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Thread: Engineering question

  1. #1
    Join Date
    Dec 2017
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    585

    Engineering question

    Building a portable shooting bench.
    Which is more stable/less flex
    1) laminate 3/4" plywood to 1 1/2"
    2) single 3/4" plywood with two
    3/4" sq alum tube stringers lengthwise.

    The al would cut weight, but would it be as
    stable ?

  2. #2
    Join Date
    Jul 2016
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    Surprise, AZ
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    249
    The 1-1/2" surface will be more rigid. If you wanted to beef up a 3/4" sheet, start by creating a 'lip' all the way around the perimeter with the aluminum, then ideally add some cross-members in both directions. It won't help with weight, but I'd use Medium Density Overlay (MDO) if it's going to be out in the weather. (MDO itself _will_ be more rigid.)

    GsT

  3. #3
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    Fresno
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    One thing that can escape us is that portable bench tops are subjected to twisting forces. IMO the best way to deal with this is to use some sort of stressed skin construction with a grid like spacer between and solid material around the edge and where legs would be mounted.

  4. #4
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    I bought one of the portable benches from the NRA store and put some quality 5/8" birch plywood on top. It's quite stable and portable.

  5. #5
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    Feb 2003
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    San Angelo, Texas (West Texas)
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    1,608

    Lite and strong!

    Quote Originally Posted by Boyd Allen View Post
    One thing that can escape us is that portable bench tops are subjected to twisting forces. IMO the best way to deal with this is to use some sort of stressed skin construction with a grid like spacer between and solid material around the edge and where legs would be mounted.
    Boyd has a great idea! Consider the construction of a hollow core door. It has 1/8” plywood on both sides and solid softwood inside around the edges. The inside is nothing but a honeycomb of cardboard. The structure is glued together and is strong, straight, and light.

    Try using 1/4” exterior plywood on the top and bottom and double 2.5” strips of 3/4” plywood around the perimeter and double 1.5” strips of 3/4” plywood on the inside for a grid. You would want to place double 3/4” plywood for leg points inside where needed. Use pleanty of wood glue, such as
    Elmer’s, and staple or nail the thing together. Paint this top and keep it stored out of the weather and it will outlast you.

  6. #6
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    Quote Originally Posted by Bill Wynne View Post
    Boyd has a great idea! Consider the construction of a hollow core door. It has 1/8” plywood on both sides and solid softwood inside around the edges. The inside is nothing but a honeycomb of cardboard. The structure is glued together and is strong, straight, and light.

    Try using 1/4” exterior plywood on the top and bottom and double 2.5” strips of 3/4” plywood around the perimeter and double 1.5” strips of 3/4” plywood on the inside for a grid. You would want to place double 3/4” plywood for leg points inside where needed. Use pleanty of wood glue, such as
    Elmer’s, and staple or nail the thing together. Paint this top and keep it stored out of the weather and it will outlast you.
    That is what I used on the old MIS SUPERTEST hydro race boat for her stabalizer. Of course many of the people will not remember that boat. And I spelled it wrong and I do not care, Oh Well.

  7. #7
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    ONTARIO CANADA
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    838
    They have not raced the Harmsworth since they changed the rules, not saying it was for better or worse, but they changed the rules. I know what the old rules say and also the new ones.

  8. #8
    Join Date
    Feb 2003
    Location
    arkansas
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    289

    bench

    the portable bench I made was welded with a steel rectangular frame to set the top on. the top is two layers of half inch plywood but the frame is solid enough to use quarter inch for the top.
    a leg is at each corner [adjustable] for strength. the tripod thing is way too hard to make solid. the legs were eyeballed on at 20 degrees and they unscrew.

    the wood screws holding the top on can be unscrewed with an electric screwdriver to remove the top for transport, also. but when in a hurry you can put it in upside down and run [ like from a storm on the prairie]

    there are two tops for it- one with carpet on top so you don't burn your arm when shooting varmints

    the right aluminum frame should work ok. I would make the frame a rectangle, because of the torque of the legs. you would need aluminum collars to weld on for the legs but the legs could be steel.

    if you used plain 3/4 inch steel square tube it would be nearly as light as the aluminum, easier to weld, and stronger.

  9. #9
    Join Date
    Jul 2011
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    Minnesota Arrowhead
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    37

    2 Inch Pink Construction Foam Core Laminated between 1/4" Plywwod

    2 inch pink construction foam core laminated between 1/4 inch plywood with 2"x 3/4" wood sides sandwiched around the edge makes a very stiff and light top. The foam can be cut out for plywood blocks where leg fasteners are located.

    Glue plywood to foam for best results and paint or poly for final finish.

    For ELR shooting use ratchet straps and tent stakes to secure the bench to Mother Earth...... makes for near concrete bench steadiness.
    Last edited by Ricco1949; 02-16-2018 at 10:23 PM.

  10. #10
    Join Date
    May 2010
    Location
    pa
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    23

    Strong/stable

    Quote Originally Posted by retired View Post
    Building a portable shooting bench.
    Which is more stable/less flex
    1) laminate 3/4" plywood to 1 1/2"
    2) single 3/4" plywood with two
    3/4" sq alum tube stringers lengthwise.

    The al would cut weight, but would it be as
    stable ?
    The top of my loading bench is two pieces of 3/4 plywood glued and screwed together. Is like a slab of steel. I put angle owrn under several edges to mount vise and barrel vise, no flex , works great. Should work for a bench top also, but not light.

  11. #11
    Join Date
    Dec 2017
    Posts
    585
    Thank you gentlemen.
    I have limited time to get this up and running,
    so while i like some of the ideas,
    they will have to wait until next time.
    I like the thin laminate core idea

  12. #12
    Join Date
    Nov 2016
    Location
    St. Louis, MO
    Posts
    27
    Quote Originally Posted by retired View Post
    Thank you gentlemen.
    I have limited time to get this up and running,
    so while i like some of the ideas,
    they will have to wait until next time.
    I like the thin laminate core idea
    While a 3/4 ply would work , a single piece of 3/4" 13 ply Baltic Birch plywood is much stiffer than regular ply. This is what I used when designing the shooting bench for my son's company.
    http://www.custommetalprod.com/shoot...shooting-bench

    I made a top for a prior bench for my own use with the hollow core construction. 1 1/2 thick oak perimeter, 1/4 MDF interior slats and top and bottom surfaces. It is supremely rigid.
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  13. #13
    Join Date
    Dec 2017
    Posts
    585
    Way too much work for me.
    Mfd with chip crack shatter due to its makeup.
    I know i just moved work benches that have mfd tops.

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