Tech Talk
What is the "Speed Limit" of a woodworking tool?
Like many of you I spent a week this spring at Ligna, and was quite impressed with what the machinery manufacturers and our European tooling suppliers were showing. A lot of the manufacturers were introducing equipment with phenomenal abilities as far as rates of production are concerned. At one time the emphasis was on labour saving automation, which was followed by the demand for increased versatility, frequently triggered by the need for shorter runs. Now the theme seems to be speed. Faster production has always been in the mind of producers, but the emphasis for higher spindle speeds and feed rates has never been greater. The advantages to improved productivity are obvious, leading to savings in labour, capitol cost, inventory, and even space. In the booth, we spoke to a lot of woodworkers who were seriously planning on, or in the process of, major modernization of their operations, utilizing the new technology. They were concerned with the most efficient way to tool their new equipment, because in many cases they were aware that existing tools were not going to be as effective as required. The common theme in a lot of these discussions was increased speeds. There is little point in buying high production equipment if you aren't confident that the tooling will be able to perform to the expectation of the machine. So in a lot of cases the conversation centered around the machine, the production expected and what tools were going to be required, and what would their limitations be. The challenge, from the standpoint of cutting tools, inflates as feed and/or speed demands climb.
For example, as the spindle speed on routers gets into the 40,000 RPM range, the quality of design and construction of the bit becomes more critical. Design details such as hook, shear, helix and clearance, that may have worked on slower speed Routers may not work, at these, as yet, unimagined speeds. (Air Routers have run at this RPM and even higher for some time, but the tool diameters are very small - running larger wood routers at this speed is a relatively new concept.) Construction details, such as machining tolerances, have to be much more precise, because any imperfections are exaggerated at this speed. Tool balancing on small diameter tools has never really been a critical issue, but again, if we are going to get into this speed range, a perfectly balanced tool is going to be vital.The purpose of these high spindle speeds is to accommodate higher feed rates, without increasing the chip load on the tool. If the tool is not machined and balanced to perfection, maximum feed cannot be obtained, with an acceptable quality finish.High feed rates present certain problems, for tool makers, on their own. In routering for example, the tool has to be strong, precise and yet can't be so big that a lot of material is wasted. Cutting pressures have to be kept to a minimum so the material can be held on the table. This is accomplished by designing the correct hook, number of cutting edges, and if required, shear angle into the router so that it cuts the material with the least resistance, while maintaining a satisfactory chip load, and finish.Similarly, the demands on tooling on High Speed Moulders or Double End Tenoners is such that the designs of traditional tooling have to be re-addressed. Rising feeds increase the loads on each wing of the tool to the detriment of the product, unless things such as the tool clamping method, number of wings and the material the cutting edge is made of are considered. Higher feed rates usually require either more wings or, a reduction in the amount of material removed, which is usually accomplished by increasing the number of cutting stations. This approach is very predominant on Double End Tenoning lines, with methods such as double hogging or hogging and milling.You may have noticed that I have avoided being specific about particular applications or recommendations - can't be hung out to dry with what I don't say. But the real reason is the long list of variables that effect feed the rate you can run your spindle, or shaft, or feed system. Hold down pressure is proportionate to feed, and so is tool diameter, spindle/shaft speed, and number of wings, as is shear or helix. Different cutting materials (ie. carbide, diamond, HSS, etc.) create different cutting pressures, as does the shear or helix, which can affect the ability to hold the material satisfactorily, thus influencing feed rate. Obviously, the amount of horsepower driving the tool has a direct relation to how fast it can cut. Believe it or not, how the tool is mounted can also have a bearing on speed. Then of course, there is the material(s) being cut and how much there is to be removed, and the type of machine you are running.Rather than me create an artificial application if anyone would like to e-mail, fax, write or phone in a specific situation or problem I would gladly plug in all the factors (and call in my network of experts) to come up with a recommendation, of either feed and speed or type of tooling, along with how I arrived at any conclusions. by: Doug Reid, President, B.C. Saw
