Welcome to Crevice Reamer's Website

How to connect motor cables to stepper motors:

How to solder up G540 motor cables:


Basically CNC machines control movement of at least 3 Axes of motion. (Axes are left/right, forward/back, up/down) Some types of CNC machines:
MILLING MACHINE: accurately cuts metal. Heavier machines are more rigid and cut hard materials easier without chatter.
ROUTER TABLE: can cut large area of wood and if rigid enough, soft metals like aluminum.
PLASMA TABLE: is like a router table, except uses an electric arc to cut sheet metal. This usually requires a water bath underneath table to contain hot byproducts. This can also be accomplished using Oxygen/Acetylene torch.
 Some are DUAL USE and can be converted back and forth from router to plasma.

ACME SCREWS are the standard for most manual mills and some CNC routers. They are just a relatively close tolerance flat-topped screw thread and give fairly high precision and low backlash while the adjustment lasts. Do not confuse Acme screws with threaded rod, which is a rougher, harsher version of screw.
Acme screws and nuts give smooth movement and accuracy but wear fairly quickly. Usually the screw wears most in the middle and less on the ends. (So it's a good idea to move your work around.) After a while, you can't use the ends because it's too tight. Still, Acme Screws get a lot of good work done. They are excellent value for their price.
Even relatively cheap ballscrews, which HAVE some backlash, are better because the backlash does not vary so often. Mach3 can compensate for backlash that doesn't keep getting worse
AXES: An axis is a direction of the CNC machine that is controlled by a motor. X axis = Left/Right. Y axis = Forward/Back. Z Axis = Up/Down (or on lathe: Z = Left/Right and X = forward/back. It is good to have as much travel as possible on these--Especially the Z. (for long tool use)  A,B,C axes (AKA 4th, 5th & 6th Axes)  are rotary or angular. A is usually the fourth axis, and can either rotate perpendicular to the X axis or perpendicular to the Z axis. B rotates perpendicular to Z axis. C rotates perpendicular to Y axis. The more axes a CNC machine controls, the more expensive it is--Both mechanically and for software.

AXIS SPEED: There are basically two speeds--Cutting and rapid. Both are set in software, typically Mach3 or emc2. Speeds are set in Inch Per Minute of axis movement. (IPM) In metric it would be mm or meters per minute.
Cutting speed is Feed or F in G code. Rapid speed is the speed the spindle moves from place to place BETWEEN cuts. Feed speed can be set as low as you desire. Rapid speed (Which you really want to be high to cover large areas) is set as high as both the electronics will provide and you are comfortable with. Generally, on a 4 x 8 or larger router, 800 IPM is not unheard of.

A: Run the table all the way left. Mark the position of center of spindle. B: Run the table all the way to right and do the same. Now measure between marks--that is your X axis travel.
Y) A: Run the saddle all the way back. Measure distance from column to rear side of table. B: Run the saddle all the way forward. Measure the same. Now subtract A from B. That is your Y axis travel.
Z)  A: Run the head down as low as it will go. Measure distance from spindle to table. B: Run the head UP as high as it will go. Measure the same. This is your Maximum Spindle Height. Now subtract A from B. That is your Z axis travel. If A measurement was Zero, then Z travel and MSH are one and the same. If CNC only moves the quill, then Z Axis travel is maximum quill travel.
BACKLASH: When reversing direction, any handle (Or motor) movement that does not also move the axis (or table or head/quill) is backlash. It is measurable directly by the dial on the handwheel or with a dial indicator. For CNC, backlash must be checked and adjusted often. In manual operation, turning the crank one full turn backwards before starting forward, will negate backlash. Mach 3 has a similar option that can be selected. Bear in mind that backlash of .003 inch is about the thickness of a sheet of paper. Depending on the accuracy needed, it may not even matter.
BALL SCREWS have large threads that allow a ball bearing to roll IN them. The ball screw nut contains many small steel balls that recirculate inside to reduce friction. The ball nuts can be extremely tight to eliminate backlash--yet still have little friction. Ball screws and nuts are extremely hard, so they don't wear out easily if kept properly lubricated.

