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Thread: segmented bowl calculator?

  1. #1
    gord in oakville Guest

    Default segmented bowl calculator?

    trying my hand at a segmented bowl...also trying to find a freeware calculator for the angle cuts on the segments. Would appreciate it if any one knows where I can locate this and download it.
    thanks



  2. #2
    J.P.Rap in Hamilton Guest

    Default Re: segmented bowl calculator?

    If you want to calculate the angles, its pretty simple. One thing to remember is since youll be turning it, the size doesn't have to be dead on.

    If all you want is the angle, divide the number of parts(segments) by 360. thats the angle they meet at. Divide that number in half to get the angle you need to cut.

    If you have a plan or a sketch to work from you have to first decide what the outside diameter is. Then you have to decide how many segments you want to have. Or... Deside on a rough size for each segment.

    Multiply the diameter by 3.14 to get the circumfrance. divide the circumfrance by the number of segments to get the large length of each sement. or...divide the circumfrance by the large length to get the number of segments.
    Get it?
    once you have that you can use those numbers with the first formula to get the angle.

    Now remember youll be turning this to size so adjust your measurments to come to a size thats easy to work with and is still very close to what you want. It may be a little bigger but don't go smaller.

    Here's an exsample...

    I need one ring 10" dia outside. I want to make it with 20 segments
    10" X 3.14= 31.4 ------ C = 31.4"
    31.4 / 20 (segments) = 1.57 ------- large side of segments measures 1.57"------ round that up to 1.625 which is 1 5/8" easy measurment to work with and very close to the size you need(slightly larger)
    Cut 20 segments at 1 5/8" and you will get a ring that is 10.4" dia.

    Start with the same ring but you need each segment to be 1/4" wide.
    C / size = # segments.
    31.4 / .25 = 125
    You need 125 segments at 1/4" to make a 10" ring.

    eg. #1 --- 20 segments into 360 degrees
    360 / 20 = 18
    18 / 2 = 9
    Cut each segment at 9 degrees.

    eg. # 2
    125 segments
    360 / 125 = 2.88
    2.88 / 2 = 1.44
    Cut 125 segments at 1.44 degrees.

    Heres the fun part.
    Glue all your segments together and clamp them with a ring clamp. Leave two opposing faces unglued so you end up with two half rings. Your cuts will not likely be exact so you can adjust (sand) those unglued faces so they match up perfectly. The tiny error in size will be undetectable.

    Finaly...If you would rather cut to 10 degrees than 9 degrees, play with the sizes until you come up with a size that is acceptable at 10 degrees. It just depends on what the critical measurment is. Diameter is usually flexable.
    Hope all that makes sense.
    J.P.



  3. #3
    Join Date
    Feb 2006
    Location
    Saint John, N.B.
    Posts
    27

    Default Re: segmented bowl calculator?

    Pick up a copy of Ron Hamptons book SEGMENTED TURNING (a complete guide). Its the best book that I have seen on this subject, no software involved as there are lots of tables in the back covering the angle requirements.


  4. #4
    Gord in Oakville Guest

    Default Re: segmented bowl calculator?

    hi JP. I have spent the last little while working up an excel table to do just what you have in script and it seems to work pretty well for that part of the calculation .Here is the difficult part: once the segment numbers have been deternimed there is the actual shape of the bowl to be considered and that shapehas a direct impact on the depth of each segment (as measured perpendicular to the chord) basically you need enough glueing surface so that the segment layers stay together and the inside and outside slope of the bowl after turning are inside the outer extremeties of each segment layer as measure horizontially through the layer.
    here is an example of what I mean. first layer is dia 5". Segment width say 1 1/2" and thickness 1" second layer is dia 7" segment width is 1 1/2 " and thickness the same. (This example pushes the extreme to only illustrate my point)

    actual gluing surface between layer is 1/2" - probably enough to hold it together but the inside slope of the finished bowl will run outside the extremeties of the rough segment unless the shape of the bowl is changed. so how do you calc this little mess?



  5. #5
    J.P.Rap in Hamilton Guest

    Default Re: segmented bowl calculator?

    Well Gord, you bring up a good point.
    Thats were design comes in and there are a number of things to consider.
    You see, there are two ways to go about this. The first is what I did in the first and only segmented turning I've done. I built up a number of segmented rings in different sizes and glued them together and turned whatever I could from the blank. This was nothing more than practice to get the steps down. You can modify this by having a particular shape in mind and build your segments to suit that shape, not conserning yourself with the design produced by the segments. This is a great way to get started and get a real good idea of what you can expect when dealing with segments.
    The second way is the way I will do my next segmented turning (when I get around to it).
    Start with a very specific shape. That shape will have a specific design created by the segments. That design is created using particular sizes for the hight and width of each of the segments(I think thats what your asking about).
    As for building a chart for all the possible parameters, I can't help you there, nor would I want to try. Heres the way its usually done.
    Draw the shape on a piece of graph paper. Include the wall thickness in the drawing. You only need to draw one side as the other side will be identical.
    Using the graph lines, mark the thickness(hight) of each segmented ring accross the page as if it was being cut from a stack of flat boards. Now you extend perpendicular lines down at the major and minor diameters of each segment.You will end up with a rectangle that will be a cross section of each segmented ring. Add some extra for error and you have your sizes.

