Arduino CNC Shield Power Routing

[Clive S]

Hi and welcome to the forum. What is a CNC shield? Its hard to answer questions without links to what you are trying to do. We don't tend to use Arduino's to run cnc machines.

Hi,
New to the forum, came from the 3D Printing world having conquered it and have to say... the open source software, firmware and hardware for 3D Printing is WAY more advanced than for CNC machines.

Not sure I understand this statement have a look at LinuxCnc and see if you change your mind about advanced open source.

There are many people on here running 3D printers as well as cnc machines.

[Desertboy]

Hi and welcome to the forum. What is a CNC shield? Its hard to answer questions without links to what you are trying to do. We don't tend to use Arduino's to run cnc machines.



Not sure I understand this statement have a look at LinuxCnc and see if you change your mind about advanced open source.

There are many people on here running 3D printers as well as cnc machines.

It's true on here most people have bigger machines so no one seems to use an arduino but the arduino cnc community is bigger than you think mainly because of shapeoko and xcarve.

At the moment it's really only good for 3 axis but you can actually wire up much better stepper drivers to the cnc shield and run the power directly bypassing the shield and get very acceptable performance for very little money.

It's not a as good as a linuxcnc solution of course but it's really not bad at all, they worked very hard to sort usb issues out and have a very decent light production solution grbl is a project to watch out for as they migrate to more powerful ARM based controllers. They have a working 4 axis solution but it doesn't all fit in the arduino uno.

I'm going to use an arduino, cncshield, 24v power supply & nema 23's with cheapo 2amp steppers for now but will get proper drivers and a breakout board relatively soon.

I see the Arduino as a very powerful cnc platform but overshadowed by better commercial solutions but at the price point it cannot be beaten.

[AcrimoniousMirth]

Hi Clive, nice to be here, thank you :)
Here's a CNC shield: http://ooznest.co.uk/Premium-Arduino-CNC-Shield
I'm designing and building a basic budget machine from some scraps I have and this system is open source and let's me run a basic CNC on a £15 system!
I've seen linuxCNC and it does seem good! I think I will try it if Fusion 360's CAM environment lets me down.
Why I say it's less advanced?
Firmware - on a 3D printer you modify the firmware as code and upload it as a very powerful and intuitive system with inbuilt support for autolevelling, LCD screens, SD cards and much much more. The most decent CNC firmware I can use is GRBL which uploads in a weird way and has very few settings.
Hardware - now here I am talking about open source and affordable, not the awesome professional machines you use!! With a 3D printer almost every single motherboard can very easily attach to a screen, SD and can be set up for many different forms of machine. With the CNC it only has axis, spindle controls and endstops. If I want to run it headless I have to attach a separate Arduino to relay instructions!
On top of that, on my printer I use "Octoprint" which allows me to control it over the web from anywhere in the world securely. The best for CNC seems to be "GRBLweb" which is also less developed. I may be able to edit octoprint for the CNC though.
Software - there are many clean and easy to use printer softwares that have a very nice and intuitive gui as well as much deeper controls. As a professional 3D technician I use Simplify-3D, one of the few paid slicers. I'm struggling to find anything on-par for CNC but Fusion 360's CAM may help!

Also the documentation is horrendous!

Please note I'm just talking about the entry level open source machines and not the professional ones, which I only dream of owning. For various reasons I'm having to go opensource.
Thanks!

[Desertboy]

Hi Clive, nice to be here, thank you :)
Here's a CNC shield: http://ooznest.co.uk/Premium-Arduino-CNC-Shield
I'm designing and building a basic budget machine from some scraps I have and this system is open source and let's me run a basic CNC on a £15 system!
I've seen linuxCNC and it does seem good! I think I will try it if Fusion 360's CAM environment lets me down.
Why I say it's less advanced?
Firmware - on a 3D printer you modify the firmware as code and upload it as a very powerful and intuitive system with inbuilt support for autolevelling, LCD screens, SD cards and much much more. The most decent CNC firmware I can use is GRBL which uploads in a weird way and has very few settings.
Hardware - now here I am talking about open source and affordable, not the awesome professional machines you use!! With a 3D printer almost every single motherboard can very easily attach to a screen, SD and can be set up for many different forms of machine. With the CNC it only has axis, spindle controls and endstops. If I want to run it headless I have to attach a separate Arduino to relay instructions!
On top of that, on my printer I use "Octoprint" which allows me to control it over the web from anywhere in the world securely. The best for CNC seems to be "GRBLweb" which is also less developed. I may be able to edit octoprint for the CNC though.
Software - there are many clean and easy to use printer softwares that have a very nice and intuitive gui as well as much deeper controls. As a professional 3D technician I use Simplify-3D, one of the few paid slicers. I'm struggling to find anything on-par for CNC but Fusion 360's CAM may help!

