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IndustryArena Forum > Metalworking Machines > Benchtop Machines > Mike's G0704 AC Servo Rebuild (Picture Heavy)
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  1. #1
    Join Date
    Jan 2014

    Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Hi All,

    I have been posting a build thread for this project on another forum, however I would love to get the thoughts of everyone here. I am nearing completion of the mechanical build portion of this project so the posts should come quickly at first. But first a little back story...

    About 5 years ago I completed a CNC conversion of a Grizzly G0704 milling machine. Like everyone at that time I chose to go with the Hoss Machine style conversion as there were not many options on the market. I was not comfortable designing my own system at the time since I was just starting out in the hobby. The conversion was not glamorous, but it worked and I've tended to use the machine more than just fixing it up. The original purchase and conversion have been more than paid off in fun side jobs. I have literally thousands of great parts that have come off of this machine.

    Fast forward to today, I am graduated from college and working for an industrial automation company (specifically in servomotor applications and control system design). I have been extremely fortunate to be able to get my hands on hardware leftover at work that I would have no justification to purchase on my own. Off and on over the last year I have been designing and building a complete system overhaul for the machine. I'm primarily focused on ease of use and reliability of the machine, but there should be huge performance increases as a result. I know everything you are about to see is complete overkill for this size machine, but I left it flexible enough to be transitioned onto a larger machine should I outgrow the G0704.

    System overview:
    The new control cabinet is a 24" x 36" x 8" sealed enclosure housing 6 AC servo drives.
    Attachment 413530
    Designed to be run from a Ethernet Smoothstepper and Mach 3/4, the Allen Bradley Ultra 3000 series drives power AB bulletin MPL servomotors.

    X Axis - 0.75 kW 5000rpm Max, theoretical rapid 1000ipm, continuous thrust 350lbf, peak thrust 800lbf. High resolution multi-turn absolute encoder (~2M count/rev)

    Y Axis - 0.75 kW 5000rpm Max, theoretical rapid 1000ipm, continuous thrust 350lbf, peak thrust 800lbf. High resolution multi-turn absolute encoder (~2M count/rev)

    Z Axis - 1.80 kW 5000rpm Max, theoretical rapid 1000ipm, continuous thrust 900lbf, peak thrust 2400lbf. High resolution multi-turn absolute encoder (~2M count/rev)

    Spindle - 1.80kW 5000rpm Max, Continuous torque 4.18Nm, Peak torque 11.1 Nm, 1:1 gearing, High resolution single turn absolute encoder (~2M count/rev)

    4th Axis - Prewired for up to 1kW. I have a high torque Alpha Wittenstein SP series gearbox which I plan to make a 4th axis with in the near future.

    5th Axis / Spare - Prewired for up to 1kW.
    The panel is wired for 40A @ 240VAC. It theoretically could pull 70A, but I don't foresee running all 6 drives at 100% at the same time. The control voltage is 24VDC which is coupled to the 5V Smoothstepper through optical isolators. All I/O points are broken out to M12 industrial connectors which include DC power and common to allow direct connection of 3 or 4 wire sensors. I have also purchased a pendant.

    Mechanically, all of the original conversion hardware will be removed and replaced with new heavier duty components that are already built (not trying to make this a build log per se). The spindle is getting the most work as the bearings have been dying a slow death over the past year. The new design will be a totally sealed belt drive (noise reduction) and feature a pneumatic drawbar. I have started this process and will share lots of pictures in the next post.

    Rebuild plans:
    -Rebuild spindle
    -Install spindle motor, belt drive, and drawbar
    -Remove old CNC components
    -Install axis motors and mounts
    -Install electrical cabinet
    -Install limit/home switches
    -Install wireway and cable routing
    -Install touchscreen computer
    -Migrate to Mach 4
    -Validate system functionality
    -Performance characterization
    -Mach 4 Pendant Configuration
    -Mach 4 LUA Scripting for servo drive serial communication (Diagnostics, true rigid tapping, absolute homing, gear hobbing, etc.)

    I'll follow this post up with some info on #1 since I'm nearly done with that part.

