How To Calculate CNC Feeds and Speeds Video


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For Your Safety

  1. The methods illustrated here are only intended for use with a CNC machine.
  2. Make certain that the workpiece is secured and that all components of the fixture are securely fastened to the table.
  3. Use a guard, eye and hearing protection at all times.

Learn step-by-step as CNC master technician Jeff thoroughly explains how to calculate feeds and speeds for your CNC machine.

What is chip load? How does the chip load determine how fast your CNC feed rate Inches Per Minute (IPM) should be? Using his CaMaster 7 Horsepower Cobra X3 CNC Machine, Jeff answers these questions and more in our latest CNC video.

CNC Feeds & Speeds - Transcript

Hello everybody, my name is Jeff with Work Against the Grain, and today I want to talk to you about one of the biggest questions I get on a regular basis, and that is; Hey Jeff, how fast should I run my machine?

Chip load is one of the most important factors when determining the speed and feed of a machine. The chip load is when the bit spins around and the cutting edge cuts away the material. The chip that comes off of that is your chip load and that's important because you're not looking to create dust. You're looking to create chips and this is one of the things that can keep the tool cooled down a little bit and prolong the tool life.

So you come to ToolsToday.com and in the search bar up here at the top we will have a look at 46172-K, which is the Amana Tool, CNC Spektra, and it's a 3/8” diameter endmill.

Once again you have some various specs here in terms of length, up, down, cut, rotation, et cetera. Then if we scroll down to the bottom here and come to pdf files, once again, we've got the CNC chip load feed and speed chart, and we'll look for the 46172 which is right here, this 2 flute up-down.

It's a 3/8-inch diameter. We're cutting in MDF. So our feed rate is 260 inches per minute, producing a chip load of 0.0072 with a ramp-down or plunge rate of 130 inches per minute.

It is really important to understand that these feed and speed charts are Amana’s recommended starting calculations and each CNC machinist may want to adjust their inches per minute depending on the size, power and stability of their machine.

For example, if I was using a desktop CNC like a ShopBot, I would run my inches per minute slower than on my CAMaster Cobra X3 4x8 with a 7 HP spindle.

So how do I maximize the power of my machine? Well, it's simple really. It's all about the chip load. The bigger the chip, the faster my inches per minute are. The smaller the chip, the slower the inches per minute are going to be.

Since my machine is capable of running much faster than Amana’s recommended starting point of 260 inches per minute for the 3/8-inch Spektra compression bit cutting in laminate, I'll set my chip load to 20,000s of an inch and use the calculation of rpm x number of flutes x chip load to get my inches per minute up to 720, running at 18,000 rpms.

Now if you'd like to run slower with your tabletop CNC, let's say 120 inches per minute, you'll need to find your chip load by using the formula: Feed rate divided by Rpm x number of flutes, which would tell you that your chip load would be 3,000s of an inch instead of 20,000s of an inch. Pretty simple, right?

Let's take a look at these bits cutting on my machine.

Okay. This is the Amana tool Spektra 46170-K. It’s a quarter inch up-down cut endmill and it's travelling at 540 inches per minute, spinning at 18,000 rpms. We're going to go through the next couple of minutes looking at normal V-carve of letters and a logo, but, although the bit is 1/2 inch at the top, the cutting edge at the bottom of the bit is less than 1/32 of an inch and so that's why we're running at 30 inches per minute.

These next few seconds of clips are a normal V-bit pocketing tool path when you just use the V-bit and you don't use a larger area clearance tool.

There's benefits to both, but I wanted to show this particular cutting method so that you could see the clean edge that you get on the melamine and then we'll come back and look at a more traditional larger area clearance tool with some of the Spektra bits.

This is showing a little bit more traditional pocket clearing prior to the V-carve, utilizing the Amana tool Spektra 46100-K -- you want to talk about a hefty little 1/8 inch cutting bit, two cutting edges, cutting 1/8 inch deep in MDF at 180 inches per minute.

Here we are again with the Amana Tool Spektra 46170-K. I'm doing an inside profile on the graphic vector just to once again show you the 540 inches per minute feed rate with the two flute up-down cut endmill.

And so again, just a little bit different cutting method. This is the Amana Tool RC-1108 again. After I had done the pockets with the larger area clearance tools, I came in and ran an inside profile with the V-bit to sharpen up all the corners.

And so as you've seen in the video a couple different ways in which to do your V-Carve pocketing outside of the letters of course, you can utilize the V-bit in its entirety or you can utilize a flat area clearance tool and then come back in, run an inside profile and tighten those corners up.

The Amana Tool 46237-K really actually gives you a pretty tight corner on the inside as you'll see in the finished product.

And then here comes one of the big boys, the Amana Tool Spektra 46172-K. It's a 3/8 inch endmill running at 740 inches per minute and if you blink you'll miss it. Absolutely spectacular bit.

And there it is. The Wentworthy Luxury Hotel and Resort sign.

I sure did have a lot of fun doing this. On behalf of ToolsToday: Hey, thanks a lot for watching.

Feed, Speed, Chip Load & Ramp Down CNC Running Parameters

3/8" Dia. Solid Carbide, Spektra™ Coated Compression Spiral Flute CNC Router Bit No. 46172-K
Feed Rate (IPM): 740
Speed (RPM): 18,000
Chip Load (Per Tooth): 0.020"
Ramp Down: 370 IPM

1/4" Dia. Solid Carbide, Spektra™ Coated Compression Spiral Flute CNC Router Bit No. 46170-K
Feed Rate (IPM): 540
Speed (RPM): 18,000
Chip Load (Per Tooth): 0.015"
Ramp Down: 270 IPM

1/8" Dia. Solid Carbide, Spektra™ Coated Up-Cut Spiral Flute Router Bit No. 46100-K
Feed Rate (IPM): 180
Speed (RPM): 18,000
Chip Load (Per Tooth): 0.005"
Ramp Down: 90 IPM

1/16" Dia. Solid Carbide, Spektra™ Coated Down-Cut Spiral Flute Router Bit No. 46237-K
Feed Rate (IPM): 100
Speed (RPM): 18,000
Chip Load (Per Tooth): 0.003"
Ramp Down: 50 IPM

60° V-Groove Solid Carbide Insert Knife Amana Tool CNC Router Bit No. RC-1108
Feed Rate (IPM): 30
Speed (RPM): 18,000
Chip Load (Per Tooth): 0.002"
Ramp Down: 15 IPM


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Produced by Jeff from Work Against The Grain

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