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Top 10 Routing Questions

Listed below are the router questions most frequently asked to columnist Van Niser.

BY VAN NISER

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.)

Q: What can be done to improve the finish on a cut part?

A: 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 tools.

 

Q: What causes material to reweld either to the part or the tool?

A: 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.

 

Q: What is the solution to small parts moving when cut from vacuum-drawn sheet goods?

A: 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.

 

Q: What can be done to avoid burns or clouding of acrylic in a hand or air router application?

A: 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-in. margin for the second pass. The second pass should be made with a three-flute acrylic finish tool.

 

Q: What is the solution to stacked sheet routing when the sheets become welded together?

A: 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.

 

Q: What is the solution to poor finish on plastic window and door parts cut on a machine designed for this purpose?

A: Try single- or double-edge solid carbide straight O flute tools instead of the recommended high-speed steel spirals if finish is a problem.

 

Q: What does a small sign shop do for a tool to cut many different plastic materials?

A: Use solid carbide slow helix or straight O flute tools. These tools will cut a range of thermoplastic materials.

 

Q: What is the difference in routing plastic and wood materials?

A: 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.

 

Q: What can be done to improve the finish on a molded or cast part held in a fixture by vacuum?

A: Use multi- (three or four) flute solid carbide downcut spiral for trimming such parts and lower spindle speed, if possible.

 

Q: What is the best tool for cutting fiberglass-reinforced parts with both CNC and air routers?

A: 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 VanNiser@Onsrud.com or fax it to (847) 362-5028.

 


Plastics Machining & Fabricating
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