Also the documentation is horrendous!

Please note I'm just talking about the entry level open source machines and not the professional ones, which I only dream of owning. For various reasons I'm having to go opensource.
Thanks!

3d printing is mainstream so lots of development has been done for it and a lot of money has been made by people in the process. CNC is still niche for the home user Mach 3 offers excellent value, linuxcnc even better. Open source tools are only just starting their development cycle and not had tme to mature like 3d printing has.

The big thing is you can't use an arduino with those you need breakout board and suitable steppers a more expensive but more professional setup.

When I've spent a month with grbl and a month with linuxcnc working I'll be able to make a better conclusion.

grbl is very powerful there's little reason for many firmware settings as you do everything with gcode, you can't run headless with grbl I remember reading it's just too much for the uno so it won't be coming to the Uno version at least but you can use a PI to control the Uno to create a nice all in one solution.

[AcrimoniousMirth]

3d printing is mainstream so lots of development has been done for it and a lot of money has been made by people in the process. CNC is still niche for the home user Mach 3 offers excellent value, linuxcnc even better. Open source tools are only just starting their development cycle and not had tme to mature like 3d printing has.

The big thing is you can't use an arduino with those you need breakout board and suitable steppers a more expensive but more professional setup.

When I've spent a month with grbl and a month with linuxcnc working I'll be able to make a better conclusion.

grbl is very powerful there's little reason for many firmware settings as you do everything with gcode, you can't run headless with grbl I remember reading it's just too much for the uno so it won't be coming to the Uno version at least but you can use a PI to control the Uno to create a nice all in one solution.

From what I've seen the open source CNC stuff has been around a good deal longer but yeah, as a niche area has had much less development by able bodied parties.
My CNC only exists because I inherited an old RapMan printer (made in like 2008) so it's very outdated and practically useless nowadays, especially compared to my own-design machine. So I took it apart and am reusing a good portion of the parts. Including the NEMA23's.
Having run some calculations my CNC shield and the drivers I'm using (DRV8825) will be adequate for the power requirements. The spindle I decided first off to modify from an old cordless drill, stripping down to the motor, epicyclic gearbox and added an ER-11 collet. Tests show that's running adequately but I may upgrade to a proper spindle if needs be...
I'm currently getting started with the higher level control electronics for the spindle, again reusing stuff as much as possible and in theory it'll work without a hitch. Planning to make that "in practice" tomorrow!

So basically, what are my goals with this thing? To make a cheap and reasonably good CNC out of scraps I have lying around and other cheap materials where needs be. So far so good.


And yes, I'm aware. Again, in many ways the CNC has been relatively straightforward compared to 3D Printers because they're less demanding on the code and setup front. The mechanics are more demanding because of the forces involved but hey, it balances out. Naturally the Pi would control the Arduino separately (much like the Octoprint setup I use on my printer); it's basically running as a computer to replace your laptop/desktop and receiving files over the web. I wouldn't dream of trying to get the uno running that on its own, it's a microcontroller and not a computer, so not designed for that sort of processing.

[m_c]

The problem with CNC machining, is it usually requires far faster and more accurate motion than 3D printing, and an Arduino is not really up to the task.
Even an ARM processor isn't ideal, as getting jitter free motion needs good clock scaling, which can be handled far better in an FPGA, which is why you'll find nearly all CNC motion controllers use an FPGA for motion generation, often paired with some form of microprocessor which handles communication and the maths for generating the motion paths, before passing the required motion to the FPGA.
LinuxCNC and Mach running via a parallel port also have the same issue, however they ultimately rely on using a sledgehammer to crack a nut, by throwing enough processing power at the problem, you can get it to work well enough it's not a problem.

And then you have the available hardware. Nearly all shields I'm sure have been designed with 3D printing in mind, where speed and acceleration requirements aren't that great, so 24V is acceptable. If you were to use those same speeds on any reasonably sized router or mill, it would be painfully slow.
Hardware really is a case of, you get what you pay for.

