ROUTING: Reduce Routing Cost$
When the economy slows down and orders
become fewer in number and far more competitive
in terms of pricing, it is important to find
ways to reduce the cost of manufacturing. In the routing
industry there have been numerous technological
advances in machines, materials and tooling aimed at raising
the efficiency (and therefore lowering the cost) of production.
In the last five years alone there have been great
advances in many of these areas. Machines have more
than tripled their rapid traverse rates and at the same
time managed to increase their rigidity through advancements
such as ceramic bearings and HSK tool holders.
Materials have increased their resistance to crazing,
scratching and breakage while being offered in more colors,
sizes and composite formulations than ever before.
New tooling technology has brought about increased surface
finishes, longer tool life, faster feedrates and less
induced stresses on cut parts through better materials
and engineered geometries.
While these improvements have undeniably helped to
increase the state of the art for plastic routing, the unfortunate truth is that most application troubles are still the
result of basic and fundamental problems. These troubles,
if not found and eliminated, invariably cause increased
cycle times, cutter usage and higher machining costs.
Because they are core machining principles, the solutions
to these problems haven’t changed since plastic CNC
machining started its rapid growth in the mid 1980s. For
that reason, it is always a good idea to occasionally get
back to the basics and review what makes for a successful
CNC routing operation.
The four core areas to address for successful and profitable
routing operations are: Material, Rigidity, Tooling
and Programming. By reviewing the fundamentals
involved with each of these aspects of the routing operation
before a job begins, the shop owner, machine programmer
or machine operator can find opportunities to
produce better parts at a lower cost.
With so many plastic grades in the marketplace today, it
makes no sense to ignore the applications support that
plastic manufacturers can supply. The fabricator, acting as
an intermediary between the customer and the material
supplier, has the greatest opportunity to select a material
which meets the customer’s specifications but is easier to
machine than similar formulations. There are numerous
resources for machining information available and they
should be utilized as early as possible to help the customer
specify the best material grade for all aspects of the
design, manufacture and final use of the product.
Whether published or residing in the experience of a seasoned
applications engineer, router manufacturers typically
have a wealth of knowledge in regards to plastics machining.
It is always a good idea to contact the machine manufacturer
for some up-front advice on different material styles.
Tooling companies can provide very timely information on some of the newer materials as well as the old stand-bys.
Due to the expendable nature of their product, tooling
companies typically have more involvement in the day-to-
day machining of products and may see a more varied
spectrum of successful applications. Knowledge of a material’s
benefits and limitations can be invaluable to
Lastly, and most importantly, material manufacturers
can be the best resource when it comes to pre-job material
selection. They typically have specialized materials
that are designed with machining in mind and applications
personnel can assist both the fabricator and the end-user
in the selection of materials that are router-friendly. Most
larger companies publish drilling, routing and sawing
specifications for their popular materials and many of
them have joined the www.plasticrouting.com website to
help develop a centralized database allowing the comparison
of material machinability characteristics between
manufacturer, grade, color and thickness.
By reviewing the characteristics of materials before a
job begins in terms of formability, resistance to damage,
machinability and customer specifications, the fabricator
can help reduce production costs while increasing the
chances of a satisfied customer.
Realistically, material specification can be a difficult
parameter for the fabricator to control. Many times the
specification is already decided when the job is offered to
the fabricator. Fortunately, this is not the case for the next
most important variable in the job: Rigidity. This
parameter is entirely up to the router operator and
is the most critical parameter over which the operator
Rigidity applies both to the machine itself and to
the fixturing of the components to be cut. (It can
also be applied to the tooling, but that subject is
better dealt with in the Tooling section.) A router
that is poorly maintained will never be capable of
achieving the results of even the oldest machine
that has been properly kept. Plastics machining is
entirely different than the routing of other materials
in that the feedrates are typically much faster than
in standard metal milling and the finish requirements
are much more precise than in wood routing.
Properly lubricated and maintained machine
slides and drive systems are essential to maintaining
optimum feedrates. Since plastic is so sensitive
to the relative motion of the cutter, any backlash or
worn track or ball areas can have a visually noticeable
effect on the part. Any play in the table or
spindle mounting systems can cause erratic marring
of the work surface. Failure to follow a preventive
maintenance schedule with the spindle can
cause concentricity problems so severe that no
tooling will produce an acceptable finish. It is
important to remember that routers are not milling
machines. They are typically much larger than a
standard horizontal mill and are built with speed as
a primary focus and rigidity as a second focus
(albeit, still a critical one). Routers are a viable
method of production if the operator understands
the limitations imposed when using a 10 foot aluminum
table versus a 3 foot steel bed as a work-surface.
