completely new to this

[superrican]

hey whats up all , im new to the machining and cnc , but always wanted to learn . im mainly a looking for hobby purposes , also maybe to aid in custom applications when im working/building/modifying cars and parts and pc parts here and there , mainly aluminum ,
anywho , im on the verge of buying the harbor freight milling machine and i caught a glimpse of a cnc conversion thats available ..... anybody point me in the right direction , with links , anytype of info , knowledge , exp .
thanks guys

[Crevice Reamer]

Hi superrican. Welcome to the Zone!

Which Harbor Freight milling machine?

CR.

[Crevice Reamer]

You may need to start with THIS:


CNC BASIC PRIMER:

ACME SCREWS are the standard for most manual mills. They are just a relatively close tolerance screw thread and give fairly high precision and low backlash while the adjustment lasts.

Acme screws and nuts wear quickly. Usually the screw wears most in the middle and less on the ends. After a while, you can't use the ends because it's too tight.

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.) A,B,C axes are rotary or angular. A is usually the forth axis, and can either rotate perpendicular to the X axis or perpendicular to the Z axis. It is good to have as much travel as possible on these--Especially the Z. (for long tool use)

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. A large enough backlash may turn a circle into a vague blob.

BALLSCREWS have large threads that allow a ball bearing to roll IN them. The ballscrew 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.

Once ballscrews are installed, manual control may not be possible. Because ballscrews 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.

Ballscrews come in two types: Rolled and ground. Ground ballscrews are best, but can cost thousands of dollars for just one screw. We small-time automators usually can't afford them.

Rolled ballscrews 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 ballscrew, it needs to first be cut to axis lengths. It is hardened material, so this is usually best done with an abrasive cutting disk.

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 ballscrews to order.

BALL NUTS: These are basically just enclosures that contain and recirculate the small ball bearings.

PRE-LOADED BALL NUTS: These have been re-loaded with larger balls. This takes up all available wiggle space and help eliminate backlash.

DOUBLE BALL NUTS: Two ball nuts with one tightened against the other to counter backlash. These are even better, but more expensive, and because they are longer, 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 breakout board accepts the cable plug and then puts each wire on an accessable screw terminal.

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.

CNC SOFTWARE:

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 seperately.

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.

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 an upper limit. 35 to 50 thousand pulses is an average amount.

OR EMC2. EMC2 is a free, open source software CNC program that runs on Linux.

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.

DRIVER CONTROLS:

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 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 higher speeds without losing steps.

MICRO STEP TO FULL STEP MORPHING: Only in Gecko 203V or G540. Allows low speed micro stepping and high speed RPMs. Morphing changes the speed to micro step at low speed accuracy, but jumps to full steps for high speed rapids.

IDLE CURRENT REDUCTION: Steppers tend to get hottest standing still. Overheat protection 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.

STEPPER MOTOR: These motors run, not by continuous current flow, but by PULSES of current. Most steppers move 1.8 degree per pulse and require 200 full step pulses to turn one revolution.

STEPPER MOTOR WIRING CONFIGURATIONS: Stepper motors usually have 2 phases and 4 internal coils. Four wire stepper motors have 4 coils inside that are internally wired as either BPP or BPS. Series motors will have four times the inductance in mH, 1/2 the Amperage rating 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 5, 6 or 8 wire motors. Allows 5 or 6 wire motors to run nearly as fast as if they were wired BPP.

BIPOLAR SERIES (BPS 4, 6 or 8 wire motors): These motors have low-speed TORQUE, but will quickly lose power 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)

BIPOLAR PARALLEL (BPP 4 or 8 wires): These motors Have good torque and retain more of it higher RPMs than any other type. Their power goes through both coils at once, but separately. (parallel) This is generally considered to be the best wiring method for steppers.

This diagram is for illustration of the above points:

http://kelinginc.net/KL23H286-20-08B.pdf

GECKO DRIVES are generally acknowledged as the best. Gecko "Vampire" drives are virtually unkillable.

