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Thread: Grinding Sound in Y-Axis and Circles/Arcs Not Cutting Perfectly Smooth

  1. #1
    Join Date
    Jun 2016
    Posts
    2

    Default Grinding Sound in Y-Axis and Circles/Arcs Not Cutting Perfectly Smooth

    Hello All,

    I have a PRT Alpa 2004 that I purchased used in June of this year. Overall the machine has been great and I have very few complaints. However, most of the work that we do requires very smooth edges and this is where I am having my only problem. To clarify, straight cuts produce very smooth edges, but curves arcs and circles of various sizes, large and small produce a decent amount of chatter

    To start, I will list everything I can think of regarding how I run the machine. Standard operation is either a 1/4" or 3/8" Compression Bit from Onsrud. We run at 12,000 RPM with our Colombo 5.5hp spindle at a feed rate of 350 in/min. We typically cut Baltic Birch and the compression helps us with reducing chipout on the top and bottom laminate layers. In an attempt to reduce our rough edges, we have moved the feed rate down to 300, 250 and 200 in/min. We have not altered the RPMs however. As we do quite a bit of production, we can't really afford to run slower than 200ipm, so I really hope running slower is not the solution!

    Regarding maintenance, I have kept the machine is good shape in the 7 months I've had it. While doing maintenance recently though, I noticed that when I moved the Y carriage by hand, it runs smoothly for a few seconds and then makes an awful grinding sound. The X axis does not do this. The grinding goes in and out but its ultimately there and does not sound right. I am careful to push from a central point on the gantry and I do not use excessive force to move the gantry. When the machine is on and motors engaged, it runs without grinding, thankfully. That noise is just very suspicious to me and does not seem right. I have checked the Rack, the Pinions, the tension of the turnbuckles, have ran the motors, free of the track and nothing seems out of the ordinary. I'm truly at a loss for what is going on.

    I've attached a picture of a rather large circle with a wavy edge. It's a little tough to see in the picture but it is certainty there and is very noticeable when running your hand over it. I have a video of the grinding but it will not let me upload it.

    Any help or insight is greatly appreciated.
    - Ben
    Attached Images Attached Images

  2. #2
    Join Date
    Sep 2006
    Location
    Garland Tx
    Posts
    2,019

    Default

    Ben…
    A 2004 Alpha… does it have the 1:1 stepper motors on it or has it been upgraded to either gearbox reduction or belt drive reduction?
    SG

  3. #3
    Join Date
    Jun 2016
    Posts
    2

    Default

    Steve, It has the 1:1 Stepper Motor, no gearbox or belt drive reductions.
    -Ben

  4. #4
    Join Date
    Apr 2007
    Location
    Marquette, MI
    Posts
    3,167

    Default

    bw...
    About half of what you show should come out with careful adjustment of the "side" rollers on the Y car. Those cars will skew or dogwalk as the direction of torque changes when you cut around a circular path.

    Make sure the interior edges of the rails are true and use a gauge stick to make sure they are exactly parallel. Then adjust the rollers so that all 4 touch all the way across the rails. Do this with the motor(s) dropped out. There is no good reason to push a stepper when powered down.

    If that doesn't improve your cuts, add a set of my belt drives. See below
    Attached Images Attached Images
    Gary Campbell
    CNC Training & Technology
    GCnC411(at)gmail(dot)com
    http://www.youtube.com/user/Islaww1
    www.cncseminars.com


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


  5. #5
    Join Date
    Sep 2006
    Location
    Garland Tx
    Posts
    2,019

    Default

    Ben…
    I wasn’t happy with my 06’ until I added the belt drives…
    SG

  6. #6
    Join Date
    Apr 2007
    Location
    Marquette, MI
    Posts
    3,167

    Default

    Gary Campbell
    CNC Training & Technology
    GCnC411(at)gmail(dot)com
    http://www.youtube.com/user/Islaww1
    www.cncseminars.com


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


  7. #7
    Join Date
    Sep 2014
    Location
    Poughkeepsie, NY
    Posts
    8

    Default

    Change your Unit Values circle value to .005 to help with the smoothness, then order Gary's belt drive units. I do mainly panel processing on a 06 PRT Alpha, best upgrade yet.

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