Once ball screws are installed, manual control may not be possible. Because ball screws turn so easily, the table or head might not hold a position, but be free to move on its own. So while you COULD install hand cranks on double shaft motors, you might have to constantly lock the gibs on the other axes and it just may not be practical. You can semi-manually control a CNC machine by jogging.
Ball screws come in two types: Rolled and ground. Ground ball screws are best, but can cost thousands of dollars for just one screw. We small-time automators usually can't afford them, unless we find a really great deal on ebay.
Rolled ball screws come in several grades. The better they are for accuracy and low backlash per length, the more they cost. We usually use a medium grade.
If you buy say a six foot length of ball screw, it needs to first be cut to axis lengths. It is hardened material, so this is usually best done with an abrasive cutting disk or a grinder.
After they are cut, each end is turned down on a lathe. Because they are hardened, this is difficult to do. One end is usually turned to one diameter to fit a bearing. The other end may be turned to several decreasing diameters to accomodate thrust bearings, threaded for clamp nuts, and turned at the end to fit stepper coupling or pulley.
Once you have determined the LENGTH of the screws you need, there are companies who will make your ball screws to order.

Ball Screw basics by Swede:

BALL NUTS: These are basically just enclosures that contain and recirculate the small ball bearings as they roll in the screw threads.
PRE-LOADED BALL NUTS: These have been re-loaded with every other ball slightly larger. This takes up all available wiggle space and helps eliminate backlash.
DOUBLE BALL NUTS (Also sometimes called pre-loaded): Two ball nuts with one tightened against the other, with a tension spring between, to counter backlash. These are even better, but more expensive, and because they are longer, sometimes cost a loss of axis travel. 
BREAK OUT BOARDS (BOBs): Control software like Mach3 or emc2 uses the many wires in a parallel port (printer) cable to send control from the computer to the drives. Rather than fastening each tiny wire in the cable to its destination, the simple breakout board accepts the cable plug and then puts each wire on an accessable screw terminal. The more expensive COMPLEX BOB will also incorporate relay drivers, spindle speed controls, opto isolation and other nice features. The downside to this though is that if one of those features blows, the whole BOB may be out of commision.
CAN I STILL USE THE MANUAL CONTROLS? DO I NEED A DRO? MANY, who install DROs do so enroute to CNC. DRO is not needed for CNC, so DRO money spent is often virtually wasted.

Everybody wants to maintain manual control at first. SOME actuallly DO it. Almost everyone quickly stops using manual control. Manual control is at least POSSIBLE if you use the stock lead screws. If you install Ball Screws though, Manual control is not feasible because there is no friction to hold the table still against cutting force. After CNC conversion, the axes can be manually controlled by jogging--Especially on a lathe--Think of it as smooth power feed on both axes.

Can I build one machine that will cut everything from wood to steel?

It's a rigidity factor. Steel and other hard metals require extreme rigidity while making accurate cuts. Wood and light Aluminum require much less rigidity. Rigidity = weight and more cost. High-rigidity, dollar for dollar, comes with lessened travels than available for low rigidity machines. Larger travel rigid machines cost big bucks.

There's also the oil and water thing about mixing oiled steel-cutting ways with sawdust. Basically you can have a very good steel cutter (and of course all other metals) or a very good Wood cutter that can occasionally also cut light aluminum.
If you try to achieve both, the result usually turns out to be mediocre for both.

CNC: Computer Numeric Control. CNC can do things that you couldn't DREAM of doing manually. Properly programmed CNC can cut a sphere or any other geometric shape. All by combining axis moves to position the cutter in 3D space.

"Where do you want to start? It's all the same complexity of work holding and tool selection that you're already used to. {In manual machining} Add the complexity of having to precisely position the part, then tell the machine where the part is and how long each tool is so it knows where everything is sitting. 

