Three keys to maximizing any cutting tool’s effectiveness or in other words, getting the maximum life out of a particular cutting tool are:
1. Select the proper tool for each application.
2. Make sure that tool is held/driven properly (tool holder integrity).
3. Make sure the tool is run at the correct feed rate and RPM for the application.
These objectives are universal for all types of cutting tools as well as all types of cutting tool materials. For the remainder of this article we will discuss these three objectives and how to apply them in a day-to- day woodworking environment. This won’t be a step-by-step process of selection; rather the subjects discussed will include a wide variety of topics that should be considered when selecting components for any cutting application.
The name of the game is “longer tool life”! Longer tool life means increased profit! Cutting tool manufacturers are faced with new cutting tool applications all of the time. New types of materials are introduced regularly as well as new types of machines to do the cutting. We are also exposed to new technology within our industry that affects how and what we are able to provide as far as cutting tool design. Selecting the correct tool and geometry is influenced by many factors and it’s very important to consider all aspects of the application in order to arrive at the correct tool selection.
Coatings May Be Helpful in Some Applications
Tool coatings are becoming more popular in applications in our industry. PVD, or physical vapor deposition, applies a thin layer of ceramic material over the cutting area of the tool. Many types of coatings are available and each type has a specific trait that it enhances such as lubricity, heat resistance, or resistance to corrosion or abrasion. In most wood cutting applications, the benefits of PVD aren’t realized due to the non-uniformity of the material. However in man-made materials such as plastic and aluminum, coatings can provide a noticeable improvement in tool life and performance.
Another type of coating being used applies a thin layer of PCD (polycrystalline diamond). Using a similar vapor deposition process as PVD, the CVD (chemical vapor deposition) coats the cutting tool in either a “thin” or “thick” film of diamond. Diamond coating is popular with very difficult to cut materials such as composites in the aerospace industry. Testing in the woodworking market has shown mixed results as CVD coating is still a rather expensive process.
As machine speeds get faster and tool holding systems advance we have been able to increase the number and types of cutting edges that are on cutting tools. By increasing the number of cutting edges the wear on each edge will be less, but it becomes critical that the chip load is correct for the material being cut. Again with equipment that is able to feed faster and still maintain a consistent chip load, we are able to introduce tooling with more aggressive geometries.
Carbide Grade – How important is it?
Carbide grades continue to evolve as the producers of carbide strive to gain a competitive advantage in their marketplace. Because there is such a wide variety of carbide manufacturers and products they make, it can be quite confusing when talking about carbide grades and which is best for a particular application. Here are some basic facts to know about carbide and how it is composed.
Carbide is a “cemented” metal which means that like concrete it has an aggregate component and a binder component. Finely ground particles of tungsten make up the aggregate and cobalt is the majority of the binding agent in almost all carbides. The percentage of cobalt to tungsten and the average size of the tungsten particles separate carbide into different grades. Typical carbide will have about 95% tungsten particles and 5% cobalt binder. Carbides with higher percentages of cobalt binder will exhibit properties of being “tougher” or “softer” and have higher transverse rupture strength. Conversely, those with lower percentages of cobalt binder have lower transverse rupture strength, are considered “harder” and more brittle, and are subject to breaking /cracking with high impacts. For woodworking tools we want the best of both worlds, in other words, we want to select carbide that is both hard and tough so that it is resistant to abrasive wear when cutting wood yet resistant to breakage so that the ultra-fine cutting edges do not chip off during normal use at high RPM. No matter which grade of carbide is selected, it is important that it be of good and consistent quality and that the tool made is done so with proper grinding technique and correct geometry.
The importance of tool holders
Almost as important as which cutting tool you select is making sure that it has the proper connection to the machine spindle. It is critical that the cutting tool is located accurately, rotates through its cutting path with little to no “run out” and is clamped properly so that there is no loss of power and no deflection from the clamping source. In the world of routing, the tool holder makes the connection between the cutting tool and the machine spindle. In a perfect world, the tool and machine would be one solid unit! In a perfect world, the tool holder would transfer 100% of the machine spindles torque to the cutting tool. We don’t live in a perfect world.
