CNC Guide

GUIDE TO UNDERSTANDING BUILDING A CNC ROUTER YOURSELF

How it started                                            I never not stop creating when my work day is over at my shop, my nights and weekends are  spent working on the things I truly enjoy RC, about 10 years ago I was constantly taking tools home from my business  to use for my hobby, and always ether  forgetting to bring something home or forgetting to return a tool to the shop , there had to be a better way, but ten years ago a cnc router was very expensive for just home use, so I built my first home 3 Axis hobby CNC Router, at last a single tool that could do so much more, drill any size hole, cut any shape, again and again with the same precision from part one to part one hundred, pc based motion control electronics and DOS programming was very crude back then, and the machine was costly and time consuming to build and run, as there were few known examples to look at or even talk to someone about, but wow that original machine was the future, and when friends and family saw what it could do they had to have one too, I found myself building machines on my time off, (and unfortunately you cannot make any profit from friends and family) instead of building things for my RC hobby, and that's how these plans were initially created , I drew up some plans for a CNC machine that the average person could build, using standard woodworking tools and parts purchased from local hardware stores, and handed them out to anyone who wanted to build a machine, I do not consider myself a pioneer of PC based motion, but I was there and very involved in the beginning, today 10 years later, with great control software and many electronic drives available, together with our time tested plans I have gotten the  Homemade CNC down to a simple art,  the plans and instructions we sell today did not appear overnight and have been refined and tweaked over a ten year period, so purchasing our plans today you will feel confident building your  DIY CNC that your finished machine will perform as advertised, I have been vigilant to keep these plans at the lowest cost possible to insure all can benefit from this wonderful technology, and want thank the many thousands of supporters and all who have helped in making this current plan set a truly global machine able to be built almost anywhere worldwide.

N. Adamo
Rockcliff Machine Inc.

CNC (Computer Numerical Control) or Motion Control is the programmed controlled  movement of a machine or  object based on either speed, distance or load.

This document will help you understand general motion control and CNC equipment with priority given to the DIY machine builder using motion control from a PC.

Selecting a CNC Router Machine Style

Flying Gantry Overview:
A flying gantry or moving-gantry machine is designed in to save space, but at the same time has the option of being made into an open-table bed. This is useful for applications like cutting straight through the table; it is slightly more complex than one traversing axis (example Axis Y will traverse with Axis X and Z). This design arrangement must bear the load of all three axis' and is not considered to be as strong as a fixed gantry layout, and is best suited for machines like plasma. laser, and light duty routers.

Fixed Gantry Overview:
With a fixed-gantry machine style, one axis or slide will be fixed to the gantry (example Axis X) with Axis Z traveling or attached to it; Axis Y is separate and fixed to the base. A fixed gantry can be made stronger because two of the three axis' can be attached to a solid, non-moving structure, but at the same time this arrangement will result in a larger machine footprint. A fixed-gantry design is almost exclusively used on full-size, vertical milling machines. A fixed gantry cannot be made in open table design.
 
Open Table:
 An open-table design is designed for cutting straight through- it is basically a flying gantry with the bed removed, and the machine is usually propped up on four legs or is mounted to side rails. This style of machine is useful for applications like plasma, laser, or if you need to cut a part that cannot be moved, like an inlay on a floor or wall. It can also be mounted to a table, if required; this style is prone to flex in the sideways axis, as the side rail bearings cannot be supported along the entire length.
 
Closed Table:
A closed table is a machine that will have the cutting surface designed in a way that incorporates the side rails onto the base. With this style of design, the machine can be made more rigid, but will have limitations on the part size to be cut, as the bearing rails block off space on the sides.
 
 
Selecting a Linear Bearing Style

Linear Bearing:
Linear Bearings are bearings that can travel in a straight line, with any type of machine cutting the linear bearing must be as rigid as possible and able to glide as free as possible, with a machine like a cnc router the clearance between rail and runner block should be very small or zero, large cnc milling machine will actually be preloaded, there are many types of commercial and DIY linear bearings, the quality of the linear bearings will directly reflect the quality of the cutting and hardness of material that the machine can cut.
 
Supported Linear Bearing:
A supported rail system is the most rigid system; in a supported rail system, the rail will be supported or bolted down the entire length of the rail, the runner blocks will house hardened ball bearings, and the rail will be a hardened shaft or rail, supported linear bearings will cost more than all other types of linear bearings, and will the best results.
 
