CNC Machining: Building and Programming
CNC Machining: A Practical Guide Get a comprehensive overview of the CNC process from beginning to end, covering the numerous machines and their applications, as well as the essential software and equipment. The CNC Machining post’s walks you through the stages of customizing a CNC machine and effectively deploying it in a real-world application. Throughout the book, there are helpful photographs and drawings. You’ll benefit from the in-depth knowledge in this comprehensive resource whether you’re a student, hobbyist, or company owner wanting to transition from a manual production method to the accuracy and reproducibility that CNC has to offer.
Common forms of CNC-controlled applications at home and in shops are covered in CNC Machining. Systems for guiding linear motion Transmission networks Servo and stepper motors Hardware for controllers The Cartesian coordinate system is a type of coordinate system. Software for CAD (computer-aided design) and CAM (computer-aided manufacturing). G code language overview: CNC systems that are ready to use.
The following are some of the goals of this post:
- To help the reader understand CNC by simplifying or demystifying it. The goal is to give the reader with an easy-to-understand, reasonable, and logical order of operations where possible.
- To provide a list of various hardware and software that I have either used before with excellent success or that have been utilized by firms with solid industry reputations.
- To provide a detailed explanation of the procedures and operations involved in CAM operations.
- To give a list and summary of the commands in the G-code programming language.
- To provide a list of useful CNC-based Web sites, forums, and other publications where the reader may learn more about the topics discussed here.
CNC Machines
This post describes the applications mentioned throughout this work, as well as a list of the most prevalent types of home- and shop-based CNC-controlled applications and the materials used in their manufacture.
Common CNC Applications
This section addresses the numerous sorts of applications that can be numerically driven or automated (or numerically controlled by computer). The applications listed are the most often utilised. The examples provided may be used to extrapolate basic and general characteristics present on most regularly used CNC machines and other applications, as well as their control.
Router/Engraver
Routers come in a variety of sizes and forms. The suitable router head, motors, reduction ratio, speed, gantry height, and so on will depend on what will be generated using a router. All too frequently, the term router is used in a broad sense to refer to a variety of machines that cut or engrave using a rotary technique. Almost any size spindle motor can be utilized, with horsepower and rpm capacity determined by the materials and tools being used. Engraving machines can be supplied with a 1/20 horsepower motor that can be driven at 40,000 rpm, but a system designed to cut plywood can have a 40 horsepower spindle that can be pushed at a maximum rpm of 18,000. Standard woodworking router heads are commonly found on hobby and entry-level equipment. In many aspects, this sort of motor differs from a high-frequency spindle head operated by a variable-frequency drive (VFD). There are several advantages to adopting a high-frequency spindle head. Among benefits include lower operating noise, longer life, higher horsepower, and the potential to include an automated tool changer (ATC).
One of the primary distinctions between these two types of units is the horsepower produced. The two sorts of heads are detailed next to help the user grasp the distinction.
Spindle Head vs. Router
People who are new to CNC routing frequently ask what the distinction is between a router and a spindle head, as both are usually referred to as a CNC router. Despite the fact that they both fit the criteria for a router, there are significant variations between the two. In this section, we will go over each of these units in detail and compare and contrast their differences.
Router Head
The usage of a normal woodworking kind of router head on hobby and entry-level CNC Routers is extremely popular. Because of its inexpensive cost, this type of motor is frequently utilized. An induction motor is the type of motor that is employed. It is important to note that if you spend a lot of time around this sort of motor while it is operating, you should wear hearing protection because they are rather noisy.
These router units are designed for general woodworking application and are intended to be used hand-held or inverted in a non-CNC router table. Essentially, they are not intended to be used in combination with a CNC equipment. They support both ends of the shaft with normal sealed radial ball bearings and can have significant run out. Most allow you to choose the rpm that is utilized. The router head depicted in Fig. 1-1 allows for rpm selection in increments of 2000 and 3000 rpm ranging from 10,000 to 21,000 rpm. They employ fixed collet sizes in 1/4-, 3/8-, and 1/2-in increments; reducer adapters are available for tooling with lower diameters (such as 1/8 indiameter bits).
FIGURE 1 – 1 Common woodworking router head.
This sort of router head will often boast a high horsepower rating, with some offering 3.25 hp or more. Below, we’ll go through both the theoretical and real wattage and horsepower ratings that may be obtained, as well as how manufacturers get their claimed figures.
Wattage is calculated as a function of voltage and current. In North America, the theoretical watts of typical home current is:
Power (W) = Voltage (V) * Current (A)
1875 W = 125 V * 15 A ــــــــــ theoretical wattage
From the definition that 1 hp is 746 W:
1875 W * 1 hp/746 = 2.5 hp ـــــــــــــ theoretical hp
This means that the most useable power (measured in horsepower) that may be obtained using a regular 15-A wall outlet is 2.5 hp. It should be noted that this figure falls significantly short of 3.25 hp.
2.5 hp is a theoretical figure. A typical induction motor will have losses in excess of 40%. As a result, you may obtain 60% of the theoretical value’s useable power (which is generous). Reworking our previous calculation to account for the typical losses involved yields:
125 V * 15 A * 60% = 1125 W ـــــــــــ actual wattage
1875 W/746 W = 1.5 hp ـــــــــــ actual hp
This computed number of 1.5 hp is less than half of the declared horsepower by the manufacturer. The reader may be confident that this real horsepower rating reflects the highest useful power that a device like this can provide.
