I’ve always only worked with solid wood except the occasional jig or shop shelf/cabinet. I will soon be doing some more cabinetry and book shelves using plywood and one thing keeps illuding me.
Maybe I’m overthinking this but after you rough cut you sheets or even if your going for fine cuts the first time, how do you keep it square? Are the factory edges reliable? How do you keep from making a paralelogram? Like I said, perhaps I can not see the trees throught the proverbial forest here but please help – its driving me nuts.
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I don't trust the manufactured surfaces to be square so I usually end up machining them off. They are usually nicked or damaged from handling etc. I usually rough cut with a circular saw then go to the table saw and using the stock sheet edge as it comes I rip the opposite side then I rip the stock sheet edge to get the finished width. Then using a cross slide I cut one end to square it up and then I cut the opposite end to finished length. My saw can rip widths up to 25 inches and my cross slide can handle stock up to 25". Any thing larger I do with a straight edge and circular saw but I do get some tear out so if it is a very critical surface I might take it a local cabinet shop which can rip to 48". Backs for cabinets etc. can be done with a circular saw as a little tear out is acceptable. Most cabinets don't require plywood wider than 25" and length isn't a problem with the cross slide. Thats my two cents worth.
You don't have to over think the situation, gcg. The good news is that most quality plywood has at least straight edges. I haven't seen any that were out of square enough to know. 25-30 years ago, some lower end construction plywood could be out of square a lot. Maybe some imports have problems but the technology in the industry isn't challenged by getting a square sheet anymore.
If you have a straight edge to work from, any cuts using the rip fence will result in a parallel cut to that edge. If the factory edge is rough or you don't want to use it in the project, rip the piece wider and then rip off the part you don't want. It helps a lot if you have a rip fence that opens enough to guide your parts. In other words, you set the fence for the size you want, not the amount you want to remove.
In rare circumstances, you may need to square an end of the plywood. This is best done after you have ripped the sheet down. Once in a while, you may run into a job that requires large panels but most of the time the pieces are manageable for someone experienced on the saw. Often the end can be squared with a sled. Smaller widths can be done on the compound slider. If the pieces are too large or you don't feel you have control, you can always use a circular saw. With a decent blade and a straight edge guide, you can get a good quality cut.
With sheetgoods on a table saw, you obviously need an outfeed table. There are times that you may want other means of support, off to the side or at the infeed end. Much of the time you will be using the rip fence, for both crosscuts and rips. You just need to concentrate on the fence and keep the work tight to it. Listen to your common sense, cross cutting a 12"x42" piece with the 12" against the fence isn't a good idea. 12" will fit on the miter bar, don't use the fence in this situation. With 24"x42" I'd be comfortable with the 24" on the fence, you have to answer that question for yourself.
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