Unsupported Linear Bearing:
In an unsupported rail system the rail will be mounted only at the ends, this style of linear bearing will have some flex and will not be as rigid as supporting the entire length of the rail, but will cost less than a supported rail system, and can be good for light cutting, if made in shorter lengths, an unsupported linear bearing can be purchased or made at a low cost with bronze bearings and precision ground shafting.
 
 
DIY Linear Bearing:
Because of the high cost of purchasing a linear bearing from a manufacturer, some builders make their own. A DIY linear bearing can be made for both supported or un-supported versions. A linear bearing made yourself can have great results, and can be made with standard tools. Our version is a fully supported design.
 
Selecting a Z-Axis Slide Design
Fixed Z-Axis Motor Design:
The Z axis can be arranged to only move the slide and cutting tool; in this arrangement there will be less weight to move, as the motor is fixed to a opposite axis.
 
Moving Z-Axis Motor Design:
a moving motor is the standard, in most commercial applications; it is usually as strong and will give more clearance in moving motor design the rail and motor move while the runner block is fixed to the opposing axis.
 
Motors
Stepper Motors:
The stepper motor is an electro-magnetic device that converts pulses of electricity into mechanical shaft rotation. Stepper motors are low cost, with high reliability, high torque at low speeds and a simple, construction. Some disadvantages in using a step motor is the resonance effect often exhibited at low speeds and decreasing torque with increasing speed. Stepper motors have multiple coils. when a specific coil is energized in the proper order, the motor will step in the appropriate direction , a typical stepper motor will usually have 200 steps to make up one turn because of this design stepper motors can keep count without the need of an encoder making electronic controls for stepper motors fairly simple and making them ideal for low cost and easy use.

Motor Mechanical Power Ratings:
Motor power ratings are measured in ounce inches or (oz.in.) example: A 100oz.in. rated motor simply means, if an arm was attached on the motor shaft sticking out one inch from center and if a 100 ounce weight was hung from the end of the arm the motor will lift it.
 
How to Select and Identify Stepper Motors:
Bipolar Stepper Motors:
Bipolar Stepper Motors will have 4 wires. They produce more torque and will require a more complicated, electronic control circuit to run properly. They are used in more applications, because can develop more speed and power than Unipolar motors.
 
Unipolar Stepper Motors:
A Unipolar stepper motor will have 5 or 6 wires. The drawback to using a unipolar drive, is its limited capability to energize all the windings at any one time. This means the torque will be reduced by around 40% compared to other motors. Unipolar motors are good for applications that operate at lower step rate speeds.

Variable Reluctance Stepper Motors:
Variable reluctance stepper motors or Hybrid motors are the simplest to control over other types of stepper motors. Their drive sequence is simply to energize each of the windings in order, one after the other
 
Stepper Motor Frame Sizes:
NEMA 17
NEMA 23
NEMA 34
 
Connecting Stepper Motors:
Series Connected:
There are two ways to connect a stepper motor, in series or in parallel. A series connection provides a high inductance and will give higher performance at low speeds.
Parallel Connected:
A parallel connection will lower the inductance but increase the torque at faster speeds.
 
Motor Resonance:
Motor Resonance is a condition where vibration or oscillation will cause missed steps and noisy operation. Naturally all stepper motors will have more vibrations, as they are moving in a series of steps, this can cause resonance; it can be caused for various reasons that include: incorrect electronic pulse timing of the steps, loose components. There are many types of dampening hubs that can be installed to stop this issue.
 
Inductance:
Stepper motors are rated in terms of inductance. A high-inductance motor will provide a greater amount of torque at low speeds and a low inductance motor will be opposite.

Sizing a Motor:
Sizing a motor is important when selecting a stepper motor or servo motor - having more power will always be a better choice. Not having enough power can cause overheating in servos, and can cause stalling in a stepper motor. It is always difficult to calculate the exact power requirements needed to drive slides on a machine, as there are many factors to consider, like slide friction, lead screw pitch and nut friction, and size of machine - these will all effect what size and power are needed in general with DIY machines the most common motor frame is a Nema23 the range of this size frame will be from approximately 100oz.in. to 500oz.in
 
Servo Motors:
Servo Motors are generally the standard in most high end systems, they can come in many sizes and are either brush or brushless. Because a servo motor is basically a dc motor, it cannot count position on it's own; it will need what is called an encoder, an encoder can be rotary or linear , a rotary encoder is usually mounted to the motor shaft and a linear encoder will be mounted to the slide or table. The purpose of an Encoder is to count the pulses or position, for example: if a rotary 1000 count encoder is used, it will count 1000 pulses per one turn of the motor. This count is sent back to the motor controller electronics, for the controller to position the motor. This routine is called the PID Control Loop. Servo Motor control is much more complicated to perform, a servo motor controller system will cost much more than a stepper motor controller.
 