Now take every move you've ever done by hand on the machine and write it down in excruciating detail (from & to points, how fast, etc). If the machine has a tool changer, coordinate all of those changes as well. Once all of that is done, dry run it at a greatly reduced speed so you're sure that nothing is going to crash.
The other way is to use CAM software. It doesn't really save you anything except the manual programming part. The added complexity is that you need to know that the CAM software is putting out proper code for your machine. It's a big time saver but it has the additional layer of complexity where you need to make sure you did everything right in there, before it ever gets to the machine.
I'm not trying to talk you out of anything, but CNC is far from just sticking a piece of stock in a machine, having the machine find it and do everything for you. It's just as complicated as you've imagined and maybe just a bit more"
There are three programs involved:
CAD: (Computer Assisted Design) A program to draw plans and maybe 3D objects with.
CAM (Computer Assisted Manufacturing) This program sets up the tool paths for the mill or lathe. It may translate the CAD output to G code.
Control: This software actually runs the mill or lathe or router from the G code. This software comes WITH certain expensive "turnkey" equipment, but usually you have to acquire it separately. Most popular is Mach3 or EMC2.
CHATTER: A shudder or shaking of the machine and part when the tool is pushed too hard for conditions. (material density, tool sharpness etc) This is an undesirable in cutting and is avoided by either using a more massive machine, or by using greater care with tool feed and spindle speed.

CURRENT LIMIT: All stepper drivers must limit the motor current to what the motor can use without destroying itself. This is done with various methods including High-Wattage-Voltage-dropping resistors, (Wasteful of power, as convert Amps to heat) fractional resistance, (limits current using low watt resistors without causing excessive heat)  switched resistance, adjustable resistors and fixed resistors. The G540 uses 1/4 Watt resistors to limit current.
DIAL INDICATOR: This is used to accurately measure a very small distance and display it on an easily read dial. These are invaluable for setting up work and Tramming the CNC machine.
Stepper drivers are the electronics that translate the pulses from the computer into useable current for the motors. They are fairly expensive and many are easily damaged. Wiring the drive wrong or disconnecting it during use will destroy most drives. You can have a powered driver without a motor connected, But you NEVER want to disconnect a motor from a driver while power is applied.
MICROSTEPPING: Some drivers are designed to artificially reduce the distance the motor will turn by electronics. Most motors have full step hardwired at 1.8 degrees and with 200 computer pulses it will complete one revolution. With microstepping set at 10 (Or one tenth) The motor will theoretically take 2000 steps (And computer pulses) to complete a revolution. I say theoretically because microsteps get just a little more vague in size as their number increases. Micro stepping operates at the expense of speed, and promises extremely high accuracy by increasing steps per revolution, but practically 8 or 10 microsteps are the limit. The computer and software can only put out just so many pulses, and the higher the step count, the slower the motor will run, unless the drive has full step morphing.
Generally, the more expensive drives (Like the Gecko G203 or G540 Vampires) offer the best features like overheat protection, micro stepping and speed morphing.
MID BAND RESONANCE DAMPINGl Only in better quality PWM drives like Gecko. Allows motor to run at medium speeds without losing steps. Often  motors connected to lesser drivers stall in mid-band and never REACH any higher speed.
MICRO STEP TO FULL STEP MORPHING: Only Gecko 203V or G540 and also the Mardus-Kreutz (unipolar micro-stepper drives) and Kreutz-4 and derivatives (K-41DIY) bipolar micro-stepper drives use waveform morphing vs speed. This allows low speed micro stepping and high speed RPMs. Morphing does micro step for smooth low speed accuracy, but jumps to full step speed for high speed rapids.
IDLE CURRENT REDUCTION: Steppers tend to get hottest standing still. This kind of Overheat reduction may 1. Cut the current down, and/or 2. Put the motor in "sleep" mode after a short wait. Both will drastically reduce heat buildup.
GECKO DRIVES are generally acknowledged as the best. Gecko "Vampire" drives are virtually unkillable.
The new low-cost Gecko G540 unit (Accepts up to 50 volt power supply and outputs up to 3.5A each motor) creates four axes of tiny morphing "Vampire" drives, combined with a sophisticated breakout board so that all you need to connect is the parallel cable, power wires, and motor cables. CNC conversion is now a LOT easier and less expensive.
SERVO DRIVES that WE can afford, use basically the same pulse system as stepper drives. Actual expensive commercial servo drives use a different, more expensive PID system.
CPR: Encoder Count Per Revolution.
Encoders: These send position and speed feedback to the controller and are rated in CPR. They are quadrature devices that require 4 times the CPR per revolution. For example: An encoder rated at 250 CPR, will require 1000 drive Pulses Per Second.

EDM Electrical Discharge Machining This is a method of machining hard metal with a series of electrical arcs. This can only be used on electrically conductive metal.

EMC2 is a free, open source software CNC program that runs on Linux computer operating system.

