How do you set the stop when you know S.E.L?

Discussion in 'Segment PRO Forum' started by TomWS, Jan 24, 2018.

  1. TomWS

    TomWS PRO Member

    I am using Segment Pro for the first time (first time doing a segment bowl at all!) and I'm not sure what distance, from the cut line, to set the stop. I had assumed that I would use the S.E.L number from the Summary page, but my first test pass ended up a larger diameter than Segment Pro predicted.
    [SOLVED See below]

    The specifics are:
    12 Segment bowl,
    Row 2: Width=2.3, S.E.L=2.01, Outer Diameter=7.5", Inner Diameter=2.9"
    I did check "Optimize Board Widths" (which changed the board width from 2.34 to 2.30) but the S.E.L and Diameters don't change in the table when I do this.

    Actual results:
    Outer Diameter=7 13/16", Inner Diameter=3 3/16"
    The width of the board is 2.306" so pretty close to match.

    I'm using a sled similar in concept to the Wedgie Sled (but using Incra hardware) to set the two fences. The stop is set pretty close to 2.01 from the cut line. UPDATE: Note that by 'cut line', I mean the line from the outside of the blade, not the cut edge of the sled (so distance from the sled edge is 2.135"). Perhaps this is my problem???

    UPDATE #2: [SOLVED] After reading thread: Title: Wedgie sled calculations I realized my error. To set the stop from my cut line, I need to multiply the S.E.L by the Cosine of the angle of the segment edge to the face of the stop/cutline. In this case it's 15 degrees. I guess I'll update the spreadsheet to add a column for the stop setting which will take the angle and thickness of the blade into account. Odd that this isn't already in the spreadsheet which begs the question, how do people set the stop given the data from the spreadsheet?
     
    Last edited: Jan 24, 2018
  2. Bob Beaupre

    Bob Beaupre Administrator Staff Member

    The S.E.L=2.01 is the actual Segment Edge Length of the piece.
    Don't look at it as where the blade is.
    When you cut the piece the actual length of the trapezoid on the back side need to be 2.01"

    Basically and divination from that number you can multiple by 3.14159 as a increase or reduction in diameter.

    2.01" * 12 (segments)= 24.12"
    24.12" / 3.14159 = 7.677"
    but since the program uses cord length instead of actual arc length there is a little difference in diameter

    So in your case: 7.8125"-7.5"=0.3125" bigger diameter
    0.3125 / 3.14159 = .09947" / 12 = 0.0083"
    so it looks like your segment edge length is actually more like 2.0183

    If I run the numbers with actual arc lengths a ring 7.5" diameter and 12 segments I get a S.E.L. = 2.0096"

    If I run the numbers with actual arc lengths a ring 7.8125" diameter and 12 segments I get S.E.L. = 2.0934"

    Difference 2.0934" - 2.0096" = .0838" not much difference.
    Plus that's if your joints are absolutely "0"
    Hope that helps and doesn't confuse you more.
     
  3. TomWS

    TomWS PRO Member

    Thanks for the fast reply. Your explanation makes sense, but where I was stuck is how to set the stop distance given the data from the summary page.

    Using the cosine to adjust the S.E.L works perfectly. My stop is a 5" block of maple clamped to my tablesaw fence (to provide plenty of clearance for cut off wedges) so my new column sets the Stop setting to:
    (SELxCOS(angle)) + 5.0 + 0.125 (thickness of the blade)
    And this reads directly on my tablesaw fence position. Works like a charm!
    Tom
     
  4. Ken Sherwin

    Ken Sherwin New Member

    I too have a digital readout on my saw and this is EXACTLY the procedure I use, including the new column in a spreadsheet. Consider that the cosine error with 12 segments is 3.5% but with 16 segments, it's 2% and with 24 segments it's less than 1%.
     
  5. TomWS

    TomWS PRO Member

    LOL! I may have mentioned that this is my first segmented turning... As long as the ring is thick enough to allow me to, uh, 'deviate' from the prescribed profile without cutting through the wall, I'm good with it. As it is, Segment Pro has this nice feature where I can indicate that I am a 'novice' and it automatically thickens the rings to deal with the occasional 'oopsie' and subsequent adjustment. I just wanted to make sure that the stack up, once I've glued it all together, has allowances on both the plus and minus sides of the walls!

    Thanks for the feedback that I'm not totally off track here.

