Grizzly G1006 Milling Machine CNC Conversion

BigJohnT wrote:

I didn't see the modbus protocol in advert.

Fourth item down, under Feature.

RS485 communication port, adopting standard international MODBUS main circuit control

andypugh wrote:

I think Jon Elson has mentioned one type of Chinese VFD which claims to support Modbus but doesn't in practice in any useable way.

That would probably be THIS VFD!

But hey, the eBay ad did say that it's "adopting standard international MODBUS main circuit control". International standards are good, right?

It looks like all VFD manufacturers would use the same Modbus protocols. Then again, it looks like the average consumer wouldn't need a PhD in electrical engineering to get their TV and DVD player to work.

I'm an electrical kinda guy. I tend to agree with Byte magazine's resident hardware hacker, Steve Ciarcia, circa 1978, who said, "My favorite programming language is SOLDER."

Some variant of Andy's simple optically isolated PWM voltage to frequency converter to generate the 0-10V analog velocity control voltage is sounding better all the time. I already have the VFD, and I probably have all of the electronic components somewhere in my 1200+ organizer drawers.

But at the moment, I'm going to wire up a power supply, a stepper motor controller, four series-parallel connected stepper motors, and a different LinuxCNC PC to test the drive system that will raise and lower the bed of the laser I'm building! Fun! Fun!

I should be posting pictures and video soon.

Until then, here's the LinuxCNC Modbus VFD link I referred to earlier. The page has links to examples of how to use Modbus communication from LinuxCNC to control VFDs from five different manufacturers (none were the inexpensive Chinese VFD on eBay, so it may be the one that doesn't implement Modbus control in any meaningful way).

wiki.linuxcnc.org/cgi-bin/wiki.pl?VFD_Modbus

The following wasn't very encouraging, either:

Because each VFD maker implements Modbus differently, a custom HAL component will most likely be needed for each VFD model.

When I decide to have LinuxCNC control the spindle speed instead of manually controlling the spindle from the VFD front panel, I'll probably use a pulse width modulated signal on a LinuxCNC output pin to generate the 0-10V analog velocity control voltage to set the spindle speed.



Z Axis - 5 Inches Isn't Enough

There's an obvious That's What She Said Joke, there.

One problem with CNC on a bench top mill is that the quill travel is only five inches, and that's not much. It's a hassle with manual machining, too. If I want to use a long drill bit in an R8 Jacobs chuck after machining with an end mill in an R8 collet, I need to raise the head on the column, and that loses my XY zero.

I've been using collets to hold drill bits and most other tooling. It works fairly well, but I'd like to be able to keep the tool mounted in a fixed tool holder so it maintains its tool height, so I can swap tools and not have them drifting around in the Z axis. I bought some inexpensive import end mill holders. The quality is OK, but not great.

I spent a couple of hours tonight, looking at ER collet holders, including some nice looking versions from Glacern.com for about $90 each. Then I took another look at the Tormach Tooling System. The quality looks to be somewhere between the $40 import ER collet chucks and the $90 nickle plated ER chucks from Glacern. The price of the TTS ER chucks is about $60 each. They don't have the long R8 stalk sticking out the top, but they have 3/4" shanks that fit a modified R8 collet. They look like they'll be easier to swap and handle, and in the unlikely event that I'll attempt to make my simple version of a tool changer, they should be easier to drop and pick up than an R8 ER collet chuck, and there's more room to maneuver over top of the shorter TTS tooling than there is with R8 tooling.

www.tormach.com/product_tts.html

They also have TTS compatible set screw end mill holders for under $30 each, which might be good for 3/8" to 1/2" end mills.

In fact, there are a lot of different tools in the TTS stable, including tension/compression tapping heads, and a single carbide insert fly cutter that apparently has material removal rates approaching that of a shell cutter and it works well on low power spindles so it should do well on my 1.5 HP bench top milling machine.

Does anyone have any comments about the TTS, good or bad? I've heard good stuff so far. I'll google for the updated impressions before making a purchase.

My basic strategy for getting the most out of the 5 inches of Z travel is to keep all of the tools about the same length. In order to do that, I think I'll buy a large set of shorter drill bits, sold as screw machine length drill bits.

andypugh wrote:

There is a new generic modbus driver. It isn't fully signed-off and included yet, but if you fancy being a guinea pig:
sourceforge.net/tracker/?func=detail&ati...578419&group_id=6744

Wow! Less than five days old! That is NEW!

I'm not sure I'm the best guinea pig because I'm still a LinuxCNC newbie, but I do want to start giving something back to the community, and this might be an opportunity to start giving back. The concept sounds a lot better to me than tweaking the existing code examples from five other Modbus enabled VFDs. I took a look at the patch. 2270 lines of code. It definitely looked to be above my pay grade.

I have so many irons in the fire that I won't be getting to the LinuxCNC control of the spindle for at least a month, and realistically, more like three months. Some other noble adventuresome soul will have probably figured out the Modbus connection for the $117 Chinese VFD by then.

The advantage I see for adding a Modbus controlled VFD to my simple parallel port configuration is that the only added hardware is a $10 RS-232 to RS-485 converter. The rest is done in code, with no custom electronic hardware to build.

The disadvantage might be that the coded solution would probably need to be recoded for each new installation of LinuxCNC, although there would be a little bit of tweaking to get the PWM running too.

I should definitely focus on bolting on the stepper motors and getting this project moving, and worry about spindle control later. After all of these years, it's going to be so nice to have LinuxCNC doing the repetitive work. I'm so unrealistically optimistic of early success that I'm deferring some simple production work in the hope that I can do it as a CNC job!

andypugh wrote:

I am pretty sure that Stepconf knows how to set up PWM spindle pins.

I'm such a newbie that I consider that to be "a little bit of tweaking".



BigJohnT wrote:

I see I need to add a manual tool touch off to my tutorials...

It's difficult for someone with a lot of experience to mentally reset to the newbie mindset. A series of very rudimentary How To Use LinuxCNC videos on YouTube could go a long way toward helping those just getting started. Maybe one series for milling machines and another for lathes? A lot of us understand the concepts of CNC and might have even acquired some detailed knowledge of a few specific issues, but have absolutely no practical CNC experience. In other words, we're coming from an engineering background and not a CNC machinist background. What's really needed IMO is a brief CNC operator's tutorial from a LinuxCNC specific perspective. This would be a good project for someone to do immediately after they learned what to do. Obviously, the best person to make these videos would be an expert in CNC and LinuxCNC who was willing to make a "baby steps" video series, but the time of those people is better spent solving the meatier problems.

The novice generally doesn't know what he doesn't know, so he often doesn't even know what questions to ask.

YouTube and the internet are great educational tools, but our society has lost a lot by largely abandoning the apprentice method of teaching skills. It's hard to beat one-on-one hands-on training with immediate feedback and a focus on mastering the skills in a logical progression. A lot of my learning on subjects like this is gleaned from YouTube videos, which are hit-and-miss at best. I feel that I could have learned more in four hours as a machinist's apprentice than I've learned in over a decade of stumbling about trying to figure stuff out on my own or hoping to learn how to be a machinist by watching random YouTube videos.

BTW - instead of the dowel, I splurged and bought a real touch-off gage. I'm probably trying to compensate for my lack of machining knowledge by purchasing pretty tools.

www.edgetechnologyproducts.com/pro-touch-off-gage.html