polyhedron is a pyramid that can have any number of

sides. The easiest method for determining the slope of the

polyhedron is by measuring the Drop and Projection of

one face. These are the distances from the center-to-the-

edge, and the base-to-the-point of the pyramid. Note that

with a polyhedron with an odd number of sides, the center

is found by drawing bisecting lines as shown in the image

below.

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Festool Kapex KS 120 User Manual Page 20

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