Crosscut Accuracy

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  • Crosscut Accuracy

    Hello,

    Past weekend I was making crosscuts on some rather large panels (17"+). I used the 5 cut method to check the accuracy of my SMT/Miter.

    (Disclosure - I have high OCD)

    My calculation leads me to believe my miter is 89.91 degrees as opposed to 90 degrees.

    Here is how I arrived at that -

    On the 5th cut the piece which was 17.3125" long, was 0.648" on front and 0.543" on rear
    0.648" - 0.543 = 0.105"
    Divide this by 4 since the error is compounding => 0.02625 per cut over 17.3125".

    Therefore my angle deviation is ARCTAN (0.02625/17.3125) = 0.0869 degrees

    Since my front portion is wider than rear portion I am 89.9131/90.0869 instead of a perfect 90/90.

    So My question is - should I try to improve this or is it futile to get any better than this. (I will have to deal with my OCD )

    Someone please check and hope you don't find it is even worse than I think

    TIA,

    Nicer

  • #2
    I have three comments.
    1. brain is not functioning enough to check your method mentally. maybe later
    2. if you are correct, less than 0.1 degree is pretty **** good. Have you tried to adjust anything by a 1/10th of a degree? It's very **** hard! I have a digital angle box https://www.sawdustzone.org/forum/di...ngle-indicator I call it an angle meter because it differentially measures angles and a large digital protractor which measures absolute angles. https://www.amazon.com/dp/B07VCQ3PPJ...NsaWNrPXRydWU=
    3. Have you located the miter zero stop flip up stop on your SMT for making repeated zero/90 degree angle miter cuts? You can set it once for your best 90 degree cut and then use it easily every time thereafter instead of relying on the scale on the SMT. The flip stop is held with an eccentric screw so it can be micro-adjusted for your perfect zero. I'm certain its described my BT3FAQ
    Non understanding your method perfectly... 0.648 and 0.543 represent what? Do you have a link to your method?

    I highly recommend both those angle tools. Not exactly the same, they are complementary to each other.
    The angle box I can zero to a table or blade position and then tilt to a desired angle. But works only in the vertical plane.
    The protractor is ideal for checking the miter angle of your blade and miter fence. You have to be careful to use the face of the blade because the teeth usually are wider than the body. which means a parallel edged spacer may be needed.

    https://www.sawdustzone.org/forum/di...e+denali+wixey
    Last edited by LCHIEN; 10-04-2021, 05:10 PM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment


    • nicer20
      nicer20 commented
      Editing a comment
      I don't have any link but I will try to write up my method soon and share. It will be good for you guys to take a look and tell me if I am doing something wrong. TIA.

  • #3
    Loring,

    The five cut method is a way of squaring a jig or miter gauge. Basically, you cut a board with the miter gauge, rotate it 90 degrees so the cut edge is now agains the miter gauge and cut it again and repeat until you've made 5 cuts. Then measure the width at each end and the difference is the total out of square error. Divide this by 4 since you've multiplied the error 4 times. Then based on the length of the final cut and your difference, you can determine the angle from square.

    Nicer,

    Less than .1 degrees is pretty dang good. If it were me, I wouldn't touch it because I would likely make it much worse, but it would still bother me.

    On a BT3x00 there are three probable sources of error.
    1. If the SMT is not sliding perfectly parallel to the blade your cut will drift toward or away from the blade as you slide it through. The same is true with the miter slot on a traditional table saw if it is not parallel to the blade.
    2. The miter fence is not at precisely 90 degrees to the travel of the SMT.
    3. Finally, slop in the SMT slides. If your slides are adjusted to be anything but snug, and you push on your miter sled slightly off center, it will rotate a tiny fraction of a degree clockwise or counter clockwise and give the same effect as having the miter fence not at 90 degrees.
    Chr's
    __________
    An ethical man knows the right thing to do.
    A moral man does it.

    Comment


    • #4
      Originally posted by twistsol View Post
      Loring,

      The five cut method is a way of squaring a jig or miter gauge. Basically, you cut a board with the miter gauge, rotate it 90 degrees so the cut edge is now agains the miter gauge and cut it again and repeat until you've made 5 cuts. Then measure the width at each end and the difference is the total out of square error. Divide this by 4 since you've multiplied the error 4 times. Then based on the length of the final cut and your difference, you can determine the angle from square.

      Nicer,

      Less than .1 degrees is pretty dang good. If it were me, I wouldn't touch it because I would likely make it much worse, but it would still bother me.

