![]() ![]() Whenever you use a router, inspect the bit first for signs of damage. It’s unsettling (but easy) to imagine the damage that can be done by metal flying in any direction at 120 mph. However, it’s incredibly important to do so when operating high-speed rotary tools. We recommend putting on your safety glasses even when you’re just walking through your shop (how often do you say, oh I’m just going to do this or that really quick?). only want to use bits that are in excellent condition. In addition to following our router bit speed chart, you want to check the condition of the bits themselves. If you feel the tool straining, or you need to really bear down on it, you need to make an adjustment. Let the tool do the work and “feel” the tool. In this way, you can maintain a safe and effective rim speed without putting any undue pressure on the tool or yourself. It worked much better than any jigsaw, and gave us a nice straight edge to sand.Īs the router bit diameter increases and/or the wood gets harder, you can take multiple passes with the router. On each pass, we plunged the bit deeper until we were through the 2+ inch thick material. When we created our circular ash table, we used multiple passes with a router to make the cut for the curved outer edge. It’s good to keep in mind that you don’t have to remove all of the material in one fell swoop. While we strongly suggest you only make cuts you’re comfortable making, you can also ease into certain cuts. Consider Taking Multiple Passes at Material That can result in a loss of control or worse. If you fail to adjust your router speed when moving from smaller to larger bits, you create a situation where you can end up cutting at 3X the speed (or more) of your smaller bits. That same router, however, drives a 3-inch bit at 178.5 mph at the cutting edge. That cutting speed occurs at the edge of the bit where it does most of its work. So, using the above example, a 1-inch router bit spinning at 20,000 rpm cuts at a rate of 59.5 mph. If we covert those into the more (American) familiar miles per hour (mph), we get:ġ-inch diameter router bit rim speed = 59.5 mphĢ-inch diameter router bit rim speed = 119 mphģ-inch diameter router bit rim speed = 178.5 mph For the sake of simplicity, let’s assume a router speed of 20,000 rpm:ġ-inch diameter router bit speed = 3.142 in. What we get are results expressed as inches per minute. Rim Speed = circumference x router speed (RPM) Now we can calculate the rim speed-or the speed at any point along the outside edge of the cutting router bit-using the following equation: Let’s first calculate the circumference of a few simple bits sizes for example:ġ-inch diameter bit = 3.142 x 1 in. Let’s start with a few different circumferences:Ĭircumference = π x (router bit diameter) The formula for calculating rim speed has you finding the circumference of the bit, calculate that to inches per minute, and eventually translating it to miles per hour. To understand just how the bit diameter affects speed, let me walk you through a few examples. How Fast is That Router Bit Speed Really? Setting the best router bit speed begins with understanding that cutting takes place along the rim. Of course, running bits too slowly can also cause vibration that damages the stock. It can also exaggerate even the tiniest imbalance in the bit or router and cause vibration or a dangerous bit failure. It’s the difference between a moderate acceleration and leaving Back to the Future DeLorean tire rubber fires. However, suffice it to say it’s an unsafe speed-for both the wood and the user-on the larger bit. Without the proper context that may not seem terrible. The rim speed difference at equal RPMs is more than twice that for the 3.5-inch bit than the 1.5-inch one! Some basic geometry quickly illuminates the fact that 1.5-inch diameter and 3.5-inch diameter bits running at the same RPMs have dramatically different rim speeds at the edge. They can be from larger plunge routers like the Triton TRA001 or smaller trim routers like the Milwaukee M18 FUEL router. Grab a couple of router bits with dramatically different diameters to get a sense of the importance of rim speed. Why You Need to Set Your Router Bit SpeedĪs a general rule of thumb, the router bit speed has to do with what we call rim speed. ![]()
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