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Thread: Table Top Not Flat

  1. #1
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    578

    Default Table Top Not Flat

    Hello Shopbot friends:

    When recently cutting a V-carving, I noticed line widths that should have been even, were not. As carving proceeded in the increasing X axis direction, the lines got narrower when they should have stayed the same width.

    Being in a rush, I put a shim under the low end of my plaque to raise it up about .030" and that made it so I could finish my V-carving. After that carving was done, I decided to re-flatten my table top using my 2 1/2" Amana planing bit.

    The next time I did a V-carving, I noticed the same problem, and thought maybe my planing bit had slipped in the collet. So I flattened my table top again, and made sure the collet was tight. Well, the problem still exists, my table is still not flat.

    I did some measuring of the area on my table top that I use the most, from (2,5) to (36, 30). Those readings are in the attachment. (I measured the gap using a set of "feeler" gauges. I didn't want to try and measure right on my table edges, lest I drop my feeler gauges onto the floor.)

    The summary of what I found:
    Moving along the line from (2,5) to (36,5), the table drops .010"
    Moving along the line from (2,15) to (31,15), the table drops .036"
    Moving along the line from (2,30) to (36,30), the table drops .049"

    Any suggestions as to how I can fix this? I have no idea how this could happen,,,,,, as even if the rails were messed up, the gantry should have held a fixed distance from the table top.

    Thank you, I hope this makes sense....... Chuck
    Attached Files Attached Files
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  2. #2
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    578

    Default

    PS: In making my measurements, I installed a 60 degree V-bit into my spindle. I zeroed the bit at the edge of my table (1,30) and used that Z height (of the spindle) for all subsequent measurements.

    I moved the bit to (2,30) then used feeler gauges to measure the gap between the tip of the V-bit and the table top. Then moved to (3,30), measured the gap, moved to (4,30) and so on............
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  3. #3
    Join Date
    Feb 2010
    Location
    SOUTH CENTRAL COLORADO
    Posts
    1,065

    Default

    I get my wood planks from a furniture maker who finishes them by running them through a 50 inch wide drum sander. Even still my planks are not perfectly flat and i always plane them flat before starting a project or at least they are in tune with my table top. Now this does not address your table but just relating my experience. Before i started the process of planning i noticed a plaque that came out like you described.

  4. #4
    Join Date
    Jan 2011
    Location
    gleason, wi 54435
    Posts
    382

    Default

    Chuck it sounds like maybe your spoilboard or plenum is springing up in the corner where you zero it. The amana bit is pretty good quality so I wouldn't suspect the shank is slipping in the collet unless your collet is worn out.

  5. #5
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    578

    Default

    Thanks guys for the replies. As notes, my collet is pretty new, maybe 2 years old now, but to my embarrassment, it has low miles.... And the fact that I really tightened it down before flattening the second time pretty much eliminates the only thing that I can think would create such a problem.

    The material I have been carving is manufactured material that is also very flat Vinyl Composite Tile. And I used to carve this material with good success (uniform line widths when doing small V-carved letters) on tiles that are 12" x 12".

    My spoil board/plenum assembly is all glued together and is very solidly bolted to the steel frame members. Hmmmmmmmmmmm................ Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  6. #6
    Join Date
    Jan 2007
    Location
    Henrico, NC
    Posts
    99

    Default

    Environmental conditions - temp or humidity variations?

    Vertical play in "Z"?

    Hmmmmmmmm.......

  7. #7
    Join Date
    Jan 2011
    Location
    gleason, wi 54435
    Posts
    382

    Default

    Chuck I have never seen a spoilboard warp anywhere close to .049" in the short time between dressing the spoilboard and running a part. It usually takes days or weeks in my experience. .049 in 34 inches might be visually detectable at slow speed. Try to slow your feed rate way down and just watch as it runs from 2,30 to 36,30.

  8. #8
    Join Date
    Jun 2013
    Location
    Pasadena, CA
    Posts
    892

    Default

    Clamp a dial indicator with a dowel rod as adapter into the collet (or attach to the z-plate) and scan the table surface manually (assuming it is smooth).
    You will see right away if that is warped somewhere or when pushing the spindle if something is loose. Also useful for tramming the spindle with a swivel arm.
    Box Joint, Dovetail and MazeMaker Software Here

  9. #9
    Join Date
    Apr 2007
    Location
    Marquette, MI
    Posts
    3,264

    Default

    Chuck...
    Your observations show a difference in height between movement under load (surfacing) and movement under no load (gap with feeler gauges)

    This is most certainly a mechanical issue that you need to diagnose.

    One related, but not often suspected issue is delamination of the bond between the spoilboard and substrate.
    Gary Campbell
    CNC Training & Technology
    GCnC411(at)gmail(dot)com
    Control & ATC Retrofits

    http://www.youtube.com/user/Islaww1


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


  10. #10
    Join Date
    Mar 2006
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    7,774

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    THIS IS THE SOURCE OF YOUR PROBLEM.....rarry....

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