Lead Screw Description
Lead Screw:
A lead screw is basically a long screw made with a continuous thread. In a CNC machine this lead screw is attached to a motor, either directly or by timing belt with reduction. And the drive nut, which is attached to the table or slide as the fixed motor spins the screw, will drive the table to to specified position, it is important to have minimum clearance between screw and nut, excessive clearance will result in chatter and inaccurate cutting.
 
Resolution Accuracy:
Whether you select servo or stepper motors, they will both have a number or count associated to one revolution of the motor shaft - this number or count is called resolution. For example, a stepper motor with 1.8 degrees, with no Micro stepping, will have to step or index 200 times per turn. The resolution can be increased, by using a Micro stepping controller, this will allow one single step to be increased by 8, or 1600 times per turn. However, with a servo motor resolution is determined by the encoder. An alternative way to increase resolution is to select a finer pitch lead screw; however, with the increased finer pitch, a slower maximum speed will incur.
 
Lead Screw Diameters:
The lead screw diameter is measured from the tip of the threads - Example: 3/8-16 this thread diameter would equal 3/8"
 
Lead Screw Pitch:
Pitch is used to determine the thread spacing of the lead screw and matching nut. Pitch is the distance the nut travels along the screw when the drive nut is turned. One turn example: 1/4-20 is a 1/4" in diameter and has a pitch of .05", if the nut turns 20 times it will move one inch 20 x .05 =1.0".
 
Lead Screw and Nut Options:
In low cost lead screw applications, a drive nut will often be made from plastic or bronze; making the drive nut from these materials will give a low friction solution, at the same time no lubrication is needed.
 
UN Thread:
A UN thread (Unified Thread) is the standard thread shape that is used on general nuts and bolts that you find on most items attached with nuts and bolt.
Acme Screws:
Acme screw threads can be made much more coarse than UN threads. They are square cut threads and can hold much more load than a v style or UN thread; they are common components that are generally found in industrial machines, they are readily available .
 
Ball Screws:
A Ball Screw uses ball bearings in a recalculating housing. Ball screws use hardened ball bearings and the screw is hardened steel, and either come in a lower cost, rolled screw or precision ground screw. Most high- end milling machines will use ball screws - they have high efficiency and can be very accurate. They will, however, be the most costly to purchase, and, as there is no ball retainers in the drive nuts, they will have to be handled and assembled with care.
 
Multiple Start Threads:
Multiple start threads are threads that have multiple entry points, they exist because a screw can be made stronger in coarse pitches and can be used for lead screws, they are made in 2, 3, 4, 5, start configurations

Allthread:
Allthread screws or threaded rod will come fully threaded and are threaded with UN threads. This is the standard thread found on most machine screws and fasteners. Allthread is very common and can be purchased at most hardware stores and can be used as a very low cost, lead screw.
 
Anti-backlash Nut:
An anti-backlash nut will have zero clearance between the screw and nut, it is manufactured to allow preload to be applied to the screw. An anti-backlash nut is very useful in a CNC machine, as it allows very precise transmission from a rotating screw to linear motion. When cutting in any machine, holding the work as rigid as possible will make for smoother, chatter-free cutting. Anti-backlash nuts can be purchased in UN, Acme and Ball screws.
 
Supported Lead Screws:
In longer length slides screw, end supporting is important. A supported screw will have a bearing mounted to the lead screw on the opposite end of the motor, this bearing support will help eliminate a condition called lead screw "whip"; at higher, lead-screw speeds an un-supported screw will become unbalanced. To mount a bearing correctly, the threads will have to be machined off to a clean diameter, in order to fit the inside of the bearing; and the bearing will have to be mounted to the machine.
 
Motor Couplings:
Three-Piece Coupling: A three-piece coupling is a flexible coupling that will help when trying to align a motor shaft to drive screw. Some types of flexible coupling are made from three-pieces: two connectors and a rubber spider. When using a three piece coupling, the lead screw must be supported at both ends.
 