      On a BT3x00 there are three probable sources of error.
      1. If the SMT is not sliding perfectly parallel to the blade your cut will drift toward or away from the blade as you slide it through. The same is true with the miter slot on a traditional table saw if it is not parallel to the blade.
      2. The miter fence is not at precisely 90 degrees to the travel of the SMT.
      3. Finally, slop in the SMT slides. If your slides are adjusted to be anything but snug, and you push on your miter sled slightly off center, it will rotate a tiny fraction of a degree clockwise or counter clockwise and give the same effect as having the miter fence not at 90 degrees.
      I agree with 2 and 3.
      On 1 the angle of the blade being parallel or not to the travel of the SMT does not affect the angle of the cut... the cut is still made parallel to the travel of the SMT. If the blade is canted a bit right or left then the result is that the cut is made on the leading or training edge of the blade that contacts the sliding workpiece.
      I guess is makes a bit of difference in the cleanliness of the cut.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

      Comment


      • #5
        Originally posted by twistsol View Post
        Loring,

        The five cut method is a way of squaring a jig or miter gauge. Basically, you cut a board with the miter gauge, rotate it 90 degrees so the cut edge is now agains the miter gauge and cut it again and repeat until you've made 5 cuts. Then measure the width at each end and the difference is the total out of square error. Divide this by 4 since you've multiplied the error 4 times. Then based on the length of the final cut and your difference, you can determine the angle from square.

        Nicer,

        Less than .1 degrees is pretty dang good. If it were me, I wouldn't touch it because I would likely make it much worse, but it would still bother me.

        On a BT3x00 there are three probable sources of error.
        1. If the SMT is not sliding perfectly parallel to the blade your cut will drift toward or away from the blade as you slide it through. The same is true with the miter slot on a traditional table saw if it is not parallel to the blade.
        2. The miter fence is not at precisely 90 degrees to the travel of the SMT.
        3. Finally, slop in the SMT slides. If your slides are adjusted to be anything but snug, and you push on your miter sled slightly off center, it will rotate a tiny fraction of a degree clockwise or counter clockwise and give the same effect as having the miter fence not at 90 degrees.
        Ok - looks like what I have seems to be reasonably acceptable then. I was thinking everyone else's saw is far more accurate than mine. After all my error seems to be less than 1/32" over 17 inches. May be I should not fret over it too much.

        Regd. #3 - I think I used to have that issue until last year during tune-up I fixed it. I think it was Black walnut 's excellent SMT service guide that I followed and removed the slop.

        Thanks again.

        NG

        Comment


        • #6
          Originally posted by LCHIEN View Post
          I have three comments.
          1. brain is not functioning enough to check your method mentally. maybe later
          2. if you are correct, less than 0.1 degree is pretty **** good. Have you tried to adjust anything by a 1/10th of a degree? It's very **** hard! I have a digital angle box https://www.sawdustzone.org/forum/di...ngle-indicator I call it an angle meter because it differentially measures angles and a large digital protractor which measures absolute angles. https://www.amazon.com/dp/B07VCQ3PPJ...NsaWNrPXRydWU=
          3. Have you located the miter zero stop flip up stop on your SMT for making repeated zero/90 degree angle miter cuts? You can set it once for your best 90 degree cut and then use it easily every time thereafter instead of relying on the scale on the SMT. The flip stop is held with an eccentric screw so it can be micro-adjusted for your perfect zero. I'm certain its described my BT3FAQ
          Non understanding your method perfectly... 0.648 and 0.543 represent what? Do you have a link to your method?

          I highly recommend both those angle tools. Not exactly the same, they are complementary to each other.
          The angle box I can zero to a table or blade position and then tilt to a desired angle. But works only in the vertical plane.
          The protractor is ideal for checking the miter angle of your blade and miter fence. You have to be careful to use the face of the blade because the teeth usually are wider than the body. which means a parallel edged spacer may be needed.

          https://www.sawdustzone.org/forum/di...e+denali+wixey
          Thanks LCHIEN for your help, as usual.

          For once, I have both the gauges you mention - have been collecting some of these over the last year

          Also, thanks for pointing out about the Miter Zero Stop. I did adjust it during my tune up last year. Remember I was struggling with the blade raising issues - and indeed your FAQ as well as numerous tune-up articles I found (including Black walnut 's SMT service guide) helped tremendously.

          Thanks a lot - as you and twistsol pointed out I will stop fretting over less than 0.1 degree error.

          NG

          PS - I will try to writeup the method I am using for angle calculation and will share ASAP
          Attached Files

          Comment


          • LCHIEN
            LCHIEN commented
            Editing a comment
            I understand the angle calculation. I assume the two values you gave are the differences in width from parallel in the two directions.

