Tormach Closed for Labor Day Holiday

Tormach will be closed Monday, September 1, 2014 for the Labor Day Holiday.

Orders received after 1:00pm(CST) on Friday, August 29th (8-29-14) will not be processed until Tuesday, September 2nd (9-2-14).

Small CNC Buyer's Guide -Engineering and Machine Design

Tormach published an engineering analysis of our original PCNC 1100 several years back, after we first released the product. That analysis is still available here and can be an excellent basis for understand the design of small CNC mills. We make reference to the original document in several places below. The engineering notes here compliment and expand on our original engineering analysis while presenting the technical topics in a manner that make it easier to do a comparative analysis.

Frame

When comparing the basic machine frames it's important to keep the various dimensions in context one another. As an example, the size of the machine should be considered in context to the amount of iron. It is a useful exercise to look at a ratio between the weight of a machine frame and cubic inches of the working envelope. Assuming the iron has been used properly, with ribs in the correct positions, a higher number suggests a stiffer machine. With the Tormach PCNC 1100, the working envelope is 2779 cubic inches (18 x 9.5 x 16.25), while the basic machine is 1130 lbs. The ratio is 0.41 lbs/cubic inch. Compare that to something like the Novakon NM-200 at 0.28 lbs/cubic inch. Building a large machine while using little iron results in flexible framework. Of course only similar configurations can be contrasted. A Bridgeport style knee mill, or any machine that invests a large amount of iron in the base, will not be comparable to a bench frame mill using this ratio analysis.

Some builders make impressive claims for heat treating or "aged castings". In fact, every manufacturer tempers their castings. Certain castings may require multiple steps, or a combination of heat stress relief and vibratory stress relief. These are standard practices.

One thing that is not a standard practice is the replacement of conventional sand casting with the more advanced method of sand-resin casting. Conventional sand casting has a great deal of variability. Some castings may have thin spots and blow holes, while others are excessively thick. Tormach has switched to sand-resin for the more critical components, like the column and base castings. Sand-resin methods provide much better dimensional control and more consistent products. Sand-resin is the same technique that Ferrari uses to build their V12 engine. You can understand the method by checking out this YouTube video.

Axis Slides and Ballscrews

Hydrodynamic or Linear

The subject of alternative axis slides is covered in some detail in our engineering analysis engineering analysis. The ultimate in the evolution of conventional slideways is an oil lubricated hand scraped polymer bonded surface (Turcite® or similar) against a ground metal surface. This is far superior to chrome on chrome or ground iron against ground iron. The other popular solution is a linear bearings.

When contrasting hydrodynamic slides to linear bearings, the fact is that both can work. Linear bearings are lower in friction, but other than that, offer few engineering advantages. We believe linear slides are more popular with Western manufacturers because they don't require the hand scraping skills of an experienced toolmaker. Technicians with hand scraping skills are still available in Asia and the labor cost is lower, so the tendency is toward hydrodynamic slides instead of linear bearings.

As a point of comparison, consider the offerings of Hardinge/Bridgeport. Hardinge offers their GX-1000 VMC in two flavors. The basic GX-1000 has linear bearings and offers rapids of 1417 IPM and an accuracy of 0.0004". The alternative is the GX-1000B, with hand scraped slides, has rapids of 1181 IPM and an accuracy of 0.0002". The hydrodynamic slides help provide a more accurate machine, although the increased friction makes for a slightly slower machine.

In the matter of ways, we suggest you don't take these engineering comparisons too literally. The example of the Hardinge VMC takes the technologies to the limit of both speed and accuracy, but with either the GX-1000 or the GX-1000B you're talking about a $70,000 machine. As a practical matter, in the class of machines we're talking about (under $15,000), either hydrodynamic slideways or linear bearings can be used to make a perfectly fine machine and neither is pushing engineering limits. The real determining factor is the cost and the quality of manufacturing, not the selection of the technology.

Ballscrews

Ballscrews are also discussed in some detail in our engineering analysis engineering analysis. We can summarize here by reviewing the accuracy grades. The ISO grading system normally applies to ground ballscrews. Rolled ballscrews are frequently used in retrofit projects and are often ungraded. When they do publish accuracy for a rolled screw it's usually a grade 7 or worse.

