Grizzly G1006 Milling Machine CNC Conversion

I already have LinuxCNC 2.51 installed in the $50 Craig's List PC, with a good latency test. I did an overnight memory test to make sure the memory was stable and there were no intermittent bit flipping errors, but I haven't done a two hour latency test. I have read about some "once a day" sort of latency problems, so I'll do the extended latency test.

I was considering the simple open loop stepper solution first, but I thought I'd pick the collective brain to avoid unwiring everything when I wanted to add encoders later.

I looked at the many offerings from MESA, but didn't see anything optimized for my unusual configuration with stepper motors and encoders. They have a good solution for steppers (5i25+7i76) and there's a good servo and encoder solution (5i25+7i77). I guess I could get the 7i77 solution and just leave the stepper motors connected to the parallel port.

I wasn't so much wanting the encoders to close the loop on the steppers and run them like servos. I mostly wanted the encoders to detect a rare following error, fault out, and stop the machine. I'm leery of open loop machines that could hit some harmonic zone, lose a few hundred steps, and then continue machining with a gross positional error like nothing ever happened. I won't be running this thing unattended for hours. It ain't that kind of machine. My jobs run for a few seconds or a few minutes. I'll be there as a part loading monkey, so I can detect any problems related to open loop operation. My parts are inexpensive, so the occasional scrapped part won't make me suicidal.

With the beefy 1600 ounce inch stepper motors, I may not need to worry too much about encoders to detect lost steps. The open loop stepper motors and manual spindle speed control may serve me well for a long time, and ultimately may be all that this import mill deserves. I'll probably want to upgrade to inexpensive ball screws, but all of my current production work is linear motions and the backlash isn't a problem. I could probably program the huge backlash into LinuxCNC as a backlash compensation to make it easier to write my point to point G code programs, lube up those Acme screws, and keep on truckin'. KISS.

I'll post some pictures when the stepper hardware arrives later this week, I'll post pictures and drawings of the motor mounts I create to mount the NEMA 34 motors, and I'll post a video of the machine making parts.

I guess it's time to buy another Sam's Club roll around tool cart to house the CNC electronics and the CNC PC, and find someplace in my cluttered basement shop to put it.

I was hoping that LinuxCNC supports a simple frequency to voltage converter. This is exacly what I was hoping to see. Thanks Andy. At the very least, you definitely saved me some googling when I got around to the VFD implementation. I'm trying to take this a step at a time, and I'm still at the stage where I'm making motor mounts. I hope to have simple XYZ motion in an evening. I'm trying to get this CNC conversion done as quickly and as easily as possible. I have many other not so easy CNC projects underway and I'm trying to get this machine to CNC productivity with the minimal distraction to the other competing projects.

I'm an EE, so the circuit is actually less valuable to me than the confirmation of the PWM signal generation in LinuxCNC. I may make am op amp circuit that can generate +/- 10VDC or 0 to 10 VDC and publish it for others to use.

My strategy will probably be to get the new spindle motor mounted and running from the VFD. I already ran the 220 VAC outlet for the milling machine when I installed the outlet for the lathe, so that unpleasant task is done. I'll get the VFD running in manual mode from the front panel and it'll be very usable for my simple needs. Then, I'll get the spindle under LinuxCNC control with PWM with the current VFD, or I'll buy a new VFD and use Modbus via the RS-232 port, through a converter to RS-485... whichever looks easier. I'm all about easier..

Thanks!

I looked into the Automation Direct GS2 VFD for my 1.5 HP spindle. The 2 HP GS2 is $251. That made me wonder if the $117 Chinese VFD with the Mitsubishi chip uses the same Modbus commands as the GS2. I bet it does. The GS2 looks a bit nicer, but they're probably both made in China. For my el cheapo milling machine conversion, I wouldn't mind saving $134.

I noticed that there were examples of using several different VFDs under Modbus control. I took a quick look at the GS2 version, but I need to compare them to see if the LinuxCNC side is similar. Or are there VFD specific Modbus commands? Even if so, I should be able to use the other example code and the Chinese VFD manual to make my own version and add it to the list for cut-and-paste support for the inexpensive Chinese VFD. BTW, what I've been calling the Chinese VFD is manufactured by Huanyang Electronics Company Ltd. Here's the current eBay auction:

www.ebay.com/itm/300652886556

My import mill has a belt driven spindle. I'm using Jon's clever dual gear tooth detector to generate a quadrature encoder on my lathe spindle. I could probably notch the spindle V-belt pully on my milling machine and use the same method, or laser cut a black polycarbonate disk for the spindle pulley and use optical switches in a similar configuration to make a quadrature encoder for the spindle, but I doubt I'll be doing any rigid tapping on that machine! Barring that, a simple one-pulse-per-revolution sensor could be fed to a LinuxCNC counter encoder to verify a rough spindle speed.