Building a Table Top SFG...some ideas

boffer wrote:I'm a big TT SFG fan.  Here's a thread listing some of the reasons you might want to try one.

https://squarefoot.forumotion.com/general-sfg-talk-f5/tabletops-take-sfg-to-a-higher-level-t41.htm  


This thread is about building a TT SFG.

In it's simplest form, a TT is a SFG bed sitting off the ground, at the height of your preference.  Kitchen counters are typically 36 inches high, and that is the height of most of my beds.  For beds 4x4 and smaller, the simplest solution is to attach a piece of 3/4 inch plywood, with a couple 1/4 inch drain holes in each square,  to the bottom of your box, and set it on something.  It could be something free or cheap like cinder blocks, an old cabinet, old roll around toolbox, sawhorses, a table, an upside down cart,  a trailer frame, a couple chairs, a picnic table or benches, a metal garbage can, a barrel, or the edge of a deck that's the right height; I'm sure you can think of others.  Perhaps you want to experiment one summer with one box to see if you like TT SFG.  These would all work, with little investment, in case you didn't like it.

Here's some ideas for a more permanent set-up.  Cinder blocks are stable and sturdy if you like the look.  If you place 2 of the block legs longwise in one direction, and the other 2 legs turned 90 degrees, you will eliminate most of the wiggle in the table.  Always place your blocks with the holes up; this is the position they are designed to carry weight in.





This is my neighbor's TT on saw horses.  They are roughly 3x8.  He spent a lot of time making quality saw horses, but now he is beginning to convert them to steel frames.





In the above picture, notice the the angle of the legs that create a large, stable footprint.  In the picture below, the top of the leg has been notched to carry the load of the horizontal board.  This is a technique that was perfected way back when carpenters wouldn't dream of buying a sawhorse.  It's stable, solid, and doesn't wiggle.  My neighbor did his the old school way-with hand tools.  Notice the hardware cloth used for the bottom.  More about that farther on.







If saw horses don't strike your fancy, maybe using 4x4 posts for legs will.  I have made TTs with 4x4 posts, but I don't have pictures of the finished product.  I did take some pictures to show how to do it.  Probably the simplest way is to use an angle hangar, available at your favorite hardware where all the other construction fasteners are located.  You'll need eight, two per leg.

This box is upside down, with the leg sticking up in the air.  I only had one angle hangar on hand for the picture, but each leg gets two.  The hangars use special nails: 8d-10d, 11/4-11/2 inches long.  You'll find them near where you found the hangars.  Important: every nail hole in the hangar must be used (I think there's 12 per hangar).  The weight of the SFG bed is under the max load of the hangar, but still, be safe, do it right.






The hangars will carry the weight OK, but they'll tend to wiggle.  Put on knee braces.  They look like this, 2 per leg.






But, if you're handy with tools, hand or power, and you would enjoy the satisfaction of making something the old school way, cut corner tenons on your leg tops.





See how the weight of the box sits on top of the post; this way nails and screws aren't carrying the weight.   Each corner should have knee braces on it.  Another plus, the 4x4 takes up less space inside the box.






These two methods of attaching posts are simple to do, and I feel comfortable recommending them because I know they will hold the weight.  rds1955 had mentioned to me the idea of using 4 inch pvc pipe for legs.  Compression strength-wise they would work, but I haven't worked out attachment and fastening details that would be feasible for most everybody.  I'd like to hear about your methods, if you've used other materials for legs.


My last suggestion for TT legs is a steel frame table.  Here's a sample:





Here it is with a box on it.  I have plywood on this box because I'm using it for an experiment this summer.  At the end of the season, I'll take the plywood off and just use the welded wire that I already put on the frame.  (I'll lose the zip ties then, too)







If you were to have one made, here's the cheapest way:  use angle iron, 1 1/2 x 1 1/2 x 1/8 for the whole thing.  Big ball park cost: 90 cents a foot for material, 1-2 hours of shoptime, depending on details.  You could spend more for round or square legs, or you could you use pvc pipe as sleeves to cover the angle iron.   Or you can keep your eyes open for stuff like one of these carts.  It was a steal for a buck each.  I figure one hour to strip it, flip it, remove the casters, and paint it.  I could leave the casters on it, but I don't have any concrete in my SFG area.







Here's some of my steel framed TTs.  I'm trying to get them consolidated this year so I can put up deer fencing.  Table sizes are all different, based strictly on what materials I had available when it was time to make a box.  TT's can be spaced closer together than beds on the ground.














