# Making Plywood Square



## scott lindsay (Jun 22, 2010)

I have watched a lot of cabinet making videos lately because I am trying to make a couple of cabinets with a top to become a desk. All of the videos talk about the plywood constructions but no one mentions how to square the plywood. I purchased plywood from Home Depot (2x4 sheets). I used the Kreg Accu-Cut to first true up one edge from perpendicular to a side. Then I measured down to the measurement for the height. After the two parallel cuts with a track for my circular saw I measure the diagonal and it turned out not to be square. Is there any tips, tricks, etc that I can do to square this error? Now in order to fix the height is going to be smaller than I wanted.

Here is a question about the sides, how do you know from store cut sheets which side is a good machined side? I watched one video that said to start by making a clean edge using the table saw (I believe it was Steve Ramsey). If the edge you pick is slightly off then the fresh edge is going to be off. As a newbie and one that keeps screwing up sheets of plywood and wasting money. There is no one around that woods with wood or even makes cabinets that is willing to help me. Any solutions to this problem?

-Scott


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## difalkner (Nov 27, 2011)

The factory edge often has printing on it if that helps any. Or it just looks different than when I cut it on my table saw so I can tell it from the factory edge. But the only plywood I cut is 5x5 sheets of Baltic Birch so this may not apply to the 2x4 cut sheets at HD or Lowe's.

David


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## subroc (Jan 3, 2015)

Check it with a square and a straight edge. Am I missing something?


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## epicfail48 (Mar 27, 2014)

Frankly, it sounds as if the problem isnt with the plywood, the problem is that when you made your cuts, they werent square. Simplest fix to that is better layout and cutting, plus making sure that whatever youre using as a square is actually square


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## DrRobert (Apr 27, 2015)

You have to have a dead on perfectly accurate square. Many of the typical framing squares won't get it in a ww'ing shop. I recommend a Starrett framing square, and even with that you have to check it. There are larger squares available, but a drywall square can be made perfect by drilling out all but one of the rivets, calibrating, and then replacing with sheet metal screws.

Second, don't assume the plywood is perfectly square from the factory. If you reference off the factory edges and corner isn't square you can easily end up with a parallelogram, as you have found.

When breaking down sheets,the cut edge is my reference. I cut 1/4" oversize & do all my measuring and squaring off the cut edge rather than the factory edge.

Hope this helps. BTW I've put more than one sheet of ply back in storage and bought a new one to start over ;-)


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## GeorgeC (Jul 30, 2008)

epicfail48 said:


> Frankly, it sounds as if the problem isnt with the plywood, the problem is that when you made your cuts, they werent square. Simplest fix to that is better layout and cutting, plus making sure that whatever youre using as a square is actually square



Checking a square for "square" is very simple. You place the short side of the square against the plywood (or even cardboard) and draw a line down the long side. Then flip the short side and draw that line again. If the lines diverge then it is not square. If one line is on top of the other the square is "square."


One of the problems with using a straight edge with a circular saw is keeping that straight edge in place while moving the saw. You have to pay particular attention to this.


It is also very easy to determine which, if any edge on a piece of plywood is straight. Use any long metal straight edge that you have and lay it along side the edges.


George


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## Rebelwork (Jan 15, 2012)

There are many ways to check this. Here are two...
Check square from corner to corner. The other is to run a straight edge you believe to be true and using a router or saw and take off just enough to clean and straighten the edge.......Rebel


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## scott lindsay (Jun 22, 2010)

A lot of good things have been written. I check for a square piece by using the diagonal method, tape measure from corner to opposite corner. The pieces I cut the other day was that I used a steel framing square by lining up one leg to my first measured mark and scribed a line. Then I put the Kreg Track (Accu-Cut) on it. My issue with this Kreg jig is that the blue handle/guide slides into the aluminum track but if you adjust it to the line the blue handle moves out a little. Not sure if it is enough to cause it to move out of square because the advertise sticky pads do not move. I asked Kreg but they will not respond to my question about that. I believe I am using the framing square correct and it is square. I also have used two different speed squares. Just things I need to check. Of course my daughter has been slapping the back of my head a lot lately so my eyes may need adjusting...lol. Really, I just do not know if I am being picky or if my tools are out of alignment. On a couple of boards the out of square is by 3/16 and others are closure to 1/4 which I think it is a lot and that means a lot of sanding on plywood edges. I have removed the factory machined edges by using my tablesaw so I could always cut my boards down to 36" height. The desk height I was going for was 37" with a layer of 3/4" and then 1/2 plywood covered with melamine. It is a taller than normal desk but she has a drafting chair she likes to sit up on.


