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Thread: errors in cutting on my prt alpha not sure what caused it.

  1. #1
    Join Date
    Sep 2006
    Location
    cnc routing, portland or
    Posts
    3,633

    Default errors in cutting on my prt alpha not sure what caused it.

    the machine was made the last year shopbot made the alphas. it has run fine the whole time. had some issues with the serial to usb adapter and a new one fixed it. I have went through two or three computers on it and a couple of hubs.

    I have seen in the last few months where the machine stopped like it hit a stop or the bit was dull or it could not plunge all the way because the dust brush was in the way. but this morning I had it happen using a 1/16" bit a couple of times. I turned the machine off and restarted the software and it seemed fine.
    but then I cut these parts it is a simple plug with the pocket centered I have cut thousands of these. but the cut changed with the 1/4" bit cut some are off center but some are ovalized. when I brought the machine home it is in the right position. So I am not sure what to do. I rebooted the computer and the shopbot it took a bit of unplugging the usb cable to get it to find the port.

    so I am wondering buy a new cable replace the usb to serial a new hub all three? or could it be just a worn out machine? I plan on getting all three new things but I am worried it will start this again.

    I dont usually turn off the computer I leave it on all week and put it to sleep on the weekends. its a pain to log into so its a pain to t urn it off every week.
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  2. #2
    Join Date
    Dec 2011
    Location
    Piedmont, SD
    Posts
    706

    Default

    Machine can run home and land reasonably close to precise location, even with worn pinions. However, once a bit is spinning against the workpiece, all kinds of torque is applied, and loose/worn gears slopping around in the rack can do precisely what your evidence shows. Notice how it gets narrower at cross grain sections (more torque), and swings wide and loose as it relaxes travelling through straight grain.

    As for the other unexplained movements, still pointing away from software, towards mechanical. Dust shoe should not impede plunge depth, unless again, something is loose (like a pinion gear on the Z)

    Loose motors and/or severely worn pinion gears seems most likely. When did you last replace pinions and / or firm up their contact with rack ?
    If that routine is up to date, perhaps the motors themselves are due for replacement.

    jeff

  3. #3
    Join Date
    Sep 2006
    Location
    cnc routing, portland or
    Posts
    3,633

    Default

    I talked to shopbot and they think a loose e stop wire or to check the drivers see if a red light is flashing when it happens. it has been working normally today. but it got a bit off on one of the runs. I think the mess yesterday is it was off a bit and it was cutting wrong.
    the pinions are about ready for replacement but they are not bad and i have them far worse. then it just makes parts a bit sloppy.
    so in the morning I will replace all the USB connections and put new pinions on.

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