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CNC machine

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noobieocer

New Member
hi, i decided to make a cnc machine(pcb etching machine) for my final year uni project and originally i thought i might require a micro controller. but with some research these machines seems ALOT simpler than i thought. seems like the stepper motors are connected to some amplifiers which are connected straight to a parallel port.

im planning to use unipolar motors because it makes the circuit simple. now i need help finding out which pins on the parallel port are used for limit switches and which are used to control motors.

also if i had 3 motors for x, y and z planes with each uni polar stepper motor having 4 wires for 4 coils how is these 12 pins connected to the parallel port.


thanks for your help
 
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noobieocer

New Member
im looking at links and i was expecting guides and schematics instead i get linked to places to buy kits. what i need is a schematic because i cant exactly buy a kit for my final year project.
 

Papabravo

Well-Known Member
What were you going to do about the mechanical parts?

Servomotors may be connected to amplifiers, but unipolar stepper motors are conncected to transistor switches. I don't think a parallel port will have enough available pins to control and monitor what is going on with the motors. I can tell you that trying to do this on a desktop is going to be a challenge.

What is your budget for this project? $50, $500, $5000, $50,000

Before jumping right into a "schematic" you might want to better define your requirements. How many motors, how much torque, what speed do they run at, how will you accelerate and decelerate the motors, how will the tool move up and down, what mechanical framework do you intend to use. This is a really BIG project -- trust me on this. It took us the better part of a year working 60-80 hour weeks to make an engraving machine.
 
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Oznog

Active Member
hi, i decided to make a cnc machine(pcb etching machine) for my final year uni project and originally i thought i might require a micro controller. but with some research these machines seems ALOT simpler than i thought. seems like the stepper motors are connected to some amplifiers which are connected straight to a parallel port.

im planning to use unipolar motors because it makes the circuit simple. now i need help finding out which pins on the parallel port are used for limit switches and which are used to control motors.

also if i had 3 motors for x, y and z planes with each uni polar stepper motor having 4 wires for 4 coils how is these 12 pins connected to the parallel port
NOT that simple. Typically steppers work in microstepping mode, which creates fractional current levels. The parallel ports from computers often have sloppy timing, which can lead to motor stalls because the pulses occur at the wrong times and the rotor can't accelerate or decelerate to meet the ill-timed pulse, and it falls out of sync completely. It's hit or miss how well parallel ports work.

There are many plans online for stepper drivers. They're all dicey. Allegro makes driver chips but all of them- pretty much every one of their product line- suffers from a problem where its minimum-on time prevents it from being able to create fractional currents thus the microstepping is very distorted and thus they're not really suitable for CNC work. GeckoDrive is the company that actually makes good drivers, and they're REALLY good. At $300 for a G540, the price is pretty acceptable.

Most people use Mach3 (some use EMC2) for the driver program. That will step the parallel port and you can assign the pins however you please, although it only makes sense to use the stock profile of pin associations. Many recommend optoisolators to avoid the possibility of power glitches (or ground loops) harming the parallel port.

Mach3 and EMC2 take in a movement script called "G-code". This is the most horribly ill-conceived excuse for a language still in use in the modern world. The concepts for its commands are insane if not horrifying. But, it is. There's a free program called PCB-gcode that you can use inside of Cadsoft Eagle to have it export boards to g-code cuts.

You will then face issues of engraver tips and runout and accuracy. If you try to use a fine-point carbide engraver on a high runout spindle, the tip doesn't spin on axis but in a circle, that will likely exceed the chipload and repeatedly break the tip off.
 
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Mr RB

Well-Known Member
...
This is a really BIG project -- trust me on this. It took us the better part of a year working 60-80 hour weeks to make an engraving machine.

Any pictures? I love looking at home-built CNC stuff.
 

Papabravo

Well-Known Member
Any pictures? I love looking at home-built CNC stuff.
This is the latest incarnation of the TLC-200 introduced in 1984. The TLC-200 was the one I developed.
 

Boncuk

New Member
I don't know of any CNC PCB etching machine except for isolation machining.

Maching is done the same way as plotting with the difference that not a pen - but a rotating tool is used.

Etching is done in tank using chemistry.

Boncuk
 

be80be

Well-Known Member
I don't know of any CNC PCB etching machine except for isolation machining.

Maching is done the same way as plotting with the difference that not a pen - but a rotating tool is used.

Etching is done in tank using chemistry.

Boncuk

Thanks for clearing that up for us
 
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