Helical Coupling: A helical coupling is another type of flexible coupling; it is made from one piece and there will be a spiral cut made like a spring, allowing some misalignment of the motor shaft and lead screw.
 
Solid Coupling: A solid coupling is what most drive screws will be attached with, they are not flexible and must be aligned correctly. There are a few different styles, including set screw locking, and clamp style. They can be made from aluminum or steel, and there will be no need for screw support on the motor end - when using a solid coupling as the motor bearings will support the screw.
 
Electrical Systems Overview
Motor Controllers
Determining Motor Controller Requirements:
Step and direction control is by far the most common PC based motor controller. There are many companies that offer motor controller circuits and systems; we recommend using a motor controller that is made or purchased with Step and Direction Circuit design, and capable of using a PC Parallel port for control. This is the most common design, which means you will many choices of control software to use, like Mach, EMC , Turbocnc
 
PC Parallel port or USB:
Currently, the most common control software and motor controllers will use the PC parallel port (25 pin connector printer port). USB connections are available but are still a rare item. Gecko systems have just released a controller for USB but it is still in the design phase.
 
Do It Yourself Motor Controller:
If you have some knowledge of electronic components, there are many motor controller kits which only require soldering. But DIY kits, that include all parts and a circuit board, can be successfully completed, with only novice skills. There is nothing more satisfying than building anything from scratch, but electronics are a different animal and mistakes can cost money, and injury. So unless you are familiar with all aspects of electronics and know what you are doing we do not recommend tackling it with your first machine. Buying a pre-made controller will be more expensive, but will give you the knowledge of what to expect if you ever decide to make one yourself.
 
Chopper Current Motor Controller:
A chopping circuit can limit the current, without getting electronic components too hot, and will be much more efficient. The chopping circuit will switch the operating voltage on and off, at high frequencies; this routine is called pulsed width modulation. The on time will determine how much current gets through to the motors. The chopping current control is best for stepper motor control, and is considered newer technology.
 
Resistive Current Controller:
Normally, with stepper motors, the voltage is set higher than the voltage rating of the motor - a way of limiting the current going to the motors, is to use a current limiting resistor. These motor controllers are called L/R drivers, L=Inductance, R=Resistance. This resistor is placed in series with the winding, and will take some current from the motor and will dissipate it with heat.
 
Integrated Control:
Integrated control means the motor controller is embedded and will accept commands from the host computer "direct connect" during the motion process. Communication, operator interface and the I/O functions are separate elements of the system. The motion is done by the computer and in this case the controller acts as an independent device. CNC (computer numerical control) applications are well suited for integrated control because the data input is "dynamic", or changing frequently.
 
Motor Step Modes:
Stepper motor controllers can have different step modes- full, half and micro-stepping. The type of step mode output of any motor is dependent on the motor controller and motors

Full Step:
Standard stepping motors have 200 full steps per revolution of the motor shaft. Dividing 200 steps into the 360 degree rotation equals a 1.8 degree full step angle. Normally, this full step mode or 1 pulse from the controller will equal 1 step
 
Half Step:
Half step means the controller will send is rotating at 400 steps per revolution. In this mode, one winding is energized and then two windings are energized alternately, causing the rotor to rotate at half the distance, or 0.9 degrees Half stepping is a more practical solution however, in industrial applications. Although it provides slightly less torque, half step mode reduces the amount "jumpiness" inherent in running in a full step mode.
 
Micro-stepping:
Micro-stepping is a relatively new stepper motor technology that can control the current degree that will subdivide the number of positions between a single step. Micro-stepping is a function of the electronic motor controller, it will enable one single step of the stepper motor to be divided into multiple steps, giving the stepper motor more resolution, and a smoother operation; most newer and higher quality motor controllers will have this function. Micro-stepping is typically used in applications that require accurate positioning and a fine resolution, over a wide range of speeds. Micro-stepping will make a stepper motor run more smoothly and more accurately.
 
Controlling External Devices
E-Stop software controlled and hardwired control
E-stop stands for Emergency Stop there are a few ways to E-Stop a machine when the motion is going wrong or is about to, Mach3 control software has a large button that will immediately stop all motion, this is considered a software controlled e-stop. A hardwired e-stop is a physical button or switch that is wired and connected to an input of a breakout board and can be configured to stop all motion, a physical hardwired switch is a more reliable way to e-stop a machine than a software e-stop, a hardwire switch to an actual power output is considered hardwired, and will stop all motion no matter what the software program is telling the controller to do.
 