        • #7
          To differentiate them I would call the Wixey a Tilt Angle Indicator and I call the Denali a Protractor.

          Tilt angle indicator
          Pros - magnetic base, zeroing capability make it ideal for setting table saw blade angle for example. Compact size; fits in pocket.
          Cons - short base line make it difficult to line up to measure some objects, pendulem movement allows you to only measure in the vertical plane.

          Protractor
          Pros - long baseline and rotating blade makes it possible to measure objects that can't be rotated to vertical and maybe have a little uneven sides. Also possible to set an angle on the blade and then use it to mark your workpiece to cut a certain angle.
          Cons - No zero for measuring relative angles. large size.



          Example 1: I find the tilt angle indicator ideal for measuring the bevel of the saw blade - zero to the table and then attach the short magnetic baseline to the side of the extended blade.

          Example 2: I find the Protractor the best way to set or check the angle of the miter fence - the long base against the fence and the blade against the blade lying flat on the table.

          Example 3: the protractor would be the way to directly measure the angle of a assembly someone gave you... you could use the tilt angle indicator (zero the base, stand the angle up and measure the slope) but some items can't be moved and/or the ability to stand it perfectly upright and not lean forwards or backwards would introduce some errors into the measurement.
          Loring in Katy, TX USA
          If your only tool is a hammer, you tend to treat all problems as if they were nails.
          BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

          Comment


          • #8

            Click image for larger version  Name:	fetch?id=845632.jpg Views:	0 Size:	90.5 KB ID:	845637

            I would criticize the way this is used... the teeth of the saw stick out some several milliinches past the body of the saw blade. The body of the gauge is touching both the blade and the teeth and the table top.
            So is the angle meter against the teeth or against the body of the blade? I would raise the blade sufficiently so that the magnetic base of the angle gauge is completely against the blade body and not touching the teeth and also completely off the table top. Otherwise the teeth sticking out will tilt the gauge slightly more than the body of the blade disc.

            Of course this is after zeroing the gauge to the table top. Making sure its completely on one piece, like the ZCTP (if that's the referene and you are sure it is parallel to the table top) and not crossing the ZCTP and the aluminum top which if not perfectly level will tilt the gauge.
            The gauge is only 2" across the side. A tilt of 5 milliinches over 2 inches is arcsin(.005/2) = .143 degrees added error.

            Not trying to be mean but these are lessons I've learned. and I think you are a perfectionist, a bit.
            Last edited by LCHIEN; 10-05-2021, 11:37 AM.
            Loring in Katy, TX USA
            If your only tool is a hammer, you tend to treat all problems as if they were nails.
            BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

            Comment


            • #9
              My method to calculate the miter angle is based on the 5-cut method developed by William Ng for squaring up crosscut sled. I found his idea and an excellent explanation in this video - https://youtu.be/UbG-n--LFgQ

              Watch at least until 6:21 mark to get the idea about compounding angles and error.

              Now equipped with this concept –

              (see attached figure for reference)
              Click image for larger version  Name:	Five Cut Method for miter angle.png Views:	0 Size:	12.5 KB ID:	845640
              After the 5th cut, lets say you get a strip which is broader on one side than the other. So your strip will look something like in the attached drawing (exaggerated) . For now, lets say your front end is wider than the rear end. Same math will apply for the opposite scenario with narrower front than the back.

              In essence, front width is x+dx whereas rear width is x. The error is occurring because angle Theta isn’t 0. In a perfectly square fence, both the long sides will be parallel, widths of cuts on the front and rear will be identical(x) and dx & Theta will be 0. Keep in mind that dx & Theta are an accumulation of 4 cuts. So actual angle mismatch is Theta/4.

              Using basic trigonometry, now Theta = Arctan (dx/y) where y is the length of this strip. Actual angle mismatch is Theta/4.

              If your 5th cut results in a strip with narrower front than the rear, the same math applies except, dx and Theta are -ve.

              A +ve error represents fence is caved in TOWARDS the blade, making the angle LESS than 90 by Theta/4. If the error is -ve, the fence is tilted AWAY from the blade, making the angle MORE than 90 by Theta/4.
              Attached Files
              Last edited by nicer20; 10-05-2021, 12:45 PM.

              Comment


              • #10
                Originally posted by LCHIEN View Post

                ................................

