Routing And Trimming
ABS is one of the most
popular plastics used by thermoformers and rotational molders. It is also one
of the most versatile from low-density foam to high-density material. ABS combines
toughness, stability, wide temperature range and chemical resistance with relative
ease of fabrication. No wonder it most often is the plastic formula of choice
given these advantages even before considering ABSs low water absorption and
hi to low gloss range in a variety of colors. These substantive properties often
dictate restrictive machining practices in other formulations. This is not the
case with ABS. There are just a few (but important) considerations when routing
or trimming ABS. It is also a reasonably priced material and happily can be
machined in a most cost-effective manner.
ABS has been used in consumer
products for years. It is becoming the material of choice in many auto/truck
components. Instrument panels, headliners, grilles, wheelcovers, decorative
trim, mirror housings, truck bed liners and bumper farings are some of the ABS
applications. Small and large appliances, refrigerator door liners, business
machine and electronic housings, luggage, toys, storage bins and flower pots
are ABS parts often trimmed by air or CNC routers. Pipe and fence materials
of ABS are used in several products requiring unique routing methods. All of
the products here mentioned can be effectively machined only if properly fixtured,
clamped or held firm before the spindle is turned on.
In many instances, CNC
routers are setup with the right tools and an elaborate vacuum system. The spoilboard
however, is overlooked and becomes the problem area. The one thing that can
make or break an ABS setup is the ability to hold a part on the table "rock
solid". ABS parts are normally quite flexible and will tend to vibrate
if not fixtured properly. There are many elaborate pod systems employed by both
point to point machines and routers. These systems can be very effective. There
are also many machines utilizing dedicated spoilboards to hold parts. This is
most often the case with ABS parts. The proper way to build a dedicated spoilboard
is often misunderstood or cut short, in the interest of time. Taking the time
to do it right will pay dividends in the form of productivity and piece part
Many consider a spoilboard
a piece of MDF or particleboard with self-stick weather-stripping and a few
holes drilled inside the perimeter. While this type of fixture may work in a
few instances, it does not often satisfy the demands made in high performance
routing. If a router is going to run at production speed, the parts must not
move. The preferred spoilboard technique employs grooving the interior area
of the gasket perimeter to allow a vacuum to reach the outermost portion of
the part. The holes are then drilled at the intersection of the vacuum grids.
This method provides a greater vacuum surface area. It is preferred to just
drilling holes in the spoilboard because it provides a "bead" of vacuum
to the outermost edge of the part, giving the best chance for a "rock solid"
hold. (See figure 1).
Once the ABS part has been
properly fixtured, tool selection is really quite straightforward. The router
bit of choice for most thermoformed sheet, 6mm or less, is the 0 flute tool,
either single or double edge. In many instances, the part can be machined while
cooling and high-speed steel tools work very well. (See figure 2). In all instances,
ABS can be trimmed and routed effectively with solid carbide 0 flute tools.
(See figure 3). A new product in solid carbide router bits for plastic applications
is the 0 flute spiral tool. (See figure 4). While available for many years in
straight or shear geometry, recent developments in CNC grinding technology has
enabled the design and manufacture of the 0 flute spiral, which provides better
chip flow control in certain applications.
One of the few problems
in machining ABS can be chip reweldment. This occurs when the chip is not removed
properly or quick enough. It can also occur when the feed rate is too slow.
These problems can be easily resolved in a CNC environment with proper fixturing
and tool selection. They can be more difficult to solve in hand held or air
routing applications. Depending on the difficulty of the set up, one may wish
to consider carbide tipped straight flute tools (See figure 5) if high-speed
steel does not provide satisfactory tool life. In these situations, carbide
tip tools may be preferable to solid carbide because of the strength of the
tool steel body. Whether the router is CNC or hand held, ramp entry into the
ABS work piece (rather than a straight plunge) will also prevent rewelding.
In any plastic routing
application, one should experiment with both single and double edge bits, as
well as both spiral and straight flutes, before choosing the best tool for the