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Thread: CNC sometimes has a mind of itsí own.

  1. #11
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    Quote Originally Posted by Gary Campbell View Post
    From your pictures and descriptions you are losing or gaining steps. You say it always happens in one location. What is happening at that location? Is there a mechanical bind? Does the dust hose come in contact with the machine? Does a connector or wire loose connection at that point? Since it ALWAYS happens at the same position, it should be easy to diagnose.
    By 'same location' I mean the same relative position of the cut on each piece as in the images. No dust hose on the machine. Dust is blown off with air hose after each run, then (eventually) swept up and dumped.

    Let me clarify what I mean by "ALWAYS happens at the SAME location". It DOES NOT happen on every run, its intermittent. WHEN it happens it is ALWAYS in the same relative location of the cut piece - end of the run on final cleanup pass just as it is approaching the 'start' point and ramping out to stop. Happened once a month ago. Happened again 2 weeks ago. End of last week it was happening about 3 times out of 7 runs - all cutting 1 unit of the the same thing as in the pictures. This was 3 different jobs. Today I cut 22, no issues other than one had a small divination on the 8th run. WHEN it happens, it is on the very last CG command then ramps out and back to a 'Home'.

    Tomorrow I will be cutting the same pieces except rather than cutting one at a time (using 24x24" cut offs from another job) I will be cutting a matrix of 3. It will be interesting to see what happens.

    I suspect the cable dragging though so much saw dust was most of my problem - there was A LOT of saw dust. Static was probably created. Yet, with my math/physics degree I find it almost impossible to think static would cause the same problem in the same relative location of all pics (WHEN it happened). I would expect it to be in random locations and different times within the run.

    Thanks to all for the very welcome input. Yes, I need to work on grounding and dust collection. I do have a 3HP Laguna cyclone collector. It is just not piped to the Bot. Home basements leave a lot to be desired sometimes but it sure cuts down on overhead.

  2. #12
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    Quote Originally Posted by coryatjohn View Post
    I'm curious about how you've grounded your machine? Do you have a dedicated grounding rod? Are you grounding every moving part separately? Is your electrical source grounded to the same rod as your machine uses? These machines and their dust collectors can generate a large amount of static, especially if the weather is warm and dry. Careful grounding can eliminate a lot of "gremlins".
    I should have stated that at install, a new 220 line was run by an electrician from the shop sub-panel. The sub-panel is a drop off the main house panel. It is a dedicated 220 circuit breaker and the ground bar used there. Essentially it is all grounded to the house ground which DOES have a ground rod. The PC is plugged into a regular 20 amp circuit. Hope that makes sense.

  3. #13
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    Quote Originally Posted by JimDav View Post
    I should have stated that at install, a new 220 line was run by an electrician from the shop sub-panel. The sub-panel is a drop off the main house panel. It is a dedicated 220 circuit breaker and the ground bar used there. Essentially it is all grounded to the house ground which DOES have a ground rod. The PC is plugged into a regular 20 amp circuit. Hope that makes sense.
    I'm guessing this is probably the root of your problem. The amount of static electricity generated by the machine is too much to rely on the ground from the electrical outlet. The machine is also highly sensitive to static shock and can go bonkers easily.

    You should do the following:

    1. Drive a standard grounding rod into the ground at the closest possible point to the machine.
    2. Run a heavy (6 gauge or greater) copper line to EVERY moving component on the machine and ground them to that rod. These lines can be daisy chained.
    3. Run a separate line from the electrical box ground line to the grounding rod. DO NOT daisy chain this line. Run it direct from the box to the rod.
    4. If you have a dust collector or vacuum hold down, ground the hoses, motors and housings.

    Be sure to attach the grounding lines to your machine securely. I used copper eyes soldered to the lines and then bolted them to the machine. You may think this is all silly and overkill but it is not. These machines aren't reliable without absolute and perfect grounding. Any moving part that isn't individually grounded isn't grounded at all.
    ShopBot Details:
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  4. #14
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    Nah, With my science/computer background I know it's not silly and overkill. Actually I am a bit surprised that, in 5 years, there has not been the dreaded comm issues and that sort of thing. That said, I'm not a big production shop. Just me and a high school guy. The Bot may run 15/20 hours a week max.

  5. #15
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    I have a 2013 PRS Alpha and before I went insane with the grounding, I would get occasional weirdness out of the machine. Typically on dry days or when cutting something really dust intensive. Since grounding the heck out of the machine (several years ago), no issues at all except when the power fails. Can't stop that.

