I/O Interface Board Recommendation For Lathe

I just joined here. I've been using EMC (still on 2.2.8) on a mutt mill for 4 or 5 years. I just found an Emco Compact 6 lathe that I'll be retrofitting using the Mesa 5i25 and 7i76 with servos on Geckos. I run a Clausing 4900 for my manual lathe, it is a nice machine. I have a chinese 9" machine I was about to convert when I found the Emco with a turret toolchanger. The only thing stopping me on the Chinese machine conversion was finding decent ball screws at a decent price. It would also have had 8" of cross slide travel for gang tooling, although I'd like to see more.

Regarding the Mesa 7i76. Am I misunderstanding that it is setup for a gecko drive servo type arrangement (no feedback to the PC)? I'd love to go real motion control with direct axis position feedback, but I think that might be beyond my ability in software and cost.

Greg

andypugh wrote:

Crikey! Have you any idea how many bugs we have fixed since then?

Some people prefer the bugs they know to the process of finding new ones.

I saw that $233.14 was billed to my credit card the evening of Friday, November 18th, so I assume that my Mesa 5i25 and 7i76 and cable have shipped. I placed the order on November 1st, but I was advised that there would be a delay because it's a new product, and I told Peter that two or three weeks wouldn't be a problem, and sadly, I was right. I'm still finding an hour or three on most days to piddle on the lathe CNC conversion. I removed the FORWARD/REVERSE switch and interlock hardware from the headstock the night before last. I won't be needing that. I cleaned up the area inside the headstock and took a good long hard look at the various options for the Z axis servo motor mounting. I may move the spindle speed gear tooth counting sensors inside the headstock where they would be even better protected and probably easier to wire.

I continue to be very impressed with the quality of the old Clausing lathe. I don't think anything is made with that much attention to detail and bomb proof durability anymore. We live in a throw away world. If I had it in me, I'd sell my Grizzly bench mill and buy an old Bridgeport or equivalent milling machine from the same era to convert to CNC, but the thought of trying to move my old milling machine out and a new one into the basement makes me ill.



dieselpilot wrote:

Regarding the Mesa 7i76. Am I misunderstanding that it is setup for a gecko drive servo type arrangement (no feedback to the PC)? I'd love to go real motion control with direct axis position feedback, but I think that might be beyond my ability in software and cost.

Against good advice and my own better judgment, I'm going to try the simplest servo setup first. I already bought the Gecko 320X servo drives, so I'm going to try to let EMC2 talk to them with open loop STEP and DIR pulses, and have the servo drives monitor the motor encoders which will not feed back to EMC2. Again, EMC2 will be running open loop control, just as it would with steppers and no encoders. However, the Gecko drives should be able to get a lot of torque out of the servo motors because there is no concern of missed steps. The servo drive will be operating closed loop with encoder position feedback. The question is whether the Gecko drives servo control algorithms can handle the task. Basically, EMC2 will tell the Gecko drives where to be and when, but there are essentially two sequential control operations. EMC2 tells the Gecko drives what to do, and the Gecko drives tell the motors what to do. This necessarily introduces additional delay into the overall control loop, That delay can cause feedback. If the two control loops have enough delay that they can become out of phase, they'll oscillate with continuous over corrections in both directions. I think Gecko makes good products, and they must have this problem fixed in some combination of servo autotuning and maybe some clever algorithms that prevent oscillation or otherwise manage the following error. At the worst case, the following error is adjustable and I should be able to set it so it won't oscillate yet will hopefully be accurate enough for the parts I want to make. At the very worst case, I should be able to have EMC2 monitor the following error and shut down if it's too great.



In other news... I stumbled upon a brand new Baldor motor on eBay a couple of nights ago and I bought it for my future milling machine upgrade. I needed to replace the single phase spindle motor with a three phase motor so I could control the spindle speed with a VFD. The Baldor is a 1.5 HP motor. It's brand new, still in the stretch wrap. It has over sized bearings on both ends. The Baldor website says the MSRP is $557, and I got it for $53 delivered! Sweet! It arrived today, and not only does it look like a $557 motor, but from a cursory glance, there's a chance the motor base may be bolt-on compatible with the existing motor. It's hard not to get side tracked converting the milling machine just enough to get variable speed control without moving belts on pulleys, which seems like 1950s Third World nonsense.

andypugh wrote:
Crikey! Have you any idea how many bugs we have fixed since then?

Yes, actually I saw the update list a couple months ago and began thinking it's time to update. It's on my list. My setup is very simple and I haven't run into any issues.

7i76 and servos isn't a natural mix. Anything which goes from step to servo puts the controller out of your hands. EMC2 normally works best with analogue or digital links to the servo drives, and the PID in the PC.

I might be misunderstanding something. I looked at the 7i76 and I thought it would be ideal as a breakout board for the Gecko servo drives and gives me all the I/O I'd need. My mill has the Geckos wired directly to the parallel port. I want some safety so the two machines don't blow each other up if there is problem. I get very good results from my mill, Aerotech slides on all axes, no backlash, 1000 line encoders with direct drive motors for 2um resolution. All three motors have tachs, so I might look into doing a different system in the future.