Rebelwork: I like you straight edge jig. I have measured using my square before but also I use a carpenter pencil shaved to use that to scribe my line. The lead is about 1/8"thk creating a nice uniform line. Maybe it is just lining up my track edge and it is not exactly truly straight. Not sure how to check that.


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## Rebelwork (Jan 15, 2012)

Sorry there just random photsmart off the internet. I personally have/had a 14" ash straight edge I used At work when the table wax too big for the Altendorf slider...


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## JohnGi (May 9, 2019)

I do certification inspections in a plywood plant. They produce mostly sanded underlayment, a better grade of construction plywood. Squareness is something I check. Out of 100 pieces, 90 will have diagonals that match exactly, 9 will mismatch by 1/16", and 1 might mismatch by 1/8". I use a calibrated tape measure traceable to a US standard. Guys in plants that produce lower grade sheathing say my results are better than theirs. If I had 2 pieces 2' x 4', I would check for squareness by direct comparison. Set them side by side on a flat surface and feel if the vertical edges match exactly. Then fold them out on the flat surface or straightedge and look for a gap between the vertical edges. I used to do the same thing in millwork plants on double end tenoners. When the feed chains wear, some pairs of lugs cut square, and some don't. The old rule of thumb was 1/64" in an 8" wide piece (0.002" per inch of width). This method easily works to that degree of accuracy, and all you need is a straightedge.


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## FrankC (Aug 24, 2012)

I basically boils down to the fact that your cuts will only be as square as you make them, it sounds like you are using partial sheets that the store has cut from full sheets, if so don't expect much of a degree of accuracy from their cuts. Find a square corner and work from there which will likely be two factory edges.


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## woodnthings (Jan 24, 2009)

*Get a 48" drywall "T" square ....*



scott67 said:


> A lot of good things have been written. I check for a square piece by using the diagonal method, tape measure from corner to opposite corner. The pieces I cut the other day was that I used a steel framing square by lining up one leg to my first measured mark and scribed a line. Then I put the Kreg Track (Accu-Cut) on it. My issue with this Kreg jig is that the blue handle/guide slides into the aluminum track but if you adjust it to the line the blue handle moves out a little. Not sure if it is enough to cause it to move out of square because the advertise sticky pads do not move. I asked Kreg but they will not respond to my question about that. I believe I am using the framing square correct and it is square. I also have used two different speed squares. Just things I need to check. Of course my daughter has been slapping the back of my head a lot lately so my eyes may need adjusting...lol. Really, I just do not know if I am being picky or if my tools are out of alignment. On a couple of boards the out of square is by 3/16 and others are closure to 1/4 which I think it is a lot and that means a lot of sanding on plywood edges. I have removed the factory machined edges by using my tablesaw so I could always cut my boards down to 36" height. The desk height I was going for was 37" with a layer of 3/4" and then 1/2 plywood covered with melamine. It is a taller than normal desk but she has a drafting chair she likes to sit up on.
> 
> 
> Rebelwork: I like your straight edge jig. I have measured using my square before but also I use a carpenter pencil shaved to use that to scribe my line. The lead is about 1/8" thick creating a nice uniform line. Maybe it is just lining up my track edge and it is not exactly truly straight. Not sure how to check that.


https://www.homedepot.com/p/Empire-...jtLTI3qE4UZy3BHeTgBoC-zAQAvD_BwE&gclsrc=aw.ds

There is an adjustable T square that can also be used to make identically spaced in marks from the edge. You just set the end to your measurement and make the marks OR use it to check the setting on your straight edge guide. They come in 48" and 24" sizes. I use the 24" for setting my edge guides:
https://www.homedepot.com/p/Empire-...ERCH=REC-_-pipsem-_-202035306-_-100653520-_-N









A drywall T square can be checked for "square" by scriblng thin lines with a fine ball point pen on either side of the long edge. Then flip it over but keep the short leg registered along the same edge as best you can and repeat scribing the the lines about 1/16" away. All the lines should be parallel!