                I would criticize the way this is used... the teeth of the saw stick out some several milliinches past the body of the saw blade. The body of the gauge is touching both the blade and the teeth and the table top.
                So is the angle meter against the teeth or against the body of the blade? I would raise the blade sufficiently so that the magnetic base of the angle gauge is completely against the blade body and not touching the teeth and also completely off the table top. Otherwise the teeth sticking out will tilt the gauge slightly more than the body of the blade disc.

                Of course this is after zeroing the gauge to the table top. Making sure its completely on one piece, like the ZCTP (if that's the referene and you are sure it is parallel to the table top) and not crossing the ZCTP and the aluminum top which if not perfectly level will tilt the gauge.
                The gauge is only 2" across the side. A tilt of 5 milliinches over 2 inches is arcsin(.005/2) = .143 degrees added error.

                Not trying to be mean but these are lessons I've learned. and I think you are a perfectionist, a bit.
                I like it when someone is being thorough - so no offence at all. I love it.

                You are 200% right on the money.

                OK - I slacked by posting a photo I shouldn't have. What you see in picture is a 71/4" blade so that is the highest it gets. I was just trying to show off my gauge and being lazy. Sorry :-(

                In reality, I have been cognizant of every bit you said and here is the real photos showing the 10" blade raised all the way up & then backed off 1/8 - 1/4of a turn. Mounting the gauge as high as possible without touching the teeth, to catch the slightest of the error as the error will grow the higher you go.

                Click image for larger version  Name:	IMG_5267.jpg Views:	0 Size:	44.5 KB ID:	845642 Click image for larger version  Name:	IMG_5266.jpg Views:	0 Size:	48.3 KB ID:	845643

                Oh and when I mounted the 7 1/4" blade to cut that ZCTP slot, I opened the side panel and set the gauge on the body of the blade avoiding the teeth to make sure the blade is 90. Of course, this still leaves a possibility that the blade can have a slop in the raised position but what can I do

                Hope you can upgrade my grade from an F or a D to at least a C
                Last edited by nicer20; 10-05-2021, 12:45 PM.

                Comment


                • #11
                  Solution for accuracy. Mouldings hide framers mistake, spackle hides the rest, at least if the moulding will be painted. (I’m not really that bad)

                  My grandfather built many houses in Norway, including his own house and I was amazed by his woodworking skill evident in the house. He made all moulding and doors (one a day). The house included a half circle stairway, probable to conserve floor space and all layout done by hand and no power tools at all. When I was there in 2001 I was able to get some of his moulding cutters and I expect that he made many of them. One of my cousins has the old family farm and his father (my great uncle ) had a very beautiful tall cabinet my grandfather made as a wedding present for his brother. Please excuse the digression but the skill and precision my gpa exhibited with hand tools was awesome.

                  Comment


                  • nicer20
                    nicer20 commented
                    Editing a comment
                    I have a high regard for all the craftsmen who built those amazing pieces with mere hand tools !!

                • #12
                  Originally posted by nicer20 View Post



                  Hope you can upgrade my grade from an F or a D to at least a C
                  This a pass-fail course and the final is self graded. Experience is the teacher. Only you can be the final grader and the results are only known to you if you want it that way.
                  Loring in Katy, TX USA
                  If your only tool is a hammer, you tend to treat all problems as if they were nails.
                  BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                  Comment


                  • #13
                    Originally posted by LCHIEN View Post
                    To differentiate them I would call the Wixey a Tilt Angle Indicator and I call the Denali a Protractor.

                    Tilt angle indicator
                    .........................

                    Protractor
                    Pros - long baseline and rotating blade makes it possible to measure objects that can't be rotated to vertical and maybe have a little uneven sides. Also possible to set an angle on the blade and then use it to mark your workpiece to cut a certain angle.
                    Cons - No zero for measuring relative angles. large size.

                    ..................
                    Mine has a Zero'ing feature with a separate button.

                    Click image for larger version

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                    I also found that you can achieve the same functionality by first opening the angle to the desired setting and then turning on the device. Have you tried that? May be it will work even if yours is missing the "Zero" button.

                    Comment


                    • #14
                      Originally posted by nicer20 View Post

                      Mine has a Zero'ing feature with a separate button.

                      Click image for larger version

Name:	IMG_5316.jpg
Views:	49
Size:	132.8 KB
ID:	845652
                      I also found that you can achieve the same functionality by first opening the angle to the desired setting and then turning on the device. Have you tried that? May be it will work even if yours is missing the "Zero" button.
                      mine only has an on-off switch

                      Click image for larger version

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Views:	44
Size:	16.0 KB
ID:	845654
                      Loring in Katy, TX USA
                      If your only tool is a hammer, you tend to treat all problems as if they were nails.
                      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                      Comment

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