The new low-cost Gecko G540 board (Accepts up to 50 volt power supply and outputs up to 3.5A each motor) will combine four axes of tiny morphing "Vampire" drives with a 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.

SERVO MOTORS, which are more expensive, do not have the starting torque that steppers have, but they maintain what torque they have into high rpms. They are usually geared down 2 or 3 to 1 to gain starting torque. Even geared down, they can still attain thousands of RPM, so speed is not a problem with pulleys. 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 will destroy themselves if stalled or if encoder fails.

CPR: Count Per Revolution.

PPS: Pulse Per Second.

Encoders: These send position and speed feedback to the controller and are rated in CPR. They are quadrature devices that require 4 times the PPS per revolution. For example: An encoder rated at 250 CPR, will require 1000 drive Pulses Per Second.

PID: A Proportional–Integral–derivative controller (PID controller) is a generic control loop feedback mechanism widely used in servo control systems.

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.

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.

It is sometimes possible, but much more difficult, to combine the upper N.C. limit switch with a N.O. home switch in the same switch. (double throw)

IPM: 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.

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 stepper system they may prevent impact damage to the motor. On a low speed 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.

MGP: Manual Pulse Generator. This allows easy manual CNC axis control without programming. Can be either a hand-wheel or joystick control

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 has an easier time.

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.

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.

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 .67 times total motor amps. EXAMPLE: Amper rating for three 3 Amp motors would be (3+3+3) times .67 = 6 Amp PSU.

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.

RAPIDS: 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.

Stepper Motors are designed to move just a tiny bit each time they receive an electrical pulse. 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.

It is important to match the motor to the load. You can't just assume that bigger is better. Bigger motors run somewhat slower than smaller motors. A router, more so than a mill, needs high rapid speeds. You will get best performance by wiring the motors in Bipolar Parallel.

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.

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. Formula for best voltage of a stepper motor is 32 times the square root of the inductance. With the G540, you will want motors with best Voltage between 50 and 65V.

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.

Ideally, this would make the machine actually move the proper amount. But if say a 4 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.

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.

CR.

[superrican]

44991-7VGA
Thanks for the feedback , lol i will be reading this through a few times ,

[Crevice Reamer]

It sounds to me like you could go with the most-bang-for-the-buck $1700 CNC Taig mill with G540. This mill is tough, ready to go, and can do some very nice work:

http://deepgroove1.com/cncmill.htm

CR.

[superrican]

Looks great , lemme ask somthing if I were to buy the harbor frieght mill and buy a kit and allll the necessary components what will my finaly bill look like?? Cuz 1700 don't look to bad

[Crevice Reamer]

I ask again: Which Harbor Freight mill?

CR.

[superrican]

44991 7vga is the part number......it doesn't have a manufacterer name , but its $449
I think I've seen it called x2

[Crevice Reamer]

Minimal CNC conversion parts & G540, two 270 OZ steppers and one 387 oz stepper plus 48V Power supply and assorted wiring would add about $1000 to cost of mill, plus your labor. Depending on what options you wanted it could cost up to $500 more.

CR.

[superrican]

So the one you had suggested , is that ready out the box? ,

[Crevice Reamer]

The Taig mill from Deepgroove1 is drop shipped in two boxes. Some bolt together assembly and squaring up required. Separate box will have G540 (Don't get the cheaper one) control box/power supply, stepper motors and motor cables.

Bolt prewired motors onto mill, connect motor cable plugs to control box, connect a straight thru male/male DB25 cable from control box to a 1 GHZ or better desktop computer running either Mach3 or EMC2 and you are ready to cut chips.

Some tooling comes with the Taig mill.

CR.

[Crevice Reamer]

Some accessories you will need:

$7 Computer cable and $10 Big-Red E stop switch:

http://kelinginc.net/CNCPackage.html

Mach3 costs $175. May be less purchased from DG1 with mill.

Great little $69 cam & design program integrates with Mach3:

http://www.d2nc.com/

CR.