CNC Tooling Basics, Part 2: End Mill & Router Bit Design

As I discussed in my “CNC
Tooling Basics for Woodworkers
” submit and the
, there are loads of little particulars that go
into the design of CNC finish mills and router bits. Only some
are essential for many digital woodworkers, so, it is a
streamlined primer centered on the fundamental particulars you should
know when selecting router bits and finish mills to be used on a CNC.

First, a diagram of the components of a CNC finish mill or router bit:

CNC tooling

Slicing Diameter is the width of reducing a part of the

Flutes are the reducing edges alongside the facet of the mill
or bit

Size of Minimize or “LOC “is the size of the reducing space

General Size or “OAL” is the size of all the mill
or bit

Shank is the world of the mill that’s clamped into the
device holder or collet.

Shaft Diameter is width of the shaft

Helix Angle is the angle of the cutters from the
longitudinal axis

CNC Cutter Design Fundamentals — Flutes

Flutes are the reducing edges you see alongside the perimeters of CNC
mills and router bits. Within the case of the spiral router bits
meant for wooden reducing, two flutes are most typical. CNC mills
can have from one to 6 flutes, although two or 4 are

So what distinction does the variety of flutes on a cutter make?
When you’re reducing wooden on a CNC the variety of flutes issues
fairly a bit.

As a woodworker, you would possibly assume that extra flutes would possibly outcome
in a cleaner reduce. In any case, in relation to noticed blades,
often extra enamel or reducing edges end in a cleaner reduce.
However, between the quick speeds that CNCs can journey, the upper
RPMs that water-cooled spindles obtain and the amount of
wooden waste produced, extra flutes are often not one of the simplest ways
to go.

When reducing wooden on a CNC we’re creating a large quantity of
chips. The extra flutes you might have means extra chips being created
per rotation; subsequently the CNC has to journey a lot quicker to
eject them. There’s even a calculable time period for this referred to as
chip load (we’ll get into that at a later date). However you
have to know that the results of all these chips piling up is
the cutter will get scorching as a result of it will probably’t eject chips quick sufficient –
so the fabric being reduce begins to burn and the bit overheats.
It’s dangerous for the cutter and probably a harmful state of affairs.

Right here’s the rule of thumb: Extra cutters imply that the CNC has to
run quicker to eject waste and keep cool. Fewer flutes
imply extra materials might be eliminated per rotation when
working a CNC at slower feed charges. Feed charges on a CNC is a
massive subject in itself, however let’s take a fast have a look at what type
of speeds I imply once I say “quick.”

A high-performance four-flute wooden reducing bit must journey
at 1,800-2,000 Inches Per Minute (IPM) to work correctly. Solely
the quickest and costliest top-of-the-line factory-level
machines utilizing 10-20hp spindles can run that quick. At that
pace, you stand behind security shields and simply watch the CNC
transfer round in an insane blur. Even three-flute
specialised cutters have to run 900-1,200 IPM – nonetheless very quick
however inside the vary of the perfect business grade CNCs.
Two-flute wooden cutters fortunately run from lower than 200 to 600
IPM — which is the actual world feed price vary of the form of
machines woodworker, smaller skilled outlets or
common cupboard store CNC are in a position to obtain. I can inform you
from private expertise that it’s nonetheless far more than quick
sufficient to do probably the most frequent process CNCs do for a woodworker:
reducing components.

OK – now for some classes discovered. After I began out I
bought a number of four-flute cutters considering they’d give a
cleaner reduce, however apart from a couple of specialised
cutters, they only don’t work for reducing wooden on a CNC. Bits
overheated. Cuts weren’t clear. Chips had been scorching and barely
burned. It simply by no means labored. Moreover those I attempted, I’m now
left with a variety of unused four-flute mills in my assortment
on account of studying this lesson first hand. So, I exploit
two-flute spiral cutters nearly completely for reducing wooden
and people are what I like to recommend. I’m not the one one. Notable
cutting-tool producers equivalent to  Onsrud and Vortex
advocate two-flute mills for woodworking on the form of CNCs
we usually use, too.

Different CNC Finish Mill Design Particulars

Helix Angles You don’t want to fret about this an excessive amount of
besides to take into account that the perfect vary for reducing wooden are
thought-about low helix when in comparison with metallic reducing bits: 22°
to lower than 30°. There are exceptions at each ends, however for
probably the most half, cutters meant for our use are inside that

What about single-flute cutters? They’re hardly ever
acceptable for reducing wooden on a CNC (there are a couple of
exceptions for specialised ending bits).  However to be used
on aluminum or laborious plastics, single flutes are most typical.
Particular single-flute cutter designs referred to as O-flutes are the
device of selection in these instances.

So in brief, the one practical selection for reducing wooden on a
CNC is to make use of cutters with fewer flutes. And that just about all the time
meaning two.

— Tim

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