About to take the plunge - Need some Design Guidance

Hi all, have been lurking on the site for a couple of months and recently kicked off my LR2 build.

Nearly completed 3D printing the plastic pieces (Ryan, these are a true work of art and engineering…amazing!)

I have a plan in mind for my table, and a lead on where to source my tubing in NJ. What I need help the most with is the control system.

I plan on buying the LR2 Kit from this site, but, I’m intrigued by the OpenBuilds Black Box having read through a lot of posts here and elsewhere that mention it.

Here’s what I think I want to have in this build, and why.

  • Auto-squaring. I just got into 3D printing back in December, and while I was researching I determined that auto-bed-leveling was very important to me. I’m not a super precise person, so it seemed smart to be able to compensate for my sloppiness using technology wherever possible. That’s why I wanted an affordable 3D printer with a BL Touch and a larger build area and why I landed on a CR-10 v2. The BL-Touch install was a piece of cake (once I flashed to a Marlin firmware). I assume that I’ll want to have dual end-stops on the Z axis and at least one end-stop on X and Y for this?
  • Z Probing. (Possibly X and Y probing too) This just makes sense to me for both one-off jobs and repeat jobs. Tool change or not, having the ability to accurately set the Z0 at the end of the cutting tool just seems like something you’d want to do.
  • Raspberry Pi with a Touch Screen. After setting up the BL Touch, the first thing I did on my 3D printer was set up Octoprint on a Raspberry Pi and use that to control every print. I’ve never looked back, and can’t imagine having to load gcode to an SD Card every time I want to print. I want the same workflow for my CNC - design on PC, export code, send to a server and then go cut at the machine. CNC.js looks like the right thing for this.
  • GRBL. Here’s one where I’m not super confident why I want it, it just appears to be more standardized and CNC focused. I don’t doubt that you all have done great things with Marlin, but it seems like a force-fit. (Having to fake having an extruder, etc.) I get that 3D printing and CNC are very similar, but having to do a bunch of Marlin / firmware editing to get the desired hardware capabilities is not part of the hobby I think I’ll particularly care for. Happy to be proven wrong.

Based on that, should I go with a full Rambo board or the OpenBuilds Black Box?

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I don’t have first hand experience with the black box. So beware of this opinion.

Let’s assume you went with the dual endstop rambo. There isn’t preconfigured firmware for dual endstops on the LR, because the Z is doubled, instead of the Y. So you’d need to flash it yourself. But after that, you would have auto squaring on Z and X. But you would lose the ability to probe in Z (there are G38 commands, but I’m not sure how all of that would work). You can attach a pi with octoprint to it, but you’d want to bring your own touchscreen (like your phone or a tablet) to control it. The v1pi image I made has octoprint and cnc.js if you want to try that.

Now let’s assume you went with grbl for the rambo. It has dual endstops, which you’d need to configure for dual Z. I am not sure, but I don’t think it will support a Z probe in addition to dual endstops in Z… octoprint isn’t very compatible with it (although there are some plugins, so maybe). But cnc.js on the v1pi would also work there. Grbl has much fewer users than Marlin, at least around here. So you’d need to be more DIY to get it going. Marlin isn’t cnc focused, but Ryan and others have done a great job understanding it, and it is really reliable. Laser engraving is the one place where I would prefer grbl, but I have ran both, and I use marlin now. Mostly because of the high frequency of updates, and compatability with boards.

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I also need to mention, that auto squaring is not as big of a deal with a LR as it is with a 3D printer. After the motors are enabled, they move in lockstep. So if you start them square, they will stay square. If you have a 12"x12" MPCNC, then an error of 1mm is enough to care in many cases. A 1mm error over 60" is not going to matter.

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Fwiw, a couple people have gotten z probing to work completely on the lowrider. I got it going in the z direction with auto square on z and the long axis.
Apparently you’ll need to define the pin for the probe. It’s ok if you define z min, which is the default, but there is a bug (or feature?) that if using the z min as the default, probing x, y doesn’t work. Defining seems to. I haven’t gotten as far as fixing mine yet, because I’m more concerned about keeping the stock square to the table.

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