Results 1 to 6 of 6

Thread: Segmented bowls: riftsawn or quartersawn lumber

  1. #1
    Join Date
    Sep 2018
    Location
    Kensington, Maryland
    Posts
    274

    Segmented bowls: riftsawn or quartersawn lumber

    Hi all,

    i am just getting into segmented bowl turning. Is there a difference if the rings are made of quartersawn or riftsawn wood? For sure it will be cosmetically different and I understand that. But I am trying to determine if it makes any difference in the mechanics of the turning. One of the things I love about segmented bowls is less tearout since you are not dealing with end grain on the sides of the bowl. Will the “feel” or the mechanics of the turning be different with a ring made up of quartersawn or riftsawn segments than one made up of plain sawn segments?

    thanks for your help

    -Dan

  2. #2
    Join Date
    Aug 2005
    Location
    Midwest
    Posts
    2,043
    Other than the esthetics, grain in one direction with tend to make the vessel grow taller seasonally and grain in the other will tend to make the vessel diameter change seasonally.

  3. #3
    Join Date
    Sep 2018
    Location
    Kensington, Maryland
    Posts
    274
    Thanks Dick. I thought that movement with segmented bowls is much less than with a solid wood bowl blank though. Are you saying that movement will happen more with a segmented bowl made from wood that was riftsawn or quartersawn versus a segmented bowl made from wood that was plainsawn?

  4. #4
    Join Date
    Aug 2005
    Location
    Midwest
    Posts
    2,043
    Solid bowl blanks can have differntial shrinkage issues that can cause them to crack because you typically have end grain and side grain on the same piece.

    Flatwork
    With 5" wide lumber, the QS/RS lumber (let's say 2% movement across and 4% movement in the direction of the thickness) will tend to shrink less acorss the width than a plainsawn piece (4% across and 2% thickness). Once glued up to make a 20" wide 1" thick table top, the width will tend to change much less with QS/RS than flatsawn because the change will be 2% of 20" (or a 0.4" change) with QS vs 4% of 20" (or a 0.8" change) with FS. In reality it wil be much less than this in a household environment. For table tops, this is desirable because QS will reduce large seasonal movement across the large width that can occur with flatsawn tops. However, the thickness of the QS table will change slightly more seasonally. Because it is based on a % of the seasonal change in that grain direction (0.4% of 1" = 0.04" which is an unrealistic worst case) it will not really be that noticeable.

    Wood does not move much along its length (fibers aligned to length).

    Turning
    If the QS white oak (for example) is used with the ray fleck/pretty side out (radially), the turning will tend to grow less in height seasonally (because it is as if you have placed the board on its side). However, the thickness will tend to grow seasonally which causes the shape to grow in diameter. However, because of the thin walls involved with most turnings and this movement is based on percentage of wood thickness in that direction, this increase in diameter is a non-factor!

    With the flatsawn material, it will tend to grow taller as if you stood the board on its side (assuming the flatsawn face is out radially). Let's say your item is 5" tall. Once this is glued back together effectively you have a board 5" wide (on its side). The bowl/vase will tend to grow in height (4% of 5" or .04 x 5" = 0.2"). Once again this is unrealistic case because the item will hopefully not be stored outdoors and see the full seasonal swing.

    In general segmented turnings will tend to grow taller/shorter seasonally (QS will grow less, FS will grow more). Because we often turn items 8" deep or less, the choice of wood and orientation is less of a concern for changes in height. Also, because of the thin wall dimensions for most turnings, the diameter change will be much less noticeable than height changes.


    It is most important to choose straight-grained wood to prevent differntial shrinkage between segments and layers IMHO!

    Good luck!
    Last edited by Dick Strauss; 02-23-2020 at 12:14 PM.

  5. #5
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    12,298
    Quote Originally Posted by Dan Gaylin View Post
    Thanks Dick. I thought that movement with segmented bowls is much less than with a solid wood bowl blank though. Are you saying that movement will happen more with a segmented bowl made from wood that was riftsawn or quartersawn versus a segmented bowl made from wood that was plainsawn?
    Talking about rift/quartersawn, or flat/plainsawn pieces doesn't make much sense without describing the orientation of the small pieces in the glueup. There is insignificant shrinkage longitudinally. The T/R ratio describes the relative tangential and radial shrinkage with tangential the highest. The overall shrinkage can give an idea of the relative difference between species.

    Good article: https://www.wood-database.com/wood-a...nal-shrinkage/

    For example, shrinkage numbers for some species (from the Wood Database):
    White Oak: Radial: 5.6%, Tangential: 10.5%, Volumetric: 16.3%, T/R Ratio: 1.9
    Walnut: Radial: 5.5%, Tangential: 7.8%, Volumetric: 12.8%, T/R Ratio: 1.4
    Persimmon: Radial: 7.9%, Tangential: 11.2%, Volumetric: 19.1%, T/R Ratio: 1.4
    Black Cherry:Radial: 3.7%, Tangential: 7.1%, Volumetric: 11.5%, T/R Ratio: 1.9
    Holly: Radial: 4.8%, Tangential: 9.9%, Volumetric: 16.9%, T/R Ratio: 2.1
    These are averages, individual samples can vary.
    These are also the maximum when going from green to oven dry. Seasonal changes can be much less.

    This is a useful diagram, shrinkage by orientation in the log.
    wood_shrinkage.jpg
    Credit Popular Woodworking: https://www.popularwoodworking.com/m...and-expansion/

    Some T/R average ratios
    T_R_Ratio_chart.gif

    Not paying attention to these might explain some of the problems I've seen (and felt) in segmented pieces that had cycled through seasons years of wood movement. Perhaps they were not sealed well.

    (Disclosure: I am not a segmented turner but an observer and wood junkie.)

    JKJ

  6. #6
    Join Date
    Sep 2018
    Location
    Kensington, Maryland
    Posts
    274
    Well, this is really interesting and helpful information. This depth of knowledge among members of this site never fails to amaze me. John, Dick, thank you both for your replies.

    -dan

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •