How do you square plywood ?

First of all, I wish to thank all of you who continuously respond to my (dumb) questions with valuable information. With the skill levels of most of you, I unfortunately don't often have anything you don't already know to offer in return.

I bought two sheets of 3/4 inch Birch plywood and soon discovered they were not square. When cutting down, I can get two sides parallel with no problem, but have difficulty getting two adjacent sides square.

The T-square I got from the big box is worst than the sheet of plywood. Granted, it was intended for cutting wall board; accurate enough for it's intended purpose but not accurate enough to get a perfect 90 degree. Are there any good (perfectly accurate) T-squares that can be used to obtain good square corners?

What methods do you use to square a piece of plywood. Is a cross cut sled my answer? How big a panel will a cross cut sled safely handle? What about larger panels? The panel I cut is 39" x 24", seems to me that would be too large for a cross cut sled.

Again, my thanks to all who take the time to help out by passing their skills and experiences along to others, hopefully some day soon I will develop some skills to start helping others in return.

Tony, I have two (well, 3 really) crosscut sleds.

The one I use the most is my medium sized sled. It will crosscut a piece up to 26" wide. This handles all the width I need for the majority of cabinets that I make (23¼" wide, before face fame).

My big sled is made from a 5' x 5' sheet of ½" Baltic Birch. With assistance, I can square a whole sheet of ply. I rarely use it, but when you gotta have it, you gotta have it.

Some folks use a router with a clamp fence on the end of a sheet to square a edge. This will work, and I've done it, but the trick here is setting your fence square without an already square reference point. Again, to trianglate 3' x 4' x 5', it takes two people to do it fast. I guess you could spend the time to make a big triangle once, then you have it.

A long term answer for me will be a sliding table tablesaw, which turns a typical cabinet saw that is really deisgned for ripping into a crosscutting MACHINE.

My advice to you would be to make a nice (or buy), perfectly 90° crosscut sled.

Tony - Here is how I square plywood panels of that size. NOTE: It helps if you have an outfeed table and a left wing extension on the TS (much safer). I use a Norm inspired panel cutter, which is nothing more that a piece of 1/2" plywood with an oak runner underneath and an oak fence along the leading edge of the panel cutter.

Procedure: Cut the panel a little wider and longer than you need the final dimension to be. Look at the panel from above and note that you have a north, south, east and west edge. Trim one edge in the panel cutter (lets trim north). Now, rotate the plywood counterclockwise so that the north edge butts up to the oak fence. You are now trimming the east edge. After you have the north and east edge trimmed measure for your final dimension (north to south) and cut the south edge. Rotate again counterclockwise and cut the west edge. You now have a squared panel.

Hope that wasn't too confusing.

Waymon...

Tony.

If your square is off a bit you can still use it to get a true 90 degrees.

From a point on a straight edge of your ply use the dud square to mark two lines. Just mark one line as you normally do and then flip the square over and mark another line.

The 2 lines will diverge from the point and true square is mid way between them.

Having established a line you believe to be square to an edge, you can prove it is square by measuring. Measure and mark 3 units on your line and 4 units on the edge from their intersection (or the other way round). The distance between the two marks will be exactly 5 units if your angle is 90 degrees. Pythogorus and the square on the hippo and all that jazz.

If you are trying to get the cross-cuts square and the long edges are in fact parallel, why don't you just use a cross-cut sled and a framing square referenced to one of the parallel sides. Usually works for me if dealing with full sheets.

Smaller pieces, I use the fence on the table saw to create parallel surfaces and then the sliding miter table for the cross-cuts. A large miter sled will also work if you don't have a sliding miter table.

I hope this helps.

Tony, remember this: The Only Dumb Question is the one that is not asked!! It may be "dumb" (aka. simple) to us, but to you it is Very important and not simple for you. Never be afraid to ask questions - we here at the creek will not judge anyone's abilities or intelligence as we are all the same here. FRIENDS!!!

Tony
There are no dumb questions
I use 3,4,5
and/or a sled.

3,4,5 when the piece is too large for the table saw

The push sled when the sheet is small enough to handle
Sled size is 32 inches by 18 inches.
Daniel
:rolleyes:

I use the 345 method myself at job sites for walls and ply, its very convenient method.

As home (you will hate me =)), I use my 8' sliding table on my combo minimax machine,and its a dream. Just reference it to he sliders fence and push her through with a finger =). As long as you have the fence adjusted square you are in business, its the quickest way to square ply I have ever seen, and by far the easiest!


-Chris

Quote:

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Originally Posted by Chris Pasko

As home (you will hate me =)), ........... push her through with a finger =).
-Chris

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No Chris, I won't hate you ..........Wait a minute --- 'push her through with a finger'........now that's a low blow! :p

Thanks everyone for your input. I'll use the good old 3-4-5 method to try to salvage the current project. I see an upcoming pause in the project list to build a crosscut sled.

I just turn my head to the side slightly and then I can't tell.