    As promised by the title, some pictures:
    Attachment 413532
    The freshly completed Hoss Machine style conversion (ca 2012)
    Attachment 413534
    The very first control panel, literally just stepper drives and a power supply
    Attachment 413536
    Got a touch screen monitor
    Attachment 413538
    Upgraded control panel (ca 2013). Ethernet Smoothstepper, CNC4PC breakout boards, StepperOnline drives, and a DMM Tech DYN3 AC servo for the spindle.
    Attachment 413540
    As installed (24" x 24" x 6")
    Attachment 413542
    Servo spindle motor with belt drive and plastic cover
    Attachment 413544
    Pretty much what it looks like today, except for some cleaned up wiring.

    I hope you will follow along with me as I complete this project. I have been very grateful to this entire community for the knowledge that is shared, and I hope to be able to give back even if it is a fraction of what I have learned!


  2. #2
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    The next step was rebuilding the failing spindle. I've been uncomfortable working on the spindle in the past as it requires a lot of care and precision as well as some tools that I don't have (arbor press, bearing pullers, etc.). That being said, my current setup has significant notching to the bearings and runs very hot and loud. They need to be replaced.

    Prior to starting work, I made a set of tools to disassemble the spindle, press the bearings on and off, and get things adjusted correctly. If anyone wants a rough set of drawings for their own use, I'd be more than happy to make them up. I think the job was much easier with these.
    Attachment 413548
    Pin spanner for removing the lower bearing retainer
    Attachment 413550
    Deep pin spanner for adjusting and removing the spindle locknut (sometimes called an adjuster nut)
    Attachment 413552
    Various rings to press bearings
    Attachment 413554
    Tool to knock out the upper quill tube assembly

    I began by removing my old AC servo, belt, and pulleys. From there, the drawbar could be removed and the entire lower section of the spindle drops out. There was a touch of surface oxidation on the spindle housing, but otherwise it looked really good. At this point I could tell that the angular contact bearing pair on the spindle itself was the source of the notching, and the upper quill tube bearings spun smoothly (I still replaced them since I had purchased new bearings). I used an aluminum disc and a deadblow to knock out the quill tube.

    I removed the spindle head casting to fill a few holes with epoxy. I have designed the new belt drive to be "air-tight" to reduce the audible noise from the system.
    Attachment 413556

    Attachment 413558

    Attachment 413560
    There was a little porosity due to using JB Kwik, but it won't affect the final product.

    Next I worked on removing the quill tube bearings. Many youtube videos show people popping these off with a pair of screwdrivers no problem, but my experience was different. After an hour of getting nowhere, I put it away for the night and went to Harbor Freight to get a 3 jaw gear and bearing puller. I made a quick tool to go on the end of the quill tube so the bearing puller had something to push against, and viola, the bearings came right off. I highly recommend the $20 to have one of these in your tool box for times in need.
    Attachment 413562
    Quick tools don't have to be pretty.

    Since I don't have any kind of press, I use my lathe to apply pressure to press parts together (pressing against the side of my toolpost). Pressing the bearings for this project is about the most force I'm comfortable applying with this method. Using a machined aluminum disc and a piece of scrap tubing, I was able to carefully press on the new bearings and reseat the snap ring.

    I'll save my angular contact bearing woes for the next post.

  3. #3
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    I had planned on spending the afternoon and evening to replace the angular contact bearings and reinstall the spindle components into the casting. I wrote up a procedure for how I was going to assembly the bearings such that I would never press across the balls of the bearing.

    First step was to freeze the spindle shaft in the freezer and heat the bearing at 250*F in the oven (limit for phenolic cage material). I waited about 30 minutes then dropped some spacers on the spindle shaft, chilled it further with a gas duster, and pressed the bearing on. This went quite easily and the bearing was seated very flat, confirmed on a .0005" indicator and my surface plate. Next I heated the spindle housing at 350*F and chilled the upper bearing. When I went to press it on, it just dropped into the housing, no press required. After it cooled, I could remove the bearing by hand. The housing measured a few tenths oversize on the bearing so the fit was a tight sliding fit. There was no radial play on this bearing. I revised my plan to include pressing this onto the spindle shaft after the shaft and lower bearing were installed in the housing.

    The next step was to heat the housing to 350*F again and chill the spindle/lower bearing assembly. After 30 min I set everything up on the lathe to press it on, but when I went to slide the shaft in, the bearing got stuck crooked by about 5 degrees in the threaded portion of the spindle housing. The thermal shrink kicked in and I was screwed. SH*T!!!. I took a deep breath and though about how I was going to remove the bearing. I tried pressing it from the rear, I tried pressing it in further from the front, hoping that it would straighten out, but neither worked.