While in the store, you can also hold it against the corner of a sheet of 3/4" plywood and just see what you get...? Typically factory plywood is made square enough for most woodworking, BUT the panel saw used to rip it to lengths at the store may not be all that accurate. When using a track saw or a circular with an edge guide it is imperative that you measure and clamp the guide accurately. In this case, measure 4 X and cut once. Use the finest marking device you have. I like a old style ball point with a fine tip. 

:vs_cool:


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## homestd (Aug 24, 2018)

You definitely need as fine a line as possible for layout. A carpenter's pencil is OK for cutting 2x4s but for cabinets you need better. Paul Sellers uses a marking knife. Like woodnthings, I use a very fine tip gel pen. The hard part is if you don't cut as accurately as you mark you may as well use a dull sharpie.


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## scott lindsay (Jun 22, 2010)

What is better, taking the factory edge and put it on my tablesaw and run it through making the opposite edge straight then flip and use tat edge as guide to remove the factory edge and then work on the perpendicular edges or using the factory edge to put square on and trim off the top edge and measure down the make the other parallel cut and then work on the factory edge to get clean edges and hope they are square?


In the past I was buying the 5x5 sheet of Baltic birch but those sheets are really expensive than the interior sanded so-called birch from Home Depot plus the 2x4 birch from HD will fit in my car since I got rid of my pickup truck. I have been wanting to make an edger jig for my tablesaw but I was not thinking of it being wide enough to straighten 2x4 sheets. I guess I could use these pieces for a different project like a drill press stand and go get a couple of other 2x4 and start from scratch to make my daughters desk.


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## woodnthings (Jan 24, 2009)

*How much it it off?*

You do need a true square reference or use this technique:
Lay your panel against a straight board clamped at the very edge of a table. Mark your panel's edges 1,2,3, and 4. {Plane edge 1 against the straight board and scribe a line along edge 2. Then flip the panel upside down so edge 1 is still against the straight edge board and scribe another line very close to the original edge 2.


If the two lines scribed along edge 2 are parallel, that means edge 1 and edge 2 are square to one another. If not, the difference is 1/2 of the error. Then you remove that amount from edge 2 . 

Theoretically, edge 1 and edge 3 are parallel as are edge 2 and edge 4. So you can repeat this process using edge 4 against the straight board.


Diagonal measurements will tell you which diagonal is different in length, but not what to do about it.


I still recommend using a drywall T square as a reference OR a good framing square. You need to trust something at some point or you will be mired in doubt forever. 



People wonder why aligning the blasde to the miter slot is the preferred method. That's because when you use the miter gauge in the miter slot to make square cuts, it must be square to the blade.

Use the framing square against the miter gauge face and the blade to check for square. This is all pretty simple, but not all that easy to accomplish. 

:vs_cool:


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## woodnthings (Jan 24, 2009)

*How much is it off?*

You do need a true square reference or use this technique:
Lay your panel against a straight board clamped at the very edge of a table. Mark your panel's edges 1,2,3, and 4. Place edge 1 against the straight board and scribe a line along edge 2. Then flip the panel upside down so edge 1 is still against the straight edge board and scribe another line very close to the original edge 2.

If the two lines scribed along edge 2 are parallel, that means edge 1 and edge 2 are square to one another. If not, the difference is 1/2 of the error. Then you remove that amount from edge 2 . 

Theoretically, edge 1 and edge 3 are parallel as are edge 2 and edge 4. So you can repeat this process using edge 4 against the straight board.

Diagonal measurements will tell you which diagonal is different in length, but not what to do about it. I still recommend using a drywall T square as a reference OR a good framing square. You need to trust something at some point or you will be mired in doubt forever. 

