Arduino CNC

Between garage sessions and dog walking I've been looking at homebrew CNC for poor people. There's quite a lot in here as well as out there so I'm going to try and bring some of it together into a single thread

Feel free to add your own links and info

Arduino CNC at model engineer

4 axis arduino project (firmware is 20-40 quid before steppers)

Arduino GRBL videos

Excellent idea, Ady

MichaelG.

I use GRBL on a Uno for my X axis power feed. Also has a Bluetooth interface and is controlled by GRBL Controller from my phone.

https://www.model-engineer.co.uk/albums/member_album.asp?a=53829

I've just got a cheap control system and a nema17 with a 100/1 gearbox

Will see if it has enough grunt to move a lathe or shaper or mill table

4 axis arduino project

This isn't "4 axis" as such - the board allows cloning of one of the axes for gantry machines and, while the "4th axis" step & direction outputs can be brought out separately, it is noted that GRBL can only control 3 axes. The GRBL developer has said that a 4 axis version of GRBL won't fit on an Arduino Uno due to lack of memory. Protoneer also has a version that fits to a Raspberry Pi, giving a "stand alone" controller where the Pi replaces the PC.

There is a branch of GRBL for the Mega 2560 board here though this too is 3 axis.

A true 5/6 axis capable branch that runs on the Mega is available here though I have been unable to compile this - I get something that reports as GRBL1.1P onto the 2560, but it doesn't appear to have compiled as 5/6/ axis, just 3 when I check the parameters. I think this may be due to having previously compiled the 3 axis Uno version of GRBL on the same laptop - during compiling of the %x version in "verbose" mode I get references to using "previously compiled" modules. Not investigated further yet, though.

Grbl Gru is supposed capable of driving either the 3 or 5 axis versions of GRBL. Universal Gcode Sender will apparently send 4/5 axis commands to the Mega-5X version, though it can only display 3 axes.

Another Arduino option would appear to be through Estlcam, which I was unaware of until it was mentioned in the thread about Joe Noci's CNC lathe. The CNC part of Estlcam is not charged for & will work without limitation independently of the chargeable CAM part.

nema17 with a 100/1 gearbox

Will see if it has enough grunt to move a lathe or shaper or mill table

I would guess that speed will be your main issue. GRBL will output pulses upto 30KHz. Assuming 800 steps/rev, your motor will require 800 x 100 pulses per output shaft revolution = 80,000 pulses per rev. I make that 22.5 revs per minute at the output shaft at 30KHz - so a low feedrate when attached to a leadscrew. Going to full steps( 200 steps / rev) would up that to 90 rpm, but even with a 5mm pitch screw that is only 450 mm / min. Always assuming that your motor will provide meaningful torque at 30KHz ?

Nigel B.

I wanted to try some CNC without a major cost. When I finished I had a functioning but not super accurate CNC mill with the inaccuracy mostly from keeping the acme thread lead screws for the X and Y. My X has about .007" backlash and the Y only at .003". I used timing pulleys and belts for the Y and Z while the X is connected directly to the X leadscrew. I wanted manual control for X and Y retained so the handwheels are left on. That required some compromises but as I learn I am glad to have them. The total cost was about $100 USD. I used an Arduino with a CNC shield and a cheap power supply. I drive it with a Raspberry Pi running bCNC.

Edited By Ronald Morrison on 13/01/2021 12:40:39

Edited By Ronald Morrison on 13/01/2021 12:43:48

Edited By Ronald Morrison on 13/01/2021 12:46:41

Thanks for that, Ronald ... I was not aware of bCNC, but have found several videos that look quite useful:

**LINK**

https://www.youtube.com/channel/UC6duiWL-qeoP1a7QbmSbpDw/videos

MichaelG.

Neither had Michael - but I found this summary more useful than much of the stuff on YT.

bCNC - Product description

I also noted that they are recommending going to a 32bit GRBL (not Arduino) - which I had already looked at a little - at least a version that runs on the (infamous) STM32 based "Blue Pill" - of which I already have several ( they used to be about £2 each).

Most of the bCNC videos on YT seem to be focused on PCB production but it seems capable of much more. Of course, I'd need a CNC machine first...

Regards,

IanT

Edited By IanT on 13/01/2021 17:20:50

I have both Universal Gcode Sender and bCNC available to use on the Raspberry Pi but use bCNC because it will show the toolpath. UGS would show it too on a more powerful computer.

You may have noticed that I have not completed the power connection to the Raspberry Pi yet but that will be done soon using the buck converter mounted on the board near the power supply to drop the 24 volts to the 5 volts that the Pi needs. My connection that I use now does not supply enough current to the Pi.

I also have a Arduino Mega 2560 set up with Marlin instead of GRBL but I haven't taken the time to do more than verify that it will turn the stepper motors with the commands.

My ancient milling machines both run on Z80 assembler.

My new one will make the leap to 32 bits.

I have written the point to point 4 axis interrupt part.

Next comes the SDIO card as I go from 25kb memory to 16Gb.