    After an hour of no success, I decided to whack the spindle shaft laterally with a deadblow to align it again (and thus dooming the bearing to the garbage can. This did free the shaft from the housing, but not in the way I had hoped. The races separated on the bearing and all the balls dropped out. SH*T!!! From this point I could see the bearing was stuck slightly in the bearing bore of the housing, and jammed into the gully of one of the threads. It looked like a 1 : 1,000,000 chance. Anyways, when I went to HF, I bought a set of 2 jaw pullers, a set of 3 jaw pullers, and a pilot bearing puller (planned to return whatever I didn't need for the job). I didn't think I would use the pilot bearing puller, but boy did it save the day. After a few minutes of fiddling with the setup, POP, the outer race was removed. Now the inner race was still thermally shrunk to the spindle shaft and was nearly flush with the nose of the spindle, I certainly wasn't going to be getting the bearing puller on there. I carefully reassembled the cage and balls and basically hammered the bearing back together (reattached the outer race to the stuck inner race). Using an aluminum ring from before, I was able to press the inner race off as well. WHEW!

    So at the end of the day, there was no damage to the spindle shaft or spindle housing, but the angular contact bearing was toast. I placed a new one on order and I will be making some tooling to make sure that the spindle is aligned when it is being pressed into the housing.

    I hate working on spindles...

  4. #4
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Also, question for everyone. I had previously purchased 7005C and 7007C angular contact bearings (15 degree contact angle). This time I mistakenly purchased 7005B and 7007B angular contact bearings (40 degree contact angle). Does anyone see an issue with using the 40 degree ones? I understand they trade some of the load rating from the radial direction for more axial, but could this be an issue? They are still rated for much higher speeds than they will be run at, and I can't imagine that the loads I will be applying to them would be anywhere near their limit in either direction?

  5. #5
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    While I am waiting for the new spindle bearing to arrive, I am doing a bit of re-wiring on the electrical cabinet. Since I finished it a year ago, I have decided to add another 3.4A 24VDC supply and a time delay relay to power the industrial PC running this system. I found the PC to be sensitive to the swing up on the power supply voltage when it first turns on, so a 1 second time delay will wait for the voltage to stabilize before closing the power contact to the PC. I'm using an AB 700-FS timing relay for this purpose.
    Attachment 413564
    In addition, I am adding 2 DPDT relays to allow Mach 4 to mechanically disconnect the signal lines from the smoothstepper to the Z and 4th axes and connect these axes directly to the feedback from the spindle drive. If I can figure out the serial communications to the drives, I should be able to set the gearing ratio on the fly to do true rigid tapping and gear hobbing. That being said, it will be one of the last things I try to get working once everything else is finished and working, but I'd rather have the wiring in there already.

    I didn't have much spare room on my 11" section of DIN rail, so I am removing all the single tier terminal blocks and replacing them with these 3 tier ones.
    Click image for larger version. 

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    This gives me about 240% increase in wiring density and just barely enough room to fit everything. With the addition of the jog pendant, power drawbar, and a 3 button operator station, I have used every one of my remaining 13 inputs and 4 outputs I saved as spares. But it all fits
    Click image for larger version. 

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    Completed 3 tier wiring, you can see how much space it saved. I haven't done any dressing of the wires; I promise I'll make it look pretty
    Click image for larger version. 

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    The original lower density terminal blocks.

  6. #6
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    While I waited for a replacement bearing to arrive, I did some more work on replacing terminal blocks.
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    I was able to fit all the new relays, and have 18 spare points should I need them.
    Click image for larger version. 

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    I also got a little help from Zoey (she likes to bite my hand when I go digging for wire ferrules in the bag)
    Click image for larger version. 

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    After I spent half an hour dressing the wires.

    I still need to land connections between the empty block on the left (the MPG pendant) and the breakout board for the Ethernet Smoothstepper, and make the connections to the new relays, but it is getting close!