Large commercial CNC equipment will often use a laser interferometer to calibrate and map screw errors, thus allowing them to get by with a grade 5 screw. Grade 5 is what is used in Milltronics, Haas, and many other conventional machines. Tormach uses a laser interferometer for machine testing, but the logistics and complexity of supporting screw mapping tables to users with PC based control is simply impractical. Our solution is to step up to a grade 4 screw. In essence, we're skipping the procedure of software compensation of screw errors and instead using a better quality screw. We feel that anything better than grade 4 is a waste of money because other errors (thermal growth, tool flex, etc) are far more significant in the bottom line of error management.

Ballscrew Precision
Grade Accuracy over 12"
7 0.00200"
5 0.00070"
4 0.00047"
3 0.00032"

Motor & Drive Architectures

These sections cover the technologies used for CNC motion control and consequences of various design decisions.

Axis Types

There are three types of axis drivers used on CNC machinery. These are AC servos, steppers, and brush servos. Our engineering white paper details some of the factors to consider when comparing the three types.

AC brushless servos: Industry standard for large commercial CNC machinery. Also used on a variety of industrial equipment.
Stepper motors: Used on some small CNC machines and a variety of industrial machines. Frequently used where low cost and high precision motion is required, such as laser printers and medical equipment.
Brush type servo: Largely abandoned in industrial applications, brush servos are frequently found in DIY and hobby projects.

Hobbyists tend to consider all servos as a single classification. This is simply wrong and overlooks the significant differences between AC brushless servos and brush type servos. In the spectrum of small CNC or Personal CNC, there are no suppliers we know of offering AC brushless servo motors. AC servo motors are the universal standard for conventional CNC (Haas, Hardinge, Okuma, etc). Stepper motors are commonly used in a variety of industrial applications, including mission critical medical equipment, while brush style servo motors are pretty much limited to the hobby world. All of the mainstream servo manufacturers (Rockwell, Control Techniques, Siemens,Yaskawa, etc) have long since abandoned the brush servo technology.

Servo versus Stepper Motion Faults & Setting Limits

This section reviews the nature of motion faults and the tradeoff between risk and performance when setting the speed limits of a machine design. We show that a servo system is not better, but different.

Stepper Faults: Stepper motor systems are open loop synchronous machines. They typically have 200 full steps in a revolution. They cannot "miss a step". When a stepper system is overloaded it can, in theory, snap out of sync. In this case it will lose not 1 step, but 4 steps. This is because the pole pattern repeats every 4th step. In practice this rarely happens, systems do not "forget steps" any more than your wrist watch will "forget seconds". Where a design is insufficient and an operation requires more torque than is available, the overload conditions result in a complete and dramatic loss of motion. Essentially the system fails with the motor stalling while making a buzzing noise. It's a very obvious failure. The way to prevent this is design a system where the maximum load required is less than the available motor torque.

Servo Faults: Servo systems use position feedback to dynamically calculate position error. When the maximum load exceeds the available torque, the position error will exceed some predetermined maximum and the system will fault with a complete and dramatic loss of motion. Like the stepper system, this is also a system failure. When comparing servo systems to stepper systems it's important to recognize that both will fail if the torque required exceeds the available motor torque. A servo system will fault with a flashing red light on the driver and there will be zero torque on the motor until the driver is reset. With a stepper system, a fault is nothing more than a large position offset and the system will continue to move. Both cases are caused by overloading the system and in both situations you will likely destroy the part being cut and break the cutting tool.

Servo systems sustain operation without faulting by allowing a certain window for dynamic error. There will be positioning errors while moving, but as long as they are kept small they go unnoticed, at least until you measure the resulting part tolerance. In practice, the allowable angular motor error window for brush style servos is considerably larger than the error that exists with normal stepper motor operation

Tormach avoids the problem of faults with stepper motors by using a disciplined and conservative approach toward engineering. The chart below compares a typical servo system to a stepper system, comparing speed to force. The curves are characteristic of the two system types. Steppers are high induction motors and the available torque begins to reduce quickly after a speed of around 30 inches per minute (IPM). This reduction in torque is due to something known as back EMF (electromotive force). Servos are also subject to back EMF, but they do pole switching 3 times per revolution, not 200 times, so the affect is only seen at higher speeds. In the system shown, the back EMF on the servo comes into play at around 225 IPM.