Freaky

I had a look at the GRBL thing today but the family braincell wasn't keen so I decided to go for a simpler approach

I decided to have a go at running the whole ballgame from the arduino including the NEMA17 stepper

Couldn't find my 12V plug thing... too much housemove stuff but found a 12V jack transformer for an airpump, which was 18V when I put it through the meter... Decided to use it anyway

I used this guys tutorial, which is brill and all I needed

Then mounted the a4988 stepper driver on the breadboard and soldered pins onto the stepper motor wires

I have found those integrated breadboards great for projects

loaded up the library and uploaded his simple routine via the usb, unplugged that and plugged in the 12V jack and waited for the puff of smoke but it ran fine

Luckily I only let it run for 30 seconds before unplugging because I had been unable to reset the pot and it was running a lot of juice. The little heatsink on the a4988 was too hot to touch. I swapped the micro phillips screwdriver head out and used the slotted head to try and adjust it, success! and I got it down to just under 0.5V from its default of 1.5V

This was a huge improvement and limits the juice at 1A (I believe), in any case there were no more heatsink issues, even when I fought it with my fingers and made it work hard

I'm cutting out the 12V adapter on the tutorial schematic and powering it directly from the green and yellow wire on the arduino(VIN and GND) to the main VIN and ground on the a4988, the voltage was 17V (yes I know!) but it at least showed me everything worked

It's pretty darned kewl and has definitely boosted my interest in the subject

Edited By Ady1 on 24/01/2021 00:32:55

And the code for a basic 2 second rotation, 1 second pause

------------------------------------------------------

// Include the AccelStepper Library
#include <AccelStepper.h>

// Define pin connections & motor's steps per revolution
const int dirPin = 2;
const int stepPin = 3;
const int stepsPerRevolution = 500;

void setup()
{
// Declare pins as Outputs
pinMode(stepPin, OUTPUT);
pinMode(dirPin, OUTPUT);
}
void loop()
{
// Set motor direction clockwise
digitalWrite(dirPin, HIGH);

// Spin motor quickly
for(int x = 0; x < stepsPerRevolution; x++)
{
digitalWrite(stepPin, HIGH);
delayMicroseconds(2000);
digitalWrite(stepPin, LOW);
delayMicroseconds(1000);
}
delay(1000); // Wait a second
}

Final note

When I adjusted the voltage pot I pre loaded the BLINK routine (like an arduino hello world) to over write the stepper program and disable the unit from doing any work while it was being adjusted

Once it was sorted I reloaded the stepper routine

Edited By Ady1 on 24/01/2021 02:00:34

Any, I'm not sure about the a4988 but on other types of driver you can adjust the pot without the motor connected.

If you connect power to the A4988 without the motor attached it instantly burns out the A4988. It took burning out 3 of them before I found the information on that. It was documented but not real well.

GRBL looks complicated because it has to be as it controls 3 motors at once, each with its own step rate. Once you have one motor set up with it, it becomes less complicated as you can adjust the other 2 motors similarly. Some of the settings can be ignored while you adjust only the ones you need at the moment.

Thanks to Ady1 for posting a way for experimenting with the A4988 with one stepper motor. Could you see using that to control a rotary table or an indexer? How about just the x axis on a mill or the leadscrew on a lathe? Maybe it would work for the cross slide. Hmm... how about two of them, one on the leadscrew and one on the cross slide to work in a coordinated fashion to precisely fashion odd shapes?

Right! Not the A4988 then. In my mill power feed I use a DRV8825 on a Pololu carrier board. This is a much more up to date driver with better performance than the 4988 and is happy for the ref voltage to be adjusted without the motor connected -

**LINK**

I've also used the 8834 which is useful for low power motors and low voltages - will run happily on 5V, use two in my Arduinome clock, one for the gravity arm reset and the other for the dial.

If you think GRBL is complicated you should try Mach 3! I got GRBL driving a simple stepper from a UNO very quickly from the serial monitor, the main complication was interfacing to GRBL Controller on my phone via Bluetooth.

GRBL would be interesting for a lathe except that it lacks threading, and a G Code sender adapted for lathe work (as far as I know). A UNO or similar running GRBL is similar in concept to a motion control board, so it ought to be possible to interface say Mach 3 to it if there was a suitable plugin.

Sounds like I got lucky, it was just too much hassle unplugging and replugging the breadboard pins

Going to be a useful thread this one

On the a4988 front the stock cooling heatsink is totally inadequate if you want to maximise its output, it's only good enough up to half power IMO

There must be some decent pro heatsinks out there for the a4988 , the amount of heat that tiny chip has to deal with is actually pretty ridiculous and testing it for overloading is easy, it will cook the end of your finger when you touch it

edit: Will test it out on the big cross slide of my lathe milling setup before too long but got Mr Inlandi Revenuie to deal with over the next week

Edited By Ady1 on 24/01/2021 13:57:03

As I think more about it I may have been leading you and others astray. I had used a CNC driver board monuted atop my Arduino Uno and had the higher voltage hooked to it for that. Thinking it would be better for the stepper motor driver module I tried to adjust the reference voltage to set the maximum current without the stepper motor hooked up. That was the mistake. That was a year ago and I'm not certain which stepper motor driver I fried. I may have fried both the A4988 and the DRV8825 trying that. I wish the person who wrote the instruction that mentioned not to do that had made it in bold and bright red. One sentence in a page that mentioned not to do that.

Interesting one here, a wire bending machine