  7. #7
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    I had watched a youtube video last week about another G0704 belt drive conversion where they warned that the inside diameter of the quill tube had significant runout. I measured mine at .006" which was a lot higher than I wanted. I removed the rear bearing using a bearing puller and covered the front bearing in a generous helping of masking tape:

    Attachment 413578

    I then spent 45 minues indicating the part to run concentric and coaxial to the spindle (major PITA with so little material to hold onto and all machined surfaces had 12 thou or more of runout). I skimmed the bore until it cleaned up.

    Attachment 413580

    Attachment 413582

    After this machining, I had about .0005" of runout when running on its own bearings. I was plenty happy with that.

    Attachment 413584

    Again I used the lathe and some tooling plates to gently press the lower bearing back onto the quill tube

    Attachment 413586

    Since I had enlarged the bore and managed to ruin both flanges on my previous spindle pulley, I got to work machining a new one:

    Attachment 413588

    (Pulley stock on the left, ruined pulley in the middle, and the old steel L series pulley on the right)

    I used a split ring tool to hold the pulley on the teeth without damaging the flanges. This allowed for work on both the bore and the hub OD in the same setup.

    Attachment 413590

    Attachment 413592

  8. #8
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Since all my parts were designed from a 3D model of the G0704 that I purchased, there were a few sizing errors that I had to correct. In particular I tightened the pulley bore to spindle spline fit to a light hand press.

    Attachment 413594

    Attachment 413596

    (TCGX insert, picture doesn't do justice for how good the bore finish was)

    Attachment 413598

    Shop kitty #2 needed to see what was going on.

    Attachment 413600

    Finishing hub OD to prep for pressing on an aluminum ring (effectively making the OD larger than available from SDP-SI)

    Click image for larger version. 

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    The finished precision aluminum ring, fitted to the newly bored quill tube.

    Click image for larger version. 

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    And pressed on with some Loctite 271.

    Click image for larger version. 

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  9. #9
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)


    I did a test fit of the pulley and it was a light hand press fit.

    Attachment 413608

    A quick check of runout yielded around .0025 at the teeth (this ended up around .0010 once the spindle was fully assembled)

    Attachment 413610

    The spindle pulley drives the spindle through 2 opposed keyways 180 degrees apart. I broach these keyways using the lathe and a custom broach bushing. This bushing has been a pain since it was cut with a significant taper on the lathe which I didn't catch until after I milled the keyways. To correct this I tried filing it, but that mostly got it out of round.

    Since the new bore on the pulley was smaller I decided to use the glue chuck method to remount the bushing in the lathe and cut the OD.

    Attachment 413612

    A light skim cut brought down the high spots until the bushing was a nice sliding fit to the bore. The keyways were filed to correct the depth. Not pretty but it worked.

    Attachment 413614

    Attachment 413620

    After broaching pass #1

    Attachment 413622

    From here the bushing is rotated 180 degrees and a key is installed to hold it at the right angle, and the second keyway is cut in the same manner.

    And the spindle pulley is done except for light hand fitting to fit the keys to the roughly machined spindle spline.

  10. #10
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    I got the replacement bearing from VXB. They incorrectly shipped me a 7007C P5, but I can't complain because it is the right size and a much more expensive bearing than the 7007B that I ordered.

    I went very slowly on the installation and had great success!

    Lower bearing was heated to 250 degrees and the shaft was chilled with a gas duster. Using the lathe it was a light press on.

    Attachment 413626

    Attachment 413628

    The quill bearing assembly was pressed into the head casting using the lathe again (dang this thing is versatile!)

    Attachment 413630

    Attachment 413632

    The rest went together without too much trouble. There was some cursing but the bearings went in without damage and the preload was carefully set with a custom pin spanner wrench. The spindle doesn't freewheel and has a slight stiffness to it. I think this is ok and I can back off the preload if they get too warm. The bearings were packed at a 30% fill using Kluber Isoflex NBU 15 spindle bearing grease. This came out to 1.95cc for the 7007C and 1.05cc for the 7005B. All the retaining rings were installed and tightened, then the spindle was generously greased for thermal transfer/anti-corrosion/vibration damping. I almost forgot to install the R8 retaining pin, but fortunately it can go through the side of the spindle housing.

    Click image for larger version. 

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    The spindle was installed in the housing and a plastic spacer was lightly pressed between the spindle and the quill to prevent rattling.

