converting X2 mini mill to CNC

[brendan_h]

I am interested in converting my mini mill into cnc. though i dont use it alot i would still like more info.

roughtly how much will it cost to convert it to 3 maybe even 4 axis cnc.
are the parts easly accesable?

depend on the cost for cnc i would also like so info on 2axis power drive

thanks

[tumutbound]

A search of this forum will turn up a lot of answers to your question.

Here's a few of site to check.
One, two,three

[brendan_h]

thanks that it help full

[Crevice Reamer]

Hi brendan. Welcome to the Zone!

For electronics, I recommend using the Gecko 540, Keling 270s for XY and 387 for Z and Keling 48 to 54V PSU for electronics.

http://kelinginc.net/

You can use THIS wire for motor cables and home/limit switches. Ground the drain wire ONLY at the driver end.

http://cgi.ebay.com/Servo-Motor-Wire...3286.m20.l1116

If you don't already HAVE them, these are excellent home switches:

http://cgi.ebay.com/6-CNC-LIMIT-SWIT...742.m153.l1262

They are NO, so only for home switches. Limit switches need to be NC. the whole set of 6 switches costs less than ONE switch would cost at Radio Shack.

CR.

[brendan_h]

yes i have no ider what you just said. im still learing

but what i found is for the motor mounts. but says you need extended X axis leadscrew?

www.cncfusion.com/minimill1.html


and for the motors and controlers. that also comes with software but i am not sure if ill need more programs?

http://www.stepperworld.com/FET3dynamo.htm

[Crevice Reamer]

Originally Posted by brendan_h yes i have no ider what you just said. im still learing

Okay, let's start with this:

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: Left/Right. 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)

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:

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.

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.

MACH3 is the hobbiest defacto best computer software for machine control. 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, opensource software CNC program that runs on Linux.

BREAK OUT BOARDS: Mach3 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.

BACKLASH: When reversing direction, any handle 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. For CNC, backlash must be checked and adjusted often. A large enough backlash may turn a circle into a vague blob.

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.

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

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.

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.

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 may need to be as fast as possible.

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

CONTROL DRIVES:

Stepper drives 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.

MICROSTEPPING: Some drivers are designed to artificially reduce the distance the motor will turn by electronics. A full step is 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.

IDLE CURRENT REDUCTION: Generally, the more expensive drives (Like the Gecko G203 or G540 Vampires) offer the best features like overheat protection, micro stepping and speed morphing.

Steppers tend to get hottest standing still. Overheat protection will 1. Cut the current down, and 2. Put the motor in "sleep" mode after a short wait. Both will drastically reduce heat buildup. Morphing changes the speed to micro step at low speed accuracy, but jump to full steps for high speed rapids. You can have a powered driver without a motor connected, But you NEVER want to disconnect a motor while power is applied.

STEPPER WIRING CONFIGURATIONS: Stepper motors usually have 2 phases and 4 internal coils.

UNIPOLAR (UP): 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.

BIPOLAR SERIES (BPS): These motors have a lot of TORQUE, but will 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): These motors Have good torque and retain more power at 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.

Steppers come in different wire numbers: 4 wire motors are wired internally to be either Bipolar parallel or bipolar Series. (Series motors have about double the inductance of the same motor wired BPP. 4 wire motors are easier to hook up.

5/6 wire motors are Unipolar and have either 1 or 2 common wires. Six wire motors can also be wired BPS.

8 wire motors can be wired up in all ways including UP, BPS or BPP.

This diagram is for illustration of the above points:

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

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.

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

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) 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 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.

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

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.

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.

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.

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.

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 thousanths of an inch. (.0004) Pulley or gear ratios add to the resolution and you must also factor in any microstepping of the drive.

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.

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)

CR.

[acondit]

CR,

You did a great job, except for those of us for whom Windows is a bad word.

Mach3 runs on Windows, while EMC2 is a free, opensource software CNC program that runs on Linux. Not for everyone but emc also provided the basis for the development of Mach.

Alan

[Crevice Reamer]

Thanks ac! I added it.

CR.

[brendan_h]

thanks theres alot in there for me that helped. just after a reply to my post earlyer

but what i found is for the motor mounts. but says you need extended X axis leadscrew?

www.cncfusion.com/minimill1.html


and for the motors and controlers. that also comes with software but i am not sure if ill need more programs?

http://www.stepperworld.com/FET3dynamo.htm

[Crevice Reamer]

You may already HAVE the extend screw--especialy if your X3 is a Micro-Mark. If not, you can buy it HERE:

http://littlemachineshop.com/1179

Those motors are too weak to run X3 Axes without ball screws. Even if you HAD ball screws, that package would only be all right if all you want to do is fool around a little before replacing it with decent electronics that will have acceptable speed/reliability.

It is FAR cheaper to buy good stuff once, than to buy something cheap only to have to replace it later. The G540 and motors I recommended would be your best performance and economy in the long run.

CR.

[brendan_h]

my mill is a X2

[Crevice Reamer]

Sorry! That was a typo. It was meant to say X2. 190 oz motors are too weak for that--Maybe a Sherline, but NOT an X2.

CR.