G CODE: Actually there are many other letters involved also. This is the language that tells the Control program how to direct the machine to make the part.
HOME SWITCHES are usually Normally Open, (NO) and are set at one of the limits of travel. When Mach orders a home operation, the axes go to the home switch location, close the switch, and then move slightly back and stop. This gives a reference position for mach to start from and position the tool. Mach3 will recognize any switch as home or limit, so the same switch can be used for both.

Inch Per Minute is the speed rating for the X, Y & Z axis motion. Cutting in a mill usually happens below 30 IPM. But rapids (Especially in a router) may need to be as fast as possible.
JOGGING: Using keyboard keys to manually move the CNC axes from place to place. Manual milling is possible using jogging.
LIMIT SWITCHES: These are usually Normally Closed (NC) switches that tell mach when an axis has exceeded its limit of travel. On a servo system they will prevent the servo from stalling and burning itself up. On a high speed servo system they may prevent impact damage or burn-out of the motor. On a stepper system they are probably not needed as the stepper motor will stall harmlessly. It is almost impossible to limit switch the lower end of Z travel because of varying tool lengths. Mach3 will also allow you to set up "soft limits" that operate independent of any switch.

MACH3 is the hobbiest defacto best computer software for machine control in Windows. It can control either Steppers or Servos. Mach operates by sending out pulses to to the drivers that control the motors. The NUMBER of pulses is limited by the speed of the computer and by Mach3 upper limit.(100K) 35 to 50 thousand pulses is an average amount.
MAGIC SMOKE: Some believe that special smoke is implanted into electronic devices at the factory. Mistakes and improper wiring can let the smoke out of the device. Once out, it is impossible to put the MS back IN and the device no longer functions properly.
MECHANICAL DAMPENER: A flywheel type adapter (Usually with some freely jangling parts) that, when attached to stepper motor shaft, can help alleviate mid-band resonance on low-efficiency drives. One of the cheapest mechanical fixes for this is a hocky puck drilled slightly off center and mounted to the second shaft of a double shaft motor. Most Gecko drives don't need them, as they control this electronically.
MPG: Manual Pulse Generator. This allows easy manual CNC axis control without programming--Similar to jogging, but using a hand-held control. Can be either a hand-wheel or joystick control


STEPPER MOTORS are designed to move just a tiny bit each time they receive an electrical pulse.  They do not operate on straight uninterrupted current as normal motors do. The Torque rating is what you get with the motor at rest. Torque falls off with increase in RPMs. To do any WORK with it, you need to carry much of that torque up to higher RPMs.

Most stepper motors are two phase. (Two separate motive coils per phase) They are rated in Volts and Amps per phase. Only ONE phase is powered at a time, so if a motor is rated 2A per phase, you only need to supply 2A--NOT 4A.
It is important to match the motor to the load AND the PSU Voltage. You can't just assume that bigger is better. Bigger motors run somewhat slower than smaller motors. High-Voltage motors run slower on lower Voltages. A router, even more-so than a mill, needs high rapid speeds. You will usually get best performance (And fastest Rapids) by Running them at Best Voltage and wiring them  Bipolar Parallel.
STEPPER MOTOR WIRING CONFIGURATIONS: Stepper motors usually have 2 phases and 2 internal coils per phase. Four wire stepper motors have 2 coils per phase that are internally wired as either BPP or BPS. Series motors will have four times the inductance in mH, draw 1/2 the Amperage and can tolerate twice the Voltage as Parallel wired motors.
UNIPOLAR (UP,  5, 6 or 8 wire motors): Unipolar motors run ONE coil at a time. One coil per phase is powered--which one depends on direction desired. These can be driven by very inexpensive controllers, but are not very efficient and usually deliver low power.
HALF COIL (HC, 6 or 8 wire motors): Powers ONE coil of a phase for both directions--second coil not used.  Allows 6 wire motors to run nearly as fast as if they could have been wired BPP:

