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Thread: Cupped Jointer Results

  1. #1
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    Cupped Jointer Results

    Refresh my memory...if a jointer is making cupped boards (both ends touch a flat surface, but the middle doesn't), what's the likely cause?

    I noticed this evening that two light passes edge jointing a 21' long board left about 2 sheets of paper's worth of gap in the middle when the edge was placed on a flat reference surface. I was tired and didn't feel like debugging it tonight, but I suspect the tables aren't coplanar any more. (Too much moving it is my guess...even though it's on a mobile base, the carpeted shop floor makes it tough to move. Can't help but pull on the tables some.)

    I'm pretty sure my technique is correct, so I figure it's gotta be the machine. I haven't checked out the tables since I first assembled the jointer a bit more than a year ago. I've got a good 4' Veritas straightedge, although I don't have any real feeler gauges. If the tables are coplanar, I think I know the rest of the setup process. If they're not coplanar, then I'll be heading into unfamiliar terriroty. Any jointer table setup tips?
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
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  2. #2
    Vaughn, I am not sure either so I won't steer you wrong by posting something I am not absolutely sure about. What I do know though, is that a regualr sheet of say computer paper is roughly .004 of an inch thick. You have the right idea, using paper shims you can get a great idea of how close you are. In your case, you are .008 thousanths off.

    When I worked for Lie Nielsen, we often used masking tape (.004) to shim our milling machines to get things just right. You would think that for a 200 dollar plane they would come up with a better system, but sometimes its the simple stuff that works the best.

    Just thought I would toss this out there so people can use paper as a feeler guage and shims. Just be sure its regular notebook paper, and not thick photo paper or some other exotic paper.
    I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"

  3. #3
    Join Date
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    Vaughn---I believe that would be a problem with the tables not being parallel. Sounds like one or both of the tables are sagging at the ends. Check out this tune up link.
    http://woodworking.homeip.net/wood/T.../Jointers.html

    Dan
    Last edited by Dan Forman; 04-15-2007 at 10:24 AM.
    "A dog teaches a boy fidelity, perseverance, and to turn around three times before lying down."
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  4. #4
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    I'm going with your outfeed table being low although other things could cause this. That was my problem when I had that symptom; as the leading edge drops to the lower outfeed the rear of the board has a variable pivot point as it trails through the cut. Tweaked the tables and all is now well.

  5. #5
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    I think Glenn is on it. If not it's the easiest to check. Just lay a straight edge on the outfeed, rotate the cutter head and see if the blades just touch it or lift the straight edge up.
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  6. #6
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    Like Jeff, my first thought was the straight edge test. Take it from there.
    "Folks is funny critters."

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  7. #7
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    A low outfeed table will yield snipe at the end of the cut, as the board drops onto the cutterhead when the infeed table no longer supports it. The rest of the board will be straight, however.

    That is a different result from tables being out of parallel, which will cause a concave or convex cut along the length of the board, depending upon whether the tables are high or low at the ends. I had this problem, and with the help of the link posted earlier, got it straightened out (pun not intended, but I'll live with it).

    Dan
    Last edited by Dan Forman; 04-15-2007 at 07:43 PM.
    "A dog teaches a boy fidelity, perseverance, and to turn around three times before lying down."
    Robert Benchley

  8. #8
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    Dan is on base here. I also had snipe when my problem was happening.

  9. #9
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    I agree with Dan about the tables. One question, where did you find a 21' board?

  10. #10
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    What kind of wood? Maybe try a different board too, as some pieces move enough to fool you (like my recent use of birch, some pieces bowed 1/16" over 36").

    If it is the jointer, the end of one table will seem low relative to the other. If all your gib screws are still tight, and the ends are low, then shimming is in order. I've never had to do that myself, so can't help you there -- I've always managed to get it by tightening the screws. The top two gib screws do more adjusting than the bottom two, so I tighten them first, then do the bottoms, then come back and check the tops. If the bed is hard to move then they're too tight.

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