People wonder why aligning the blade to the miter slot is the preferred method. That's because when you use the miter gauge in the miter slot to make square cuts, it must be square to the blade.

Use the framing square against the miter gauge face and the blade to check for square. This is all pretty simple, but not all that easy to accomplish. 

:vs_cool:


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## sancho57 (Oct 23, 2011)

Since you have a track saw I(Im assuming you do. Check out TSO products GRs and parallel guides. It will make your life easier.


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## scott lindsay (Jun 22, 2010)

woodnthings said:


> You do need a true square reference or use this technique:
> Lay your panel against a straight board clamped at the very edge of a table. Mark your panel's edges 1,2,3, and 4. Place edge 1 against the straight board and scribe a line along edge 2. Then flip the panel upside down so edge 1 is still against the straight edge board and scribe another line very close to the original edge 2.
> 
> If the two lines scribed along edge 2 are parallel, that means edge 1 and edge 2 are square to one another. If not, the difference is 1/2 of the error. Then you remove that amount from edge 2 .
> ...


That is something I should have thought of but it never occurred to me. I guess these Forums are helpful. I will need to try this along with some other suggestions made.


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## scott lindsay (Jun 22, 2010)

sancho57 said:


> Since you have a track saw I(Im assuming you do. Check out TSO products GRs and parallel guides. It will make your life easier.


I have a KREG track saw system but at the moment am not happy with it and am not sure if it keeps the cut true. I think there is a slight design flaw but that is just my opinion. I have not heard of TSO Products or GR's. I was looking at True Trak but I guess the one area I need to investigate is my marking ability. The carpenter's pencil may be to thick of a guide line to get a nice close square cut. I am going to have to try a marking knife or a very sharp round pencil mark.


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## woodnthings (Jan 24, 2009)

*Yep, expert advice for free .....*



scott67 said:


> That is something I should have thought of but it never occurred to me. I guess these Forums are helpful.



There was some doubt in your mind prior to this thread? 

Actually, we are all really a bunch of hacks with big egos .............








:vs_OMG:


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## denisd (Apr 15, 2020)

I'm a beginner also so I can't say that I can add to those that have replied. What I might be able to help with is explaining things from a beginner's perspective - and I mean beginner. All I'm about right now is practicing box joints, building small boxes, and some needed jigs - what you're building is beyond the scope of where I presently am with woodworking. 

I had many problems with "squareness" and I was wasting a lot of plywood so I went back to the basics that would take place before cutting a board. I'm not at the level where I have a cabinet saw or saw-stop or anything of the kind. I have a Bosch job site saw and I've had it for a few years and just couldn't get things working right. In fact, I was about to throw it away and give up or I'd have to buy a better saw.

I started watching plenty of videos. I learned that many 'beginners' that are now instructing on youtube started with a job site saw. How was this possible?

I dug into my owners manual and watched plenty of videos on squaring the blade to the fence etc. and waddya know? It was all my fault. My fence wasn't square (I got it to .024 on a 96" run which I'll never do anyway), as suggested by others in the forum, I tested my T-square and other squares for 'squareness' and found that those cheap squares except for one where not square - and I was depending on them! I'm not ready to spend on a starret square yet because I want to learn a bit more and I've got to get some ear protection. Man, this hobby is becoming expensive! I also found that my blade was not parallel to the table even though it 'comes' that way from the factory.

So from one beginner to another here are some things I learned:

Go back to your equipment and make sure the blade, rip fence, and miter gauge are within some basic specs that you can live with. (A must do)
Build a table saw sled - after you've squared everything else up - then test square your sled by using the 5 cut method. (A must do)
Buy cheap rip blades and combo blades. Don't use your good stuff on plywood. (Learned the expensive way)
Don't practice on plywood - it kills the blades. At the least use throw-away blades with plywood or prepare to send your good stuff back for sharpening. (Learned this the expensive way)
Use pine for practice. It's soft and doesn't kill your blades.

Good luck on your wood journey. 

