So, it turns out if you make the frame 7’ x 11’ 1.5" wide (84" x 133.5") you can get a grid of 2x4s with 15" spacing, which is perfect for an 18" wide frame of plywood.
Plus about 7 sheets of plywood. 3 sheets for the back to be completely covered and 4 to make the double thick 18" frame on the front. This will leave a 48" x 97.5" pocket for sheets goods to be worked on.
I was thinking of using a router to put in 1.5" wide and 3/4" deep mortises (might be wrong term) in the 81" and 64.5" lengths, so that they can be interlocked. If more stability is needed, can add some similarly interlocked 15" lengths and insert them in the 15"x15" openings.
This does leave plenty of scrap left over, but I like the optimal configuration for work area and allowed frame space for the Maslow 4.
That certainly looks sturdy enough. There’s no such thing as too rigid, but I’ll make sure to do some testing to see how rigid the frame truly needs to be, you might be able to get away with less reinforcement than that.
for a torsion box the members actually don’t contribute that much strength, most of the strength is from the skins on each side. even a thin skin (1/4" or 1/8") can produce a very stiff panel if there is suitable spacing.
@dlang _ Good to see you. Yep I still submit 4 small torsion boxes hanging on a X of 2 diagonal members would work,be strong, less work, less material less cost.
as a note, you can get solid, cheap torsion boxes 80’ long by 24-36" wide in 2" sizes, just get hollow core doors, they are very stiff for their weight. (and if you have a thickness planer, are pretty easy to cut down to size. They make great shelves for heavy stuff)
@Bee bracing sheets are cheaper and stronger than diagonal members. Diagonal members are preferred mostly when weight needs to be conserved and in particular a strength to weight ratio achieved especially for spanking where dead load becomes a significant problem. In this case that is less a problem. Costs could be conserved by choosing cheaper (thinner) members and sheet materials but by replacing sheets with diagonal members you are foregoing some stiffness and strength. By adding extra members as diagonals you are just adding weight and cost.
Hollow core inter doors often have field structure composed of cardboard honeycomb. with just a rim of solid wood or other material. Might be something we could use to either reduce the number/size of internal framing members or increase stiffness of the current design away from those members.
The back side is I think always under tension rather than compression. If true a very thin skin can be used, say 1/8 plywood or paneling. The front has to be supportive enough to minimize flex when supporting the mass of the sled. A minor issue for vertical designs but something to be aware of when cutting thinner material or pieces smaller than the base when the machine is horizontal. If the field is close packed like with a glued cardboard honeycomb a pretty thin front skin could also be used though I’d probably go with 3/16 or 1/4 just for mechanical resistance to point damage.
Can you share native (or STP) files of this model? I don’t know if you can post them here, or some other means that’s convenient to you, but I like this frame idea and I’d like to see about how I might be able to add t-slot rails to it.