Stepper vs Servo

The gradual decay of available torque on a stepper system is a pitfall for system designers who are unfamiliar with the nature of steppers. It's typical for an inexperienced designer to test a system out to maximum performance and then back off a bit in speed. While we only show data to 300 IPM on this chart, in fact the stepper system would work at higher speeds, yet the servo system shown clearly fails around 270 IPM. A designer might test to maximum speed and then set the program limit to something less. With a servo system, this isn't much of an issue. Servo systems have a clear and distinctive fall off in torque, so "seat of the pants" approach to engineering works OK. If the system failed at 270 IPM and the designer programmed the controller to never use more than 225 IPM, things would work just fine because 225 IPM is within the performance envelope of the servo system.

Steppers are a bit trickier due to the slow gradual fall off in torque. Seeing the stepper system can move at than 300 inches per minute, a designer might set the system limit to 200 IPM, which seems conservative. Never the less, if the system demanded 200 lbs of force (vertical axis is force) at 200 IPM, the system would fail with a loss of steps. Following the graph you can see that the stepper force plot crosses the 200 IPM mark at around 180 lbs of force.

These are complex concepts for the average consumer and make it difficult to evaluate specifications, but it may be useful to draw a couple of data points for comparison. The stepper performance shown above is actual empirical data taken from a Tormach PCNC 1100 machine using a 640 oz inch motor. We didn't calculate force using ballscrew transmission ratio, but actually tested true force levels using an in situ dynamometer, so all friction and inefficiencies are included in the numbers. From this data we decided to set our axis limitations at 90 IPM rapids. This keeps the machine always above 400 lbs of available force for cutting, even at the highest speeds.

Both machines work at their rated speed; it's simply a matter of weighing the value of speed against the risk of position loss. Stepper systems have a reputation for losing steps. We believe that the reputation stems from the fact that far too many stepper system designers push the envelope, accepting the risk of lost steps for the benefit of extra speed. Tormach takes a different approach with very conservative engineering. Rather than finding a speed limit and backing off a certain percentage, we test for actual force data and pick conservative force minimums when setting machine parameters.

Servo versus Stepper in Dynamic Error

Dynamic error is the position error that occurs during motion. Every machine has some dynamic error and it increases in size as cutting forces increase. Dynamic error will show up in the work as deviations in the cutting path, which means errors in the shape of the part you cut. Part shape is more strongly affected by dynamic error when cutting curved shapes, circles, or diagonals. It rarely shows up on rectangular parts. With stepper systems the dynamical error is extremely small, while with brush style servo systems the dynamic error can be large and highly variable. In this section we look at the physics of both steppers and servos to understand why this occurs.

As noted above, a stepper motor is a synchronous machine. It develops torque as the rotor shifts out of sync with the stator. The relationship between rotor and stator position is very strong. Maximum torque is generated when the error between rotor and stator is 1 step, which happens to be 1/200th of a motor revolution. This is peak torque, the point of incipient failure due to torque overload. In operation the actual torque is much smaller and the actual error, being proportional to torque , is also smaller. We can use the Tormach axis configuration as an example. It has direct drive on a 5 TPI ballscrew, one step is 0.001" in axis motion. As we mentioned, stepper systems should be designed with operating forces far below peak torque. For example, a heavy cutting operation may require 100 lbs of force at a speed of 50 IPM. Looking at the graph above, we can see that 50 IPM has peak available torque as 750 lbs. As 100 lbs of force would be demanded while peak force available at 50 IPM is 750 lbf, the actual motor error due to dynamics would be 100/750 or 13% of a full step. Translated to axis motion this is 0.00013". In practical terms this is insignificant and other factors, such as tool stiffness, would be more significant.