    Attachment 413638

    The pulley was installed with the keys and finally the steel "top hat" was screwed on. Final assembled runout at the pulley was just around .001 TIR. All non-critical rotating components were within .003". Runout in the taper is roughly .0003-.0004. I wish this was a little better, but it will be good enough. (I have to keep telling myself that this is a $1000 machine, not a Mori Seiki).

    Click image for larger version. 

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  11. #11
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    For the motor pulley, I modified the setscrew to press in a brass tip. This prevents a scar on the motor shaft when tightened and prevents stuck pulleys.

    Attachment 413642

    The depth of the pulley when installed in the housing is critical to maintain pulley alignment to the spindle. I used the 3D model to find the correct distance between two surfaces I could measure between, then I used a height gauge and a dowel pin to set the depth. The depth was slowly adjusted using a screw on the end of the motor shaft.

    Attachment 413644

    Attachment 413646

    And a final fit test with the belt:

    Attachment 413648

    I had to stop here because I forgot to order bolts long enough to mount this housing to the spindle casting.

  12. #12
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    I am finishing up some wiring for the pendant, 240V wiring (rather than the temporary 120V test wiring), RS-485 network, and relay wiring.

    I have an Ultra 3000 (1kW) drive set up for testing on my bench. I am recording the average current draw at various speeds on the motor with no load. This will help me when I go to measure the current draw of the spindle during break-in and measure the power loss and efficiency of the spindle drive train. Since I am powering this test unit at 120VAC, I am bus voltage limited to ~3000rpm. When powered at 240VAC, the motor will easily reach 5000rpm.

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    Measured Current Draw:
    0 rpm - 0.0A (Some jittering current centered around 0A)
    500 rpm - 0.174A
    1000 rpm - 0.195A
    1500 rpm - 0.230A
    2000 rpm - 0.255A
    2500 rpm - 0.276A
    3000 rpm - 0.280A

    Here is the speed-torque curve for the motor I am using. The curve is generated on a slightly higher power output drive, but the peak torque I can achieve will be nearly identical.

    Click image for larger version. 

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    - - - Updated - - -

    Got some new bolts in the mail and got the spindle assembled. Unfortunately, working just from a CAD model bit me again and not all of the mounting holes on the top of the spindle line up (guess the Chinese factories put holes wherever they please). I'm hoping I can open up the counterbored holes on my aluminum mount to get things positioned better. Of course now I don't have a mill to use so I'll have to butcher it on the drill press...

    I was able to get the motor and belt mounted on 3 out of the 4 screws and got it up and running. I am slowly breaking in the bearings/belt and taking detailed measurements of torque consumption, temperature, and noise as I work up in speed. I'll post those results when I'm done testing, but I can say right now that it is a LOT quieter. At 1500rpm it measures about 10dBA less that my lathe running at 550rpm with no gears engaged. The lathe is quite comfortable to run without earplugs.

    I have only run it up to 1500rpm so far, but the highest bearing temp was 89 degrees in a 72 degree ambient temp (I'm right next to the furnace).

    All in all it seems to be going well, stay tuned for test results.

  13. #13
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    So I haven't had so much time to work on this at night but here are some basic tests up to 1750 RPM.

    Original Velocity Tuning Gains:
    P: 200
    I: 20
    D: 0
    zero speed response kind of spongy, small surging sounds at speed, velocity drops under simulated load.

    Ambient Temp: 72 deg - Fluke IR Temp gun

    Ambient Noise: 34 dBA (Furnace Off) "Wisper"
    Ambient Noise: 67 dBA (Furnace On) "Traffic"
    Ambient Noise: 79 dBA (Lathe on) "Alarm Clocks"
    Noise readings taken at 1', microphone pointed away from source

    All tests run for 20 minutes or longer for reading to reach steady state.

    Test 1: 100rpm
    Starting Current 0.98A
    Lower Bearing Temp: 74.0 deg
    Upper Bearing Temp: 72.0 deg
    Case Temp: 72.0 deg
    Noise: 39 dBA "Quiet Library"

    Test 2: 200rpm
    Starting Current 1.19A dropped to 1.16A
    Lower Bearing Temp: 74.0 deg
    Upper Bearing Temp: 73.0 deg
    Case Temp: 73.4 deg
    Noise: 45 dBA "Quiet Street"

    Test 3: 300rpm
    Starting Current 1.286A dropped to 1.168A
    Lower Bearing Temp: 74 deg
    Upper Bearing Temp: 75.8 deg
    Case Temp: 75.2 deg
    Sound Level: 50 dBA "Quiet Street"

