Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine - Page 2


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Thread: Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine

  1. #13
    Registered he1957's Avatar
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    Default Re: Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine

    The sound of that X axis manual move by itself is very loud and sounds like the bearings are shot. Take the plate off and try the individual trucks.

    The other thing of note is the change in pitch of the motors across travel; this seems evident in both X and Y but what's interesting is the timing - it seems consistent in a distance/time relationship. A bit odd me thinks.

    (The Z sounds a little tired too).

    If everything checks out mechanically, then have a look at your power supplies. For the circle components, both motors are running, drawing more current. Sounds like a power supply problem. If you have an oscilliscope, see if there is ripple on the DC power lines (bad filter caps). Failing the 'scope, try a DVM on the power lines and see if there is a variation of more than a few millivolts between load and no load, between just X, Y and X and Y together.

    I'm guessing there may also be a loss of power on one side of power delivery (A and B) but the machine is losing position.

    Try single X and Y movements + and - and mesaure the distance (with a ruler), rinse, repeat - perhaps that may show if lost position(s) is/are random or consistent. If consistent, check settings as per previous post otherwise mechanical/electrical - perhaps both?

    Belt adjustment is typicallly just a few elongated slots under the motor mount plate screws; there may not be much movement so if the belts have stretched, they may need replacing.

    Just a few thoughts.



  2. #14
    *Registered User* dgolden's Avatar
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    Default Re: Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine

    Quote Originally Posted by coherent View Post
    I hate to get you chasing another possibility, but I didn't see in the thread what software you are using. I'm going to assume Mach 3 since it's pretty common. UCCNC also has some of the same settings. Anyway, there are a couple settings in Mach that can cause issues when cutting arcs/polylines. Instead of getting to far into specifics, do a little researching on CV (or constant velocity) mode and settings. Incorrect settings or values can cause some pretty strange cuts depending on your gcode output (G01, G08, G64 etc in your code). If the post processor you are using isn't "in tune" with your Mach settings it can cause issues. Some of the settings effecting cuts are constant velocity vs exact stop, look ahead, absolute or incremental. If the settings aren't correct for the output gcode there will be issues cutting IJ arcs vs polyline arcs etc. I've even seen strange things on straight polylines depending on the post processors output and Mach settings. Of course if this is a mechanical issue, this is all a moot point. But if you can save or write down all of your current settings before changing anything and do a little research on Mach's CV settings and taking a closer look at your gcode it may worth checking into.
    Ok thanks for the idea. Yes I am using Mach 3. I should be able to get by the shop again this weekend to finish checking the bearings and pinions with another person helping, so I hope to either pinpoint or rule out a mechanical problem.

    The thing is though, the test program I ran at the guy's house before I decided to buy it was much more aggressive than any I've tried to run since, with a bigger end mill going deeper into harder wood, but it was going so well that I stopped the program before it got to the circular profiles, since it was looking like it might hit the clamps... so I'm not sure if the circle/arc weirdness is a pre-existing issue or not. If the circles would have worked at that time, then his settings should be fine now too I would think.

    That noise really bugs me though, it really seems like a mechanical slip or something, since it even vibrates the covers. Maybe both Y-axis pinions are slipping independently and creating some weird resonance... Who knows.



  3. #15
    *Registered User* dgolden's Avatar
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    Default Re: Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine

    Quote Originally Posted by he1957 View Post
    The sound of that X axis manual move by itself is very loud and sounds like the bearings are shot. Take the plate off and try the individual trucks.

    The other thing of note is the change in pitch of the motors across travel; this seems evident in both X and Y but what's interesting is the timing - it seems consistent in a distance/time relationship. A bit odd me thinks.

    (The Z sounds a little tired too).

    If everything checks out mechanically, then have a look at your power supplies. For the circle components, both motors are running, drawing more current. Sounds like a power supply problem. If you have an oscilliscope, see if there is ripple on the DC power lines (bad filter caps). Failing the 'scope, try a DVM on the power lines and see if there is a variation of more than a few millivolts between load and no load, between just X, Y and X and Y together.

    I'm guessing there may also be a loss of power on one side of power delivery (A and B) but the machine is losing position.

    Try single X and Y movements + and - and mesaure the distance (with a ruler), rinse, repeat - perhaps that may show if lost position(s) is/are random or consistent. If consistent, check settings as per previous post otherwise mechanical/electrical - perhaps both?

    Belt adjustment is typicallly just a few elongated slots under the motor mount plate screws; there may not be much movement so if the belts have stretched, they may need replacing.

    Just a few thoughts.
    Sorry, I didn't see this post until now. Very interesting ideas. I think you might have something with the power supply idea. Make sense that it's freaking out when 3 motors are running at the same time. No oscilliscope sadly, but I probably know someone with a voltmeter.

    I did calibrate x and y over a distance of 12 inches and on those single axes alone they seemed to hold the right calibration within 1/16" or less over the course of a couple tests, and I could zero out a home position, then jog all the axes individually and goto home and it would go right back to the same spot, but after running the test program it would get out of whack again every time pretty much, and after it was done the home position would be off by 1/4"-1/2" in x and y. Haven't done any calibration or testing of the Z yet, but it does sound a little squeaky.



