Been following this site for a little while and about the time I registered here I had built myself a Grizzly 8689 cnc machine. Well shortly after I built it I ended up getting rid of it for various reasons. Anyways, I ran across a LMS 3990 the other day and purchased it today. So I got the LMS with a CNCFUSION kit, 270 oz. Kellogg steppers, controlled by an Arduino/GRBL setup in an Automation Technology case, and came with all the factory parts and manuals. I ended up paying $1200 for everything.
Now for some questions. What kind of limitations come along with the Arduino/GRBL setup? I feel the steppers are a little small esp for the Z, correct me if I'm wrong. I still have Mach3 CamBam and Cutviewer,, so am I going to be in need of a system change if I want to run the Mach3 instead. If so would love to hear a good recommendation as I can't seem to remember much of my prior research on this stuff. Any help or would be greatly appreciated.
Thanks Guys
I have been using Grbl for quite some time and it is very stable. I will list the pro's and con's as I see them.
Grbl pro's
1. Stable and clean step pulse train. Grbl on the Arduino is doing nothing else except running the machine. It is not running a bloated operating system, so it isn't being diverted to doing other stuff. This in my opinion is a huge benefit.
2. Grbl only relies on a simple serial stream from a host. The stream is loads faster than required, so isn't a problem. The serial stream doesn't have to have superior timing because it doesn't affect the stepper timing. Stepper timing is all handled by the Arduino and Grbl.
3. Since Grbl only requires a simple serial stream, the host computer feeding it can be just about anything. I personally use an old low power netbook and it works fine. You aren't limited to desktops like many recommend when running PC based step generators. Like I said, I use an old netbook, so don't have to have a giant desktop PC attached to the machine.
4. Grbl is basically an external step generator that costs about $5
5. There are many interface programs that work with Grbl. GrblGru is pretty impressive and you can read about its progress here on CNCZone. There are many others though. I actually wrote my own which adds back in the missing canned drilling cycles.
Grbl Con's
1. The G-code set is limited, but it has all of the basics. If you don't plan to hand code this isn't really a problem for milling since the CAM software can generate complex shapes using the command set that Grbl does have. The biggest thing it is missing is canned cycles, and cutter radius compensation. If you don't use them then you won't miss anything.
2. The official Grbl firmware is only 3 axis. However, there is a 4 axis port for use on the Arduino Mega 2560. The Mega only costs about $7
3. there is no spindle synchronization, so Grbl isn't a good choice for a lathe, but for a mill you can survive without sync.
4. Grbl is limited to about 40kHz step rate. Officially it is stated that the max is 30 kHz, but my testing has convinced me that 40 kHz can be done. My G0704 runs 0.2" pitch ballscrews at 1/8 microstepping and I can reach 200 IPM and only be at 26.7kHz.300 IPM would be 40 kHz and I did successful testing at that, but can't really run there because I had to have the gibs too loose.
Here is a little video of my G0704 running both LinuxCNC and Grbl. Grbl run the same code faster in the video, but LinuxCNC has since got an upgraded planner and LinuxCNC and Grbl are at the same cycle time now.
I would recommend giving Grbl a try before discounting it.
LMS 3990 purchase. How'd I do?
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