The most common type of tool holder in the market today is the collet style tool holder. It consists of three main parts: the tool holder body, the collet, and the collet nut. Within this system, as many as five (depending on spindle taper) separate mating surfaces are introduced, all of which present an opportunity to introduce run out and reduce torque applied while cutting. While this is a very economical and convenient style of tool holding, be aware that others systems are available that are more accurate and provide up to 100 times more clamping force than the collet style, shrink fit and hydraulic-style holders to name a few. It’s important to know that when you are trying to eek every last ounce of performance out of your tools, the tool holder is an easy place to make improvements.
In some cases we are able to integrate the cutting tool and tool holder into one unit which solves most of the issues. When that is not the case, you need to make sure you have selected the appropriate system for what you expect to get out of that application. If you do use collet style tool holders, follow these basic steps to get the best results possible and maintain safety.
Make sure when you change the tool that you clamp the tool holder in a proper tool changing fixture.
A torque wrench should be used when tightening the collet nut. It is critical that the nut be tightened to the proper foot pounds; over tightening and under tightening are both bad for your tools and can be dangerous to your operators.
When putting the tool holder and tooling together, make sure that everything is clean and in good working order. When installing the tool shank into the collet, be sure that at least 75% of the internal round portion of the collet’s I.D. is filled with “full round” tool shank. Inspect the collets closely as they are an important link in the chain. Resins released and superheated during the cutting process will migrate up the slots of the collet and will build up over time. Use only nonabrasive cleaning methods. Collets are made from heat-treated material and experience a constant “heating and cooling” cycle under normal use. That fact along with normal mechanical wear from tightening and loosening means you need to replace them every 600 hours of use.
Many styles and sizes of collets are available. One of the more common sizes is the ER40. These tool holders are used to hold and drive a wide variety of tool diameters ranging from 1/8” up to 1” shank diameters. One common application for routing is for thru cutting with 3/8” diameter solid carbide router bits. Due to the overall size of the ER40 collet and the relatively small diameter of the 3/8” shank, we frequently see issues of slippage or breakage when increased demand is placed on the cutting tool. Under normal cutting the customer gets decent cutting results. But if the material gets harder or the user tries to feed faster, problems can develop. It’s a good example of tool holder integrity, and the solution is to either switch tool holders to a smaller collet size such as an ER32 or SYOZ25 or to a different style holder altogether.
Tool Balance Adds to Tool Life
Tool balance is an important factor to consider for optimizing your cutting tools’ performance. Improperly balanced tools will cause poor part finish, uneven tool wear, reduced tool life, noise and possible machine spindle failure and damage. Some things to keep in mind when considering tool balance--even though you have a perfectly balanced holder and perfectly balanced tool, every time the tool is changed the balance of the entire system can be off due to inaccuracies in the clamping. Make sure you are starting out with balanced components and that you are doing everything you can to locate that tool accurately each time it is changed out. ISO standard for cutting tool balance is a G2.5. With today’s high speed spindles, that rating falls a bit short when getting to RPM ranges above 24,000. The two key factors to keep in mind with regard to balance are speed (RPM) and diameter. The higher the speed or the bigger the diameter, the more important the balance becomes.
Protecting your machine’s spindle is very important to the overall life and efficiency of your routing tools and obviously the machine tool itself. Here are some quick dos and don’ts:
*Set up a warm-up cycle, especially if the machine is not used every day.
*Do not leave tooling in the spindle overnight or for long periods of time (this can reduce drawbar spring life).
*Do not use unbalanced tools.
*Watch for any marks or discoloring on the tool holder taper (these may be indicators of a problem).
*Keep tooling in good condition.