  4. #16
    *Registered User* dgolden's Avatar
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    Lightbulb Electronics

    Did a little googling on the electronic components, and here's what I've come up with.

    STEPPER MOTORS (Photo):
    Keling Technology
    https://www.automationtechnologiesin...l34h295-43-8a/
    NEMA34 HIGH TORQUE STEPPER MOTOR 906 oz-in
    KL34H295-43-8A (1/2" Single Shaft)
    906 oz In. Hybrid Motor
    1.8° /200 Steps Per Rev.
    6.1 Amps Current Per Phase (Bipolar Parallel)
    8-wire Bi-polar or unipolar,
    NEMA 34 Frame

    DRIVERS (Photos):
    Keling Technology
    https://www.automationtechnologiesin...rivers/kl8060/
    KL8060 Digital Bipolar Stepper Motor Driver 24-80VDC 6A - 32 bit DSP Based
    1: Supply Voltage 24 up to 80 VDC
    2: Dip Switch Setting (Current): 2.0,2.57,3.14,3.71,4.28,4.86, 5.43, 6.0A
    3: Dip Switch Setting (Micro Step):
    2,4,8,16,32,64,128,256,5,10,25,50,125,250
    3: Suitable for 4, 6, 8 wires motors
    5: Full or Half Current Mode: Sw4: 0= Half Current
    6: TTL compatible and Optically Isolated Signal I/O
    7: Short-voltage, over-voltage, over-current and over temperature
    protection
    8: Pulse input frequency up to 400 KHz
    9: Support PUL/DIR

    BREAKOUT BOARD (Photos):
    C10R10.1-S688-46
    https://cnc4pc.com/Tech_Docs/C10R10_USER_MANUAL_V2.pdf
    DIGITAL INPUT SPECIFICATIONS:
    On-state voltage range - 2 to 5V DC
    Maximum off-state voltage - 0.8V
    Maximum operation frequency - 4 MHz
    Typical signal delay - 10nS

    DIGITAL OUTPUT SPECIFICATIONS
    Maximum output voltage - (5V power supply voltage) + 0.5V
    Typical output current - 24mA
    Maximum off-state voltage - 0.44 V
    Maximum operation frequency - 4 MHz
    Typical signal delay - 10 nS
    Time of transition to high impedance state - 12 nS*

    POWER SUPPLY (Photo):
    (I think?) KL-7220, 72V(No load), Max 20A,Unregulated Power Supply, 110VAC/220VAC
    https://www.automationtechnologiesin...-4-axis-kit-7/

    I'm guessing the guy who recently replaced the electronics purchased the kit at that link, which includes the same drivers, breakout board, and motors, and then just got an extra motor and driver for the A axis. However, the power supply does look slightly different on mine, with more heatsink fins and some additional "stuff". Sorry, complete electronics noob.

    ROUTER
    PORTER-CABLE 75182 Variable Speed Router Motor
    https://www.amazon.com/PORTER-CABLE-.../dp/B0007SXHXM
    Amps - 15 Amps
    Collets - 1/2 in
    Horsepower - 3-1/4 HP
    Motor Diameter - 4.2 in
    No Load Speed - Soft starting 5 speed at 10,000, 13,000, 16,000, 19,000, and 21,000 rpm
    Power Tool Type - Corded

    Here's the video tour of the box:


    Again, I'm still pretty clueless when it comes to electric, but from what I understand this is plugged into a 110v 20amp circuit. The guy who sold it to me was pretty clueless too, all he said was "it will run on normal house electric, just make sure you have it on a big breaker"

    So... from these specs, should it be OK on the circuit I'm using it on?



  5. #17
    *Registered User* dgolden's Avatar
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    Default Real Progress

    Had a pretty successful day at the shop. Took off the X-Axis rail and did a de-rusting treatment, and greased up that and the bearing, which seemed ok, just a bit gunked up. Found out that the motor mounts have no allowance for adjustment at all, they screw right into threaded holes in the plate. After taking the motor off the belt though, that bearing for the pinion axle or whatever spins freely, so that's not a problem.

    We put the motor and belt back and reattached the pinion and tightened the set screws again, and put it all back together to run a test with the covers off to see if anything was slipping. Tried the cardboard test several times without moving anything, and it ran perfectly inside the grooves it cut the first time around without losing the home position. Tried it with the router plugged into a different 20 amp circuit and it didn't seem to make any difference.

    So we decided to do a test in wood, and behold, for the first time, it ran a longish test program with no problems. None of the belts or pinions or axles seemed to be slipping. In the end the overall width of the circle varied ever so slightly, so I re-calibrated all axes to be less than 1/16" off over 40" in X and Y and less over 3" in Z.

    Then ran a real test program with a rough in pass, which still gave those weird noises on the circular profiles, but didn't lose position:



    and a finish pass, which seemed to run perfectly.



