Router Bit Speeds
George VondriskaDescription
George Vondriska demonstrates why you need to change the speed of your router based on the diameter of the router bit you are using for your woodworking projects. A WoodWorkers Guild of America (WWGOA) original video.
Click here to download a router bit speed chart.
One question that I get all the time is why variable speed in routers is so important. And the answer to that has to do with the diameter of the router bits. The rule is that the larger the diameter, the slower the bid has to run. And let me help you understand what that's all about. So here we've got a three and a half inch diameter bit, and a bit that's about one and three eighths inch in diameter. Now I've got some circles drawn on this board. So three and a half, one and three eighths in diameter. Now, if we go back to some geometry, we can figure out that the circumference of this circle is nearly 11 inches. The circumference of this circle is just a little bit over four. So imagine that that circle is a straight line. And what we're talking about is the time it takes to get from one end of the line to the other. And on this one if it's a straight line, the time it takes to get from one end of the line to the other. So that's the distance or the speed that we're gonna get when that bit is spinning. Because this distance is greater than this one. What it means is that what's called the rim speed, out here on the edge is greater than this bit, when they're running at the same RPN. So here are the numbers. If I run my router 22,000 RPM and I run my inch in three eights diameter cutter in there, the rim speed, right out here around the edge is about a hundred and twenty five miles an hour. On this three and a half inch diameter cutter if I run at the same speed, if I run at 22,000 RPM, I'm going over 200 miles an hour about 230 miles an hour, way too fast for the bit. So although they're at the same RPM, when the diameter is bigger, the circumference is bigger. So the rim speed then is also higher that's where it gets dangerous. If we slow this bit down, to 12,000 RPM or so, that brings the rim speed down to about a hundred and twenty five miles an hour. That gets it in a safer range. Now that still sounds real fast, but that gets it in a safe range as a rim speed for this cutter. So the larger the diameter, the bigger the circumference, the faster the rim speed of it. So we have to slow those bits down big diameter, low RPMs
Problem is this George, RPM and MPH don't compute if you don't know the math. It would be better to explain prm to rpm so 22k rpm dialed down to 16k rpm as an example.
George references 125mph in the vid. Is that a hard fast rule to go by? I have a set of router bits, and not knowing better at the time, ran them too fast. Now a few the bits have clear burn marks on the bit. This indicates to me that the bit is damaged an no longer good. Lesson learned. Since then I've slowed down the speed, but didn't know if there was a good hard fast rule.
Is it ok to use a cnc bit on your router? If not ... why?
I understand the maths but don't get why it's "more dangerous" for the larger bit to be spinning so fast. What is the effect of the faster speed on the work piece and me?? I have a fixed speed router so don't know what to do!
How does shank size affect router speed and bit diameter?
I knew to use slower sppeds with larger bits but didnt understand why. Its nice that wwgoa can explain things in a simple way thats easy to understand and makes sense
I really appreciate videos like this. In addition to the instruction, you provide simple explanations and examples. The "why" helps me to retain the information. Thanks!
Just watched George Vondriska's video on router bit speed. Not having used a router in over thirty years and new to woodworking, do the newer routers all come with multi speed controls?