Any Flex in Benchwork?

Discussion in 'FAQs' started by jpohl, Jan 2, 2004.

  1. jpohl

    jpohl New Member

    I am working on my first bigger layout. I am about done with the benchwork. My intention with the benchwork is to be able to disassemble the legs to move it when need be. When the table is on the legs, it is pretty rigid and sturdy.

    The table is 48"x78" constructed of 1x4's and 1/4 plywood on top. I will be glueing three 1/2 insulating styrofoam on top of that (with some cuts for scenery in the styrofoam). See attached diagram for Open Grid placement of boards. I have two 78" 1x4's running left to right, and 4 1x4's from front to back connecting to the 78' boards. Then I have a series of 1x4's glued and screwed down to the 46" boards as braces to add rigidity to the table.

    When I lift a corner of the table right now there is about 1/4 to 1/2 inch of play when lifting the corner before the opposite corner starts lifting off of the ground. My question is, will this be an OK amount of flex in the over all table for whenever it may be moved?



    Attached Files:

  2. railwaybob

    railwaybob Member

    Hello Jeff. To reduce the flex, you need to screw and glue some "gussets" into each of the corners. This can simply be some 1"x 4" glued/screwed along each side, or triangular pieces of wood.
  3. Ralph

    Ralph's for fun!

    That sounds Ok to me Jeff. I suspect the styro top will be flexible as well and will tolerate movement w/o throwing track out of allignment, etc. I gues I'd avoid scenic techniques with plaster that might crack with movement. For added stability how about triangular braces under each corner?
    Ralph (who is not a carpenter) :)
  4. railwaybob

    railwaybob Member

    Hello Jeff. With all of that bracing, something's wrong if you've still got some sag when you lift the frame - especially if it's made out of 1" x 4" (¾"x 3½").

    After looking a bit closer at your diagram, it appears that you have your bracing with the 3½" side up. This doesn't add a lot of stability to your frame. You should put all of your bracing so that it is ¾" side up as I've shown in the diagram below.

    To add extra stability, you might want to add some "gussets" - triangular pieces of 1" x 4" screwed and glued into each of the 4 corners.

    If you're using styrofoam, you might want to consider going directly to 1½" or 2" styrofoam. With all of that bracing, you shouldn't have much need the ¼" plywood.

    For some ideas on how to do this, visit my website.

    Attached Files:

  5. Russ Bellinis

    Russ Bellinis Active Member

    The foam will probably eliminate the flex. Foam is very rigid.
  6. zeeglen

    zeeglen Member

    Any flex in a movable platform can be rough on plaster scenery and trackwork.

    I had a similar problem with trying to make rigid a 2' x 4' plywood on a framework of 1x3s. Same corner to corner twisting effect when no corner legs used (see the avatar, cables balance it).

    Installed tight diagonal 1x3 bracing from corner to opposite corner with angled cuts where the existing joists already ran. Screwed the diagonals to the plywood. With that change the platform became so rigid was able to eliminate 2 cross joists and keep only a center joist and 2 end joists . The platform has virtually no corner to corner twist at all now.

    If you try diagonal braces on your platform, you may also need to lay a plywood gusset on top and fasten the diagonals to it. I cannot explain the mechanical reason why this works, but it does.
  7. railwaybob

    railwaybob Member

    Hello Glen. The reason you got rigidity was that you incorporated a triangle into your design. In geometry, the triangle is known to be immovable. That's why you have lots of triangles in bridges. While it looks like a form of rectangle, it's completely made of triangles.

    Whenever making any rectangular structure, such as a module or benchwork, you can cut down on the amount of wood you need, but concurrently increase the stability of the frame if you incorporate triangular shapes such as diagonals or corner gussets.

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