Cnc machining handbook pdf

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CNC Machining Handbook About the Author Alan Overby received a B.S. in Electrical Engineering from Arizona State University. He has. Cnc Machining Handbook Building Programming And exams for the NCLEX, Failed the NCLEX - Help is here (PDF) Levels of Automation in. Implementation By Alan Overby [EPUB KINDLE PDF EBOOK]. Read Download Online Free Now Cnc Machining Handbook: Building.

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Results 1 - 10 G Codes - Program Example Using Canned Cycles 1) A part program is written, using G and M G and M Programming for. eBook Machining Handbook. Reference: File format: *.pdf (approx. MB)»Download now for FREE«Printed books (similar). Fundamentals of CNC Machining. A Practical Guide for .. Best Practices Machining Parameters. would fill volumes and is beyond the scope of any one book or course. The goal of . Read the Reading Assignment for each lesson (PDF).

Even if the part is designed in metric. Inserts must match the tool holder. An additional suggestion is to make use of an accurate measuring device. CNC mills require calculating speeds and feeds in advance. A complete list is included in Appendix B.

This ensures all parts are loaded into the exact same position each time. The vise has two jaws; a fixed back jaw a front jaw that can close and open to grip or release the part. Because the location of the moving jaw varies depending how much force the operator uses, it is best to locate the WCS in reference to the fixed jaw. The fixed jaw position is not significantly affected by clamping force. Notice that, because the fixed vise jaw does not move regardless of how tightly the vise is closed, the WCS Y- origin does not change.

In other words, the Y-origin is repeatable. The concept of repeatability is essential to precision machining. If the datum shifts for any reason, it is impossible to make any two parts exactly alike. When using a vise, locate the WCS so the part lies in the forth quadrant: Vise force can even significantly deform thin parts if excessive force is applied.

Since this position does change based on clamping force. Whether a new WCS must be defined. As mentioned earlier. As shown in Figure This variability is so large that it is common practice to mark the closed position of the handle with a black marker or use a torque wrench to ensure the clamping pressure is consistent between parts.

Fixture Offset G54 can be used to machine both sides. A new Fixture Offset is defined G55 to shift the datum to the point shown. By turning the part as shown in Figure Maintaining close machining tolerances requires being fastidious and consistency of work.

Small chips or even excess coolant under a part or vise can cause problems. The vise stop has also been lowered so the stylus contacts the face of the part.

This helps ensure the hole will be located precisely on the part side. As a practical matter. It is also worth noticing that. If making many parts without a second vise.

Notice that the WCS used in Job 1 and 2 cannot be used because the part standing on end is much taller. The best practice is to maintain as many reference surfaces as possible whenever the part is rotated. Machine set up is best done after the program is completely written.

Figure 8: As long as the part is positioned where the tool can reach all machining operations it can be located anywhere in the machine envelope. Understanding how they work and to correctly use them together is essential for successful CNC machining. To complicate matters further. This is done using machine Tool and Fixture Offsets. They make setups easier because the exact location of the part in the machine envelop does not need to be known before the CNC program is written.

There are many offsets available on CNC machines. In conjunction with Tool Offsets. If the tool wears or breaks and must be replaced. Fixture Offset Z may or may not be used. In its simplest use. All tools are set to a known Z-position. The CNC machine needs some way of knowing how far each tool extends from the spindle to the tip.

This makes it very easy to reset tools if worn or broken. This value is entered in the TLO register for that tool. In fact. This method is fast.

Both the 2nd and 3rd methods also require the distance from the tool setting position the top of the block or tool probe to the part datum to be found and entered in the Fixture Offset Z. All tools must be reset whenever a new job is set up. The method shown in the center is much better and used in this book. The machine adds the two values together to determine the total tool length offset.

Follow the procedure in use at your facility or refer to your machine tool documentation to determine which method to use.

A method for doing this is included in Lesson 6. The tool is jogged to the part datum Z and the distance travelled is measured. Problems with this method include the need to face mill the part to the correct depth before setting tools. When this method is used. It does this slowly lowering the tool until the tip touches the probe and then updates the TLO register. A tool probe is very similar to the block method.

