dglenn: Lego-ish figure in blue dress, with beard and breasts, holding sword and electric guitar (lego-blue)
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Last year at Pennsic, I built a platform out of three full sheets of plywood and some 2x4s and 1x4s. The idea starting out was to be able to level my tent on gently sloping ground (because my poles were starting to bend from setting it up on a slope yeat after year) and get the floor of the tent out of the way of runoff from rainfall. Camp was crowded, and it turned out to be useful to be able to add legs to one end and perch my tent on a rather steeper slope and free up some gentler grade for somebody else. I'm going to do it again, but incorporating improvements suggested by neighbours last year: I've not made any progress over the past year except to flatten out the plywood again by stacking most of my dining room and a large bass amplifier on it for eleven months (it was warped when I took the platform apart at the end of War last year), so I'll be assembling it all on site again, but the plan is to do it in such a way that it comes apart into three separate sections and a small number of carriage bolts for the ride home, instead of a pile of about twenty pieces of wood and a rather large number of screws.

This brings me to where I need to borrow a clue. Each sheet of plywood will be screwed to a 2x4 frame with 1x4 joists reinforcing it. The question is, how do I want to lap the corners of each frame?


|               |  \
+-+-----------+-+  this
| |           | |  edge
| |           | |  bolts
| |           | |  to
| |           | |  next
| |           | |  unit
| |           | |   |
| |           | |   |
| |           | |   |
| |           | |   |
| |           | |  /
|               | 


| |           | |
| +-----------+ |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| +-----------+ |
| |           | |


| |             |
| +-----------+-+
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
| |           | |
+-+-----------+ |
|             | |

D:  something else

E:  doesn't matter


Also, I'm guessing that in this configuration I'll want the joists to run short-ways across each panel, right?

The whole thing winds up being 12'x8', which is just a few inches bigger than the floor of my tent (nominally a 9x12 but it's more like 8x11.5 -- anyhow, it fit on the platform last year, and plywood sheets are 4x8, right?).

There are 10 comments on this entry. (Reply.)
posted by [identity profile] whc.livejournal.com at 07:59pm on 2006-08-02
I vote for E, as long as the lengths of the 2x4s are adjusted to give the correct overall size. (yes, plywood sheets are 4x8 feet, at least in the USA)
posted by [identity profile] whc.livejournal.com at 08:00pm on 2006-08-02
BTW, C is rarely seen in construction framing.
posted by [identity profile] siderea.livejournal.com at 09:35pm on 2006-08-02
I'm under the impression that C is the weakest configuration in sheer.
posted by [identity profile] siderea.livejournal.com at 09:43pm on 2006-08-02
Er, shear.
posted by [identity profile] whc.livejournal.com at 12:36am on 2006-08-03
I'm sure it is, but the plywood will provide plenty of bracing.
zenlizard: One lizard to another:  "Please to be shutting up now!" (Default)
posted by [personal profile] zenlizard at 08:06pm on 2006-08-02
I tend to agree with E; except you *may* want to consider having the 2x4s from each section overlap the otehr section enough to be able to get a pair of bolts into each section.
posted by [identity profile] ceo.livejournal.com at 08:24pm on 2006-08-02
Yeah, I don't think it really matters, as long as you have joists running the length of the platform (which I guess is short-ways across each panel, yes).
posted by [identity profile] cellio.livejournal.com at 11:49pm on 2006-08-02
I don't think it matters (other than "not C"), but I'm very slightly inclined toward A. The joists (yes, they should run parallel to the 4' sides, not the 8' sides) are going to be nailed in from the sides, so if you do A your end pieces will be nailed in from the top and bottom edges (as laid out here). That seems better than doing everything in the same direction, for reasons I can't really justify.

You might ping Filip of the Marche about how he put together the sections of the Pennsic dance floor. That floor takes way more stress than I think your tent platform will. :-)
posted by [identity profile] writerjanice.livejournal.com at 03:24am on 2006-08-03
Will you be able to do any fab work before leaving? Also what kind of help do you have for setup and teardown?

I have a design for modular wooden platforms that typically are built out of 3/4" plywood and 2x4s. usually setup on 4x4 or round pole type uprights..
But they require some time on the shop to fabricate each unit (best size tends to be 2' by 2' squares.)

The problem with working with full 4x8 sheets as the size factor for each panel is that a.) they will warp, b.) heavier cross-bracing is required to prevent the floor from swaying and "drumming" and c.) regardless of bracing they will warp...

I would think in terms of at least cutting them into 4' by 4' panels.

posted by [identity profile] garnet-rattler.livejournal.com at 03:48pm on 2006-08-06
Well, its probably moot by now for this year, but I generally use 'B' when the long sides are being bolted together. This puts longer single beams facing together and should be a bit stronger if all of the 2x4 joints are equally strong. For those, I suggest two 5-inch long #14 flathead screws through the longerons and into the ends of the shorter bars.

A pair (or three if you're planning on dancing a lot on it) of 2x4 pieces parallel to the end pieces* will be plenty of bracing and even 1/2-inch plywoood should be ok if you secure it to the frame with c. 20 or so #10 or #12 wood screws at least 2-inches long. Drill and countersink everything, polyurethane the entire platform well to seal it and your platform(s) should last on the order of twenty years, even going out to Pensic every year. At least, all of the many lofts I've built this way have ... ;-)

* Again, two ~5-inch #14 flathead screws through the longeron and directly into the ends of the pieces. Also, perhaps its obvious, but the 2x4s should have the ~two-inch side against the plywood, such that their larger cross dimension is perpendicular to the plywood surface, as that's where the strength is needed. I've done it the other way in special curcumstances, but never without careful thought on how critical the need was. 'X's mark the location for holes for 3/8" carriage bolts to attach 2x4 leg pieces and you can add more holes along the length to bolt the platforms together.

PS: I had nice ascii diagrams of the design but lj inisisted on mangling them so I took them out. If they would be of use to you, let me know and I'll forward them via email or something.



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