    Here's a little more...

    Think of a wedge cut from a piece of wood. The wedge is 4" at the top and tapers down to a point. The angle doesn't matter. At some point that wedge will measure 1/4" accross. If you cut one inch out of the wedge at that point, you can easily get the 1/4" segment you are looking for.

    If you made a whole pile of these wedges and glued them all up and stacked them, you would end up with a cylinder (sort of). The angle you cut the wedges at will determine the wall thickness of that cylinder. Lets forget about the angle for a moment and say we have a 12" D cylinder with a wall thickness of 5". You could mount that on the lathe and turn a nice vase thats just under 12" accross the top and just over 2" at the bottom.Each of the rings would have segments slightly smaller than the one above it even though they all started out the same size.
    If that made any sense to you...and I hope it does , then consider this. All you are doing by cutting smaller wedges and segments is removing material that would other wise have to be removed at the lathe.
    This in turn reduces waste. You could further reduce waste by cutting the sides of the rings on an angle. Infact this is how I did my first one.
    I took rings that were 2" accross the section and cut them on a 45 deg angle to produce two rings that stacked one on top of the other.

    This is getting all too confusing and Im just getting started.
    I hope that helps clear things up a bit but Im going to draw something up and Ill post it later.

    Till then
    J.P.

    Hope this pic works.
    My one and only segmented bowl.
    Count four pieces from the top (All the pieces between the horizontal pieces). Thats one ring.
    look down to the third ring set of four pieces(with horizontals). Both those rings came from the same rough ring. They are identical but one was cut from the other then seperated with a different ring.
    Count down four and you will see the other half of the one seperating #1 and #3. Again #2 and #4 are identical and were originaly one rough ring.
    Get it?




  6. #6
    woodguy Guest

    Default Re: segmented bowl calculator? *LINK*

    One of the best web sites I have seen on segmented bowls.



    http://www.turnedwood.com

  7. #7
    woodguy Guest

    Default Re: segmented bowl calculator? *LINK*

    Have used this software a lot (free 30 days).
    Like it a lot.---- No connection with them personaly.



    http://www.WOODTurnerPRO.com

  8. #8
    J.P.Rap in Hamilton Guest

    Default Re: segmented bowl calculator?

    That link covers it pretty well. Better than anything I would have drawn up in paint.
    The vase below was turned by Jim Vasi.
    It was he who gave the demonstration at my first meeting of the GHWG. He covered quite a bit and it was that demonstration that inspired the vase I did.
    Google Jim Vasi and you will find lots of his stuff.
    J.P.



  9. #9
    woodguy Guest

    Default Re: segmented bowl calculator?

    Both his and yours, very nice.



  10. #10
    Join Date
    Feb 2006
    Location
    Freelton, ON
    Posts
    721

    Default Re: segmented bowl calculator? *LINK*

    Gord - here is another site. I think this might be the guy that inspired Jim Vasi. He has written a book and has downloadable templates for segments. John at Woodchuckers has a new video on segmented work that we just added to the GHWG library as well.
    Mike



    http://www.smithart.us/

  11. #11

    Default Re: segmented bowl calculator?

    Quote Originally Posted by gord in oakville View Post
    trying my hand at a segmented bowl...also trying to find a freeware calculator for the angle cuts on the segments. Would appreciate it if any one knows where I can locate this and download it.
    thanks
    this one is pretty simple just play with it a minute its easy to figure out and free http://www.sawmillcreek.org/articles/4/

  12. #12
    Join Date
    May 2010
    Location
    Peterborough
    Posts
    637

    Default Re: segmented bowl calculator?

    You can also check out Scotty Lewis's articles on designing and gluing up a segmented bowl in our Aug/Sept issue.
    ______________________________________________
    Rob Brown
    Editor - Canadian Woodworking & Home Improvement

  13. #13
    Join Date
    Feb 2006
    Location
    Mount Hope Ont.
    Posts
    7,531
    Real Name
    J.P.

    Default Re: segmented bowl calculator?

    Gee. I hope Gord wasn't waiting six years to get that answer.
    J.P. Rap Mount Hope Ont.
    Carpe Ductum (Seize The Tape)


    "In this world, you must be oh so smart, or oh so pleasant." Well, for years I was smart. I recommend pleasant. Elwood P. Dowd

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