Error management is one of the areas where AC servo systems are significantly different than brush style servos. AC servo systems operate with complex algorithms and include what is known as feed forward terms. These are essentially predictive terms, anticipating motion torque requirements to reduce dynamic error. AC servos also include sophisticated tools for system tuning, with computer driven automatic tuning routines.

Brush style servo systems operating on step commands are limited to simplistic PID algorithms for motor control. PID is an acronym for Proportional, Derivative, and Integral. The PID algorithm is a math equation which takes position error as its only input. The output of the equation is the torque command for the motor. The simple truth is that a PID based servo controller can provide no torque and no motion unless position errors exist. In practice, brush style servos often have significant position errors during motion. The problem can be masked by the fact that there will be no position error when the machine stops. The integral term of the PID algorithm will eliminate static error, but dynamic error, that is error during motion, will necessarily be non-zero. Without the predictive feed-forward terms of the AC servo, the brush servo will lag behind during a move and then catch up at the end, showing near zero static error while sitting still. The problem for a system designer is that dynamic error can be nearly impossible to capture and, unlike AC servo drives, brush servo drives rarely include proper tools for drive tuning.

Spindle Design

Spindle Motor and Drive

    For the motor and drive, the most common solutions are:
  • Single phase induction motor on line voltage
  • Three phase induction motor driven by variable frequency drive
  • Brushless DC motor and driver

Single Phase Induction Motor and Line Voltage

This combination is typical of retrofit CNC mills which were originally designed as manual mills. As part of that they will usually include a complex set of step pulleys or gears to achieve different spindle speeds. Single phase induction motors require starting circuits, capacitors, and special start windings. They use a speed sensing mechanical contactor that switches out the start circuit after the motor comes up to speed. There are lots of things to go wrong in a single phase induction motor.

A practical and effective CNC mill needs variable speed. A variable frequency drive (VFD) requires a 3 phase motor, not a single phase motor. This makes conversion to variable speed a troublesome process, requiring both the addition of a VFD and replacement of the original motor.

Advantages: Built to common international standards
Disadvantages: Speed fixed to line frequency. Reliability of single phase induction motors is lower than 3 phase or PM motors.

Three phase induction motor and VFD

The industrial three phase induction motor is the most reliable and cost effective electric motor ever produced. Unlike the gizmo in a single phase induction motor, a three phase induction motor has little more than steel, iron, and copper. There are no capacitors, contactors, or permanent magnets, all of which are components which can be subject to decay. Induction motors are asynchronous machines, so there is no need for a rotor position sensor. Three phase motors are manufactured to industry standards (NEMA or ISO) and the VFD motor drivers can be easily configured to use any three phase motor.

The speed range available with this combination depends largely on the type of VFD. The low cost VFDs use a design referred to as Volts to Hertz, or V/F (F stands for frequency). This sort of VFD will provide a speed range of about 10:1, with the highest speed being about 10 times the lowest speed. The torque falls off dramatically on each end, so the effective speed range is more like 8:1 since there's no point in going slow or fast if you cannot deliver the torque necessary to cut.

A large step up in performance comes from a sensorless vector VFD. Unlike the V/F type of drive, the vector technology provides sophisticated algorithms to control current, voltage, and frequency automatically. They can adjust as needed while the load changes. With better torque at both high and low speeds, the effective speed range can be 25:1. Beware of suppliers who advertise higher speed ratios (ratio of highest to lowest speed). Any vector drive can make a motor spin at a very slow speed but there is no effective torque if the low speed is taken too low. The need for low speed on a mill is associated with things like drilling large holes in steel or tapping with large taps. Generally speaking these are operations that require significant torque. It's easy to set the minimum speed exceptionally low and looks good on a specification sheet, but it's misleading if you cannot do effective work at the low speeds.

Induction motors are rated for power at synchronous speed, which means 60 Hz. In general terms, they act as constant horsepower devices above synchronous speed, all the way up to the back EMF limit, where torque falls off rapidly. Below synchronous speed they at as constant torque devices, not constant horsepower devices. This characteristic can be improved a bit with proper tuning on a vector drive. The general nature of the speed/power profile is shown in the chart below. This shows the wide power band that is one of the finer attributes of an induction motor when used with a vector drive. In the Tormach mill, we limit the maximum speed to the point where we're just beginning to feel the back EMF limitations, around 90% on the graph below. In our applications synchronous speed is around 45% speed, where you see the corner between constant torque (left of 45%) and constant power (right of 45% speed).

