Dead stops, also known as “dwelling in the cut,” can lead to premature tool wear and failure. When changing directions of travel or when cutting small pieces, a one second stop at 18,000 RPM generates enormous heat and no means of extraction. Imagine rubbing your hands together 300 times per second – a sure way to a blister. This is more of a machinery and software issue. Certain programming techniques can help to compensate, such as ramping, use of loops at sharp outside corners, and the use of exit ramps.
Plunge cutting, while this is the oldest and most widely used method of entering the material, it is not always the most efficient. Plunge cutting can lead to chips wrapping around the router bit after repeated plunges. Whenever possible you should Ramp into the cut. This eliminates the heat generated during the plunging process and can eliminate burn marks at the plunge point. Plunging can also cause the bit to “walk” because there is no centering point; this will be evident as oval holes and entry points larger than the diameter of the tool. If you cannot ramp in, a good alternative is to plunge down outside of the workpiece and enter from the side. Spiraling in can also help; whatever it takes to keep the router bit moving.
Routing holes is never the optimum choice. Use drills for drilling, routers for routing. Drills turn at much lower RPM than routers do; router bits generate too much heat when drilling. Drilling just a couple of holes per sheet will significantly reduce the life of your tooling; in fact, you will probably dull more drilling the 2 holes than cutting the entire piece. If you do not have drill heads to take advantage of European type boring bits, turn the RPM down as low as possible, 4-5000 RPM at most, and plunge as fast as possible, an upshear will help to remove the chips if hold down is not a problem. On deep holes “pecking” can sometimes help.
Small parts and scrap pieces can become projectiles if left after the cutting process without sufficient hold down. They can also be sucked into the dust collector and cause a blockage. Skin cutting and the use of tabs can help to hold small parts.
Collets & Torque WrenchesOver-tightening of the collet and collet nut is a common mistake. Most operators assume that the tighter the better – this is not true and can lead to premature tool and collet wear and tool breakage. Collets are the most misunderstood and overlooked part of the CNC, often the cause of poor finish, short tool life, and unnecessary machine wear. Collets are made of spring steel and are subject to distortion when put under undue pressure. It is highly recommended that collets be tightened to manufacturers’ specifications with the use of a torque wrench
Fires, yes it happens. A tool left in the same place for a sufficient amount of time can and will start a fire. It is important never to leave a CNC running without an operator; you wouldn’t believe how fast things can go wrong. The dust collection system and the vacuum system will aid in the fires speedy travel. If this ever happens to you, beware of flash-back when the vacuum is turned off. When it is safe to do so, it is important to remove and examine the bleeder board and table underneath, embers can remain and once again flair up.

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You may also be interested in reading other excerpts from our CNC Manual: Router Bit Tool Geometry, Tool Materials and Their Uses, Factors To Be Considered Before Selecting Your Tool, and Collets & Tool Holders Maintenance.