While many of the words used by different CNC machines are the same. The official name of this language is RSD.

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Most machines have a vocabulary of at least a hundred words. Table 1 and Table 2 on the next pages show the most common G and M codes that should be memorized if possible. These thirty or so words are best memorized because they appear in almost every CNC program and knowing them helps you work more efficiently.

Always refer to the machine documentation for the exact words and syntax for your CNC machine. While at first this language may seem arcane. It was therefore designed to be as compact as possible. Programs that use multiple tools repeat steps two through nine for each.

Blocks are arranged in a specific sequence that promotes safety. The G-code language was developed when machine controls had very little memory. Each sentence in a CNC program is written on a separate line. This is due in part to machines having different configurations and options. John Parsons. They read like a book. Drill N26 G80 Cancel drill cycle. Rapid to safe plane. While these rules are covered in this chapter. N15 G40 X Hole N27 Z1. N32 G90 Reset to absolute positioning mode for safety.

Tool T2 0. N28 M5 Spindle Off. N25 G98 G81 Z Rapid above hole. Position N7 G43 Z1. End N29 M9 Coolant Off. Program Format The program in Figure 1 below machines a square contour and drills a hole. N9 G01 Z N16 G00 Z1. N33 M30 Reset program to beginning. Line move to cutting depth at 18 IPM.

N8 Z0. Machine N11 Y2. Program T1 0. Contour N12 X2. On CW. Position N24 Z0. Move N22 X1. N13 Y To N23 G43 Z1. N14 X Some codes have different meanings depending on how and where there are used. Simple CNC Program 5. To N6 G00 X N21 M8 Coolant On. Drill hole canned cycle. H2 Rapid to safe plane. N2 T1 M6 Load Tool 1. Change N18 M9 Coolant Off. Move N5 M8 Coolant On. N10 G41 Y0. Depth Z-. CDC Left. Offset 1. Lead in line. H1 Rapid to safe plane.

N19 T2 M6 Load Tool 2. N17 M5 Spindle Off. No decimal point is used. When called. K Arc center Z-vector. G1 A The angle is in degrees and up to three decimal places precision.

Q Used in drill cycles. B Rotation about Y-axis. S Spindle speed in RPM.

Pdf cnc machining handbook

X X-coordinate. O Program Number. D Tool Diameter Register Used to compensate for tool diameter wear and deflection. A complete list is included in Appendix B. N Block Number. P Dwell time. G1 G41 X1. C Rotation about Z-axis.

D Cutter diameter compensation CDC offset address. Table 3: Y or Z-axis respectively. I Arc center X-vector. Codes are either modal. D is accompanied by an integer that is the same as the tool number T1 uses D1.

H Tool length offset TLO. Z Z-coordinate. Y Y-coordinate. T Tool number. The table below lists the most common address codes. R Arc radius. G G-Code preparatory code. Most modern machines use these codes. M M-Code miscellaneous code. It is always used in conjunction with G41 or G42 and a XY move never an arc. J Arc center Y-vector. G-M Code Reference. Code Meaning A Rotation about X-axis. F Feed rate. G18 G3 X. Certain drill cycles also use J as an optional parameter. Expanded definitions of M-codes appear later in this chapter.

Because they take up control memory most 3D programs do not use block numbers. G1 X1. Accompanied by G4 unless used within certain drill cycles. In the G17 plane. Most G-codes are modal. Expanded definitions of G- codes appear in the next section of this chapter. Block numbers are integers up to five characters long with no decimal point. Feed rates can be up to three decimal places accuracy for tap cycles and require a decimal point. G43 H1 Z1. Certain drill cycles also use I as an optional parameter.

It is always accompanied by an integer H1. G Preparatory Code Always accompanied by an integer that determines its meaning. This is an integer that is preceded by the letter O and has no decimal places. G2 X1. Only one M-code is allowed in each block of code. G1 Z-. It is an integer value with no decimal. Z Z-Coordinate Coordinate data for the Z-axis.