[Desertboy]

The problem with CNC machining, is it usually requires far faster and more accurate motion than 3D printing, and an Arduino is not really up to the task.
Even an ARM processor isn't ideal, as getting jitter free motion needs good clock scaling, which can be handled far better in an FPGA, which is why you'll find nearly all CNC motion controllers use an FPGA for motion generation, often paired with some form of microprocessor which handles communication and the maths for generating the motion paths, before passing the required motion to the FPGA.
LinuxCNC and Mach running via a parallel port also have the same issue, however they ultimately rely on using a sledgehammer to crack a nut, by throwing enough processing power at the problem, you can get it to work well enough it's not a problem.

And then you have the available hardware. Nearly all shields I'm sure have been designed with 3D printing in mind, where speed and acceleration requirements aren't that great, so 24V is acceptable. If you were to use those same speeds on any reasonably sized router or mill, it would be painfully slow.
Hardware really is a case of, you get what you pay for.

The CNCshield is designed for grbl which is cnc router firmware not 3d printing! It can pass up to 36v to steppers (It's designed for a hobby machine after all) but if you need 60v to the drivers you can do that easily as well. Most people use cheap ass Polou steppers which are not suitable for 36v but you can get a lsightly more expensive driver than will push 36v fine or wire a real driver to replace the cheap chip drivers the cncshield is designed to take on board.

Of course it's not as good as much more expensive solutions but it's very powerful for the price (£25 including 4 stepper drivers!) and not as useless as you might think but I will move to a breakout board solution relatively soon I consider it the least essential purchase right now in getting the thing built and cutting.

Ardunio and cncshield are also very good for testing nema's so when I do upgrade I will have a simple test bed for the recovered motor's I collect.

grbl is very stable these days, maybe not the quickest of course but they are rock solid stable.

"The controller is written in highly optimized C utilizing every clever feature of the AVR-chips to achieve precise timing and asynchronous operation. It is able to maintain up to 30kHz of stable, jitter free control pulses."

[m_c]

The CNCshield is designed for grbl which is cnc router firmware not 3d printing! It can pass up to 36v to steppers (It's designed for a hobby machine after all) but if you need 60v to the drivers you can do that easily as well. Most people use cheap ass Polou steppers which are not suitable for 36v but you can get a lsightly more expensive driver than will push 36v fine or wire a real driver to replace the cheap chip drivers the cncshield is designed to take on board.

That CNC shield is just a glorified header board, with pinouts optimised for grbl. You could just as easily use it for 3D printing.
Regardless, what I was highlighting was the more stringent requirements for CNC.

Of course it's not as good as much more expensive solutions but it's very powerful for the price (£25 including 4 stepper drivers!) and not as useless as you might think but I will move to a breakout board solution relatively soon I consider it the least essential purchase right now in getting the thing built and cutting.

Ardunio and cncshield are also very good for testing nema's so when I do upgrade I will have a simple test bed for the recovered motor's I collect.

Just for clarity, I never said an Arduino is not a useable option, it's just not an ideal one.

grbl is very stable these days, maybe not the quickest of course but they are rock solid stable.

"The controller is written in highly optimized C utilizing every clever feature of the AVR-chips to achieve precise timing and asynchronous operation. It is able to maintain up to 30kHz of stable, jitter free control pulses."

And if you have a look at the grbl source, you'll see it's using a similar smoothing algorithm to Repetier (which incidentally has a nice explanation on how it works). It may be jitter free, but in order to achieve the jitter free, you have to compromise accuracy. And then to achieve the higher pulse rates, it starts scaling steps, so you loose even more accuracy, and introduce a certain amount of jitter.

If I didn't have as much work to do just now, I'd try connecting an arduino to a datalogger, and see just how jitter free the output really is.

P.S. the technobabble may impress your average arduino coder, but all they're ultimately doing is handling pulse generation in native AVR C, and relying on ISRs for timing. The only thing optimised other than good coding technique, is avoiding using C++ and the arduino compiler, which is inherently bloated.

[AcrimoniousMirth]

The CNCshield is designed for grbl which is cnc router firmware not 3d printing! It can pass up to 36v to steppers (It's designed for a hobby machine after all) but if you need 60v to the drivers you can do that easily as well. Most people use cheap ass Polou steppers which are not suitable for 36v but you can get a lsightly more expensive driver than will push 36v fine or wire a real driver to replace the cheap chip drivers the cncshield is designed to take on board.

