G0704 CNC AC Servo Rebuild (Picture Heavy)

plastic sheeting and wood framing
Clear shower curtain + 1" PCV pipe + fittings = disposable enclosure. Shower curtain is already reinforced at the top and has holes for zip ties.

Should last a couple years until you get around to building something swank.
 
God that's pretty machine. Can't wait to get a shop tour!
That's the one I built last year. Buddy wanted one so we just dived in and now his wife is runing the business making signs. He built the frame, and I built all the motion hardware/rails/drive system and the controller. It's had over 30k pierces since we built it without a single issue. He also has a big brake now so we can make enclosures...

In the middle of a much larger, higher-end plasma now. It'll be 6x12, DMM servos, with a built-in bridge crane and running under UCCNC.

Sorry, not to hijack the thread but I can't stand hearing you whine about not having access to equipment just up the road from you. ;)
 
In the middle of a much larger, higher-end plasma now. It'll be 6x12, DMM servos, with a built-in bridge crane and running under UCCNC.

That'll be quite the sight! I wouldn't even know where to put something like that.

Sorry, not to hijack the thread but I can't stand hearing you whine about not having access to equipment just up the road from you. ;)

It's just that every time I whine, I find out about a new machine that you have!:D
 
So, almost a year since my last check in on this thread. I've been using the machine quite a bit and I've been super happy with it. I have made 30-40 different parts for a steam engine I'm helping a buddy build and it really does nice work.

A while back I posted about the work on this machine and the LUA code, so I figured I'd update that checklist:
  1. Rebuild spindle - DONE
  2. Install spindle motor, belt drive, and drawbar - DONE
  3. Remove old CNC components - DONE
  4. Install axis motors and mounts - DONE
  5. Install electrical cabinet - DONE
  6. Install limit/home switches - DONE
  7. Install wireway and cable routing - DONE
  8. Install touchscreen computer - DONE
  9. Migrate to Mach 4 - DONE
  10. Validate system functionality - DONE
  11. Performance characterization - DONE
  12. Mach 4 Pendant Configuration - DONE
  13. Mach 4 LUA Scripting & Servo drive serial communications
    1. Pneumatic drawbar release - DONE
    2. MPG functions - DONE
    3. Cycle start, hold, and stop buttons - Still haven't used these, the touchscreen computer is fine for what I do.
    4. Spindle Enable/Disable - Removed this, don't want it
    5. Spindle Orient - Removed this, don't want it
    6. De-ref all when disabled - DONE
    7. Auto Enable Soft Limits - DONE
    8. Power On cycle/Start-Up Menu Script - DONE
    9. Stop machine for faults and alarms - DONE
    10. Drive Serial Communications - DONE
    11. Spindle Load Meter - DONE
    12. Absolute Homing - DONE, slightly buggy, discussed below.
    13. Rigid Tapping - Code is there, but never scripted the G/M codes and never tried it
    14. Gear Hobbing - Code is there, but never scripted the G/M codes and never tried it
    15. Fix Cycle Timer - DONE
The Absolute homing script is the coolest thing I've added to this machine and I use it constantly. I do have one gripe. Sometimes, one of the axes fails to update with the number received from the drive, but marks itself as homed (rather than failing if the drive returns a bad serial packet, which does happen rarely and works). If I keep hitting the button 2-3 times, then all the axes will home correctly. I've been doing the lazy thing and just homing 4-5 times, but I really should investigate this issue.

The 5000 rpm spindle and load meter are awesome and I've had zero maintenance on it this entire time. The pneumatic drawbar is my favorite addition to the CNC and I am constantly using it.

The ballscrews and the flatness of the ways are the worst part on this machine. I think if I could get the machine ways ground or scraped and replace it with some nice double nut ground ballscrews, the machine would be much more accurate and rigid.

I've thought a lot about getting another larger CNC, but the truth is that for a lot of what I do, I would prefer a manual mill for quick setup and stock squaring. I mostly need a simple drill press setup or a facing cut and taking the time to boot the CNC or write a program isn't worth it. I may be moving soon, so adding a bridgeport to my shop will be on my mind.

Thanks again to everyone for following along with me on this thread!
 
Wow! 2.5 Years since I last posted on this thread. I thought it might be a good chance to look back on the CNC conversion and discuss what works well and what does not.

I should note that I have used this machine a TON over the past 10 years and expect to be using it long into the future. Even imperfect as it is, it has enabled me to do so much with my hobbies.

