Advanced Engraving Techniques: Using Your Engraver as a Router
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Many engravers have no idea that their simple engraving system can double as a light-duty router in many applications. Oftentimes they are purchasing products from other sources that they could be making themselves. The difference is a little knowledge and some simple tools. This is not for everyone, however. You must be willing to experiment and learn.
Routers are simply a three-axis cutting system controlled by your engraving or sign-making software; essentially, a larger engraver. The only difference is that the routers are designed for more demanding jobs and require you to work without the aid of a nosecone.
Many high-end industrial and signage engraving applications are done on router systems. These large robust systems are designed with heavy-duty cutting in mind. Often, these systems are large enough to accommodate a full 4' x 8' sheet of material or greater. The router system's cutting heads may be commercially available routers used by woodworking craftsmen or high-speed, hi-frequency motors designed to cut through stubborn stainless steel. Whatever the job, routers can be an expensive and oftentimes unnecessary purchase if you have the occasional requirement for deep engraving in metal, high-density plastics or simple sign foam.
The router system may be compared to a light industrial milling machine. In its uses, it will not have the benefit of a nosecone riding on the material1s surface. Routers are generally not very flat by design, and the user will have need to create a flat surface for mounting the material to be cut by facing a sacrificial surface. In a typical sign shop the router will be used to cut out large letters in thick acrylic or Plexiglas. You can consider the engraver as a much smaller, light-duty version of the industrial router. For the occasional job, your system may be modified slightly to open you to new moneymaking opportunities.
BASIC REQUIREMENTS TO USE YOUR ENGRAVER AS A ROUTER
Many engraving systems may double as a router for special applications. The difference, for our purpose, is the type of cutting tools we will use to accomplish the job. The requirements for routing with your engraver are rather simple.
The first requirement is that the system must have a robust engraving motor capable of taking the extra punishment of heavy-duty cutting. Many small systems cannot handle serious deep engraving, and there is a risk of failure of the engraving motor when under serious loads or stress. It would be wise to get the opinion of the equipment manufacturer before attempting any deep engraving.
The second requirement is that a collet spindle be used. This will ensure that a wide selection of cutting tools can be used for the application and associated materials. The third requirement is that the system be 2 ½ -D or 3-D capable in both the hardware and operating software. Obviously, a system with a motorized Z-axis is required to take advantage of the 2 ½ -D and 3-D effects.
TOOL MATERIAL CHARACTERISTICS
To complete the transformation from engraver to router, some explanation is required about the various cutting tools that may be used. Some of this we have discussed before, but it will be helpful to review it again in this context. However, we will not go over all of the various types of tool geometry again: If you need a refresher on this, turn back to the section on Cutters in Chapter 3.
Do not panic when looking at the extensive list of router bits offered by your local hardware store or router tool supplier. If you are unsure about which tool may work best in your application, ask. Tell the supplier details such as the type of material you intend on cutting, how deep you will go, and the speed (rpm) of the engraving spindle. This will help narrow down the cutter possibilities.
The following explanations apply to cutting tools that you may use in your collet spindle as well as a commercial router. Many companies providing router systems have bridged the gap between routing and engraving so all of this information can be used. Many engravers now have a system that can support a commercial router head as well as an engraving head. If your system doesn't have this capability, you may find hand routing an interesting option that increases your ability to offer much larger signage than can normally be produced by your engraver. If you are not this adventuresome, then stick to maximizing the routing opportunity provided by your engraving system.
High Speed Steel (HSS) bits are the most common, least expensive and strongest tools available. Although steel bits can be sharpened sharper than carbide bits, they will dull more quickly. Inexpensive bits can range from a couple of dollars up. Use these cutters when working with aluminum, soft woods, ABS or poly plastics. Do not cut particleboard, plywood or any cardboard/paper materials with steel bits. If you do, as the bit becomes dull it will overheat, smoke and possibly start a fire in dry material. When the bit is getting dull, it will take on a gray to black appearance.
Tungsten Carbide (TC) bits have a carbide tip braised on to a steel shank. They are cost-effective (about two to three times that of HSS), and very durable; however, they are only available with straight flutes. Carbide tipped tools are used for plywood and coarse composites as well as Formica.
Solid Tungsten Carbide (SC) tools generally enjoy a prolonged life and stay sharp when treated with care. These bits are about five times as expensive as steel bits. Identification of solid carbide tools is usually easy. They will be heavier than steel tools and have a gray appearance that extends the length of the tool, even the shank. Keep in mind that carbide tools are more brittle than steel and can break at the shank if the cutting edge is too long for the job. These bits are used when working with wood composites, hard woods, plastics and other composite materials.
Step One: Install a collet spindle in your engraving system.
If you did not initially buy a collet spindle with your engraving system, one may be purchased for about $500-$750. This may seem like a big expense at first but consider the flexibility as well as the return on the routing job you are doing. If you have to sub-contract the work to another shop you may be paying a substantial mark-up that would easily cover your spindle investment.
If you are unfamiliar with the use of a collet spindle, turn back and review the Spindles section in Chapter 3.
Step Two: Level the engraving/routing surface.
