Engineering question

[retired]

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 ?

 

[GeneT]

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

 

[Boyd Allen]

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.

 

[vtmarmot]

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.

 

[Bill Wynne]

Lite and strong!

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.

 

[Bill Gammon]

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.

 

[Bill Gammon]

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.

 

[ray porter]

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.

 

[Ricco1949]

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.

 

[JEFFPPC]

Strong/stable

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.

 

[retired]

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

 

[powderbrake]

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.
www.custommetalprod.com/shooting-ta.../product/326-precision-varmint-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.

 

[retired]

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.