This code is called tape rewind character a holdover from the days when programs were loaded using paper tapes. R is also used by drill cycles as the return plane Z value. The maximum length of a comment is 40 characters and all characters are capitalized. It is an integer value always accompanied by M6 tool change code. G83 Z-. G83 X1. Comments Comments to the operator must be all caps and enclosed within brackets. Up to four places after the decimal are allowed and trailing zeros are not used.

Coordinates are modal. G1 Y1. S M3 T Tool number Selects tool. K vectors. G59 Fixture Offset 6. G90 Absolute coordinate programming mode. G84 Tap cycle. G80 Cancel drill cycle. Most machines now allow the leading zero to be omitted.

G91 Incremental coordinate programming mode. G3 Counterclockwise arc. G28 Return to machine home position. G56 Fixture Offset 3. Older controls required G-codes to be written with a leading zero. Used to position the machine for non-milling moves. G58 Fixture Offset 5. G98 Drill cycle return to Initial point R. G2 Clockwise arc. G83 Peck drill cycle. G1 Line motion at a specified feed rate.

Code Meaning G0 Rapid motion. End of Block This character is not visible when the CNC program is read in a text editor carriage return.

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G55 Fixture Offset 2. G54 Fixture Offset 1. The most common G-codes are shown in Table 1 and a complete list and their meaning is included in Appendix B. G43 Tool length offset TLO. G81 Simple drill cycle. G82 Simple drill cycle with dwell. G4 Dwell. The definition of each class of code and specific meanings of the most important codes are covered next.

G-Codes Codes that begin with G are called preparatory words because they prepare the machine for a certain type of motion.


G57 Fixture Offset 4. M5 Spindle stop. It is always used with a coordinate position and is modal. A incorrect offset or coordinate move can crash the machine faster than the operator can hit the emergency stop.

M4 Spindle on Counterclockwise. M9 Coolant off. They control machine auxiliary options like coolant and spindle direction. M6 Change tool. G0 does not coordinate the axes to move in a straight line. Code Meaning M0 Program stop. G0 X0. A complete list of M-codes is included in Appendix B. M2 End of program. Unlike G1. M1 Optional stop.

M30 End program and press Cycle Start to run it again. Table 2: Common M-Codes 5. Press Cycle Start button to continue. M8 Coolant on. The table below lists the most common M codes and their meaning. Only one M-code can appear in each block of code. G0 Dogleg Motion Caution: The rapid speed of some machines can exceed 1. Use the rapid feed override on the machine when running a program for the first time.

M3 Spindle on Clockwise. G3 commands counterclockwise arcs. Figure 3: The amount of offset is entered in a CNC control D-register. Tool Diameter Offset Value D1 0. G40 cancels cutter compensation. G17 is the machine default. The wear register can be thought of like a table that the control refers to with every move.

Additional offsets are used to machine other sides of the part. The Z value is the distance from the tool reference point for example. It is always accompanied by an H-code and Z-move. The process for finding the TLO detailed in Lesson 6.

The TLO can be thought of like a table on the control: Tool Length Resister Z H1 These offsets can be thought of like a table on the control: G1 G41 D1 X1. G43 Tool Length Compensation G43 activates tool length compensation. G54 X0. If there is no deviation. CNC Operation. Work Offsets Tip: G54 is usually used for the first machining setup. The X and Y values represent the distance from the machine home to part datum XY. Z position to the part datum.

Work Offsets The TLO is combined with the active fixture offset on the control so the machine knows where the tip of the tool is in relation to the part datum. All drill cycles are accompanied by G98 or G99 that determine how high the tool retracts between holes. R is the feed plane and Z is final depth of the tool tip. Canned Cycle vs. N85 G00 Z0. Expanded Code G81 Simple Drill Cycle This cycle makes holes by feeding to depth at a programmed feed rate and then retracting at rapid rate.

G43 H1 G98 G81 X. Canned Cycle Equivalent Motion: They are used for hole making and allow one compact block of code to command many moves. N G00 Z0. XYZ coordinates. It is accompanied by G98 or G G0 Z1.

