Cut Quality From Various Cutting Tools – Part 1 – Grinders & Rotating Tools

a new series of posts we focus on the cut quality you can expect from a
number of different tools. We start our series off with a quick safety
note and then take a look at Grinders & Rotating Tools

When trimming or cutting any cured reinforced fibers, all cutting edges of the tool are going to be dulled quicker than they would when cutting wood or metals. It is the abrasive nature of composite materials. Composite materials carry residual heat along the surfaces in which are cut. If proper care is not taken the results can lead to poorly trimmed edges, a headache from how slow an improper process can be, and worse, possible delamination of the composite’s structure. Delamination is caused by separation between the composite fabric layers. This causes the part to fail structurally in compression. Delamination defeats the purpose why multilayered composites are made in the first place. However, there are an array of tools that can be selected to ensure all composite parts can be effectively cut and trimmed to needed parameters after cure.

Practice makes perfect, it is suggested to use scrap parts or other surfaces to effectively vet any new tool or cutting blade used. Different brands of tools may have attribute differing speed, sharpness, thickness characteristics, thus cutting differently than others. While no brand may be definitively better than the other, having experience and practice with a given tool will yield better results.

Safety note: While cutting / drilling / sanding any composite, wearing proper protective equipment (PPE) is important. Composite dust is an irritant. A mask or respirator will keep composite dust from possible irritation of throat and lungs. A sleeve will keep the dust from coming in contact and irritating skin. Properly sized, cut resistant gloves will provide peace of mind and allow for precision while using tools for cutting. Please DO NOT forget safety glasses and ear plugs. In addition, a shop vac with vacuum hose placed near or under the trim area will aid in mitigating any dust caused by cutting or sanding laminate edges if a down draft booth is not available. A “shop” fan can also be used to push particles and dust out of the area that otherwise may be lingering or suspending in the area.

Tip: While trimming laminates, dust or particle accumulation incoming to face or skin may be mitigated by simply swapping the direction of circular bits. If possible, have the diamond wheel or sanding block going into the laminate, down or away from whom is performing the cut. This will mitigate pieces and particles being cut from the part that would otherwise be aimed toward hitting the neck or facial areas. Clear face shields are also utilized to eliminate issues when chips or pieces of laminates possibly coming back toward the face.

When cutting or drilling any composite part, blades or bits should always be sharp. Heat dissipation while cutting is the biggest challenge when cutting most composite laminates. Dull blades or cutting surfaces only add to the amount of heat placed on the laminate surface. Using a sharp blade will increase productivity and provide a more accurate cut.

Grinders & Rotating Tools

Pencil Grinders, Right-Angle Grinders and even routers offer the most superior support when cutting through Carbon Fiber, Kevlar, or Fiberglass composites by hand. These tools range from pencil grinders and dremels that fit neatly in hand to bigger and more powerful right-angle grinders and routers. Rotating tools offer a versatility that is unmatched by other tools. Whether the laminate is curved, is locked by tight spaces, thick or thin, a rotary tool with the right cutting surface will provide a confident cut and a quality laminate. For hand cutting purposes, a router is not recommended as most router bits are extremely hard and brittle. Use of a CNC machine for use of routing are preferred for this method of cut. It is important to note that trail and error are common when cutting any laminate surface.

Pencil grinders or straight die grinders are used widely for cutting laminates of great variations and thicknesses. There are multiple attachments that can be used to polish, cut, sand, and prep composite laminates. The handheld tool uses a rotating spindle at its front and uses high speeds to perform needed tasks. Dremel tools are also commonly referred to as pencil or die grinders and are the same “type” of tool. Dremel, a brand of a tool, is commonly used to perform the same types of work on a composite laminate. While Dremels / die grinders / pencil grinders are the same type of tool, some apparent differences should be noted. Die grinders are generally larger and have more power to cut through thicker laminates. Honing the power usually takes use of both hands. Dremels are weaker but are easily held with one hand and have faster rotation. Dremels also variate speed easier, with just a push of a button.

The bulk of heavier cutting is more effectively performed using a die grinder that is pneumatically powered. Needs requiring a quick “touch-up” or where precision is needed, using smaller bits or files with a Dremel will allow the user more versatility with a laminate, getting into tighter areas where finer precision may be needed.

Right-angle grinders are like straight grinders but have a head that is perpendicular to the body of the tool. Right angle grinders can be used to cut through laminate surfaces but are most used to perform final sanding and prep for secondary bonding purposes. These grinders may also allow for getting into tighter to reach places where a straight die grinder may not fit.

When selecting a grinder or rotating tool, options between electric and pneumatic power are usually a top question. It is important to note that speed does not equate to power. Torque behind a slower rotating pneumatic tool will take much more laminate to “stop” a blade from spinning. As with a smaller electric option, they can be stopped or slowed much easier by thicker laminate pieces. Though most electric options usually need to be plugged in, cordless models are available for an additional price. Electric grinders are generally less powerful than pneumatic powered tools but are usually lighter and faster, like a Dremel. Cordless options do provide an advantage in portability as they will fit in the most compact areas. Pneumatic tools are known for providing the needed power and torque for any job. They are generally much cheaper but require an air compressor for use. Pneumatic tools also take more practice to master precision cutting needs as they carry more power. It is common to perform over cuts of ¼” or greater while using pneumatic grinders for initial cutting of parts. Afterword, going over the same areas with a right angle grinder with an abrasive sanding bit to achieve a close / final finish as required per dimensional needs.