Preventive maintenance of CNC routers is
critical to long term operation when part surface
finishes are critical.
While machine rigidity is critical to consistent
performance, fixturing is equally important to individual
performance per part. As has been stated in
previous articles, surface finish for metals and plastics
is typically measured in millionths of an inch.
Consider that even .001” of part movement is 50
times the magnitude of what is generally considered
a good surface finish. With such a low margin
of error, it is essential that everything possible be
done to allow the machine and cutting tool a chance to
produce optimum finishes.
Fixtures should be rigidly built and mounted to the
worksurface. Vacuum supply should be oversized whenever
possible and hard fixturing should be securely mounted
and without slop. When dealing with 5-axis fixtures,
unsupported overhangs should be minimized and vacuum
distribution should be brought as close as possible to the
area being cut. Friction enhancements such as rubberized
coatings or gasketing sheet foam are always a good idea.
With the thousands of available choices for tooling, this
could seem to be a difficult parameter to optimize.
However, the contrary is actually true. The reason for the
large selection of available tooling is the fact that it has
become so specialized over time. The best methods for
specifying tooling for a particular job are either published
resources or vendor representatives. Published resources
can be recommendations from material suppliers, empirical
test data such as www.plasticrouting.com, or vendor
catalogs with tool selection cross references. Experienced
vendor representatives or applications engineers can also
be of infinite value because of their knowledge of similar
applications and the pitfalls to avoid.
The goal for best performance is to find the tool geometry
that was developed specifically for the type of material
being cut and the machine being used (i.e. 3-axis, 5-
axis, carving, etc.). Additional factors that should be considered
- Tool Material: Carbide for finish, steel for sharpness,
diamond for life.
- Tool Diameter: Is 1/4 inch required or can 3/8 inch be
used to produce a better finish?
- Cutting Length: Are stub length tools available for better
- Shank Diameter: Cutting diameters smaller than the
shank can lead to tool breakage.
- Helix: What are the part hold-down parameters?
Should low helix, high helix or straight cutters be used?
Once material, machine rigidity, fixturing and tooling
have all been selected for best operating practices, the
final step is programming the part path. There is a
tremendous amount of material published concerning this
process, but by just focusing on the basics a good probability
of success can be assumed. Some general rules of
thumb for routing of plastics:
Cut Direction Matters: In almost all cases the conventional
cut or climb cut side will produce a better finish than
its counterpart. The best method for determination is trial
and error. Compare both the finished part and the scrap for
edge quality. If the scrap is better, reverse the cut direction.
For empirical data, once again www.plasticrouting.com can
be consulted. As a starting point, larger tool diameters typically
work better in a conventional cut presentation and
smaller diameters are work-piece specific.
Chiploads: Chipload is the size of the chip being
formed. It is the result of the number of cutting edges, the
spindle RPM and the feedrate. Router bits work best at a
very specific chipload and can perform quite poorly even a
few .001 inch from the optimum value. Consult with the
tooling manufacturer for a good starting point and then
vary feedrates or RPMs to determine the best cutting
zone for the particular job.
Cutter Entry: Router bits that plunge directly into the
work piece can wrap long chips, deform part edges or melt
the surrounding surface. Always ramp or helically plunge
into a scrap area and rout to the part edge to prevent
Scrap: Try to minimize the amount of unsecured scrap
and thin wall scrap that is present. Poor scrap control can
lead to part ejection, vibration and broken cutters.
A thorough review of each of these fundamental areas –
Material, Rigidity, Tooling, and Programming – can eliminate
many of the problems that arise every day in the routing
industry. Far too often fabricators have spent money and
time fine tuning programs and part paths for optimum
cycle times when building better fixtures or selecting different
tooling could have doubled feedrates with minimal
additional effort. Poor programming has been solved
many times with custom (i.e. expensive) tooling when
rewriting cutter entry cycles or part paths could have
resulted in immediate solutions and the use of off-the-shelf
Perhaps the worst example and unfortunately the most
common is the application where the machine must be
run at a minimal feedrate to prevent chattering of the
part. If machine condition is preventing fast feedrates, fix
the machine – do not decide that the maintenance cost is
prohibitive or the downtime is not possible. Once machine
wear begins, it accelerates quickly. It must be caught in
the beginning and fixed promptly to prevent a myriad of
With a solid return of Back to the Basics fundamentals
in the routing process, delays can be eliminated, cycle
times optimized and costs reduced.
For more information, click on the Author Biography link at the top of this page.