Horse Power vs Speed

Tormach mills use a premium grade 3 phase induction motor and a sensorless vector VFD. Our VFD supplier is Control Techniques, a division of Emerson. Emerson is a world class supplier, manufacturing VFDs from 0.37kW to 1.9 MW (0.5 hp to 2500 hp). Development of our digital spindle drive is documented here. We've enhanced performance considerably through a process of tuning and performance testing, working closely with the Emerson factory engineers over a 3 month period. Emerson wrote an article about the development for Machine Design magazine.

Advantages: Very reliably system with a well established track record. Because these systems are built to widely industry standards there is no risk of obsolescence. Excellent speed stability, wide speed ratios, and a wide power band are available if vector type drive is used.
Disadvantages: Although most drives have auto tune features, tuning to achieve peak performance requires engineering expertise.

Permanent Magnet Brushless DC Motor and Drive

Brushless DC (BLDC) motors are synchronous machines which use a Hall effect position sensor to provide timing for coil commutation. Similar to AC induction motors, they have solid state rotors. Where the rotor of an induction motor is iron and copper, the rotor of a brushless motor contains permanent magnets. Under high current and stall conditions, they can be subject to demagnetization, but in practice this rarely happens. BLDC motors are generally long lived and robust devices, although certain Chinese manufactured models have been subject to higher failure rates due to high temperatures from a combination of insufficient cooling combined with hysteresis heating of the stator coils. When they run cool they tend to work fine.

There are few industrial standards applied to PM motors and drives. They are most commonly made as 3 pole stators, but the coils can be wound for any voltage a designer might select. The angular position and interface to the Hall effect sensor must be consistent between the motor and drive. The net result of this is that the motors and drives are usually specified as a set, frequently from the same manufacturer. They are manufactured by dozens of small Asian and a few domestic companies. None of the mainstream VFD or servo manufacturers (Rockwell, Control Techniques, Yaskawa, etc) supply BLDC motor drives, but they have become common in embedded applications such as treadmills and washing machines. The consequence of this is that the end user is dependent on the machine integrator to provide future support for the motor and drive. If the drive or motor dies, there is little chance that an end user can source equivalent components other than through the machine integrator.

BLDC motors are subject to significant torque ripple. This can be understood with a parallel to a gas engine, where there is a torque pulse that comes with the firing of each cylinder. This has little bearing on a machining application unless the user is trying to accomplish high torque – low speed tasks such as tapping with large taps. At higher velocity the inertia of the motor rotor and spindle will eliminate any velocity ripple and the torque ripple becomes irrelevant.

BLDC motors are more compact. For a given power rating, a BLDC motor will be physically smaller and lighter in weight than an induction motor.

BLDC motors are constant torque devices, so they deliver power proportional to speed. This characteristic is true all the way from zero speed to peak power speed, where the torque starts to crash due to back EMF limitations. This is shown clearly in the chart above. The power rating for a BLDC motor is usually a continuous rating at its peak. This can be understood by considering two 1 hp mills, both with a 100 to 5000 RPM rating, but one with a 1 hp brushless DC motor and one with a 1 hp induction motor and vector VFD. At 4500 RPM they will both be able to deliver at around 1 hp. At 2500 RPM, the DC motor will only deliver about ½ hp, while the induction motor is still putting out 1 hp. At 1000 RPM the DC motor is down to around ¼ hp, while induction motor is at ½ hp. The solution to this problem is to oversize the DC motor and drive. A 3 hp brushless motor system will be needed to match the power capability of a 1.5 hp induction motor through the majority of the speed range.

Advantages: Compact torque source. Motors are normally robust and long lived.
Disadvantages: Larger system is needed due to a more narrow power band. BLDC components are not interchangeable due to the lack of common industrial standards. Motors and drives must be matched, usually by the drive designer.

