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I have some decent lengths of oak 1"x4" leftover from another project and would like to create a table top out of the pieces.
The table I am looking to create is not large, it will be a bedside table, it will be roughly 18" x 18".
What I need to know is the best way to join them to avoid them being un-even on the top (as in what you walk on with a hard wood floor) and to avoid warping and bowing in the future.
Well I would tend to use my biscuit joiner to join all the pieces. Try to avoid flat sawn pieces in the middle of the table top and if you have flat sawn lumber then make sure you alternate the orientation, you want one up and then one down etc it will reduce the overall cupping motion across the whole top.
An alternate that could be done is to run the boards edge first on a table saw or run a router bit to make a groove on each long side (~1/4" - 1/2" deep), I'd go with 1/4" wide. Then make 1/4" stripe slightly narrower than the depth of the two side grooves together. This will be like tongue and groove, (it is called a spline joint the spline being the strip of wood) and it will be solid.
visual:
If you are still worried about it attach a strip near each end of the top across the glue up on the underside, it can also be used to attach it to the bottom or legs. It will also stiffen the whole top making it stronger for all kind of use.
@bowlturner gives some excellent suggestions. Let me just add a few things:
Be sure to use cauls. They are pieces of wood laid across the top of the boards being joined to keep them aligned (and to spread clamping pressure).
Make sure to alternate the position of the clamps. Have some clamping from the top and others clamping from the bottom. If you don't, you'll end up bowing the surface. I actually had this problem when I made my countertops--it wasn't visible on the first couple of rows, but at the end, there was significant bow that had built up.
You'll need a lot of clamps. There are some formulas out there that tell you how many you need, but I'd rather build than do math, so I just use as many clamps as I can fit.
In addition to biscuits and splines (as mentioned by @bowlturner), you can also use dowels. I ended up using a spline for my countertops. (As an aside, because they were bowed, I decided not to use them for a countertop. I bought Ikea countertops, was quite happy, but noticed that theirs were just as bowed as mine--though the joints were better. I ended up using the Ikea countertops for my countertop and the ones that I made for a workbench surface.) Here's a picture of how they turned out (maple with a shellac finish).
With today's glues, a simple butt edge joint works just fine. The boards need to be jointed well (the edges very straight, and I like a slight hollow towards the center ensuring the ends are tight and don't gap in the future). Clamping cauls will keep the boards aligned (I make my own from fir 2x4's). There will always be a slight misalignment of the boards at the joints that will need flattening (the same using splines, dowels, biscuits, or nothing). Sanding (by hand or random orbital sander) can work, but takes a long time. Some cabinet shops can sand or plane wide panels. I use hand planes for this step.
Many believe splines, dowels, or biscuits strengthen the joint, and they do not. A butt edge joint is just as strong. These methods can also cause the underlying dowel, etc. to "telegraph" into the finished top due to dissimilar wood/grain direction, etc. As for alignment, I have used each of the methods, including routered glue lock joints, and simply edge joining the boards and using clamping cauls to align them provides the easiest and most aligned assembly of all the methods.
