CNC Router

Overview

"What is the CNC Router good for?"

A Computer Numerically Controlled Router can cut wood with higher precision than conventional methods (jigsaw, table saw, miter saw). It takes files that you draw in CAD or render to a vector format and cuts along those vectors. When used properly it produces a clean and consistent cut along the cut surface. It is one of the coolest tools the node has to offer.

Technical Details

The work surface is approximately 65” x 145”. 2 Stepper Motors control the gantry movement. These are powered by the ShopBot motor controller. This is a beige computer tower with a red switch. It is not actually a computer and you need to remember to turn it off before you leave. The spindle motor is a xxxx W AC motor controlled through Variable Frequency Drive. It can operate between xxx and xxxx RPM. The controller is the blue box on the wall and power to the controller is applied through the wall switch below the blue box. Acceptable CAD formats are: .dxf, .svg, .dwg, .eps, .ai, or .skp.

Terms

End Mill - this is a special type of bit for the router designed to cut in all directions.

Flute - is the spiral cutting feature on the end mill. More flutes means smaller chips.

Gantry - is the frame that the X and Y stepper motors move across to position the end mill.

Stepper Motor - A high precision motor which can move in very fine increments. Stepper motors have current applied to their windings, even at rest. This is called holding current and can damage the motor if left on too long. Make sure to turn off power to the gantry motors once you are done using the CNC Router. The power switch for these is on the beige computer tower beneath the desk.

Feed Rate - This is the rate at which the end mill moves through the cut, not the speed of the end mill itself.

Chip Load - This is a number that represents the size of the chips produced by the end mill and is critical to the quality of the cut.

Step-over - This is the amount of overlap that the end mill makes when going into uncut material. You can think of it this way, when mowing your lawn, you leave part of the lawnmower over grass that you have already cut. The amount of the lawnmower that overlaps uncut grass is the step over (Todd's Analogy). Stepover should be between 1/3 and 1/10 of the tool diameter. Use a larger stepover for softer materials and a shallower step over for hard materials.

Tool Path - This is the path that the end mill will go through during the cut. You can make any vector or grouping of vectors into a tool path and each tool path can have it’s own cut depth and assorted settings.

Conventional Cut - the flutes cut counter to the XY direction of travel

Climb Cut - is when the flutes cut into the piece in the same direction as the direction of travel. This can be dangerous as the forces generated pull at the piece more than a conventional cut and it carries a higher risk of sending your piece flying. Don’t use this setting.

Tear Out - is when the material is ripped out of an area where it shouldn’t be. This generally refers to stripping the veneer off of plywood and can happen during the cut or also during tab removal after you are done cutting.

CAD

The first step is to create CAD files of what you want to cut. The files need to be in a suitable format such as .dxf, .svg, .dwg, .eps, .ai, or .skp. LibreCAD is a free and open source 2D CAD program for Windows, OSX, and *nix systems that can output .dxf’s. Inkscape is another program that can produce .svg outputs. Additionally, you can import certain 3D files to do 3D carving however that is not currently covered in this guide.

Selecting an End Mill

There are different types of end mills of different sizes, flute types and counts. A thinner end mill can do a better job at detail but may need to run at a lower feed rate to keep the chip load in a good spot. There are a few end mills to choose from on a shelf above the spindle motor controller. If you don’t see the one you want to use, feel free to purchase one and donate it to the node.

Flute Types

Straight Flute - great all around end mill, decent chip removal [1]

Up Spiral - great chip removal, can tear-out the top of thin veneer such as finish grade plywood [2]

Down Spiral – poor chip removal, no tear out, slower feed rate [3]

Compression – combination of up and down spiral, great all around end mill, great for plywood or laminated sheet goods. [4]