Power Comparison to Larger Conventional CNC

While there are standards of physics and engineering that guide power ratings of motors, the manufacturers of larger conventional CNC machines have taken liberty to define their own methods for rating spindle power. Milltronics has a good treatise on this on their web site at http://www.milltronics.net/Resources/Images/TruthInSpecifications.pdf that explains the situation. If Tormach were to use their principles for spindle power rating the specification for spindle power would be significantly higher.

Spindle Mechanicals

Spindle Taper

Small milling machines can use one of three tapers, Morse #3, R8, or a 30 taper (BT30, CAT30, National 30). The R8 taper is by far the most common. R8 is handy because there is a plethora of low cost R8 tooling available. Morse tapers are troublesome because tooling tends to stick due to the shallow slope of the taper.

The 30 taper designs require much more expensive tools, typically 3x the cost of R8 tooling. Part of the added cost is due to the more complex geometry required by the drive lugs. Drive lugs are necessary if the design is such that an operator is allowed to push the spindle with extremely high torque. This can occur if the spindle is setup with low gear ratios and a 3 hp or greater spindle motor. Conditions like that would slip an R8 tool but not a tool with drive lugs. While this can be considered a positive attribute of the 30 taper, the fact of the matter is that a 30 taper is not necessary in a machine that has less than 3000 lbs of iron in the frame. These same torque levels, the sort of torque that would slip an R8 tool, will also create flex in a 1500 lb frame. A lightweight machine should simply not be driven with the sort of torque that requires drive lugs on the tool, it's a bad match between frame and taper.

Spindle Bearings and Spindle Cartridge

Spindle bearings can be pressed directly into bored holes the cast iron of the spindle head, or they can be pressed into a turned spindle cartridge. We prefer the advantages of a spindle cartridge as it provides a more accurate alignment, easier replacement, and provides a convenient design for upgrades. A switch to a high speed spindle or higher precision spindle can be accomplished with a simple cartridge substitution. It takes less than 10 minutes to remove or install a spindle cartridge.

The use of a cartridge style spindle may seem like a minor engineering detail, but it can become important if you ever need to replace your bearings. Tormach stocks replacement spindle cartridges in both R8 and BT30 tapers as well as offering a spindle rebuild service. Spindle bearings are specified by either their ABEC (Annular Bearing Engineering Committee) number, or by an ISO 492 number. Wikipedia has a decent bearing overview and ABEC description, so we will not bother to repeat the information here.

Don't be impressed by claims of angular contact preloaded bearings in a spindle. Any mill, even a drill mill, will use angular contact bearings that are preloaded to maximize precision. Tormach uses ABEC 7 (specifically DT7008 lower pair, DT7007C upper pair) and is conservative in the engineering. Bearings can be classified by their ABEC (Annular Bearing Engineering Committee) or their ISO (International Standards Organization). The specifications are a complex collection of tolerances which impact both speed and precision. An approximate cross reference between the two systems is shown in the chart to the right, with the higher ABEC numbers representing higher levels of precision.

ABEC ISO 492
ABEC1 normal class 6
ABEC3 class 6
ABEC5 class 5
ABEC7 class 4
ABEC9 class 2

Spindle Transmission

Our engineering white paper reviews some of the factors to consider when comparing the design alternatives for spindle transmissions. The short version is this: gear drives are noisy and limited to low speed spindles, while belt drives are quiet, low cost, and suitable for higher speeds. When a gearbox goes south, you better hope you have manufacture's support for replacement parts because one gear can take out the entire gearbox. Belt drive systems have few problems, with the worst case being a possible belt replacement.

    When considering belt drive designs, there are several variations available.
  • V-belts are low cost, dependable, and easy to change with step pulleys. They can slip under slow speed high torque conditions unless designed properly. The Gates Super HC® belts are a big step up in performance over the classic V-belt. By adding a concave shape to the walls of the V, the belt grabs better and can deliver more horsepower in a smaller profile while using less belt tension. Belt tension adds lateral force on the bearings.
  • Cogged belts are effective for large torque and slow speed. They can use small diameter pulleys because the teeth on the belt prevents it from slipping on the pulleys. These are more expensive and cannot be used on step pulleys. Cogged belts can become noisy at high speed.
  • Poly-V belts are better at high speed. Essentially, a Poly-V is a series of miniature V belts, all lined up on a flat belt. They are quiet, yet can transmit a great deal of power in a small profile.

