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Router Feeds & Speeds

In today's market of CNC routers this is one of the questions we get asked the most. Unfortunately, there is no perfect answer to it because of the huge variety of machines, tools, and operations being performed. However, we do have some recommendations and starting points for you to work with.

Specifying the Proper RPM's

For the most part all router bits are made to be run between 10,000 and 20,000 revolutions per minute. The general rule on this is that the larger the diameter of the tool the slower the RPM's should be. The whole problem with specifying RPM's comes down to friction. The faster a bit spins the more friction in generates during the cut. This friction can cause a multitude of problems some of which include poor tool life, burning of the material being cut, and poor cut quality. The goal in the big picture is to use the slowest RPM's possible for each application. Some of the limiting factors to faster RPM's are chipload of the cutting tool and feed rate limitations of the machine. A tool with a small chipload will clog up with chips and not be able to eject them. This can lead to poor cut, part movement, burning, and tool breakage. A machine with limited feed ability can mean that a fast RPM will cause burning of the material as the bit will spend too much time in the same place as it cuts.

Feed Rate Specification

We all know what feed rate is right? Well lets look at some of the reasons it is the most important factor in determining the proper use of your cutting tools.

When a cutting tool is used at the proper feed rate for its RPM's it will do five things.

  1. Clear its own chips from the flutes.

  2. Cut the material without pulling or tearing out the fibers.

  3. Cut the material without burning or burnishing the cut edge.

  4. Cut without displacing the part being cut.

  5. Cut without breaking the tool.

All of these factors are important to the production of your quality products. Setting your feed rate should be the most important part of setting up every router bit you use.

Chip Load Specification

This is the elusive measurement that keeps so many people from getting their setups right. Chip load is the measure of the thickness of material removed by each cutting edge during a cut.

Putting Them All Together

Now here is were the difficulty begins in determining the proper setup for your tool, material, and application. All of the specifications discussed are inter related. This means that if you have absolutely none of these specifications you cannot figure out the proper setup for your machine. That is were you either begin experimenting or you turn to the cutting tool maker to give you the information you need. Lets begin with the formulas for figuring out each of the specifications you need.

RPM's = feed rate* / (number of flutes x chip load)

Feed Rate = RPM x number of flutes x chip load

Chip Load = feed rate* / (RPM x number of flutes)

* Feed rate is in inches per minute.

As you can see you need to know at least two of these to figure out the other, not real practical is it? So here is what you can do. Look at the chart below for some of the information you need and adjust the specifications for changes in your actual setup. Since chip load is the hardest thing to know this will make figuring out your specifications a great deal easier.

Don't forget! These figures are starting points for your setups. You will need to adjust feeds and speeds up or down until you get the finish or production rate you desire. These are not exact specifications to treat as law.

Chip Loads for Wood

All chip loads are based on using 1/2" diameter bits, cutting 3/4" material, and cutting at 18,000 RPM's.

Tool Type # of Flutes Hard Wood Soft Wood Man-made
Upcut Finisher 1 0.0125 0.0125 0.0000
Downcut Finisher 1 0.0125 0.0125 0.0000
Upcut Rougher 2 0.0174 0.0181 0.0167
Downcut Rougher 2 0.0167 0.0174 0.0160
Upcut Finisher 2 0.0097 0.0083 0.0111
Downcut Finisher 2 0.0090 0.0076 0.0111
Upcut Chipbreaker 2 0.0104 0.0090 0.0118
Downcut Chipbreaker 2 0.0097 0.0090 0.0118
Upcut Rougher 3 0.0106 0.0093 0.0102
Downcut Rougher 3 0.0102 0.0088 0.0102
Upcut Finisher 3 0.0060 0.0056 0.0074
Downcut Finisher 3 0.0056 0.0051 0.0074
Upcut Chipbreaker 3 0.0074 0.0065 0.0079
Downcut Chipbreaker 3 0.0069 0.0060 0.0074
Upcut Ballnose 2 0.0097 0.0083 0.0111
Compression 1 0.0222 0.0250 0.0333
Compression 2 0.0125 0.0139 0.0181
Mortise Compression 2 0.0125 0.0139 0.0181
Compression 3 0.0093 0.0102 0.0130
Compression 4 0.0000 0.0000 0.0208
Compression Chipbreaker 2 0.0125 0.0139 0.0181
Straight Flute 2 0.0083 0.0056 0.0111
Upcut Low Helix 2 0.0167 0.0174 0.0153
Downcut Low Helix 2 0.0160 0.0167 0.0153
Upcut Low Helix 3 0.0106 0.0093 0.0102
Downcut Low Helix 3 0.0102 0.0088 0.0102

Chip Loads for Plastics

All chip loads are based on using 1/4" diameter bits, cutting 1/4" material, and cutting at 18,000 RPM's.

Tool Type # Flutes Soft Plastic Hard Plastic Foam
Upcut High Helix 2 0.0000 0.0000 0.0049
Upcut Low Helix Finisher 2 0.0076 0.0069 0.0000
Downcut Low Helix Finisher 2 0.0069 0.0063 0.0000
Upcut Low Helix Finisher 3 0.0056 0.0051 0.0000
Downcut Low Helix Finisher 3 0.0051 0.0046 0.0000
Upcut Low Helix Finisher 1 0.0194 0.0181 0.0000
Downcut Low Helix Finisher 1 0.0167 0.0153 0.0000
Straight O-Flute 1 0.0194 0.0167 0.0000
Straight O-Flute 2 0.0083 0.0076 0.0000
Upcut O-Flute 1 0.0139 0.0111 0.0000
Downcut O-Flute 1 0.0125 0.0111 0.0000
Upcut O-Flute 2 0.0076 0.0069 0.0000
Downcut O-Flute 2 0.0069 0.0063 0.0000

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