N70 Z0. P is used to pause the tool feed rate at the final depth to create a clean countersink or counterbore finish. This breaks the chip. Another version of this cycle. P in seconds. The tool drills an incremental distance Q and then fully retracts from the hole. The simplest form of this cycle is shown in Figure 8. G43 H1 G83 X. G43 H1 G98 G82 X. K parameters to reduce the amount of peck as the hole gets deeper. The parameters for the tap cycle are identical to simple drilling G The only common use of G91 is in combination with G28 to send the machine back to its home position at the end of the program.

It then stops and reverses the spindle at the bottom of the cycle to retract the tap. G90 G98 Return to Initial Rapid Height This code is used in drill cycles to retract the tool to the clearance plane set in the next previous block between holes to avoid clamps.

G43 H1 G84 X. G90 Absolute Positioning This code commands the machine to interpret coordinates as absolute position moves in the active Work Coordinate System.

G91 Incremental Positioning This code commands the machine to interpret coordinates as incremental position moves. The machine must be set back to G90 mode in the next block as a safety measure.

G91 G28 Z0. Rigid tapping precisely coordinates the spindle speed and feed to match the lead of the thread. G43 H1 G98 G81 Z All programs are written in absolute coordinates. G90 G0 X1. G99 mode is the machine default and is used when clamp clearance between holes is not an issue.

Initial Rapid Height Z1. G43 H1 G99 G81 Z If the machine requires an air supply. Observe extreme caution at all times. Ensure the work area is clear of any loose tools or equipment. The machine power button is located in the upper-left corner on the control face. Be sure to clean the work area and leave the machine and tools in the location and condition you found them.

USB flash memory. The main breaker is located at the back of the machine. Warning Never operate a CNC machine or any shop equipment unless you have been properly trained on its use. Follow all safety rules. Check the machine maintenance manual if you are unsure about how to service it.

The CNC control references these values in the table each time a motion is commanded. Multiple registers are needed because most parts use a different fixture offset for each side of the part machined. Think of the Offset registers like a table in a spreadsheet. The CNC operator finds the fixture offset values by jogging moving the machine from the machine at its home position the CNC program datum. In other words. Use of the Fixture Offset Z is covered in the next topic.

This can be any point on the part. Most machine controls support at least six fixture offsets. The method described here and detailed in Lesson 6. Alternate Tool Setting Methods describes three other methods that can be used to set up the machine tool length offsets.

The approach shown in Figure 10 involves using a dial indicator and this process is detailed in Lesson 6 CNC Operation: Set Fixture Offset Z. To use the method described in this lesson on Haas Automation machines. Another advantage is that the TLO can be reset easily. Refer to the Haas Programming and Operation manual for instructions on set this parameter. The tool set position can be a tool probe or. Figure Fixture Offset Z There are many ways to set tool and fixture offsets.

The TLO is found by jogging the spindle with tool from the machine home Z-position to the tool setting point on the machine. If a tool wears or breaks. This can be the top of a tool probe. The distance travelled from home to the top of the block is recorded. Detailed instructions on the following pages show how to operate the control. Familiarize yourself with the location of buttons and controls. Clear 2 Air Supply: If it is.

Press the T and then T the 1 buttons. JOG 2 Jog Increment: Setting tools requires manually jogging the machine with hands in the machine work envelope. Keep your eyes on your hands and the tool position at all times. Use extreme caution and observe the following rules: Select Erase Prog: Select Jog Increment: G54 8. Retract in Z. ADD a shift amount to the offset X-value. SET 18 Spindle Stop: Set jog direction to -Y and rotate handle one full turn clockwise.

From no chips underneath. DOWN 6 Origin: This is the incremental distance between the top of the block and the top of the part. To set the Tip datum to Z-. No decimal point. The program name must be an integer up to five digits long. Once a program is proven. Wear compensation is used only on contour passes. When running a program for the first time. For example: Target Feature Size: When used.

It is not used for face milling. Subtract the Actual from the Target sizes and enter the difference into the CDC register on the control for that tool. Check List Buttons 1 Offset Page: Once the tool is cutting. Do not leave the machine unattended.