The original setup on the Emco lathes is open loop 5 phase steppers on a reduction to the ball screw. They are said to be very accurate and repeatable. I'll have to look into the kind of resolution it had, before deciding on the encoders and whether or not it will be direct drive. Compared to open loop steppers I can't be much worse off? I guess that's not the case. Steppers have to be within a very small angle of commanded(if it's not losing steps), where as the Gecko setup could be 256, probably much less, encoder counts out at any given time.

If I understand Geckos, they try to move the servos according to what EMC sends. Gecko keeps track of location. The old G320 I have could only fall behind(or overshoot) 128 encoder counts before faulting. In my case this would be 0.256mm or .010". Is there any way to check the following error using the existing encoders, has anyone done it to see how well it works? In practice I don't have any issues where I think this is a problem except one area. During a rapid retract from hole milling the tool will occasionally clip the edge of the top of the hole. I'm unsure if this is due to the following error, my clearance plane is much more than the 0.256mm. I mill in G64 and that's something I've been meaning to look into for a while. The current 320X has selectable 256, 512, 1024, 2048 count allowable following error before faulting. The more I think about this, the more I talk myself into real time feedback for the lathe. I just have no idea what it takes and the programming of the components scares me.

Is there any benefit to running C1 or C3 ballscrews instead of C7 with compensation?

Sorry for the random questions. I probably need to dig up a thread on setting up a live closed loop system with Mesa cards.

Greg

Any reason you are set on closed loop? The stock steppers were not very powerful, and performed great. $79 will buy you a stepper with 2x the stock torque, and the 201x drivers with 1/10th micro stepping are cheap and reliable. The machine just isn't heavy or fast enough to justify closed loop costs.

-Sam

I have my MESA I/O boards, so I should probably let this thread die, but I hate to start a new thread for my lathe CNC conversion. Maybe I should?

This may be a boring video for many of you, but it's a big deal to me. My lathe is finally connected to 220 VAC through an inverter, and it just turned under power for the first time. While it was turning, I made my first ever lathe machining operation.



Yeah, I'm doing a CNC lathe conversion when I am not even a lathe operator. This is going to take a little while to safely climb up the steep learning curve.

Hopefully, now that my lathe is finally running, I can do the CNC conversion in bite size chunks, with a little reward after each bite when I add a new feature that's useful.

I may try to make a simple turned plastic tool later today, when I get back from Christmas with the whole fam damily.

The spindle seems to turn at the proper speed and hold speed under a light load, but I can stall it by hand. There's probably a current limit programmed into the VFD (inverter) as a factory default that prevents burned up motors. I seem to remember reading that in the manual a month or so ago when I got the VFD. I have a 2 HP inverter and a 3/4 HP motor, so I think I'll need to set the current limit to match 3/4 HP. That may ramp up the speed faster, or the ramp time may be another programmed parameter in the inverter.

The HY02D223B inverter is made in China and seems OK so far. The manual is Chinglish, but I'm fairly accustomed to that. If this internet thing keeps up the way it's been going, pretty soon we'll all be speaking some mishmash of various languages, like the street slang in Blade Runner.

BigJohnT wrote:

Do you have EMC controlling the spindle?

Not yet. I don't even have a breaker or motor starter controlling power to the inverter. Motor speed control is currently an awkward front panel operation on the VFD. I think I can make it easier with the JOG button, but I haven't played with that. I can also put a potentiometer on the inverter for a speed control.

What's next on the list?

What's next? Getting EMC to control the spindle speed?

Short term, I need to program another parameter in the VFD to allow greater motor current. The speed is fine but the torque is weak. Then I need to center drill and tap that UHMW dowel, turn it over and face off the other end and maybe chamfer the edge to make a production tool to cut rubbery tubing. Then I have a much smaller version of that tool to make. That's the "getting to know you" phase of my relationship with my new lathe.

Longer term, I'm at the point where I have most of the electronics, so I need to draw a schematic, then stare at the electrical enclosure and decide where everything goes, put it there, and start wiring!

I'll probably give first priority to installing the three gear tooth Hall Effect sensors that will comprise the absolute quadrature encoder that will allow EMC2 to control spindle speed. After that, it's limit switches, mounting the servo motors and driving them via EMC2. Simple, eh?

I wonder if I'll get around to the EMC2 part before there's a live CD with EMC2 2.5 that can talk to my MESA hardware.

The lathe looks a bit rough, but the electronics should be top shelf (other than my Chinese VFD). All control electronics will be mounted in the big bottom drawer of the roll around cart, with muffin fans for cooling. I have Igus cable track to allow the drawer to open and close. Pimp stylin'. I'm an ELECTRICAL engineer, so the parts with the moving electrons must look good!

get inserts designed for cutting aluminum the ones with the honed and sharpened cutting edges for cutting any plastics.

I know that carbide inserts designed for cutting steel have relatively rounded edges to avoid chipping, and they aren't good for cutting plastic, or making light finish cuts in steel for that matter. I don't currently plan on any production plastic parts, and these initial plastic machining jobs are the very definition of low tolerance. I have filed your suggestion away for future reference if I do need to cut plastics. This forum won't make me a machinist, but I have absorbed a lot of good information online.



It's Christmas night. I'm going into my basement shop now to play with my toys.