Breakout Board:
A breakout board can be used to isolate and extend the parallel port, for external devices like limit switches, and turn devices on and off, like a rotary tool, automatic clamping, vacuum table, or whatever device you want to control while running your machine. Most pre-made motor controllers will have connection points or external devices, but if the DIY controller is made a breakout board would be advisable. An opto-isolated breakout board will isolate connections to protect your computer port from accidental short-circuits. The opto-isolated circuit sends the signal through a LED, and will receive the light with a phototransistor. When
the parallel port switches the signal to on or high, an LED will turn on - the phototransistor sees the light and relays the signal. Your computer sensitive electronics are isolated from your external devices. The input signals are transmitted with light and not through hard wired connections, so any higher destructive voltages or accidental shorts will never reach your sensitive computer electronics. An opto-isolated breakout board is not an absolute must, but will help to protect your PC, also some motor controllers are single axis drives, and  using a breakout board can make it easier to connect multiple axis's.
 
Charge Pump:
A charge pump is an electronic circuit board which is a safety device used on PC based CNC. controls like Mach it will send a 12.5 KHz signal through one of the computers parallel port pins. A charge-pump board will act like a traffic light, if the charge pump sees a 12.5 KHz signal it will continue; but, as almost everyone knows, Windows can do unexpected things like stall, crash, blue screen. When any issues with Windows happens and Mach looses control, the charge pump board will stop all motion to the machine.
 
Limit and Home Switches:
Limit switches are used for two purposes, one is to stop any damaging, over travel; a slide can only travel as per its design. Using a limit switch will tell the control software when it is at its maximum travel limit, and to stop all motion before a crash occurs. Limit switches are not
mandatory but will help in a crash. The second use, for a limit switch, is homing - this function
is used at start up, or in between cuts. Homing will set a reference point or machine zero for the starting point; homing is a useful feature for making multiple parts when using fixtures. It will reference all motion from the same point every time, eliminating the need to manually find an exact starting point.
 
 
Parallel Port Description and Pin Outs Interface Chart
Pin No
Name
Direction
1
Strobe
Out
2
Data0
In/Out
3
Data1
In/Out
4
Data2
In/Out
5
Data3
In/Out
6
Data4
In/Out
7
Data5
In/Out
8
Data6
In/Out
9
Data7
In/Out
10
nAck
In
11
Busy
In
12
Paper-Out
In
13
Select
In
14
Linefeed
Out
15
nError
In
16
nInitialize
Out
17
nSelect-Printer
Out
18-25
Ground
 
Machine Control Software and Computer Requirements
Overview:
Machine control software is the program that runs on a PC, and will communicate with the motor controller to command the correct amount of steps and the direction to the motor controller, and eventually to the machine. A control program is also capable of storing the machine specifications
to correctly calibrate the amount of steps to equal the linear movement commanded, and at the same time will also do other functions like manual jogging, zero points, and conversion in inch  and metric units.
 
ARTSOFT Mach3:(Windows XP)
Control software is the most common control software, it can run from Windows, and control
up to six motors. It also includes lazy cam which will convert CAD drawing to motion, and has
many features required in CNC Machine tools, we will use Mach3 for our make a part and cut
tutorial. Computer Requirements for Mach3 is Windows XP with a parallel port.
 
EMC (Linux)
Enhanced Machine Control (EMC) is a software system for computer control of machine tools
such as milling machines and lathes, EMC is free software with open source code, It can
simultaneously move up to 6 axes and supports a variety of interfaces. The control can
operate true servos (analog or PWM) with the feedback loop closed by the EMC software
at the computer, or open loop with "step-servos" or stepper motors. Motion control features
include: cutter radius and length compensation, path deviation limited to a specified tolerance,
lathe threading, EMC runs on Linux using real time extensions. Computer Requirements for
EMC is a PC with a parallel port.

TurboCNC (DOS)
Turbocnc is another great stable Control Program it runs from DOS (Disk Operating
System) and will run gcode Computer Requirements for Turbocnc is a PC running DOS with
a parallel port. Turbocnc is good low cost alternative for using a lower speed PC that cannot run
Windows and is used by many.
 
G-Code
G-code is the name for the programming language that controls CNC machine tools.
It was invented by the Electronic Industries Alliance in the early 1960s, and is still
used today, and is the programming language, that we will be using in our example.
M-Code
M-Codes are mostly used to operate external devices within the program, turning
coolant on and off, or spindle on off, they are also used to end the program.