Running the same operation again should result in the feature being exactly the target size. Measure across a finished feature on part and compare it with the desired value. A common error is setting the Fixture or Tool Length offset incorrectly. At the very least. It is important to clean the machine after each use to prevent corrosion.

Allow at least minutes at the end of each day for cleaning. The XY axes are normal to the machine spindle and Z is used only to position the tool to depth either in a feed or rapid motion.

Every feature can be reached with the tool approaching either from the Front or Bottom views. The Z axis is used only to position the tool at depth. There are. There are several cutting planes in this example.

The term. The move to the cutting plane is a straight down feed. Each Z-level can be machined by positiong the tool at a fixed Z-level and then moving the XY axes to remove material. All machined features lie parallel to the XY plane. A more accurate term. Figure 1 shows a prismatic part.

CNC Machining Handbook - A. Overby (McGraw-Hill, 2011) WW.pdf

This part is typical in that it includes both 3D and 2D features. The tool feeds to depth Z and then only up to two axes can move at once X-A to make the feature. Most consumer goods. The 2D features are the top face 1. Geometry was draw flat XY and then the Y-axis values were converted to A-rotational values.

Figure 3 shows half of a stamping die. The most common setup is with the rotary axis mounted parallel to the CNC X-axis. With axis substitution machining. The revolved surfaces require XZ tool motion. The fillet requires XYZ tool motion. Even the flat 5 and cavity roughing though technically planar require 3D toolpaths because the adjacent revolved surfaces and fillet must be considered to prevent gouging the part.

Axis substitution paths are illustrated in Figure 4. The calculations required to calculate these toolpaths are highly complex and the subject of the next lesson. This type of motion is very complex and is actually a sub-category of Simultaneous 5-axis machining.

Simultaneous 4th and 5th axis machining is beyond the scope of this course. Open the View Orientation dialog and select Front view so the part displays as shown in Figure 1. Highlight the option Top. Select Update Standard Views. Knowing which machining operation to use to make which feature is sometimes obvious. For example, the slots in Figure 3 are created using a Slot Mill pocketing operation, the large extruded cut using 2D Pocket, and the Chamfer using Chamfer milling. However, sometimes these decisions are not so obvious.

You may wonder, is the large flat where the holes begin a 2D Contour or 2D Pocket? Furthermore, which features on this part should be machined from the Top and which from the bottom?

The operations the CNC programmer chooses and their sequence depends on a bewildering number of factors, including feature size, tool used, capabilities of the machine, feature tolerance and how the part is gripped. The rest of this chapter will introduce how to begin looking at 2D parts and begin making CNC process decisions.

To begin with, in most cases you want to first machine the side of a 2D part that has the most features; finishing as much of the part as possible with the first CNC setup. This is often the Front view of a part designed in SolidWorks. In this example, that means machining the side with the slots first Front CAD view rather than the opposite side.

Table 1 lists the common 2D toolpaths by type and common use. For example, 2D contour, chamfer, and fillet toolpaths are often accomplished using the 2D Contour menu selection. Of course, where each function is located will be slightly different depending on the CAM product, but this list is appropriate to most modern CAM. Table 1: It is probably obvious to you now that manufacturing is an exceedingly complex process.

Many factors influence every decision and often more than one solution to any problem. Either the part is right within tolerance or not. Some knowledge and experience will help you settle many of these variables and greatly simplify the job of planning CNC processes. Toolpath Notes 1 Face It is common practice that the first machining operation roughs and finishes to the highest flat surface of the part. Face paths overlap the sides of the loop selected. Contour 3 2D Machine outside of boss.

Contour 4 2D Pocket Use Pocket to rough and finish enclosed loops. You could also use a Drill operation to make this hole, but would Pocket Mill center-drill the hole first. Ensure subsequent drill does not wobble and thus is located precisely.

Create chamfer for this hole. Pocket Mill Table 2: Figure 4 shows parameters common to 2D tool paths. Clearance Height is the first height the tool rapids to on its way to the start of the tool path. It is usually set 1. Rapid Height is the second height the tool rapids to, and the height the tool retracts to between moves unless set higher to clear clamps. It is usually set to. Feed Height is the last height the tool rapids to before starting to feed into the cut. No rapid motion occurs below this height.

