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Thread: Table Saw Miter Cut "U" Shape

  1. #1

    Question Table Saw Miter Cut "U" Shape

    Howdy, so I am racing to get some boxes made for Christmas gifts. I am trying to cut the 45 degree miters on my table saw using a cross-jig. I clamp the work piece in place and use stop blocks, but I get an odd U shape to the cut. The board is milled flat and square prior to making the cut. Any idea what is happening here? My blade is calibrated to the miter slot and my rip and parallel cuts are fine. It is just these miters that are killing me. Ideally I would use a shooting board, but I don't have one and I don't have time to make one before Christmas. Any help would be amazing.
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    Last edited by Mike Geig; 12-15-2019 at 6:31 PM. Reason: changed image to embedded

  2. #2
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    Too much movement in your crosscut jig would be my guess.
    Aj

  3. #3
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    It is possible that the jig could move away and then back to the desired feed path. I feel that it is unlikely that it would be consistent. Have you checked the blade alignment at 45*? Folks often go to great lengths to get the blade parallel to the miter slot at 90* but, don't finish up by adjusting when at a bevel. Everything is great until you start making bevel cuts.

    The material is clamped to the fence and the sled rides in the miter slot so they are fixed in position. If the alignment is off the (crooked) blade plane could be flexing as it tries to conform to the unforgiving and misaligned feed path of the material. Easy to check. Just set your blade to 45* and check it like you do at 90*. A thou or so won't hurt you too much but, 4 or 5 thou starts to get problematic.

    22124 Alingment 010.jpg
    Last edited by glenn bradley; 12-15-2019 at 9:59 PM.
    “Falsehood flies, and the Truth comes limping after it,”
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  4. #4
    Looks like your board is going though at a slight arc, rotating presumably with the axis on the miter bar. I'd check that your sled is not loose as mentioned above and that it is rigid enough to not flex. Beveled cuts are have more blade engaged compared to a 90 cut, and what works at 90 may strain at 45.

    Also, any chance your blade is getting a little on the dull side? That could cause you to muscle through the cut and could give you the a little pivot against the miter slot. Again it would show up at 45 more than 90.

  5. #5
    What blade are you using to make the cut? Is the blade dull? When is the last time you checked the blade alignment to the miter slot? Slop between the miter gauge and the miter slot can also cause this problem.
    Lee Schierer
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  6. #6
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    Don't race, nobody wants a box with your bloodstains on it. Better to make excuses and deliver later.

  7. #7
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    Quote Originally Posted by Lee Schierer View Post
    What blade are you using to make the cut? Is the blade dull? When is the last time you checked the blade alignment to the miter slot? Slop between the miter gauge and the miter slot can also cause this problem.
    Lots of good advice here. I was also wondering about the blade and if you are getting deflection because it is dull or a thin kerf.

  8. #8
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    I'm with Todd on this. I've had some problems in the past while using a thin kerf blade and having the blade raised up for a higher cut, i.e., while on a sled for example. While using the same blade, I had to install a deflection plate to avoid this. The simplest thing would be to check blade deflection first.
    SWE

  9. #9
    Thanks for the info everyone. Follow up:

    -The blade is sharp, though it is a 10" 60th finishing blade (full kerf) so there is a little pushing involved
    -It's a good point about checking for square while at 45 degrees. I've only tested for square at 90 degrees. I will check on that
    -The whole thing is on a sled, but I will check for slop / flex with the rails and fence
    -Something I forgot to mention, when using this sled, there are burn marks on the back-half (closest to fence) of the cut. I agreed that this would indicate an alignment issue, but seeing how test cuts came out fine I wasn't sure

    Thanks again for all the help

  10. #10
    Quote Originally Posted by glenn bradley View Post
    It is possible that the jig could move away and then back to the desired feed path. I feel that it is unlikely that it would be consistent. Have you checked the blade alignment at 45*? Folks often go to great lengths to get the blade parallel to the miter slot at 90* but, don't finish up by adjusting when at a bevel. Everything is great until you start making bevel cuts.

    The material is clamped to the fence and the sled rides in the miter slot so they are fixed in position. If the alignment is off the (crooked) blade plane could be flexing as it tries to conform to the unforgiving and misaligned feed path of the material. Easy to check. Just set your blade to 45* and check it like you do at 90*. A thou or so won't hurt you too much but, 4 or 5 thou starts to get problematic.

    22124 Alingment 010.jpg
    Unfortunately, it seems I'm not cool enough to view images on this site.

  11. #11
    Unfortunately, it seems I'm not cool enough to view images on this site.
    It's not coolness, it's the $6 a year you don't pay.

  12. #12
    Quote Originally Posted by Bradley Gray View Post
    It's not coolness, it's the $6 a year you don't pay.
    Ah, I didn't know that was a thing.

  13. #13
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    Others with comments are right. I also wonder if the piece is possibly lifting slightly from the surface of the sled. I had an opposite problem with small pieces I was cutting for boxes but it turned out the thin would was cupped after resawing and planing.
    Rustic? Well, no. That was not my intention!

  14. #14
    Your banana cuts and burn marks would indicate that you blade is skewed to the right when tilted. Thus your board is being forced upwards, ramping up onto the blade. As you exit the cut the board is able to drop back down, hence your arc. If i was pinched for time, I would cut my miters a 16th long, then trim to final length on the other side of the blade. If I wasn't pinched for time, I would calibrate my saw.

  15. #15
    Quote Originally Posted by johnny means View Post
    Your banana cuts and burn marks would indicate that you blade is skewed to the right when tilted. Thus your board is being forced upwards, ramping up onto the blade. As you exit the cut the board is able to drop back down, hence your arc. If i was pinched for time, I would cut my miters a 16th long, then trim to final length on the other side of the blade. If I wasn't pinched for time, I would calibrate my saw.
    Good idea. I will give that a try in the short term

    Turns out my blade is .0004 off at 90 degrees and .0012 off at 45. After Christmas I will get to fixing this but need a faster solution for now and this might be it.

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