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I am building a go bar deck and have 3/4 inch Baltic birch 24x24. I also have some 1/4 inch Baltic birch plywood. The go bar deck will seat on my workbench when I am using it. It is 1 3/8 inch mahogany. I am wondering if the 3/4 Baltic birch plywood on the bottom and the top is think enough. I could glues us the bottom and the top with the 1/4 plywood to get to about 1 1/4 inch each but being tight in nature I don't want to use it if I don't need it. Any thought as to whether the 3/4 inch Baltic plywood is enough or do I need to than the bottom or the top thinker.

I am using 7/16 inch by 36 inch rods for the supports if that makes any difference.

When I check the forum I youtube I see folks are using a total of 1 1/2 inch plywood mostly and I guess I am wondering if that is necessary or possible overkill. Maybe I should just go buy more 3/4 Baltic birch and be done with it but I would like to use the 1/4 inch stuff that I have to get rid of it.

Thanks for any thought you may have.
Chuck
Yes this is my first attempt at building jigs so I can build my first acoustic which I have plans for as a L-00.

Thanks again for your thoughs

I use 2 thicknesses 18mm birch ply top and bottom.
I commonly used 20+ rods at 8lb push each for X braces, maybe more for bridge plates.
And 80+ rods at 4lb for gluing tops and backs on ribs.

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You'll get significant bow of both top and bottom plates if only 3/4". You can add a 2x4 in an "X" to both plates to stiffen them up easily.

Or just use construction grade plywood and glue 2 3/4" pieces together to get 1-1/2". Much less expensive than using BB.

Here's one I just made. double up 3/4" MDF for the top and bottom. 1-1/2 square vertical supports. Works great. viewtopic.php?f=10101&t=48048

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Definitely sturdy up the bottom. It doesn't matter if the top bends, but your radius dishes will change shape if the bottom flexes.

The only reason it's nice to have the top stay "flat" is so there is uniform flex in the go-bars. If some of them are just long enough to do the job, with a flimsy upper deck, adding 10+ bars some of the rods can actually straighten out thus become ineffective.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

The top and bottom have different needs. The bottom needs to not flex at all, because it is the backing for the dished workboard. If the bottom of the go-bar deck flexes, so might the workboard, and then you might not get the radius you planned for.

The top just needs to not utterly fail under the stress. It can flex all it wants to, and nothing bad happens (unless it fails).

I use my workbench itself as the bottom, and a single sheet of construction grade plywood as the top. It works great.

My experience has been a little different. My deck is on the flimsy side, to be honest. The top and bottom are both 3/4" baltic birch, and the extensions are just 3/8" threaded rod threaded into T-nuts pressed into the ply. I've never noticed any deflection. However, once it's loaded up, it's sturdy as a ballast thanks to all the new tension.

That said, it's certainly easy enough to put a nice little X-brace across the top of your deck or double up the ply like Rod suggested. I really like the quote by Charles Fox in his signature right now: "There's really no wrong way, as long as the results are what's desired."

This is a picture of a glue-up I did recently, gluing the back to the rim. I guess you could say the radius dish adds a de facto second layer to the bottom.

Here's mine. I doubled up the Baltic birch top and bottom. Cabinet is on castors so I can pull it out and rotate it to access all sides so I can clean up the glue squeeze out.

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If you really want to use up the 1/4", there are a few options:

- Laminate 2' x 2' squares to get to the 1-3/8"+ thickness (6 layers of 1/4"/6mm plywood). This will likely be a little heavier than and as stiff as two layers of 18mm plywood.

- Use torsion box construction with 1/4" faces and dimensional lumber for the core grid, edges, and corner blocks. A torsion box built with 2x stock will be stiffer and significantly lighter than a laminated plywood top or bottom plate.

Here's a video on torsion box construction from Fine Woodworking Magazine, Other than making sure there is a solid wood block where the support rods pass through the plates, the design work is simple, but there will be a lot more labor involved versus laminated plywood.

http://www.finewoodworking.com/2007/05/15/build-a-torsion-box-assembly-table

Another thing to consider is going with the Stewart MacDonald go-bar deck support tube design, We just did two more decks with other students, with one choosing to use thick-walled electrical conduit for the support tube and the other bare 3/8" all-thread rods. The conduit adds an amazing amount of stiffness to the deck - so much so that we have bin-type storage above the fixed deck in the shop. The added cost for the additional stiffness and resistance to rotation of top plate versus bottom is about $12 (the conduit and four 'T' nuts). This cost may be offset by using 1/4" or 5/16" all-thread instead of the larger sizes, as the rod is in pure tension, with the conduit support tubes providing the rigidity.

http://www.stewmac.com/How-To/Online_Resources/Jigs_and_Fixtures/Go-bar_Clamping_Deck.html

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The way I do mine:

I have a freestanding laminated maple topped workbench with bench dog holes. It is 30" wide and 60" long, so I can afford to temporarily devote half of it to use as a go bar deck when I need the deck, then I disassemble the deck when I don't need it. The bottom of the deck is just my bench top. I use bench dogs to grip the dished work boards and not let them rotate during use. Since the bench is freestanding, I have good access to 3 sides of the deck, which is handy. The top of the deck is just a single sheet of 3/4" construction grade plywood. It flexes a little, but it doesn't matter. The supports consist of all thread rod fished through 1" plastic conduit, bench dog holes in the bench, and holes in the plywood, with washers and wing nuts at the ends. The plastic conduit defines the height of the deck, and the all thread rod snugs it all together. It all works great. The downsides are the assembly and disassembly time (10-15 minutes) and not having it up all of the time. However, in a shop my size, I need to not waste space, and being able to tear down the deck when I don't need it saves a lot of space.

So thank you all. After reading and looking at pictures I am now wondering what length my rods to hold the braces should be the steel threaded rods that I was going to use are 36 inches. .i was planning on using 1/4 inch hardwood dowels but now I am wondering if I do then how far down do I put the top on. I am using wing nuts to move the top plywood up and down. How Will I know how much the 1/4 inch diwels need to flex to hold gown the brace? Do i just experiment first without the braces in and just make sure the top or bottom plates take the shape of the radius disk?

Chuck--

A way to go (not the only way, but a way) is to buy fiberglass driveway markers instead of the wooden dowels. The wooden dowels need to hit a sweet spot on the bending; that is to say, you need for them to flex a little but not so much that they break. The fiberglass markers are just fiberglass dowels. They won't break unless you try to fold them in half.

I use 3/4" plywood for the top and bottom of mine. Works great.