While I know there are a huge number of Instructables on how to build various tables, I thought I would add my own for my most recent project. This is my first post here so I would welcome any positive feedback or questions to clarify steps.

My goal with this Instructable is to share with you:

The reasoning behind my various design decisions.
The process I went through in putting this table together.
Things I would do differently a second time around so you can learn from my mistakes.

So first off I would like to talk about what I wanted in this table as that was crucial to my later design decisions.

I wanted a tall "pub" height table with the finished height being right around 41 inches (104cm). In addition to simply enjoying the look of tall tables like this it also makes the top a great standing work surface.
I wanted a large table 4'x7' (122cmx213cm) This size of table is very uncommon as it is quite wide, however I often play tabletop games and wanted the large space to set things out and play.
I wanted an "industrial look" I also found similar things described as "steampunk" but I wanted something simple with clean lines and an exposed metal look.
I wanted it to be mobile. I wanted to be able to easily move this around my kitchen and into my living room by myself, which is what motivated me to put it up on casters. I also wanted it to be easy to move from one location to another so it is designed to break down into essentially flat components for easy transportation from one apartment to the next.

With these general goals in mind I was able to draw up some quick sketches of what I wanted to build and I then proceed to start work on the most time consuming piece the wood top.

Step 1: Building the Top: Material Selection and Milling

Material Selection:

My first thought when looking into this was to go to my local big box home improvement store and buy some of their nice milled poplar. This would let me assemble the table top much faster than messing with trying to mill my own material. However I as I started to look closer I found that many of the pieces in the sizes I wanted were heavily warped. Unwilling to pay premium prices for warped lumber I turned my attention to a local hardwood supplier where I was looking into purchasing some hard white maple. When I found that it would cost me at least 280 US dollars I decided that I wanted to experiment a little bit before investing that much money as I had never built a wood top of this size before.

I decided that at least to start I would experiment with much cheaper Douglas Fir which is readily available for construction purposes. (In the end I decided that I was so pleased with this finished product I would save my money and build the whole top out of 2x4's which ended up saving me $200. I will say the downside to this is that it is a soft wood and makes the table far more prone to scratches and gouges)

Milling:

I knew one of my biggest challenges would be that I lack access to a jointer, which if you don't know is a piece of equipment made to give your lumber nice flat square edges, which are crucial for a tight fitting table. I decided to think outside the box and use a portable planner to try to square the edges for a tight fit. To test this technique I purchase the best Douglas Fir 2x4's I could find and I attached four of them together with screws at the ends. to allow them to stand up on end as they went through the planner. This technique worked pretty well but absolutely requires material stands on both ends to allow you to deal with the big heavy 8 foot piece. I flipped the piece back and forth to mill both sides of the skinny side of the 2x4's so that in the end I had removed the bevels and produced fairly straight pieces to work with. I also milled my pieces down more than necessary in an attempt to make the final product look less like it was made of 2x4's. I eventually used this process to mill down 15 2x4's so that they were relatively straight and square.

(One piece of advice is to mill and glue the top as fast as possible to minimize warping. In the long 8 foot pieces I was surprised how much the material would want to twist.)

Step 2: Building the Top: Gluing and Planing the Sections.

Gluing up your sections:

Because I had access to a planer I decided that I would glue up sections of my table together separately. So I made five sections each made of three 2x4's this made them just wide enough to be run through the planer again after the glue dried. As for the actual assembly you can theoretically do this with just glue and wood clamps but I would suggest buying a biscuit joiner as I felt this made assembly much easier and produced a much flatter top then would have been possible without one.

(When using the biscuit joiner you can easily just go down your piece marking both sides of your joint so that your biscuits holes line up, this is what I did. In hindsight I would make a template so that the biscuits are in the same spots throughout the table. This will make your finishing cuts much easier as you trim the ends to length so if you want to hit the biscuits and have them be visible you know where to cut and they will be even in all the joints. With my table I had no idea where they were at located after planing off my marks, so I ended up with various random biscuits of different sizes visible along the edge.)

When gluing them up make sure to apply a even coat of wood glue along the entire edge as this will give your piece the most strength and give you less visible gaps in the final product. You are then going to need some large clamps to secure the whole thing while it dries. I suggest pipe clamps, as you can get them in whatever length you want and you are able to get a lot of pressure with them. If you don't have any you can buy the clamping portion online or in a store and then go to a local store that sells pipe and buy and have them cut and thread whatever length you want your clamps to be. (http://amzn.com/B0012YNJRO)

(My tip for gluing the sections is to not bite off more than you can chew. There is a lot of surface to cover in glue and biscuits to set in if you try to do to much your glue will start to dry before you can get the clamps on and your seams won't be as strong as they should be. Also a second pair of hands for this part is very helpful if you can get them.)

Final Planing:

With your individual sections glued up now is the time to plan them down to the final thickness you want your top to be and to remove as many defects and chips as possible, run each piece through alternating sides until they are both clean and smooth and all your sections are identical thicknesses.

Final Glue Up:

With your sections read for assembly get your biscuit joiner back out and put another set of holes on both sides of your joints. Then once again apply a even layer of glue and your biscuits and clamp it firmly together. T

Step 3: Building the Top: Finishing

Finishing:

Trim the top to its finished size, I took off roughly six inches from each end which allowed me to get rid of all the screw holes from when I first started squaring the wood sections.
The first step and one of my least favorite is several sessions of filling holes and cracks and then sanding the top down again. I eventually sanded the whole top down to a 220 grit sandpaper as was recommended by my stain. This is the part I find the hardest but where you can make such a huge difference in the appearance of your finished product so try not to rush it.
I used a router to round down the top edge but left the lower edge square to fit firmly against my angle iron base that I would be building next.
Finally stain the top whatever color you would like, I ended up choosing Minwax natural stain, as the lighter stain did not make imperfections stand out like some of the darker stains I tested on the scrap ends did.
Finally I finished with 3 coats of semi-gloss polyurethane to help protect the soft wood tabletop.