Tormach uses a belt drive transmission with Gates HC belts, but provides two step pulleys to allow a ratio change between the motor and spindle cartridge. The spindle motor drive, a vector technology VFD, provides a significant speed range of 25:1 (5150 RPM to 200 RPM) with just one pulley ratio, but when considering the full scope of machining applications we find that certain applications require a combination of high torque and low speed. Here we're thinking of things like drilling one inch holes in steel or milling work hardening materials like stainless steel. The ability to do a ratio change between the spindle and the motor doubles the available spindle torque and offers the opportunity to change the whole personality of the machine. In the high belt position you have a full range mill with excellent capability in both steel and aluminum, while in low belt you transform it into a workhorse with the brute force needed to take on the tough jobs in tool steel, stainless steels, or other difficult materials that require both low spindle speed and high torque. It's almost like two different machines, yet the change only takes about 45 seconds.

Controller

The mill controller and control software are important parts of your CNC mill. The most common control programs are EMC2, running under Linux, and Mach3, running with Windows. Tormach equipment runs with either, but Mach3 is by far the most popular. Most people assume that the Mach3 implementation is similar on different machines, but there are actually significant differences between vendors in the level of integration and support.

The standard approach for others is to provide a basic Mach3 configuration file (XML file), using the generic Mach3 installation provided by Mach3, and redirecting the customer to Mach3 for answers to detailed questions. The generic Mach3 installation includes configurations for a variety of machine times (plasma, mill, lathe, etc) and defaults to a user interface that supports all functions for all machines. It offers an overwhelming variety of features and functions, many of which are simply not relevant to a 3 or 4 axis mill.

At Tormach we take a different approach. We create our own installation program. Our installation installs the custom designed user interface and the Tormach developed XML configuration file. The configuration tools provided by Mach3 offer a staggering array of options, many of which can disable or even damage your machine. Tormach has sealed off the conventional configuration and created a separate configuration tool, a small software program that allows you to do what you might need for configuration without risk. Of course we also allow full configuration control for those who want to dive in deeply.

For guidance on Mach3, other vendors will direct their customers to the generic Mach3 manual (download here). The manual was written by John Prentice. It was written for Mach3 version 1.84 (circa 2006). There have been at least 70 software releases since version 1.84. At this writing Mach3 is in version 3.042.029. John Prentice is still active in working with Mach3, but he is now an employee of Tormach. Our manual is continually improved and enhanced. The code descriptions in our manual have long since been corrected from the 2006 original. We've added both helpful graphics and G code examples. Our installation program also automatically installs all of sample files in the machine controller. You can read a code description in the manual and then run the sample code on your machine. Our manual is comprehensive and combines both machine issues and software issues. It's always available for download and we invite comparison.

Mach3 is extensible and programmable system. The Tormach installation of Mach3 includes functions that do not come with generic Mach3. One example is our support for reversing tapping heads. Reversing tapping heads make quick work of tapped holes, but they can be frustrating to use because the G code needs to have feed rates that are consistent to the thread pitch, spindle RPM, and reversing ratio of the head. Our version of Mach3 includes our custom tapping macros. Simply enter the thread pitch and call the M code in your program. This is just one example. Tormach has created custom program features to help you use a digitizing probe, calculate feed rates, configure tool change position, and much more.

A machine controller is a marriage of computer and software. In recent times the relationship has occasionally proven difficult. With Windows Vista replacing XP and the drive toward Energy Star compliance, there have been quite a few compatibility issues between Mach3 and desktop computers, many of which have stumped the authors of Mach3 themselves. Tormach has made a serious investment by becoming a Microsoft Embedded Partner and developing a special operating system for Mach3, something we call MachOS. We combine MachOS with a compact industrial computer to create a Windows based appliance, a dedicated controller with both hardware and operating system optimized for Mach3. This development has eliminated compatibility issues and is something that no other CNC vendor has been able to match.