    Test 4: 400rpm
    Starting Current 1.254A dropped to 1.170A
    Lower Bearing Temp: 76 deg
    Upper Bearing Temp: 77.4 deg
    Case Temp: 77.4 deg
    Sound Level: 55 dBA "Normal Conversation"

    Test 5: 500rpm
    Starting Current 1.274A dropped to 1.218A
    Lower Bearing Temp: 77 deg
    Upper Bearing Temp: 79.2 deg
    Case Temp: 77 deg
    Sound Level: 56 dBA "Normal Conversation"

    Test 5: 750rpm
    Starting Current 1.349A dropped to 1.274A
    Lower Bearing Temp: 81.2 deg
    Upper Bearing Temp: 82.6 deg
    Case Temp: 79.2 deg
    Motor Temp: 84.2 deg
    Sound Level: 68 dBA "Traffic"
    Noticable 3-5Hz surging with higher frequencies. Kinda annoying

    Test 6: 1000rpm
    Starting Current 1.360A dropped to 1.299A
    Lower Bearing Temp: 85 deg
    Upper Bearing Temp: 86.4 deg
    Case Temp: 82.4 deg
    Motor Temp: 88 deg
    Sound Level: 68 dBA "Traffic"
    Much smoother sounding than 750rpm
    Quieter than my lathe at 550rpm and no gears engaged

    Test 6: 1250rpm
    Starting Current 1.480A dropped to 1.375 A
    Lower Bearing Temp: 87.2 deg
    Upper Bearing Temp: 89 deg
    Case Temp: 84.6 deg
    Motor Temp: 90.6 deg
    Sound Level: 72 dBA
    Higher pitched than 1000rpm, slight high pitched squeaking can be heard
    Quieter than my lathe at 550rpm and no gears engaged

    Test 7: 1500rpm
    Starting Current 1.55A dropped to 1.464A Cold Start after sitting all day
    Lower Bearing Temp: 89 deg
    Upper Bearing Temp: 90.6 deg
    Case Temp: 84.0 deg
    Motor Temp: 92.8 deg
    Sound Level: 72 dBA
    Occassional Fluttering sound?

    Shortly after starting the 1750 rpm test, I heard a somewhat loud clicking sound. Due to the hole misalignment to the casting, I did not have the top hat installed above the spindle pulley which allowed the pulley to slightly work itself up the spindle shaft until the key was just kissing the housing. I stopped the spindle and installed the top hat. At the same time I also released belt tension so the numbers following this point will no longer be correlated to the above testing. That being said, the lower belt tension gives a much smoother and quieter running noise. I can pretty much only hear the motor noises instead of the belt noises! I made sure everything was set up correctly and ran at a full range of speeds up to 3000rpm. It all sounds amazing. I also retuned after turning on the low pass filter. Here are the new gains:
    P: 1000
    I: 280
    D: 25
    LPF Bandwidth: 350Hz

    Now the spindle is incredibly stiff and the only compliance is the slightly looser belt. There are no unwanted resonances or oscillations. All of the velocity surging is gone and it maintains speed within +/- 1 rpm even when simulated loads are applied (I grab the spindle nose by hand).

    As a benefit, the lower belt tension reduced the running current draw down to about 0.9A after taking off motor bearing losses. This equates to a belt drive (and spindle bearing) efficiency of around 90-92%. I'm pretty pleased with that.

    I also got my hands on a calibrated Fluke temp gun, so the numbers are reporting a touch higher but I trust them.

    Test 7: 1750rpm
    Starting Current 1.15A Significantly loosened belt
    Lower Bearing Temp: 96 deg
    Upper Bearing Temp: 98 deg
    Case Temp: 89.8 deg
    Motor Temp: 98 deg
    Sound Level: 77 dBA
    Adjusted belt and installed top hat. Sound is very very smooth. Total volume registers higher, but upper assembly is removed and everything sounds much better.

  14. #14
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    As always, everything takes longer than I planned, however I did have a very productive weekend.

    I started by moving the smoothstepper from my old enclosure to the new one (thereby committing to the new panel).

    Attachment 413666

    I completed wiring to the 3rd smoothstepper port, added all the relays, and finished the terminal wiring. I opted to add an additional 2 relays so that the power draw bar solenoids were not powered directly from the voltage converter boards.