*Heed the manufacturer’s spindle manual (if unusual jobs come along such as repeated drilling cycles or something else out of the ordinary, check the manual to make sure that your spindle is rated for the application).
Also make sure that you use only clean, dry, filtered air for the pneumatic tool changer, clean filtered water if the spindle is water cooled and proper inverter settings and a clean power source.
Select the Proper Feed Speeds
Selecting the proper feed speeds and RPMs for your cutting tools is the final important step in maximizing tool life. Tools run improperly will produce poor part finish, shortened tool life and excessive wear and tear on your tool holding systems and machine tools.
Since you may already know the tool diameter you will be running and the material that you will be cutting by this point in the game, it’s generally easiest to select an appropriate running RPM and then calculate the feed rate from there. On a typical CNC application you will be selecting RPMs for a couple of different types of tools. For boring bits (drilling) and router tooling (cutting), most boring tools will be run in the 3000 to 6000 RPM range and plunge rates of 1 to 4 meters per minute. Routing tools will generally be run from 8,000 to 24,000 RPM and feed rates up to 50 meters/min. There is no steadfast rule for selecting your exact RPM. However, in general, smaller diameter tooling will be run at higher RPM ranges and larger diameter tooling will be run at lower RPM ranges.
One rule that should be adhered to is maximum surface feet, which is a function of RPM and tool diameter, and should never exceed 15,000 sfm (surface feet per minute). To calculate, simply take the tool diameter multiplied by pi multiplied by RPM and divide by twelve.
Surface Feet=(3.14 (pi)x diameter x RPM)/(12 (to get feet per minute))
Keep in mind that heat generation is directly proportional to RPM; the higher the RPM the higher and faster heat may be generated. The very fine point of the cutting edge can quickly reach very high heat if the chip load is too small or not kept constant. Most machine tools will need to slow down to make corners or interpret complex geometry so keep that in mind when selecting operating RPMs. Machine spindles will also have a power curve which means that they generate maximum horsepower at a specific RPM. At faster or slower RPMs, the spindle may have significant loss of horsepower so in some applications it may be important to select an RPM that maximizes horsepower.
Once you’ve selected the operating RPM, you can then calculate the feed rate based on obtaining the proper chip load for the material you are cutting and other factors that may apply to your application. To select the proper chip load a good place to start is to reference a chip load chart like this:
This will give you a good starting point for selecting chip loads and you may refine your selections over time with experience and talking with others about their applications. The thing to keep in mind is that maximizing your chip load will maximize your router bit’s life. Many factors will affect what chip load you will be able to run at so it’s not as simple as just running a heavy chip load. But again, running a tool at the largest possible chip load will almost always give you maximum tool life.
The following is the formula for calculating your desired feed rate once you have selected the chip load and RPMs that you will be running:
Chip Load=(Feed Rate (I.P.M.))/(RPM x number of cutting edges)
So for example:
Chip Load=(864 (I.P.M.))/(16,000 RPM x 2) Chip Load= .027"
A few more techniques should be considered that can dramatically increase tool life for most routing applications. One very common cutting application is machining panel material that is laminated on two sides with either melamine or HPL. When cutting laminated material, the router bit’s cutting edges will wear heavier directly at the laminate lines, basically causing small grooves to form in the cutting edge where it comes into contact with the laminate material. So if the tool is oscillated during the cut, that wear line is spread out over a greater area and thus provides much more run time for the bit.
Common line cutting is a programming technique that utilizes only one pass to separate parts in a nested operation providing a finished part from both sides of the tool as it cuts, thus eliminating the need to go around each part individually.
With the competitive nature of our industry both domestically and internationally, it’s imperative that you realize the maximum benefit of every investment you make into your company. Tooling can be one of those large expenditures that will get your attention when you take a look at the balance sheet for the year. Hopefully this article provides some food for thought and gives you some basic knowledge on ways that you might improve your routing tools performance and increase that bottom line.
Source: Vortex Tool Co. Visit www.vortextool.com or call (800) 355-7708.