Since no nosecone will be used, you would be well advised to level the work surface by using a flat, sacrificial surface. Many manufacturers of engraving systems cannot hold extremely tight flatness tolerances on the T -slot table or engraver bed. This is not a problem for most engravers due to the use of the nosecone and float of the engraving spindle. When routing, however, we will need to create a flat area for our material. In the case of doing cutouts such as thick letters or shapes, a sacrificial surface can be destroyed after some use and then replaced as necessary. Simply use a piece of 1/8" or 1/4" scrap material, MDF, Plexiglas, acrylic or PVC and perform the following procedure:
Mount the sacrificial material securely to the work surface or t-slot table. Install a fly cutter - a broad cutting tool with a geometry that will give a flat surface cut, much like a large end mill-in the spindle and find the lowest level on the sacrificial surface. Set the surface at this position using your software or hardware as designed. Using the shape of a square or rectangle in your software program, generate a "sweep" or "island" fill tool path and route this object with a depth of approximately 1/16 of an inch. By following this procedure the table surface will be parallel with the end of the cutting tool at all times and ensure an even depth of cut over the entire surface of the engraving table. This procedure of surfacing the table will have to be repeated, as the surface of the sacrificial material becomes uneven from excessive cutting.
It's important to note that the depth of cut is also affected by the flatness of the material to be cut. If you are not doing cutouts, you can still expect some variance in the depth.
Step Three: Secure the material to be cut.
Fastening and holding techniques may include the use of a vacuum table. This can be the most secure and practical way to hold down material if it is available for your system. It's important to understand that material with a significant bow cannot be drawn down regardless of the size of vacuum pump used. Vacuum tables are generally used when performing cut-out routines.
Some type of positive securing of the material is necessary. It can be dangerous to have the material move when a free hanging tool is cutting. It is likely that poorly secured materials will result in broken tools and a damaged job. Double-sided adhesive tape is one easy way of holding smaller pieces of material and can take out the bowing in a sheet of material, or consider clamps, generally held in position by T -nuts and screws. Dog clamps like those used in the machining industry can be very effective. Check with the manufacturer of the engraving system for their recommended holding methods.
NOTE: When using any type of clamps or fixtures, be sure to set sufficient "Z-clearance" to clear all clamps.
Step Four: Set-up for non-nose riding cutting.
Many recently manufactured engraving systems come with a proximity sensor that detects the material's surface each time the nose-cone touches the material. If your equipment has this device, turn it off. Obviously this sensor would trip each time the cutting tool touched the surface, and you would not be happy with the results.
In the Z-axis for most engraving tables, the down pressure or spindle pressure may be increased. If possible, lock the spindle against any upward movement. This is usually accomplished by rotating a locking ring to increase the spring pressure to its maximum. When plunging into hard surfaces, the spindle will try to move up. When this happens, keeping proper cutting depths will be impossible unless the spindle is locked.
Finally, determine the proper set-up in the operating software. If you use a non-proprietary program, several settings may be made to set the proper depth of cut. Once the surface has been set either manually or through the electronics controller, you may not need a software setting. Some programs may override the controller settings so caution should be used when setting the surface and depth.
Step Five: Apply lubricant and you're ready to rout!
GUIDELINES FOR QUALITY ROUTING
A CNC (computer numerically controlled) router (in many instances) is a large format, multi-headed commercial router used in many special industrial applications. A common example of these computer controlled routers are those found in the wood working industry. Carved doors or cabinet faces are produced using CNC routers. The router is very similar to an industrial milling machine in that the router head or motor is in very high use. There are significant differences in cutter bits used in CNC operations compared to those used in manual or pin routers (pin routers are the commercially available version we might use in our own home workshop). A CNC router will have an 80% duty cycle.
This means that the cutter will be in the work piece 80% of the time. This compares with 10-15% for a manual pin router. A CNC router will push the cutter through the material at a much faster rate than a manual router. The significance of these two differences is that the cutter will run much hotter with the CNC router. Excessive heat will destroy router bits quickly. This is why it's important to select the proper router bit and to apply some sort of cutting fluid to prolong the life of the bit.
Plunge routing produces very severe axial loads on the tool as well as the router motor. To reduce these axial loads, plunge tip cutter bits should be used. If at all possible, the router motor should be allowed to enter the material from the side in an effort to reduce axial loading. Other options for reducing axial loads include spiraling the bit in and/ or entering the material from the side.
The most important tooling recommendation is that only sharp, dynamically balanced tools be used in a CNC router. Customers that perform cutter sharpening should be aware that an improperly balanced cutter operating at high speeds is dangerous. The useful life of the cutter as well as the spindle bearing is greatly affected by an unbalanced cutter.
Tools should never be longer than are absolutely necessary for the application. Extra length causes vibration, tool deflection and poor edge quality. Cutter length should never exceed 4X the tool diameter (except when cutting foam). Always use the largest cutter shank possible. Large diameters increase tool strength and reduce the possibility of breakage.
The CNC router will push a dull tool through the material it is cutting; however, the radial (side) loads that the router motor will experience may severely damage the spindle shaft and cause premature bearing failure. It is imperative to monitor the sharpness of your tooling. Tools should be changed at the first sign of poor edge quality or increase in operator effort to maintain feed rates. A CNC router does not recognize that a tool's edge is dull or sharp. Therefore, when a tool is dull it no longer cuts, and will instead be forced through the material.
Adhere to the set feed rates of the machine and tool per the specific application. Underfeeding (slow feed rates) can cause excessive heat buildup and therefore excessive friction and burning. This results in limited tool life. Overfeeding (excessive feed rates) can cause tool breakage. The router bit should be allowed to "bite" or "cut" its way through the material. Remember, you want to create chips, not dust, so keep the spindle rpm slower and feed rates up for most applications. It will sometimes be necessary to reduce feed rates to obtain maximum cutter life.
If you experience unsatisfactory performance from your cutter, there is no single solution that will work in all situations. Every situation is different and may require a slightly different solution. Contact the tool manufacturer and explain the problem. Most will make recommendations regarding the proper tool for the application as well as optimal feed rates based on the spindle rpm.