    It's an inexpensive and relatively simple fix. Maybe $40 for wire and the grounding rod. You can buy it all from Amazon or Home Depot.
    ShopBot Details:
    PRS Alpha 96x60x12
    4hp Spindle
    12" indexer
    Aspire
    Rhino

  6. #16
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    Just one word of warning, to may ground wires can cause a ground loop which will cause a whole lot of problems for you. Best to check the ShopBot documentation for recommended grounding.
    Ron Moorehead
    R&S Design
    ShopBot PRS Aphla 48 by 96
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  7. #17
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    Quote Originally Posted by JimDav View Post
    Update - mostly good news. Cut 22 circles today - all perfect except one with very slight deviation in the expected place. 22 more tomorrow of this, then 50 more of a similar part.

    However - interestingly, between the 3rd from last and 2nd to last, somehow the Bot decided my X zero point changed about .45 inches. Lower left corner WAS 0,0. That point changed to -.45,0. I did nothing but change the plywood blank. Gremlins at work.

    Only deference between today and Friday/Saturday - I cleaned up the saw dust that the cable was dragging over, then started cutting after zeroing. That potentially could have created some static but really weird the deviation was ALWAYS at the same place.
    That's a lot of circles. Naturally the CnC machine is getting bored and drawing outside the lines; give it a more complex shape now and then to keep it happy.

    My initial thought was dust buildup is causing drag/slipping/catching or confusing a proximity sensor and you should try adding more circle loops to a cut to see what happens. But the randomness of the miss-cut suggests a communication issue, so the static comments are more likely. And good point on avoiding ground loops!

    Also, I don't know anything about your machine, but is it using a USB connection? If so, you could try a different USB port on your PC -- if you are using a port on the back, try one on the front. I know that sounds silly, but I had a scanner that would work great but sometimes screw up right at the end. After trying literally everything else, it turned out the the USB ports on one side of the machine didn't quite meet the USB spec for current and the voltage would drop during communication and sometimes glitch, but the ports on the other side had a different USB controller and were to spec. I swapped the ports and never had a problem again. Kind of a long shot, but a simple test.

    Perhaps even a longer shot is the power supply in your computer is dying. It sounds like an old machine. Does it sometimes not boot up the first time you turn it on, and you have to press the reset button to get it to boot?

    You say you don't have dust collection, dare I even ask what the inside of the computer looks like...? Dust buildup could cause it to overheat towards the end of a job.

  8. #18
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    Quote Originally Posted by skintigh View Post
    That's a lot of circles. Naturally the CnC machine is getting bored and drawing outside the lines; give it a more complex shape now and then to keep it happy.
    Love your comment. Don't know about the machine but I sure get bored. It does get other things to cut besides these.

    I come from a career in the IT field and understand what is going on inside the box probably better than modern day 'computer' people from a bits & bytes point of view. Yep, I've flipped around some dials and changed program code on the fly in both octal and hexidecimal. Those were the really fun days. I've been around for a looooong time. Seen the industry grow up. Yes, sometimes seemingly silly things can, and do, make a difference.

    Per your comment about a dying computer - nah, it's fine. Boots up fine. It sometimes gets a good cleaning.

    So, 50 more circles tomorrow same thing but a bit smaller and no hole for a plug. Next weeks job is another job like this - 60 circles but 30" in diameter. After that is another job that is not a bunch of circles so may be the machine won't be bored.

    I think everything is under control now. Even let my mid-teen helper run the Bot this afternoon.

    Thanks for your comments.

  9. #19
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    Quote Originally Posted by ron_moorehead View Post
    Just one word of warning, to may ground wires can cause a ground loop which will cause a whole lot of problems for you. Best to check the ShopBot documentation for recommended grounding.
    The key point in avoiding issues with grounding is to ground everything to a single point, like in one rod.
    ShopBot Details:
    PRS Alpha 96x60x12
    4hp Spindle
    12" indexer
    Aspire
    Rhino

  10. #20
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    If you add a ground rod, doesn't that introduce a second ground point? Is not the building electrical system ground functional? Adding one is asking for trouble.
    Gary Campbell
    CNC Training & Technology
    GCnC411(at)gmail(dot)com
    The Ultimate Woodworking Machine
    http://www.youtube.com/user/Islaww1


    "We can not solve our problems with the same level of thinking that created them"
    ó Albert Einstein


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