Beginning
in a small workshop in the centre of Pesaro, Italy in 1964, CMT Utensili
has gradually developed into what it is today – a modern, efficient
manufacturing centre located just a few miles from where it all began.
Two generations of the Tommassini family have worked and invested to
make “Construzioni Meccaniche Tommassini” available to every
woodworking industry and individual craftsman around the world. Even
after having achieved a world wide distribution, CMT still holds fast
to one main objective – to produce only the highest quality woodworking
tools possible.
Materials
CMT believe that to produce the best router bits on the market, you
have to start with the best possible raw materials. CMT have spent the
last 30 years researching the two primary components of all their router
bits, boring bits and drill bits.
Fatigue
Proof® Steel
The shanks and bodies of all CMT bits are machined from solid bar stock
steel. CMT use Fatigue Proof® Steel made by Von Moos Stahl in Lucerne,
Switzerland. The special qualities of this steel come from the actual
process by which it is made. Von Moos Stahl manufactures its steel bars
with an exclusive hot drawing process which results in a unique combination
of properties;
• Superior strength
• Excellent machinability
• High level uniformity
• Minimal distortion
• Exceptional resistance to fatigue
• Remarkably high resistance to abrasion
These characteristics can allow the steel to withstand even the most
demanding mechanical and thermal stresses. It is easy to understand
why this is the same steel chosen by Porsche and Ferrari to make their
engines, and why CMT feel it should be the same steel used to make their
woodworking tools.
Cerametal®
tungsten Carbide
On any woodworking tool, the carbide edge is what actually performs
the cut. It must be strong and resistant to work better and last longer,
and using an inferior quality carbide means making an inferior quality
bit from the start. Every CMT bit is made using only premium grade tungsten
carbide from Cerametal® in Luxembourg, the most technologically
advanced producer of carbide for woodworking tools in the world. Carbide
compound is a compression of carbide powder chemically bonded by cobalt
and tungsten. The quality of the compound is determined by the closeness
and uniformity of the compressed granulates. CMT’s specially formulated
carbide produces a homogenous, very fine grain composition which is
exceptionally durable, lasting longer and gives you more resharpenings
from your woodworking tool.
CMT
carbide sample – note the uniformity of granules. They are evenly
distributed with no spaces or granules outside the accepted area of
tolerance. An example of high quality carbide
Leading European manufacturer of woodworking Tools – notice the
large granules. This indicates the use of re-cycled carbide powder,
resulting in oversized granules. A large granule can chip off the cutting
face edge leaving a gap which causes splintering when cutting.
Leading American manufacturer of woodworking tools – the dark
gaps are caused by uneven distribution of cobalt, creating open spaces
making the carbide exceptionally porous. The carbide crumbles more easily
and wears down more quickly.
Geometry
and Design
CMT bits are specially designed with rounded shoulders between the cutting
edges so the bit makes a more shallow initial cut into the workpiece
then proceeds smoothly and therefore radically reduces kickback. This
anti-kickback design is automatically included in every bit designed
with a diameter of 3/4” or larger.
When
holding a bit vertically, one can see the cutting edge is often slanted.
This shear angle determines the way the cut is executed and each angle
is specifically designed for working in certain materials to optimise
performance and finish. In general, shear angles are preferred over
straight because their cutting edges remain in continuous contact with
the workpiece which produces a softer less choppy cut.
The
hook angle or rake is created by the slant of the cutting edge towards
the centre of the bit, and is the angle at which the cutting edge meets
the stock. Its purpose is to make a clean smooth entrance and remove
the stock, to leave the cut looking as finished and splinter free as
possible.
A minor feature that makes a major difference to the performance of
a bit is the clearance from the cutting edge to the body of the bit.
This serves as a very important free space for sawdust to move and escape,
otherwise blocking and burning will result.
All of the above have the highest consideration from CMT’s experienced
designers and engineers when a new cutter is put into production. The
CMT design team are constantly innovating and reacting to ideas from
the worldwide woodworking community.
How we produce our high quality bits
1
– All bits originate from high quality bar stock steel
2 – Turning is done on state of the art CNC machines.
During turning, the ball bearing seat, bit body and main shank are formed.
CMT centres all bits for precision balanced machining. The small hole
at the bottom of the shank and top of the bit guarantees the bit has
been held between centres ensuring concentricity at all stages of production.
It is worth noticing how smooth the finish is even at this initial stage.
Although this finish will be removed during the rest of production,
CMT rightly believe that it is important to start accurately to finish
accurately.
3 – After turning, the bits are milled which includes
making the seats for the carbide flutes. In this important step, the
straight or shear angle is established, and the profile is defined.
The milling department is equipped with both traditional Swiss milling
machines and automated loading CNC machines.
4 – The brazing process sees the carbide tip fused
onto the steel body at 420ūc either on an open flame by highly skilled
welders, or by an induction process. After this step, the bits are placed
in normalising ovens set at a temperature of 400 – 450ūc to relieve
the stress that occurs at such high temperatures, then gradually bringing
them down to normal temperatures. This important step protects the security
of the braze, the solidity of the carbide, and ensures the safety of
whoever finally uses them.
5 – CMT is immediately recognizable by the trademark
orange PTFE coating applied to the surface of their bits. PTFE is a
non stick substance that prevents residue accumulating on the bit. It
was designed by CMT and PTFE factory technicians to be a unique industrial
strength substance specifically designed to meet the requirements of
woodworking tools and is baked on at 420ūc for durability.
6 – CMT’s highly advanced grinding and sharpening
department consists of automatic and semi automatic diamond wheel machines
and CNC machine centres. By precision balancing each bit from start
to finish CMT guarantees the ball bearing seat and shank diameter are
ground to be perfectly concentric. The grinding and sharpening is carried
out in 3 separate operations – The first grind on the steel shank
leaves a micrograin finish of 0.8m/mm µ. This smooth finish on
the shank is critical, and determines how well the bit fits into the
powertool or machine. A rough grind results in a poor clamp and wobbly
rotation.
7 – The second grind is the sharpening of the carbide
cutting edge to a 0.4m/mm µ micrograin finish. This is only done
on automated CNC machines that are equipped with as many as 8 axes for
maximum accuracy. On coupled sets such as stile and rail cutters, the
machines are programmed to sharpen as a pair to guarantee perfectly
matching profiles.
8 – The third grind is made on the ball bearing seat
for a micrograin finish of 0.8m/mm µ. This is crucial, as any
difference between this and the bearing diameter will result in the
bit rotating irregularly.
The bits are then laser etched and packaged in high quality and visible
clear re-usable containers. These can be used to provide safe storage
for your cutters either in the workshop, or on site.