The Good & The Great:
  • Mach 4: Love this software and it has enabled me to accomplish any feature on my machine that I wanted to add. The software is well featured and miles beyond where Mach 3 left off. My only gripe is that the software can become corrupt after a power loss if the computer does not shut down correctly. I wish they would fix this, but for now I have a backup of my machine profile stashed on a flash drive in the machine enclosure. Only happened once in 3 years.
  • Ethernet SmoothStepper (ESS): In my opinion, this remains the best motion control board for high performance Mach 4 machines. The ESS offers the most inputs and outputs, as well as the highest output pulse rate, needed for high resolution servos. Unfortunately at this point I've managed to use every input and output. Hoping they release an option to link multiple ESS's to one Mach 4 profile for additional I/O.
  • AC Servos: the choice to use AC servos on this CNC is one of the best features on the whole machine. The high speed, high resolution, and excess of power give very high fidelity motion control. The servo drives have given me nearly zero issues since I installed them. The high accelerations that these motors provide drastically improves cycle time; much more so than simply higher rapid speeds.
  • 5000 RPM Servo Spindle & Belt Drive: the spindle changes have greatly increased the functionality of the machine. The belt conversion is very quiet, and the 5000rpm capability is very well suited for the smaller tools required by this machine with mediocre rigidity. I'm currently looking at modifying this design to trade off torque for increasing the speed. A fair bit of effort was done to enable servo positioning of the spindle for indexing and rigid tapping. Truth be told, I have not used any of the "position servo" features of the spindle to date, but the compactness, power density, and speed of the AC servo has absolutely been a worthwhile feature.
  • Power Drawbar: The Hoss Machine designed 3 stage air cylinder and pneumatic drawbar is an excellent feature and has been perfectly reliable. The fast tool changes and repeatable tool length from the TTS style tool holders is a must for the machine. Considering adding a 4th stack to the air cylinder to increase applied force and changing the belleville springs to increase the toolholder grip force.
  • Size & Affordability: Surprisingly, I have not grown out of the capabilities of this machine for the most part over the last 10 years. For the components I tend to work on, this size machine seems to suit my needs. Would I love a 40x20 CNC bedmill? Sure. But I can't justify the size and expense of purchasing and maintaining such a machine for the work I do today. Down the road, I might consider something along the lines of a PM-940M, however the G0704 is sticking around for the foreseeable future.
  • Probing: This was a more recent addition. I purchased a $60 probe from AliExpress and I have been blown away with the repeatability and ease of use of a mechanical touch probe integrated into Mach 4. I want to take a bit of time to update some of the probing macros in Mach, but I expect I'll be using this instead of edge finders going forward.
The Bad & The Ugly:
  • Roton Ballscrews: These were the best "low cost" ballscrews available for CNC conversions back in 2012 (at least that I knew of). They were touted as the best solution by Hoss Machine who was the guru for G0704 CNC conversions back a decade ago. In truth, these are "transport grade" ballscrews with a rated lead error of 0.012" per foot and no backlash specification. I've attempted to repack these screws with oversize balls several times, but they have consistently had poor backlash in the 0.0005-0.003" range. These are high on my list to replace with something better.
  • Way Fit: The Grizzly G0704 represented the best conversion machine available on the market at the time in 2012, however it has always suffered from a few fit and finish issues, particularly in the ways and gibs. I've taken some limited corrective actions over the years, but the poorly fitting ways pose a challenge to getting the gibs well adjusted over the total travel range. I know my machine has several "bumps" at particular locations on the ways which cause binding. Also the gibs need shims behind them to fully tighten. Improving the way fit with some hand scraping would go a long way to improve accuracy and rigidity. Even a quick scraping job should do a lot to improve these issues.
  • Alignment: I never performed a significant alignment check of the machine, but I do know the column needs to be squared, and there is some nod in the headstock. Both of these should be easy enough to fit with a bit of scraping. I now own a tenths indicator, cylindrical square, and granite square which should allow me to directly quantify the accuracy of the machine alignment.
  • Absolute Homing: This feature was great in principle (home the machine from data in the servo drives, without going to find the home switches), however it has been unreliable due to LUA scripting issues. If I can resolve these, then I would move this item to the "good" list.
  • Lubrication: As a manual milling machine, the G0704 has no oiling provisions for the ways. During my CNC conversion, I did not add a one shot oiler or anything else like it. This means that trying to get oil on all the ways is messy business, and frequently this means the ways get no oil at all.
  • Coolant & Chip Management: Due to the lack of any rudimentary enclosure, I do not use any mist or flood coolant, even though I have both available. I am also hesitant to use tools which throw chips any distance, or machine steel frequently. I may be considering a simple enclosure to permit the use of flood coolant in the machine.
  • Chip Protection & Way Covers: The stock way covers on the G0704 do not last particularly long, and I have real issues with keeping chips out of the Y axis screw and nut. This has led to premature wear and poor positioning. If I replace the ballscrews, I will need to consider a more robust chip protection method.
  • Spindle Runout: Even with mid-grade angular contact spindle bearings properly installed and preloaded, the spindle has 0.0004" TIR runout. I am convinced this is error in the spindle taper grind and combined with 0.0002" TIR of runout from the precision R8 TTS collet, gives a minimum of 6 tenths of runout on my tooling. TTS toolholders seem to average 0.0003" TIR, and the ER collets I am buying now contribute another 0.0002". This substantial stack-up of inaccuracies means I have a hard time getting tools with acceptable runout. If I can get the rest of the machine in good enough shape to make this possible, I'd like to use a PCD boring bar to hard turn the spindle taper right on the machine. This hopefully could give near zero runout and correct a bell-mouth I believe to exist on the spindle taper.

I'm looking towards starting a 4th generation of modifications and upgrades to this machine. I'll primarily be focusing on the items listed above to improve overall machine accuracy, reliability, and ease of use. I will likely start a new thread as I work through this.

-Mike
 
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4th generation of changes/modifications!!?? Goodness... I have not even finished mine!! :face slap:

Looking forward to the updates!!
 
4th generation of changes/modifications!!?? Goodness... I have not even finished mine!! :face slap:

Looking forward to the updates!!
I might just enjoy having a project to work on the machine - who knows!
 
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