Of course it's not as good as much more expensive solutions but it's very powerful for the price (£25 including 4 stepper drivers!) and not as useless as you might think but I will move to a breakout board solution relatively soon I consider it the least essential purchase right now in getting the thing built and cutting.

Ardunio and cncshield are also very good for testing nema's so when I do upgrade I will have a simple test bed for the recovered motor's I collect.

grbl is very stable these days, maybe not the quickest of course but they are rock solid stable.

"The controller is written in highly optimized C utilizing every clever feature of the AVR-chips to achieve precise timing and asynchronous operation. It is able to maintain up to 30kHz of stable, jitter free control pulses."

Well said! I'd like to add that it's even cheaper than £25 now! CNC shield and Arduino UNO coming to about £10-15 total now including the cheap pololus.
I knew I'd be using NEMA23s (part of the limitation of me recycling old bits) so I reused some old DRV8825 drivers which as you say are capable of 24-36V and higher currents, so are suitable for the NEMA23s. Those back in the day would've cost me about £7 so you're right, cheap as dirt for hobbyists :)

[AcrimoniousMirth]

The problem with CNC machining, is it usually requires far faster and more accurate motion than 3D printing, and an Arduino is not really up to the task.
Even an ARM processor isn't ideal, as getting jitter free motion needs good clock scaling, which can be handled far better in an FPGA, which is why you'll find nearly all CNC motion controllers use an FPGA for motion generation, often paired with some form of microprocessor which handles communication and the maths for generating the motion paths, before passing the required motion to the FPGA.
LinuxCNC and Mach running via a parallel port also have the same issue, however they ultimately rely on using a sledgehammer to crack a nut, by throwing enough processing power at the problem, you can get it to work well enough it's not a problem.

And then you have the available hardware. Nearly all shields I'm sure have been designed with 3D printing in mind, where speed and acceleration requirements aren't that great, so 24V is acceptable. If you were to use those same speeds on any reasonably sized router or mill, it would be painfully slow.
Hardware really is a case of, you get what you pay for.

The other guy who replied makes some good points.
We are advised to use the latest uno as the clock is designed for faster rates. I can't say it requires "faster and more accurate" motion than 3D printing honestly, especially not at a hobby scale. My 3D printers has travel moves of 400mm/s happily, can print at a good 100mm/s and maintains accuracy on the micrometer scale without an issue. I haven't had much experience with CNCs but in general they seem slower than my printer and the bits larger than my nozzle, rendering certain forms of accuracy less reliable.
Naturally if I wanted to invest several hundred in a CNC I would so and the quality would be much better. However I don't. This is a hobby build from scraps and cheap pieces that'll get used for sure, but not that much, I'm guessing.
Ah, many shields ARE designed for 3D printing, but that's why you make sure to get a CNC shield, designed for higher power throughput. My RAMPS board is designed for 12V but I easily modified it to 24V. However I still wouldn't use it for CNC work as half the stuff on it isn't needed. The CNC shield is capable of up to 36V, adequate for a hobby machine, and plenty for what I need.
I should note again, this isn't an industry scale or quality machine I'm aiming for. I just had a fun idea to reuse some old scraps lying around and it'll be an entry point for if I do want to create something more professional! 3D printing is my real joy but there's nothing wrong with expanding my skills, knowledge and tool bank :)



Honestly, what I really would need guidance on is the homing sequence. If I'm understanding what I've read correctly; the XY are homed to the 0 corner on the machine in "machine coordinates" and the Z (spindle) to its upper limit, also 0.
As the machine knows the maximum cutting depth (Z max) once you've put in your cutting bit you then jog the tool down till it touches the top of the material you plan to cut. This then gives the machine the "cutting coordinate" offset 0 from world coordinate 0.
Knowing the maximum depth and that this new machine coordinate = cutting coordinate 0 it knows the new range in which to cut.

Correct?

So in practicality, the machine is homed to a designated corner with the spindle at its highest, material is clamped, cutting bit inserted and jogged down to touch the material and that then registered by the machine, then cutting may begin.

This is my one true sticking point, the rest I'm comfortable with now that I know the shield isn't feeding the Arduino too.
Thanks for all the help :)