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Proper answer would involve asking what exactly you want to run.

Easier answer, as much as you can afford.

What ram should I get?

Storing files would be whatever size SD Card you get for the Pi, it has nothing to do with the 2GB/4GB/8GB variants (those are designating the amount of RAM on the device)

How many GB raspberry pi do I need? Would like to store some projects files on it. 

As far as my testing has shown, on my cobbled together 7c81 clone SPI works on the RPi 5.
I received my RPi5 around Nov\Dec 2023 and can't say I've noticed any hardware issues. Booting from a NVME drive has shown no issues, I've run octoprinter on it, once again no issues.
Speed wise even when running via a SD card is night and compared to my RPi400, which has a slightly faster CPU than the RPi4. Actually to be fair it is a bit of a beast.
No trouble building Linuxcnc packages, even with 2 cores isolated, tho I suspect this may not be needed when connected to a Mesa board.
Bang for buck a PC from the last ten years is far better value.

Personally I'm still undecided whether to use my clone with an EPP interface with a PC or with the RPi5 via SPI.

To tell the truth I'm in 2 minds whether I actually want to CNC the lathe, the only reason I started to convert it is the AUD $600 to get hold of a new screw, maybe it would be worth it, if only to have one of the few Myfords with a leadsrew that isn't worn.

Back to topic.
Whilst the RPi is able to run Linuxcnc not a lot of info for the official Raspberry Pi foundation images are applicable, as it is only really the RPi kernel sources that are used, needed for use of loading overlays, the rest is pulled from Debian arm64 repos. Config.txt must be edited to enable the SPI interfaces. And Linuxcnc will need building from source to have the hm2_spix driver. Last time I looked the pre built packages pre dated the new driver.
Re Tommy's comment regarding a small SBC controlling a large CNC machine, how would you feel riding a bike at 220-240 kph ( on a race track of course) that's ecu is controlled by a Motorola microcontroller ? Cos that's the brains used in a lot of Ducati's and Moto Guzzis around 2000 vintage. Very hackable, very easy to download the operating code off and disassemble. Even a fully unqualified shit kicker like myself was able to do, the one and only time I did anything with C Sharp.

Your remedy is working as it should and now i can set correct value, thank You. But I forgotten to tell that linearity of voltage 0-10V is terrible, I used scale for make it "more linear" and that works like a charm. Before on raspberry pi 4 i didn't noticed that strange behavior, it was simple as that to calculate resolution etc, but I also didn't use qtdragon display, when I switched to rpi5 then I noticed those strange things.
Now I bend it little by cheat real max rpm so its almost fit, but I don't like doing things in a slapdash way.
Below table how analog output voltage works for me...
value [RPM] / VFD frequency [Hz] / Uout [V] .
3000 30 0.8
6000 93 2.36
12000 220 5.6
18000 350 8.6
20000 396 9.6
21000 400 9.7

Not exactly sure what this is all about, but
1. RPI is not a good choice anymore, there were several hardware versions of RPI5 with many issues
2. There is a ready made image for RPI5 that works out of the box
3. SPI does/did not work at all on RPI5, but Scot has done some work on it so by now it probably works
4. To expensive for what it is
and personally (after buying 3 of RPI3)
5. having a very small SBC controlling a big machine is ...
6. to damn weak for comfortable use
7. to much hoops to jump just to get things working, so utmost respect for whoever made the images
8. for the same price a good used PC or laptop can be bought, and everything works.
-
As for making user experience better, utmost respect, see with ScotA if he needs help with SPI

Thank you cornholio.

I'm looking to cut wood for building boats.

If I run into issues doing the above well, I earned a living doing Unix driver and kernel work a while ago; I would like to contribute now if I could. I have experience with a number of device driver debugging and kernel development techniques.

Let me get some hardware and software in. Again, if there is a certain feature that doesn't work that should work, let me know.

Thanks,
Tom Alborough

You coming at this arse about. Which makes me wonder if this is for academic purposes, a potential commercial endeavor or a tech blog.
First one decides on the type of cnc machine they want to build, then they choose the controller to suit.
The simplest entry point for one who has no plan for their actual "cnc machine" would be.

A Lenovo M73e tower, preferably with an i5, the appropriate MB to Parallel Port cable ( there's some trickery with the cable that enables the PP hardware) and a generic Parallel Port breakout board. I've recommended this combination as I know it works, I have tested it with a lathe for basic functionality. I actually found this machine on the side of road with a celeron processor, which I swapped out for an i5 (3470 I think) and an SSD from the "useful box".

What people want is something that will run their hardware (their cnc machine be it a plasma cutter, lathe, mill router, laser tube profiler, PnP machine, cnc soldering machine) at a price point they can afford. As you can guess this is quite an expansive list.

Hello cornholio,

I get your point.

I would like to buy (some kind of a) Raspberry Pi 5 and the electrical hardware needed to make a CNC machine. The reason I'm writing to you is to ask you this: What should I buy? I'm not looking for a configuration that works. I'm interested in a configuration that people want to work. What hardware do the readers want to load software on and run without any hitches?

Thanks,
Tom Alborough

If you want true "as easy as an installing an app on your cell phone" buy a commercial cnc machine from one of the Big Boys.

This is all I have left to say on the matter.

Hello cornholio,

Thank you for your reply!

I see your point about "AI".

In your reply you separated the "CNC" part of the task (feed speed, etc.) from the "system" part of the task (boards, drivers, etc.). I agree with your split and then assert the "system" part of the solution should "just work".

LinuxCNC on Pi 5 should work as easily as say Google Maps on Android, with no system experience required to install and use the application.

Do you see folks in this thread who believe a better experience is possible? Who exactly would champion a better experience for Pi 5 and LinuxCNC? I believe many of the people who answer the system questions posed in this thread would also be contributors to an effort to revise the code. I have seen similar efforts succeed.

Let me know!

Thanks,
Tom Alborough

Economically the RPi5 or RPi4 is not a great choice when compared to an ex corporate PC. The only advantage is a very small foot print and the ability to use a SPI interface board.
 

Hello cornholio,

Thank you for your response!

Have you read the entire thread ? I have browsed the beginning and the end of the thread. I noticed the need for both new and experienced users to ask for and get high-level support from this thread. My observation is that over time, it would be good for the need for high-level support to go down rather than stay the same or go up.

I have seen situations like this and I have seen a group of people improve the situation. I would be happy to talk more about it.


Have you downloaded and written the LinuxCNC image to an SD card ? I have done the exact same thing with a variety of mass storage devices and operating system images.


What hardware are you wanting to use ? I haven't gotten to with that yet. My observation is that (ChatGPT) is warning people away because the Pi 5 / LinuxCNC combination has issues.


What is your end goal ? I would like to buy (a Pi 5) and some popular controller and stepper motor hardware and load LinuxCNC with as much as much of a chance of success as loading and running an application on my cell phone.

(-- Out for the evening...)

Thanks,
Tom Alborough

Have you read the entire thread ?
Have you downloaded and written the Linuxcnc image to an SD card ?

What hardware are you wanting to use ?

What is your end goal ?