Step 4: Building the Base: Design Choices

Seating:

One of the biggest things for me was trying to avoid that terrible moment when you get stuck with the table legs or bracing in your foot space. In an effort to facilitate this I went with squares for the leg, this gave me a strong stable support and also allows your to stick your knees through the open space when sitting on a chair. I also set them about six inches back from the ends of the table so that you would be able to slide your stool underneath. The center bracing is far enough in that I have not found it to be in the way at all.

Assembly:

You can assemble the legs and brace easily as one piece upside down and then flip it over and drop the top down onto it. this makes it much easier to get the top lined up and in place.

Transportation:

The metal frame consists of 4 pieces 2 leg squares, one brace assemble, and a support frame for the wooden top. The support frame is attached with screws to the top and is designed to stay with the top permanently. The frame can easily be taken apart into those pieces and laid flat for transportation.

Finish:

You have a number of options available to you, you could easily sandblast and powder coat or paint the base any color you like. There are also a number of options available to rust or patina all the steel, or you could even hit it with a torch to cover the whole thing in heat marks. I liked the look of the simple bare steel so I left it as is.

Step 5: Building the Base: Support Frame

Support Frame:

This piece serves three functions:

It holds the top flat and helps it resist warping with time.
It provides a unique aesthetic and makes the top look far more substantial.
It allows you to not have to worry about screwing and unscrewing the wood top every time you want to move it, and what you will do when the screws strip out.

Dimensions:

The outer dimensions are just an 1/8th of an inch shorter in length and width than the wood top. This prevents the metal frame from sticking out and creating a little ledge at any point around the wood top. and the inner braces are set 8 inches in from the ends. These braces not only strengthen the frame I was able to screw through these into the legs with

Materials:

2x2x1/8 Angle Iron two lengths of 20 feet

Construction:

I am lucky enough to have access to a full welding and fab shop so I simply used the iron worker to cope the ends of the angle to make nice tight joints. If you lack access to that you could use a saw to just create mitered corners, or you could use a grinder with a cut off wheel to hand notch all the angle iron. I then used a punch to put holes in all the pieces to screw up through to attach the top placing one about every foot. This could easily be done with just a regular hand drill as well just make sure that your holes are the proper size for the screws you will be using. Hex head self drilling sheet metal screws. You could also drill through and use bolts and nuts to attach it if you wanted too.

Step 6: Building the Base: Legs

Material:

2x2x.065 Square Tube two lengths of 20 feet.

4 Inch Stem Casters (at least 2 locking, preferably all 4)

Matching sized coupler nuts

Construction:

The first thing you are going to want to do is clean your material as it is likely to be covered in a light coating of oil to prevent it from rusting. Next you will want to decided where you want the seam to be on your frame, especially if you don't plan to paint the frame. Keep the position of this seam in mind as you make all your miter cuts to build your square frames. Once you have your cuts made, figure out what pieces will be your bottom piece you then need to drill out and wield in your coupler nuts. This will allow you something to screw your casters into once the everything is finished make sure to test them out before doing your final weld up. Weld up your seams and you will be ready to move onto the next step.

(Casters can get very expensive if you get nice ones but I found some decent cheap ones that were sold in a pack of four that are designed to be used with metal rolling racks. With a load capacity of 400lbs I felt perfectly confident attaching them to my table.)

Step 7: Building Your Base: Bracing

Design:

I used a piece of square tube attached to some angle to form a basic brace across the bottom of the frame I then used lengths of 1x1 steel tube to create an x shape cross piece. This was welded to the 2x2 cross brace so that when you are finished the center bracing is all one solid piece that attaches with plates and screws at both the top and the bottom of the legs.This bracing serves to stiffen up the whole design so that there is essentially no movement in the frame once it is assembled. You could easily figure out the angles and lengths with some basic trigonometry but I chose to decide on it in the moment making them as I went. I also made them asymmetrical so that they were tucked in farther on the bottom then on the top. There are a ton of different ways that you could build the brace, but I do highly recommenced that you make full cross bracing as the legs will wobble without it.

Step 8: Final Advice

I felt like I learned a lot making this and it tempts me to make another one using my newfound experience. Some suggestions I would make would be.

Consider having your wood top run the other way. By running your wood the short direction of 4 feet instead of the longer 7 it would make working with the individual pieces easier and I believe it would make it easier to get nice square straight edges on them. Also with shorter pieces you could probably get away with using a smaller portable bench top jointer which are far more affordable than their free standing big brothers.
I would make the metal support frame first and attach it to the top as soon as I got it all glued up this would have allowed me to pull the top flat before sanding, routing, and finishing it. Giving you a better product.
I would try to spray on the polyurethane as it was nearly impossible for me to get rid of visible brush strokes, probably as a result of my own lack of skill and the heat in the middle of the summer in the desert.
If you lack access to a welder I would suggest making a wooden support frame for the table and then going with the black iron pipe legs made with pipe fitting that are very common. That would also give you a great industrial look and would require no tools to build.
If you build a tall 41 inch table like mine you will need to find around 29 inch stools for them to be the proper height for the table.