    Attachment 413668

    The extra blue cable is RS485 over Cat 5 cable for communications to the drives. I need to drill 2 new cable gland entries, and when those are done, I will pull this cable out to the computer. Hidden in shadow next to the 1606 AB power supply is a thermostat which will shutdown the drives should the temperature exceed 130*F (The limit for non-derated drive operation).

    Attachment 413670

    Here you can see the RS485 network between the drives. In the short term, this allows me to talk to all 6 drives through their configuration software Ultraware, but hopefully some scripting though mach will allow me to pull diagnostics and set parameters on the fly. I know the drives are capable, but just need to learn LUA. If anyone has experience with this, please message me!

    Click image for larger version. 

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    And to finish off, I wired up the 50A power connector and ran hooked up 240V power. After a careful startup, the panel was live with no blown components or tripped breakers. The power supplies were adjusted to get the correct voltage under load. It is pretty!

    Click image for larger version. 

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    I also added two new wires to the spindle drive I/O connector (bottom right, thin grey cable, blue wires zip-tied to it). These are the spindle motor encoder output which connects to the larger 2 relays and allows electronic gearing between the spindle and the Z or A axes (rigid tapping or hobbing).

    The curly Q red wire coming off of the power supply is a temporary wire that will be replaced once the timing relay arrives. This will let me power the PC even without that component.

    At this point, I am going to put the electrical panel on hold until the motors are completely mounted.

    I still need to correct the poor mounting hole placement for the spindle housing.

  15. #15
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Got the spindle mount fixed up last night.

    First thing I did was tear down the existing setup. When I did, I found a substantial amount of belt dust inside the housing. I'm hoping this was from when I forgot to install the top hat and the spindle pulley worked itself loose. I cleaned it all up and I will check on it in the future. Those pulleys should be axially aligned within a few thou and completely parallel.

    Attachment 413676

    Attachment 413678

    My design includes a felt washer that gently rubs against the top hat OD to help seal in noise. The original adhesive back didn't cut it, so I used some GOOP to glue it on.

    Attachment 413680

    Attachment 413682

    From there I used some reamers, and endmill, and a few drills in my cordless drill to open up the mounting holes and counterbores. It isn't very pretty this way, but it will all be covered by other components. I still can only get 3 screws to go in, but at least it lines up now. I could file the other hole down the road, but it isn't needed.

    Click image for larger version. 

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    Click image for larger version. 

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  16. #16
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    From there, the upper puller plate assembly is mounted. There is only a few thou clearance around the top hat, so alignment is critical. The pneumatic cylinder is mounted on these posts.

    Attachment 413688

    Click image for larger version. 

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    Attachment 413692

    Finally I ran the spindle at 2800 rpm (max at 120VAC) for around an hour. The bearing temp rose to around 130F. This isn't crazy but a bit higher than I was hoping for. The Kluber IsoFlex NBU 15 grease has a service temperature up to 130C (266F) and the bearings have a service temperature of 250F which is the limit for the phenolic cage. I hope to not get anywhere near this, but it does give me a hard limit.

    Since I have been adjusting so many things, I'm going to hold off on the running torque/temperature measurements until the assembly is complete.

    As a note, I have found that the timing belt runs the smoothest with a very low tension. As I get it tighter, the taught belt acts like a guitar string and generates significantly more noise. Unless I have issues with compliance in the spindle when stationary or with teeth jumping under high load, I will leave the belt just hand tight. It also consumes far fewer amps when a touch looser.

    Click image for larger version. 

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  17. #17
    Gold Member
    Join Date
    Nov 2009

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Nice work

    Sent from my iPhone using Tapatalk Pro
    A lazy man does it twice.

  18. #18

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    With V-belts and fairly loose tension I don't get much if any slippage, I can't imagine a time belt would either. I have a 2.2kw motor and a rotary encoder so I should be able to detect slipping pretty easily. In my opinion, a lot of people over tight belts. If it's controlling valve timing then fair enough, for something like a spindle it doesn't need to be super tight.

  19. #19
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Edit: Double Post Removed

  20. #20
    Join Date
    Jan 2014

    Re: Mike's G0704 AC Servo Rebuild (Picture Heavy)

    Edit: Double Post Removed

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