I'm really new to the whole woodworking world and am taking on a fairly large project. The project requires me to edge join two pieces of 3/4 " plywood, 75" long by 27" wide. The plans call for a splice but I'm wondering if pocket holes could be used instead. It seems much easier than routing grooves and cutting a splice. Any suggestions would be greatly appreciated.\
You can do this type of project. As Bob said it is done all the time. For the future it is a good idea to include some information as to materials, end use, stress by use when finished, and particular problems. Even if those problems are your lack of tooling, or skills, everyone here is in the same way, no one knows it all, and no one has the perfect shop with every tool their hearts desires. To help you better we need to know things like the following. What kind of plywood? Baltic birch is miles different from A/C shop grade and the way they screw up is different. What is the end use of the project? Wet locations have a couple more issues that need to be planned for in the beginning. Which edge is getting the joint? The 75" or the 27"? After you join the two are they going to be a table top or a counter top or base for a mural on the wall. From the clues in your description you make me wonder if you are not talking about a groove and spline? Cut a groove in the plywood edge and then add a cut spline (long strip) of wood (the third wood piece in the equation) that is inserted between the two mated pieces? If my guesses are correct, then you are planning to make a spline joint along the 27" dimension? To spline the 75" way makes no sense at all to me. So then the other way is two 75" long pieces joined across the 27" butts and then you end up with a 27" wide board that is 150" long. Is that the idea? If so, no problem with the pocket screws. I would use glue on the joint, and try to finish with the longest maxi head screw I could. There will be a bunch of stress on that joint coming from the ends, sort of a lever working on the end. In that case I would not even consider anything but the pocket screw. The spline or dowels will give you more glue surface and a dowel in the ends helps distribute the weight, but none the less, pocket screws. If there is high use and stress on the joint I would not be afraid of using screws every 2.5" to 3." across the joint. One more tip: You may not be aware that the mill edge of plywood is never square. You will need to be dead on square. A slight off square at 150" is impossible to fit. I would even trial fit the boards in place before you make the joint, if you can. There isn't a one of us that hasn't had some sort of unpleasant surprise.
Feel free to correct or disagree anyone.