Top of Stock is the top of the finished face of the part. This value is used as the reference plane for depths.

Stepdown is the depth of material removed with each cutting pass. This illustration shows one pass, but for deeper cuts or harder materials, many passes may be required to cut to the final depth.

In this book. High speed loop transitions between cut passes produce a fluid tool motion that place less stress and wear on the CNC machine.

Figure 5: The large diameter of facing mills and multiple carbide insert cutting edges provide for very high material removal rates. Toolpath Centerline represents the actual coordinates in the CNC program. A smaller finish pass ensures a flat surface and good surface finish. Z Stock Allowance is the material remaining on the finished floor of the part to be removed by subsequent operations.

Facing Facing is often the first machining operation. Use a face mill when possible for all but the smallest part. When planning roughing passes. It is used to cut away excess material and finish the highest flat face of the part. Depending on how much stock is removed. Figure 6: If using new tools and conservative machining parameters. Use Cutter Diameter Compensation CDC on high tolerance features so the tool path can be adjusted at the machine if needed to account for tool wear and deflection.

This way. This ensures even cutting pressure on the finish pass and thus a more accurate part. When possible. The compensation value is found by measuring the part feature and subtracting the actual dimension from the desired dimension.

The difference is entered in the control CDC register for the tool. The next time program is run. Activate CDC while the tool is away from the part so this angle move happens away from the finished part surfaces. CDC is activated at the end of the line on which it is called. The line-arc moves shown in Figure 4 provide ample clearance for the tool for this purpose. Cutter Diameter CDC must be turned on or off with a line move.

Notice how the tool moves at an angle from the start to end of the lead-in line. These serrated mills can remove material at a far faster rate than finish end mills. An example of a spiral pocket with helical entry is shown in Figure 6.

CDC is not active during the roughing cuts. If space does not allow a helical entry. They do leave a poor finish on the floors and walls that must be finished with a separate finish tool and operation. Pocketing Rules for Pocketing: Rules for Slot Milling: HSMWorks recognizes the slot feature and applies a slot milling strategy. In HSMWorks. This ensures a clean bottom edge and. Then machine the chamfer. To prevent cutting too deep. Chamfer mills are of various tip angles are in high speed steel.

Rules for Chamfer Milling: Radius Milling Rules for Radius Milling: This method saves purchasing a radius mill and is suitably efficient for prototype and small production manufacturing.

Corner round tools are available in high speed steel. Center Drilling Rules for Center Drilling: This helps prevent subsequent drill tools from wobbling and thus ensures they will be positioned precisely. Full retract peck drill cycles take more time than partial retracts. Deeper holes use a Peck Drill cycle where the tool is retracted after removing a small amount of material typically.

Be sure to provide additional depth to compensate for the tool tip and include a breakthrough allowance to prevent a flange or burr on the bottom. Drilling Rules for Drilling: Consider tapping these holes by hand rather than on the CNC.

Use the manufacturers recommended drill size for form taps. Tapping Rules for Tapping: Refer to the tapping head documentation for proper use.

Turning There are many different configurations of CNC lathes. This chapter discusses one of the most common lathe configurations. Discussing every lathe configuration is beyond the scope of this book.

Milling vs. Lathes work by spinning the part and moving the tool. Some have two spindles. There is also variation between similar machines. Tools are bolted to the turret using a variety of specialized holders. The lathe should not be operated if this glass is cracked. The window is made from a special high impact glass. CNC Lathe 1 — Sheetmetal Protective housing that contain cutting chips and capture coolant for recycling.

There is one operation of any given CNC machine that cannot be au-tomated, and that is for you to wear the appropriate eye safety glasses!

I cannot over-stress the importance of wearing protective eyewear. Any of the processes involved in a CNC operation will produce cutting swarf i. Thus, proper eye protection is a must. Also keep or install all safety guards on your machinery. Moving and rotating parts can and will pinch and hurt youthe machine will not stop when you yell ouch! Common CNC Applications This section discusses the various types of applications that can be driven or automated numerically or numerically controlled by computer.