The foregoing methods use only ONE coil of a phase at a time, so are about 2/3 as powerful as the following methods.
Bipolar just means that BOTH coils of a phase are being energized at the same time.
BIPOLAR SERIES (BPS,  4, 6 or 8 wire motors): BPS wired motors lose their torque very quickly as they run faster and will stall at relatively slow speeds. Their power goes through first ONE coil of the phase and then the other. (series) Some 4 wire motors are wired Series internally. You can tell this by the inductance, which will be very high, and the Amperage, which will be fairly low.
BIPOLAR PARALLEL (BPP,  4 or 8 wires): BPP wired motors retain more of their torque at higher RPMs than any other wiring method. Their power goes through both coils of a phase at once, but separately. (parallel) This is generally considered to be the best wiring method for steppers. Some 4 wire motors are wired BPP internally. You can tell this by the inductance, which will be fairly low, and the Amperage, which will be fairly high.
BOTH BPS and BPP wired motors start out with equal torque:

This diagram is for illustration of the above points:

Stepper motors operate on pulses of current. Usually 200 pulses will turn a motor one full revolution. Steppers generate their maximum torque while standing still. As speed increases, the motor loses torque and will stall when it loses too much.

First let's try to understand the wiring inside a stepper motor. Stepper motors come with 4, 5, 6 or 8 wires. A 4 wire motor is wired Bipolar internally and will be either a series or parallel motor. Generally, series motors have 4 times the inductance and 1/2 the Ampere rating than a parallel motor will have.

Hold your hands apart, palms facing you. Curl down the middle three fingers, and extend the thumbs left and right. The curled fingers of each hand represent a coil. Both of your hands represent one phase of a 2 phase stepper motor.


This has the same Voltage & Amperage as Unicoil below. Half coil wiring uses only ONE coil per phase. Let's say the left hand is that coil. Sending current pulses into the left thumb and out the left little finger will turn the motor one way. Sending current pulses into the little finger and out the thumb will run the motor the OTHER way. Half coil wiring is a method of wiring a six wire Unipolar motor to a Bipolar driver and  getting the most speed out of it. This method WILL reduce torque by about 1/3 though. You would not use this method on an 8 wire motor, since Parallel is so much better.


Unipolar drivers are the simplest to make. They are not very efficient drivers and will not give best power though. Unipolar motors generally have five or six wires.

Now touch your little fingers together. This represents the "center tap" or "common" wire. Applying current pulses to the thumb of left hand, and out the little finger, energises one coil and the motor will turn one direction. Sending the current pulses into the thumb of the right hand will energise the other coil and run the motor in the OTHER direction.


Keep your little fingers together. For a Series wired motor, the little fingers are just spliced together. Your hands are now 2 coils of a Series wired motor. The current pulses come in the left thumb, travel through the first coil, are joined to the second coil by little finger splice, and travel through that coil and out the right thumb. Since the current travels through BOTH coils, this is a bipolar wiring method. Starting the pulses into the RIGHT thumb will reverse direction. Series motors lose torque very rapidly as RPM increases and will stall at relatively low speed.


Now, without separating the little fingers, fold the right hand over onto the left. Now the little fingers AND the thumbs are joined. The current flows into the thumbs and immediately through both coils and out the little fingers. This is a parallel connection. Again, both coils are energised, so it's bipolar. Starting the current pulses through the Little fingers will reverse direction. These represent 4 wires out of an eight wire motor. The other phase is wired the same. This method carries useable torque to the fastest RPM and is generally accepted as the best way to wire CNC motors.

"These are more expensive, but are similar to steppers in that they both have maximum torque at zero rpm, the fact they have a fairly flat torque curve up to their maximum rpm which can be from 4000 to 10,000 rpm for BLDC & AC types, allows the benefit of applying gearing which reduces the torque/frame motor/drive size to very economical sizes.
Servo motors are also equipped to tell the computer (through encoder feedback) exactly where the motor is at any given time so there are no missed steps. Stepper motors can stall and miss steps unbenownst to the operator until the finished part is measured. Servo motors require the controller to shut the drive down in case of stall or run-away if encoder fails to avoid destruction."
Contributed by Al_The_Man.
Each system has its pros and cons. Steppers used with proper power supplies are reliable, consistent and cost effective--That's why most hobby applications use steppers.

