ROUTING: Top Ten Routing Questions
Over the past 1 1/2 years, as
we have been discussing
plastics routing, some questions
keep coming back. Many questions
are material specific and many
are associated with several plastics.
Here is a summary of the more frequently
asked questions. (All reference
CNC routing of plastics unless otherwise stated.)
What can be done to improve the finish on a cut part?
Vary feed rates and spindle speed and use solid carbide
tooling with material-specific geometry. For soft plastics,
use single-edge solid carbide straight or spiral plastic O
flute tools. For rigid plastic, use double-edge solid carbide
straight or spiral standard or O flute plastic geometry
What causes material to reweld
either to the part or the tool?
Follow the advice given in the previous question and avoid dwelling in
the cut by better programming techniques
such as exit ramp corners
rather than stop-and-go corners and
ramp in rather than straight entry boring. Heat, of course,
causes welding. Increased feed speeds and/or decreased
spindle speed helps stop heat build-up.
What is the solution to small parts moving when cut from
vacuum-drawn sheet goods?
The cutting forces may overcome the vacuum. Reduce the
cutter diameter to the same thickness as the material cut
(i.e., 1/8-inch diameter for 1/8-inch thick material) and use
the straight or slow helix downcut O flute solid carbide tools.
What can be done to avoid burns or clouding of acrylic in
a hand or air router application?
Use two tools, one to rough out the shape and one to trim.
Both tools should be solid carbide. The roughing tool can
be a straight or spiral designed for acrylic routing. The
first cut should leave approximately a 1/8” margin for the
second pass. The second pass should be made with a
three-flute acrylic finish tool.
What is the solution to stacked sheet routing when the
sheets become welded together?
In some instances, spiral tools can accentuate this problem.
A solid carbide straight O flute is recommended,
either single or double edge, depending on feed rate and
spindle speed. When fixtured properly, the individual
sheets become a natural chip breaker.
What is the solution to poor finish on plastic window and
door parts cut on a machine designed for this purpose?
Try single- or double-edge solid carbide straight O flute
tools instead of the recommended high-speed steel spirals
if finish is a problem.
What does a small sign shop do for a tool to cut many different
Use solid carbide slow helix or straight O flute tools.
These tools will cut a range of thermoplastic materials.
What is the difference in routing plastic and wood materials?
Plastic materials vary in consistency and abrasiveness
from soft thermoplastics to abrasive-reinforced thermosets,
just as wood varies from soft pine to abrasive teak
or MDF. One tool will not cut all plastics materials well,
just as one tool will not cut all wood. Additionally, plastic
materials have unique physical properties that require
unique geometry for an optimum finish. It is the exception,
rather than the rule, when one tool will cut both plastic
and wood or wood composites well.
What can be done to improve the finish on a molded or
cast part held in a fixture by vacuum?
Use multi- (three or four) flute solid carbide downcut spiral
for trimming such parts and lower spindle speed, if possible.
What is the best tool for cutting fiberglass-reinforced parts
with both CNC and air routers?
Trimming fiberglass can be accomplished with standard
solid carbide FGR (fiberglass router-diamond cut) tools in
both environments. Routing parts in a CNC environment
is best done with chipbreaker-type solid carbide tools.
Routing fiberglass by hand is best done with straight flute
carbide tools (for added cutter body strength).
If you would like to contribute a question or topic for a
future article, please submit it to firstname.lastname@example.org or
fax it to 847-362-5028.
Van Niser is Director of Plastic Application Engineering at
Onsrud Cutter. Readers are invited to send questions to
Van Niser at Onsrud Cutter, 800 Liberty Drive,
Libertyville, IL 60048, E-mail: email@example.com.
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