Setting the Best Router Bit Speed
Using a router to form beautiful finished edges on wood is an analog to painting a drab room – in a very short amount of time with minimal effort, you can make dramatic improvements in the aesthetic of the work. But with just a little woodworking experience you’ve probably noticed that there are many ways to do things incorrectly and really very few ways (or just one!) to bring about the desired result safely and efficiently. The nuance of routing has much to do with bit speed and its interplay with bit diameter, stock hardness, feed rate, and bit sharpness. Although more manufacturers are printing suggested bit RPMs on packages, bit speed information isn’t always readily available. So how do you know? Well, fear not – here’s a quick guide to setting the best router bit speed.
Setting the Best Router Bit Speed
1. Rule of thumb: it’s about the rim speed. Grab a couple of router bits with dramatically different diameters to get a sense of the importance of rim speed. They can be from larger plunge routers like the Triton TRA001 or smaller trim routers like the Ridgid R2401 – it doesn’t matter. Some basic geometry will illuminate the fact that a 1.5-inch diameter and a 3.5-inch diameter bit running at the same RPMs will have dramatically different speeds. The rim speed difference at equal RPMs is more than twice that for the 3.5-inch bit than the 1.5-inch one.
Without context that may not seem terrible, but suffice it to say it’s an unsafe speed – for the wood and for the user – on the larger bit. It’s the difference between a moderate acceleration and leaving Back to the Future DeLorean-at-88 mph tire rubber fires. It can actually burn the wood but it will also exaggerate even the tiniest imbalance in the bit or router and cause vibration or a dangerous bit failure. Of course, running bits too slow can also cause vibration that damages the stock. Here’s a general RPM guide (please refer to the manufacturers’ recommendations and keep in mind the speeds they suggest are maximum):
|Diameter||Max RPM +/- 10%|
|Up to 1-inch||22,000|
|1- to 2-inches||20,000|
|2- to 2.5-inches||18,000|
|2.5- to 3.5-inches||10,000|
Generally, the rim speed will be around 100 to 120 miles per hour. You can’t clock that, so use the RPM as a proxy for rim MPH.
Work with the Router, Not Against It
2. Take a pass. Although we strongly suggest that you only make cuts you’re comfortable making, this isn’t what we mean here. In this case, keep in mind that you don’t have to remove all of the material in one fell swoop. As the diameter increases and/or the wood gets harder, you can take multiple passes with the router. In this way you can maintain a safe and effective rim speed without putting any undue pressure on the tool or yourself. Let the tool do the work and “feel” the tool – if it’s straining or you are bearing down on it so hard that you’d be off balance if it gave way, you’re doing it wrong.
Check Your Bits
3. Only use bits in excellent condition. 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?) but it is incredibly important to do so when operating rotary tools. It’s unsettling but easy to imagine the damage that can be done by metal flying in any direction at 120 mph, so whenever you’re using a router, be sure to inspect it first for signs of damage. If there’s even the slightest hint of damage, get a new bit. This goes for grinders and grinding wheels as well. Bits can accumulate sap and wood material so be sure to wipe them off after each use to keep them in good, sharp working order.
Variable Speed or Fixed?
4. Don’t use large diameter bits on fixed speed routers. Fixed speed routers have one speed usually near the high end of the RPM range. That means they are only appropriate and safe or the smallest diameter bits. Don’t try larger bits or to employ any after market device designed to lower the RPM.
The router is one of our favorite workshop tools – you can turn ordinary dimensional lumber into a beautiful piece in a very short time. To ensure the best results, setting the best router bit speed is the place to start. If you’re a Pro and you have a router speed tips, add them in the comments below—or share them with everyone on Facebook, Twitter, and Instagram.