NEMA = National Electrical Manufacturers Association. They set the USA electrical standards.
NEMA SIZES: Both steppers and servos may come in different Nema flange sizes.
Nema 23= 2.3 inch flange. Nema 34= 3.4 inch flange etc. We usually use either the smaller Nema 23 or the somewhat larger Nema 34. The torque may overlap between the sizes, but generally the larger motor runs cooler due to more frame to dissipate heat, but also runs slower due to higher detent torque.
For example, a 500 oz Nema 23 stepper motor will be working hard (and getting hotter) to attain the torque at which a 500 oz Nema 34 will be easily cruising. Generally, power is added by extending the length (stack) of the motor.

Generally, we want to use smaller, faster motors that are well matched to their Voltage and Amperage requirements.
OPTO-ISOLATION: This protects the computer circuits by translating electron impulses to light and then back to electron impulses. A short circuit cannot go in reverse across the light barrier.

PID: A Proportional–Integral–derivative controller (PID controller) is a generic control loop feedback mechanism widely used in servo control systems.
POWER SUPPLY (PSU): Both types of motors run on DC Voltage. The power supply simply converts ordinary alternating current into smooth DC at a Voltage for CNC motors. Choosing the proper voltage to match drivers/motors is one of the most important decisions needed. You NEVER want to install a switch on the DC side of the power supply.

You CAN have a FUSE on the DC side, but no switch. There is no problem if the power is cut on DC side. The trouble begins when you turn the switch ON. The PSU allows slow buildup of power when AC is switched on--But drives may suffer catastrophic power surge when DC is switched on.
One power supply, sized to power the lowest Best voltage motor, is all you need. EG: Two 60V motors combined with one 83V motor = Must use 60V or less PSU.
Stepper motors need around 20 times their rated voltage to perform at their best. For example, a motor rated at 2 volts will perform best, without stalling or losing steps, with a 40 volt power supply.
For the EXACT Max/Best power needed for a stepper motor the formula is 32 times the square root of motor inductance in mH. EXAMPLE: A motor with 4 mH inductance would need a 64 Volt PSU. The PSU must be sized for the lowest voltage motor--So a 64 Volt motor combined with an 85V motor would need a 64V PSU. You would then pick the PSU that is at or as closely below 65V.
Series wired motors can run at higher voltages--but there is a cost in speed performance.
AMPERAGE: To determine the PSU amperage required the formula is 0.6 times total motor amps. EXAMPLE: Ampere rating for three 3 Amp motors would be (3+3+3) times .60 = 5.4 Amp PSU. Some apply a safety margin and use 0.67 as a factor instead. You only consider the Amps for ONE phase of a 2 phase motor. A motor rated at 3A per phase will count as 3A in the calculation--NOT 6A.

PPS: Pulse Per Second.

PULLEYS are used to increase torque by gearing down the motor RPM. However, stepper motors get weaker as speed increases, (To a limit of 800-1500 RPM depending on PS voltage--up to 20-25 times motor rated voltage if the drivers can handle it.) so most of the gain in torque results in lost speed. That's why most stepper motors are connected direct drive.
QUILL: This is a spindle shaft that allows the tool to be moved up and down separately from the head--Usually by a lever/wheel arrangement as on a drill press. Most dedicated CNC machines do not have a quill, and it is usually removed or locked during a CNC conversion of a manual mill. (Because CNC head moves are adequate and extending a quill lessens the tool rigidity.) 
RAPIDS: AKA Free air moves. Non-cutter axis moves to get quickly from one point to another. These are cumulative, so if they are slow it slows down the whole job.
The way to get best rapid speeds is to be able to get torque at high RPMs. This is accomplished by matching the motor's best voltage to the power supply voltage. Higher voltage pulses charge the coils more quickly and maintain torque to faster speeds.
The actual motor RPM  get will depend on your drivers and power supply. First find the inductance of the motor wired the best way for your driver--Usually Bipolar Parallel. Formula for most efficient motor voltage is 32 times the square root of that inductance.
If you run the motor BPP at that voltage and at full motor amps, and have enough PPS from the computer, you will get the maximum rpm possible. If it is too fast for your liking, you can always slow it down (with no ill effects) in software.
If you run the motor at LESS than that Voltage, and/or with a less efficient driver, you will get proportionately less RPM before stalling and losing steps.
Using the G540 as the controller, (and you should if you can, it's the most bang for the buck) You can operate with a max voltage of 50V. With the G540, you will want motors with best Voltage between 50 and 65V.
RIGIDITY: The basic solidness of  a CNC machine. A more rigid machine can take deeper cuts without chatter. Heavy machines are usually more rigid than light ones. A more rigid machine is usually more accurate also.
RESOLUTION: The measured (In mm. or inch) amount of accuracy possible in an axis move. This is a combination of number of steps per motor revolution and number of turns per inch of the lead screw. For example: A direct-drive Stepper motor with driver set for full step will take 200 steps for one full revolution. If that revolution turns a ballscrew with 5 turns per inch, then there will be 1000 steps per inch or a resolution of one thousanth of an inch. (.001) If that same motor was turning a 20 turn per inch Acme screw, the resolution would be 4000 steps per inch, or 4 TEN thousanths of an inch. (4 Tenths or .0004) Pulley or gear ratios add to the resolution and you must also factor in any microstepping of the drive.
Bear in mind that there is no free lunch. Computer pulses are limited, and usually Finer resolution comes at the cost of lower Rapid speed.