    Unfortunately, shortly after the end of that video, it started screwing up again. I think the cable carrier chain was off by 1/4" or something and smacked into the Y motor and knocked the pinion loose again, so here is the final result.

    So it looks like it was that simple after all. Just set screws knocked loose in transit... fingers crossed. Going to go back next time and put some blue loctite in those set screws and de-rustify the Y axis rails and try a few more intensive tests.

    Thanks again for all the input and help, and I'm still happy to hear any more insights and advice if anyone thinks of anything.

    Attached Thumbnails Attached Thumbnails Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-half-good-jpg   Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-good-rough-test-jpg   Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-motor-pinion-mount-jpg  
    Last edited by dgolden; 10-31-2018 at 09:01 AM.


  6. #18
    Registered coherent's Avatar
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    Default Re: Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine

    Glad you seem to have found the issue. It's not unusual to not have any motor adjustment on a direct to screw drive setup. The motors are mounted exactly in line with the screw/shaft and any adjustment between the motor shaft and screw is at the coupler which is normally a 3 piece type with a nylon or plastic hub in the middle, or a one piece that is flexible. I'd recommend oldham type as they compensate for misalignment while still being very precise. Solid type are ok, but only if everything is aligned absolutely perfectly so are rarely used in CNC machines. The spiral flex type are polular on small machines but tend to fail/break more easily in my experience.
    If you had to "de rust" things you may want to do a thorough job of cleaning and lubing and/or replace anything that's an issue. Everything should be clean and well lubed. Rust, friction and dirt etc don't play well with precision, smooth CNC machinery operation as you have already found out..



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    Default Re: Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine

    Make sure you put some good grease on those linear rail ball bearing carriages. I use THK AFC grease on my linear carriages but it is rather expensive stuff. Mobil EP1 is a decent alternative. I bought a tube from Granger for about $8.



  8. #20
    *Registered User* dgolden's Avatar
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    Thumbs up Problem Probably Solved

    Quote Originally Posted by coherent View Post
    Glad you seem to have found the issue. It's not unusual to not have any motor adjustment on a direct to screw drive setup. The motors are mounted exactly in line with the screw/shaft and any adjustment between the motor shaft and screw is at the coupler which is normally a 3 piece type with a nylon or plastic hub in the middle, or a one piece that is flexible. I'd recommend oldham type as they compensate for misalignment while still being very precise. Solid type are ok, but only if everything is aligned absolutely perfectly so are rarely used in CNC machines. The spiral flex type are polular on small machines but tend to fail/break more easily in my experience.
    I'll definitely look into the oldham couplers for the Z axis, which is on a direct to screw setup. Right now I think it's just in a sleeve with set screws that connects the motor shaft to the screw in line. Probably not the best, but haven't noticed any issues just yet.

    Everything else besides the Z axis is on rack & pinion and driven by a belt setup like this which runs from the directly mounted motor to a shaft that goes through a press-fit bearing which looks like this on the other side, except normally with a pinion gear on that shaft. So there's no ability for adjustment that I can see there, except for just changing belt size. Either way the belts aren't slipping after all it seems.

    As you can see in that last picture, and more clearly in this one the X axis pinion set screws must have been slipping for a while, since they have worn a groove in the shaft. I didn't notice this before, but a friend pointed it out, and you can see that the shaft wore down the cupped ends of the set screws as well. So I'm guessing the last owner who was also a novice just kept tightening them down, and not using loctite or anything, and it kept wearing things down more and slipping.

    So we got some brand new set screws, and put them down into that groove and set with loctite. Then after waiting a cautious 24 hours, ran the same test that slipped halfway through last time and got a better result outside of a somewhat poor surface finish. So it seemed to do the whole thing with no real problems. Still have more tests to do though, and over a larger area.

    Quote Originally Posted by coherent View Post
    If you had to "de rust" things you may want to do a thorough job of cleaning and lubing and/or replace anything that's an issue. Everything should be clean and well lubed. Rust, friction and dirt etc don't play well with precision, smooth CNC machinery operation as you have already found out..
    Quote Originally Posted by jfong View Post
    Make sure you put some good grease on those linear rail ball bearing carriages. I use THK AFC grease on my linear carriages but it is rather expensive stuff. Mobil EP1 is a decent alternative. I bought a tube from Granger for about $8.
    Last weekend we cleaned all the rails and took all the motors off to test the bearings, and all 4 linear bearings on the Y axis were pretty much silky smooth after removing the surface rust on the rails. We have packed all the linear bearings and greased the rails with white lithium grease which I saw recommended elsewhere, as we happened to have it in the shop already, and things seem to be quite a bit smoother and quieter now. We'll see how it holds up over time, and I'll make a note of the ones you recommended for future reference.

    Thanks again for all the help and recommendations!

    Attached Thumbnails Attached Thumbnails Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-belt-setup-jpg   Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-groovy-shaft-jpg   Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-worn-screws-jpg   Rack & Pinion X Axis Slipping/Binding on Big Used Mystery Machine-ok-test-jpg  



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