Open grid can be structurally sound. However, if you are really looking at a single tabletop, you don't need to worry about splicig the ply, except possibly at a couple locations (that is, assuming you frame it and aren't intending just to drop a sheet of ply across a couple of sawhorses) because the frame provides the structural integrity. For access just build in a couple of hatches (straightforward with foam).
Before you dive too far in, I suggest looking at the Virginian as well as last year's and this year's project layouts for construction ideas, even if you aren't looking at those track plans. Several good options on benchwork there.
I've had no trouble using 1/4 ply on framed table benchwork (2x4 modules) since the frame provides the structural support but would probably go with 1/2 or 3/4 if I were doing cookie cutter style. But if you do a 1x2 or 1x4 frame, 16"OC, you can probably just use the foam without any ply beneath it at all.
jim
MikeyChrisAre the castors cylindrical rather than circular? Sounds like it from the dimensions. I didn't think castors would work, but may try it. I have short weave carpet with a foam underlayment over concrete. Castors would be a bit better than the "movers' because they are easy to attach to the legs. Thanx again.
I should have clarified that my casters are about 7/8" width and 1-7/8" diameter.
The legs on my layout are made per the Virginian example (thanks to David Popp); see MR Feb 2012, pg 35 if you have it. The legs are an "L" made with "select" pine 1x3 combined with a 1x2. Near the bottom you can see in the photos below that a piece of 2x2 is put in the inside of the "L", and a piece of 1x3 is also added on one side. It all provides a large enough square to accommodate the caster plate, which is screwed in. It's all glued and finish nailed (love the air gun). You can also see 1x4 cross pieces between the legs, near the bottom on the sides and back, to tie them together and reduce strain when moved. The 4th 1x4 is, higher, at the bottom of the fascia, to make getting underneath the table easier (for fossils) from the front. And the legs also have 45-degree braces near the top. It all is fairly well unitized.
I imagine I would have chosen somewhat wider casters but those would have required a wider base wood plate for them, which would not be hard to do, plus it would tie the caster to a single unit of wood instead of the 4 pieces as I have it. But if doing it again for this size layout I'd probably do the same again as it works fine.
A tangent...if you're making this size layout, and have any possibilty of moving it (e.g., to another house), one hindsight I have is not making mine modular (2-3 pieces). As it is, it's gotten fairly heavy and I'm not sure it could be managed over the handrail to get it down the stairs. If I ever have to move it, and not start on a whole new layout (depends on the next house) I may have to cut it in half and figure out how to reassemble it and get the joints "level". Easier to address at the start. Might slow you down a tad to figure it out or add a bit more support and/or two more legs.
Good luck and have fun!
Paul
Modeling HO with a transition era UP bent
MikeyChrisdoctorwayne, Does the tongue and groove underlayment need bracing at the t & g joints? If I can find some t & g here that isn't too rough/warped, that may work fine. Thanx.
No, this stuff is intended for sub-floors, and is put in place with the 8' t&g joint at 90° to the joists. The 4' t&g joint, though, should occur atop a joist.
When you cut the two sheets to make the 4.5'x10' table top, remember that to make the joints, you'll be using the tongue of the long side of the first sheet and the groove of the short side of the same sheet - I'd simply take 1' off the width of the sheet on its long grooved-side and position that cut edge at one edge of the table. Also, remove the tongue from the 4' side of this sheet, and position this edge at the edge of the table's end.Cut a full-length 1.5' wide piece off the second sheet, making sure that it includes the grooved edge, and, after removing the tongue from the 1.5' end, join it to the piece already installed.Finally, from the remainder of the second sheet, cut a piece 2' wide from the side with the tongue, then trim its length to 4.5'. Insert the tongue into the grooves at the ends of the already installed sheets and fasten it in place. This joint should have a joist beneath it.
If you want a smooth surface, get it in firply rather than the more usually-used spruce.
Wayne
Thanx again to all who replied. I found all the information useful. I ended up building a 5'x11' butt joint frame with 1x4 sides and ends and 1x3 joists except for two joists that were T girders built from a 1x2 a 1x3. The T girders supported seams between plywood tabletop. To get a 5'x11" table I will have two sheets of 1/2" plywood ripped to make an 18" section and a 30" section. The two 30" sections will form the middle of the table, with the 18" sections (cut down from 8' to 5') cover each end. The plywood will sit on 1x3 joists that are set 1/2" below the top of the perimeter 1x4's, similar to MisterBeasley's 5x12 layout. I opted for plywood rather than insulation board because I wasn't sure how to mount switch motors under the insulation board (I like using screws so I can move things around and adjust them). There are four legs built as described in the MR VIRGINIAN article (with castors). If I had it to do over, I might just use 2x4's for the legs. The table is done except for adding gusset plates to the leg supports and installing the plywood. I am sure there will be issues when I try to "drop the plywood in" to the frame because(although I made every effort to keep things square) I am sure the frame is not perfectly square. I tried to build the frame 1/8" too long and too wide to allow some "slop", but I didn't end up with much "slop" room. We shall see. I'll post photos when I finish. Thanx again. I would have not used castors had Paul not told me they work on carpet. Glad i asked. The frame moves around fine, and is pretty rigid. I know the plywood will add considerable weight, but i am confident it will work. Mike
Not sure if the 4 legs will give the continued support required for the finished layout. It may seem rigid now, however a single 1x4 spanning 9-11ft (not sure of cantaliver) will sag over time. Additional angle bracing may help, but w/o a horizontal tie to the legs, they will spread as it sags.
Modeling B&O- Chessie Bob K. www.ssmrc.org
Hi Bob,
Thanx for the input.
bogp40 Not sure if the 4 legs will give the continued support required for the finished layout. It may seem rigid now, however a single 1x4 spanning 9-11ft (not sure of cantaliver) will sag over time. Additional angle bracing may help, but w/o a horizontal tie to the legs, they will spread as it sags.
I built my layout this way, I cut 4 foot wide 2 inch thick pink foam so I had a table 6 feet wide by 8 feet long. Made three of these tables then joined them with clamps, so I have a layout that is 6 feet wide by 24 feet long at the moment.
These tables can easily be moved by two guys, lightweight, but also strong.
So if I ever move, just detach the clamps, and unscrew the legs and take them up the basement stairway.