STEPS PER INCH (SPI): Are used to set up machine software to accurately move the axes. The usually 1.8 degree per step motor will need 200 full steps to turn one revolution. The TPI of the lead screws will determine how many revolutions will move the axes one inch. Multiply this by the number of micro steps and you have the basic step per inch factor. In Metric, this would be steps per mm or steps per meter.
Ideally, this would make the machine actually move the proper amount. But if say a 6 inch move is called for, but the machine moves more or less, you may need to tweak the SPI up or down a little. Mach3 accepts decimal amounts here.

THC Torch Height Control. Electronic circuitry that automatically maintains cutting distance from material for Plasma Torch.

TPI: Threads Per Inch.
TRAMMING: A process to make all axes of a machine tool perfectly perpendicular to each other. If these axes are not perfectly aligned, then the parts made will be out of intended specification or shape.
There is no maximum limit for IPM. High IPM is a measure of the drive/motor efficiency. Good efficiency equals lower chance of missed steps. It is NOT just about cutting speed--Cutting speed will be influenced by material and force required. Inefficient systems may not be able to provide sufficient force to cut at optimum rates without stalling and missing steps. Many have cursed stepper systems as no good because their inefficient systems lost steps.
FIRST: Understand that YOU can always set the upper limit of your IPM by software control. You can easily slow down an efficient CNC. It is very difficult and often very expensive to SPEED UP an inefficient CNC.
High IPM really saves time when your spindle has to move from one place to another without cutting. Time saved always translates into money saved during production.
If you have lots of time to waste, have no intentions of ever doing any kind of production, will NEVER want anything like an automatic tool changer (or multiple fixtures) and/or are not dealing with a large area to cover like on a router--Then by all means limit your upper rapid speed. But do it in software--NOT by crippling your machine with inefficient components.
Everybody at first says "Wow that's expensive!
Let's look at what a G540 is:

The G540 electronics combine with the tiny G250 drives to make them unkillable, and equivalent to a lower Voltage/Amperage G203V. The G250 alone is not nearly as good.


$600: Four junior unkillable "G203Vs" with built in microstepping to full speed morphing and mid range resonance dampening.
$120+: Optoisolated 4 axis breakout board with spindle speed control, limit and home connections and built in logic power supply.
$200: Worth of time and aggravation wiring up and troubleshooting myriad connections that are already DONE internally with G540.
$015: Motor cable connectors.
Priceless: All this in a tiny package that just requires connection to 2 power supply wires, up to 4 motor cables and one computer parallel cable and it's up and running.
$935+ Total value for only $299.
The only downside is that you need to expend the effort to choose your motors for best power within (Or as close as possible to) the 3.5A, 50V G540 envelope.
Of course, you can do what MANY do and go for a $50 to $100 cheaper solution that may either prove unreliable or turn out to be unsuitable and need to be replaced after awhile--That may NOT be a money saving choice.
ON a milling machine, you want the maximum Z height possible. This translates into column size and weight to maintain rigidity. The mill column does not have to move so it's easy to just add weight to stiffen it.
On a CNC router though, the gantry moves and the head must move both vertically and laterally. Just adding weight is not a solution for rigidity. Rigidity is mainly accomplished by limiting travel. Therefore, for a router the goal is to keep the Z height as LOW as feasible. The generally accepted router Z travel is 6 inches.


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