The listing includes the most commonly used applications. Basic and general features found on most commonly used CNC machinery and other applications and their control can be extrapolated from the examples given.

Depending on what will be produced with a router will have a direct relationship on the proper router head, mo-tors, reduction ratio, speed, gantry height, etc. All too often the term router is generically used to mean various things, but it boils down to a type of ma-chine that uses a rotary process for cutting or engraving. Virtually any sized spindle motor can be used, with its horsepower and rpm capability depen-dent on the materials and tooling being worked with.

It is common to find standard woodworking router heads installed on hobby and entry-level machines. This type of motor is quite different, in many ways, by in compari-son to a high-frequency spindle head controlled by a variable-frequency drive VFD.

The benefits of using a high-frequency spindle head are many. Among these are the reduced noise of operation, longer life, increased horsepower, and the ability to incorporate an automatic tool changer ATC. One of the major differences between these two types of units is their power ratings or the horsepower developed.

To help the user understand this difference, the two types of heads are discussed next. Although they both meet the criteria as a router, there are distinct differences between the two. Here we will specifically discuss what each one of these units are and contrast the differences between them.

Router Head The use of a standard woodworking type of router head is quite common on hobby and entry-level CNC Routers. The reason why this type of motor is used so often is because of its low cost. The type of motor used is referred to as an induction motor. Note that if you spend much time around this type of motor while it is running, you will want to wear some type of hearing protection, as they are quite loud. These types of router units are intended for general woodworking use and are designed to be used primarily hand-held or inverted in a non-CNC router table.

Basically, they are not designed nor intended for use in conjunction with a CNC device. They utilize standard sealed radial ball bearings to support both ends of the shaft and can have rather high amounts of run out. Most have the ability to select the rpm used. The router head shown in Fig. This type of router head usually will claim to having a rather high horse-power - some boasting 3.

Below, we will discuss both the theoretical and actual wattage and horsepower ratings that can be achieved and conclude with a mention of how the manufacturers derive their claimed values. Wattage is a product of voltage and current.

The theoretical wattage of regular household current in North America is: Note that this value is far short of 3. The value of 2. A typical induction motor will have losses of more than 40 percent. Reworking our above equation to reflect the typical losses involved yields: The reader can be assured that this actual horsepower value is reflective of the most usable power a unit such as this can deliver.

So how did the manufacturer come to their stated value? They are using a measured value of the amperage required at the time of start up for this particular induction motor. This is known as in-rush or start-up current. This occurs for a very brief time as it is a spike in the current and is intrinsic to induction motors. The time the current spikes is so brief that it does not trip the circuit breaker in your electrical access panel. If you use the above equations, you will find that roughly 20 A of current are initially drawn left to the reader, as an exercise.

Nonetheless, in the end, it is unused power. If you need to keep start-up costs to a minimum, going with a router head is a viable option.

Obviously, depending on several factors, the bearings will often need replacement. This is easily accomplished in-house by the user by making their own simple tool, as the one shown in Fig. This tool prevents the rotor from rotating so the unit can be disassembled and the old bearings removed with a bearing puller. Spindle Head Spindle heads are physically analogous to a router head, but they work in conjunction with a spindle drive known as a variable-frequency drive [VFD] and are frequency controlled to vary the revolutions per minute.

Spindle heads are designed and intended for heavier-duty CNC use and typically come with ceramic-style bearings, which are resilient to the higher loads being placed on them. They also yield very low amounts of shaft run out. Available in a wide range of sizes, they are a constant-torque type of mo-tor that can develop the actual rated horsepower or kilowatts as claimed by the manufacturer.

Other than the smallest of these units, the power require-ments are typically 20 to 30 A at V. Typical sizing for hobby to small-shop production can range from 1. The 3 hp unit shown in Fig. Spindles run very quietly and are available with various options for cooling, including a fan driven from the shaft, an electrically operated fan, and even water cooling see Fig. It is the function of the variable-frequency drive to supply three-phase power output to the spindle itself.

In fact, all spindles are three-phase. It is the power input to the VFD that can either be single- or three-phase.

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