So, how did the manufacturer arrive at their claimed price? They are utilizing a measured figure of the amperage required at start-up for this specific induction motor. This is referred to as in-rush or start-up current. This happens for a very short period of time since it is a spike in the current and is inherent to induction motors. The current spikes last so long that they do not trip the circuit breaker on your electrical access panel.
Using the aforementioned equations, you will discover that around 20 A of current is originally drawn (left to the reader, as an exercise). Nonetheless, it is unused electricity in the end. Going with a router head is a reasonable alternative if you need to reduce startup expenditures to a low. Obviously, depending on a variety of conditions, the bearings may frequently require repair. This may simply be done in-house by the user by creating their own basic tool, such as the one illustrated in Fig. 1-2. This tool stops the rotor from turning, allowing the device to be dismantled and the old bearings to be removed with a bearing remover. These bearings are available online or at any car parts store for $10 to $15 per pair.
FIGURE 1 -2 Bearing removal tool.
Spindle Head
Spindle heads are superficially similar to router heads, but they function with a spindle drive (also known as a variable-frequency drive [VFD]) to alter the revolutions per minute. Spindle heads are built and optimized for heavier-duty CNC operation, and they often have ceramic-style bearings that are durable to greater loads. They also produce very little shaft run out.
They are a constant-torque type of motor that can provide the real rated horsepower (or kilowatts) as advertised by the manufacturer. They are available in a variety of sizes.
Except for the smallest of these machines, the power needs at 240 V are generally 20 to 30 A. Typical size for hobby to small-shop production ranges from 1.5 to 7 horsepower, depending on material type and feed rates. PDS Colombo makes the 3 hp unit depicted in Fig. 1-3, which is quite popular and dependable.
FIGURE 1 – 3 / 3 Horsepower spindle head.
Spindles work silently and have a variety of cooling options, including a fan driven by the shaft, an electrically controlled fan, and even water cooling (see Fig. 1-4).
The variable-frequency drive’s job is to provide three-phase power output to the spindle. All spindles, in fact, are three-phase. It is the power input to the VFD, which might be single-phase or three-phase. A spindle-speed controller card can be used as a controller hardware alternative.
FIGURE 1 – 4 Variable-frequency drive.
With the VFD, the user may turn the spindle on and off, run forward or backward, and change the frequency or revolutions per minute on a granular level. These controls may be accessible directly from the controller software interface or by G-code commands in the cut file. If necessary, the user may still manually operate the spindle via the interface placed on the variable frequency drive itself. When purchasing for a hardware controller, some form of spindle interface medium should be considered as standard or as a low-cost upgrade option. If you want to buy or update a router table system, check sure you have this capability.
The common collet system used for these sorts of devices is the ER series (Fig. 1-5), with each compression collet size matching the diameter of the tooling being utilized.
FIGURE 1-5 ER25 collet system.
This is quite convenient since you don’t have to buy tooling that always has the same shaft diameters, as with the collet system on routers. There are also certain spindles that employ a drawbar kind of clamping mechanism (pneumatic or electrical), which allows the tooling to be changed out automatically. This is referred to as an automated tool changer (or ATC). In combination with this adaption on the spindle head, banks of various sized tools are placed in a permanent area in the router table. In the controller software, the information for each tool, such as diameter, length of cutter, and so on, as well as its exact Cartesian location, is kept in a table. The usage of Gcode allows for automated tool change-outs without the need to tap off the Z each time it is accessed.
Engraving machines employ tiny spindles and servo motors. Because the tooling is so tiny (usually 1/8-in diameter or less), the spindles may readily reach rpms in the 40,000 area. The image (Fig. 1-6) illustrates an after-market engraving spindle that accommodates 1/8-in diameter d I a m e t e r conical tooling.
FIGURE 1-6 Engraving spindle.
Resolution
It is less vital for machines with a narrower operating envelope to be able to travel at high speeds. However, with bigger format machines, speed is essential in determining how long it takes the cutter head to traverse from one end of the table to the other. The degree of reduction employed in the transmission system is critical in terms of speed (provided the same motors and drives are used).
For every given general system, a certain number of steps (think of them as driving signals) will be connected with creating a particular amount of linear motion – usually 1 in Engraving machines often have 10,000 steps per inch, although a large-format table (8 or 10 feet long) may only have 2000 steps per inch. The difference between these two cases is a power of five. As a result, the unit with 2000 steps/inch would move five times quicker with the same rpm motor.
However, the granularity of cutting abilities would be much reduced.
There will be two transmission options for these machines:
rack and pinion and screw. In general, tables with a working envelope of 4 feet or more employ a rack and pinion transmission mechanism.
When employing rack and pinion, a reduction device that fits between the motor and the pinion gear is necessary. Without a reduction mechanism (i.e., going direct drive), the system’s resolution will be rather poor, and the cut quality will suffer substantially.
Short spans and, most commonly, the Z axis, a lead or ball screw provide transmission – with lead screws being the more common choice of the two. Screws are offered in a variety of threads/inch values, with the Z axis often receiving a higher resolution value than the X and Y axes. The application (such as 3D carving or mold casting) usually determines whether or not to have better resolution on the Z axis.
Next post about Hold-Down Methods & Vacuum & T Track Grid Work & Double-Sided Tape
To be continued….