    I'm looking forward my first segmented turning!
    Tom
     
  6. Bob Beaupre

    Bob Beaupre Administrator Staff Member

    OK I have a older table saw. what kind of saw do you have or is this a add on you have added to your saw
     
  7. Ken Sherwin

    Ken Sherwin New Member

  8. Bob Beaupre

    Bob Beaupre Administrator Staff Member

    Then did you upgrade your fence from the original? I image you did. If so what did you do?
     
  9. Ken Sherwin

    Ken Sherwin New Member

    I put an Excaliber fence on it more than 10 years ago. I got it and my Dubby from an In-Line Industries booth at a small road show. General has since stopped making the fence.
     
  10. TomWS

    TomWS PRO Member

    I didn't mean to imply that I have a digital readout on my scale. It's just the ordinary stick-on tape with magnifying lens, but it is calibrated so 1" reading IS 1.0 inches between the fence and the fence side of the blade. With the setup I have, the sliding 'wedgie' fences are on the other side of the blade and, when I made the stop block (which is 5" long), I inadvertently referenced it to the Wedgie cut edge and, consequently, need to add 5.125" to any cut thickness I want to make. It's not a problem as it is constant and I simply add it in when I calculate the stop position.
    I toyed with the idea of moving my Wixley Planer thickness gauge to this application because it's pretty much useless on the planer - the battery is always dead whenever I want to use it and calibrating is a PITA after putting in a new battery. But, the scale works in reverse of what I'd want, so I won't use that.
     
  11. Ken Sherwin

    Ken Sherwin New Member

    To use my Wixey saw scale, I carefully cut part way through a board exactly 1" from the end of the board. When doing a setup, I engage the board in the blade and the sled, pull them back, and set the offset stop. Since this places the stop exactly 1" from the blade, I can then set the absolute position of the saw scale at -1" (I put the fence and stop on the left side of the blade) and can then set the cut length directly from the readout.
     
  12. mfisher

    mfisher Super Moderator Staff Member

    I do a more basic approach. On a scrap piece of .125" thick wood I cut the end at the angle of my segment. (5degrees for 36 segment). Then using a digital caliper I set it to the desired SEL. From there I mark the wood.
    I place the wood along the set fence on my cutting sled till the mark is at the edge (outside) of the saw blade. I move the stop up to the stick. Then cut a test piece and measure. Then do any fine tuning to achieve the SEL.
    SEL should be measured using the miter angle, not 90 degrees from the blade to the stop.
     
  13. Bob Beaupre

    Bob Beaupre Administrator Staff Member

    That's pretty much the same as my process also.
     
  14. mfisher

    mfisher Super Moderator Staff Member

    Main reason I posted was after looking at the digital saw fence (WR700) I was a bit confused on how it could be used for the SEL reading. Think I figured it out.
     
  15. Halling51

    Halling51 Member

    I thought the S.E.L meassuer is the same on either saw you use?
    For me the meassuring is something I need to find out on my saw! How I do it does not matter at all?
    I don't need to be told about Cos and Sin. I think this is far out and are just making segment turning a NOT good idea for someone trying to understand in a good way.
    I am not happy to follow a subject like this!
     
  16. Ken Sherwin

    Ken Sherwin New Member

    The way to not have to deal with the complications is to mark the segment edge length of the stock you are cutting your segments from (after you cut your first angle, of course). Set your stop so that the blade cuts just on the waste side of the mark, just like would cut any other piece on a saw without a readout.

    The only time the cosine comes into consideration is if you want to use the saw readout directly. Because the segment is at an angle to the blade and fence, the length of the part you just cut will be longer than the distance from the stop to the blade.
     
  17. Halling51

    Halling51 Member

    I still don't see the sence to do it more complicated then nessesary!
     
  18. Halling51

    Halling51 Member

    This is my final answer to this.
    I have been working with wood, lumber and timber since 1960. Making doors, windows, meassuring items for the same. Also in the beinning we made stairs, I think you need accuracy for this.
    But I never have seen so many explanations for a thing to do as this threat. If you make a jig and let your skills take part there is no hokus pokus. A cut is correct when you find the correct way to do it - in your workshop and make a first try for the first ring either open or not.
    Thanks for reading!
     
  19. Brett Niland

    Brett Niland PRO Member

    Truer words, Tom. My first attempt has a "step" and glue line on the interior where I didn't line up right. In spite of the misstep, just that one bowl has me so completely hooked, it's a borderline obsession. That's my first and only warning for you sir. You finish that glue up and get that sucker on the lathe and it's all over for you. Haha!

    Brett
     
  20. Ken Sherwin

    Ken Sherwin New Member

    Yep. The action of a piece on a lathe is called 'The Vortex' for a reason.
     
    Brett Niland likes this.

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