40 SERVO 02.2017
It has been a while since we started
this project, and it’s time to make
some chips. In this installment, we’ll
go over spindle hookup.
By Michael Simpson
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What is a CNC Spindle?
A spindle is the rotation portion of a CNC machine on
to which a cutting tool is attached. While technically the
spindle is the shaft itself, it has become common place to
refer to the motor and shaft assembly as the spindle.
There are many shapes and sizes of spindles. First, let’s
look at low speed and high speed versions.
Low Speed Spindles
Low speed spindles are used
primarily in machines that need to do
milling operations on metal. They are
needed when drilling larger holes
may be required or for turning very
large tools. Milling machines like the one shown in Figure 1
use a low speed spindle. This spindle will run at a range of
500-2,500 RPM. Since most motors don’t run slowly
enough, a belt or gear reduction is used to slow down the
spindle shaft in most cases. Needless to say, we won’t be
using a low speed spindle on the KReduCNC.
High Speed Spindles
Most CNC machines designed to mill wood, plastic, and
some non-ferrous metals use a high speed spindle. While
there are several varieties, I will be talking about two types:
routers and rotary tools.
Router spindles can be broken down into full size and
trim routers. The routers shown in Figures 2
and 3 are full size routers. Due to their weight
and size, they are used on larger CNC
machines. These are both 2-1/4 HP routers.
They have plenty of power for most
operations, and work well for cutting wood,
plastics, and aluminum.
Full size routers can handle tool shanks
from 1/4” to 1/2” and with adapters or
special collets, down to 1/8”.
The routers shown in Figures 4 and 5 are
trim routers. Most trim routers work just like
their larger counterparts, but are smaller and
produce less horse power. These routers are
just under 1 HP.
Trim routers are common on many small
to medium CNC machines. Most can handle