TT SFG bottoms:  Plywood vs. hardware cloth


I've heard a number of folks say they've had plywood bottoms on their TTs for over 5 years, and I believe them.  But in my climate, it would never happen.  That's why I use hardware cloth for my bottoms.  All my boxes are made of pressure treated 2x's lined with 6 mil plastic.  

Folks with plywood bottoms also say their boxes warm up just as quickly as their boxes on the ground.  I would say my hardware cloth bottoms warm up a little slower.  Maybe 7-10 days.  For my gardening practices, it's irrelevant.

Don't try to save money using chicken wire.  It won't work.  Hardware cloth can be attached with screws with washers, nails bent over, wire fence staples, or ?.   I space mine every 5 inches or so.

For a 6 inch tall box I recommend  putting in 3 bottom supports on 12 inch centers, using 2x2s.  If the box is taller, you could use 2x4s on 16 inch centers.  I mount mine inside the box using 2x4 hangars.  The hangar comes with nail holes for 2x4s.  You'll have to drill a hole where marked for 2x2s.  With a little patience, all the fasteners can be hidden on the inside of the box.  Be sure to fasten to the bottom supports, too.






I waited till my neighbor was at church so I didn't have to tell him I needed some 'what not to do pictures".  Here he used old hand railing which is OK.  But, the spacing is way too wide, and it's secured with one screw.  Nails and screws aren't intended to carry weight like this.  If you put your supports inside the box, there's no visible sag.






Here's an old bed frame.  The springs offer enough support to use chicken wire..






For TT beds bigger than 4x4, you're on your own.  A 4x8 bed holds over half a yard, and when the soil is saturated-we're starting to talk about some serious weight.  Personally, for a 4x8 bed I would increase the size of the boards.  So unless you have free/cheap wood on hand, two 4x4s are probably cheaper and easier to build than a 4x8.

These are just some ideas to get you going.  If you have suggestions that have worked for you, please post them.

How do you attach the plywood to the bottom? do you screw it in under the 2x's or do you attach a ledge on the inside.
I am trying to decide what to do with the one I built

moswell wrote:Boffer - did you find that the foam insulation worked in helping to heat the box?

Goosegirl wrote:Ralitaco - just had to tell you I LOVE your avatar!!!

boffer wrote:

boffer wrote:For a 6 inch tall box I recommend  putting in 3 bottom supports on 12 inch centers, using 2x2s.  If the box is taller, you could use 2x4s on 16 inch centers.  I mount mine inside the box using 2x4 hangars.  The hangar comes with nail holes for 2x4s.  You'll have to drill a hole where marked for 2x2s.  With a little patience, all the fasteners can be hidden on the inside of the box.  Be sure to fasten to the bottom supports, too.

Pappy Slip wrote:



Pappy

ralitaco wrote:...what method you find works best to secure the Hardware cloth to the wood. (staples, screws w/ washers) Also how far apart do you space them? 
In the above picture I see it wraps up on the outside of the box...any structural reason for this as opposed to having it on the inside?...

ralitaco wrote:...do you keep it at that height for the entire length of the box thereby allowing the eventual sag to be somewhat hidden by the sides?...

ralitaco wrote:...Which foam board do you use? Is it the Blue stuff? Does it prevent any of the sagging? Do you cover it with plastic? How long has it lasted?...

boffer wrote:See how the weight of the box sits on top of the post; this way nails and screws aren't carrying the weight.   Each corner should have knee braces on it.  Another plus, the 4x4 takes up less space inside the box.






These two methods of attaching posts are simple to do, and I feel comfortable recommending them because I know they will hold the weight.

boffer wrote:My last suggestion for TT legs is a steel frame table.  Here's a sample:





Here it is with a box on it.  I have plywood on this box because I'm using it for an experiment this summer.  At the end of the season, I'll take the plywood off and just use the welded wire that I already put on the frame.  (I'll lose the zip ties then, too)

boffer wrote:I'd notch the plywood corners to fit around the posts.  Then I'd use 1/4x2 or 2½ galvie lags spaced 6-8 inches around the plywood perimeter to attach it to the 2x frame.

Then I'd sit in the middle of box and ask my wife if she could live with the little bit of sagging that she saw!

jimmy cee wrote:I recently elevated my beds and omitted the hardware wire..
With 3/4" flooring along with 15 inches off the ground I'm not at all concerned
about anything coming up from under.. I did apply a good quality weed barrier and that was just to keep the mix in