- denis


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## kwoodhands (May 1, 2020)

Break the panels down oversize to a manageable size. I use 2x2" aluminum angle for straight edges. Attach straight edge to panel making sure it overhangs the panel at least 1/16". If screw holes will be objectionable than a heavy duty toggle clamp at each end of the straight edge will suffice. The angle is 1/8" thick and won't affect the squareness of the rip unless the rip is less than 10" wide. I drill and tap with 10/32 taps and fasten the toggle clamps with short screws.
Make the cut, remove the straight edge and saw the other side to dimension. Now you have two parallel sides. 
If the work is not to large I use a crosscut sled to saw the short ends. Sometimes you can saw the short sides with just the fence. If the work is long be careful for kickbacks. 
I used to use a wood square that I made for use with a circular saw or a router. I lent it to a friend who passed away before returning it. I never asked the widow for the square, did not think it would be right I suppose.
This square had a lip similar to a speed square. The square pushed up to the edge and clamped before sawing.
mike


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## scott lindsay (Jun 22, 2010)

denisd said:


> So from one beginner to another here are some things I learned:
> 
> Go back to your equipment and make sure the blade, rip fence, and miter gauge are within some basic specs that you can live with. (A must do)
> Build a table saw sled - after you've squared everything else up - then test square your sled by using the 5 cut method. (A must do)
> ...



Denis,


I like what you wrote. I am at the same point you are at. Yes, this hobby is expensive. I have checked rip fence and to the blade and it is square. My miter gauge has a pin that allows you not to go past 90°. I used the miter yesterday and it seems to be off a little. The ripping along a fence seems to be accurate but trying to rip a 30" long x 19" wide is not easy running it against the rip fence and not have to move so I use the Kreg Track and my Craftsman Circular Saw. At first I thought that this system is not working. I cannot guarantee that I installed the circular saw correctly. I am thinking about trying a different track system or a new straight guide. Rockler has one that clamps on the edges. I also read a book where you take two 1/2" or 3/4" MDF or Plywood and make your own guide. I may actually try that one. As far as square lines I have used a couple of different ones including my T-square from my drafting days. Everything I am using seems to be pretty square. I draw a line with the T-square and line up the Kreg jig. I start to cut and the first 6" inches it is cutting on my line then it seems to start moving away from the line. The track has a sticky bottom so I know it is not moving and I know the saw moving along the track is not sliding but half way down a 24" straight line with the edge of the saw path lined up on that line, it still does not cut right on that straight line. I think I am going to try the plywood jig next.


-Scott


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## kwoodhands (May 1, 2020)

Scott, your miter gauge can be made dead square with the following method. All machined tables , cabinet, contractor or band saws have the miter slots accurately machined to 90°. First flip the zero stop out of the way and loosen the lock knob. Turn the gauge upside down, slide the bar in the slot til the head hits the table edge and is flush to the table edge. Lock the knob, the gauge is dead square to the slots. If the stop is adjustable, move it to zero.
My saws have the fence in the way, I made a jig from MDF with the 90 & 45 ° slots routed into the MDF. I have a table from an old Craftsmen contractor saw that is bolted to the right of my cabinet saw. Sometimes I use the miter slots in this table if I don't have to move a bunch of stuff to get at it.

mike


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## epicfail48 (Mar 27, 2014)

kwoodhands said:


> Scott, your miter gauge can be made dead square with the following method. All machined tables , cabinet, contractor or band saws have the miter slots accurately machined to 90°. First flip the zero stop out of the way and loosen the lock knob. Turn the gauge upside down, slide the bar in the slot til the head hits the table edge and is flush to the table edge. Lock the knob, the gauge is dead square to the slots. If the stop is adjustable, move it to zero.
> My saws have the fence in the way, I made a jig from MDF with the 90 & 45 ° slots routed into the MDF. I have a table from an old Craftsmen contractor saw that is bolted to the right of my cabinet saw. Sometimes I use the miter slots in this table if I don't have to move a bunch of stuff to get at it.
> 
> mike


"All machined tables , cabinet, contractor or band saws _are supposed to_ have the miter slots accurately machined to 90°"

Never assume that a machine was built properly without verifying, otherwise youll screw up a project later down the line. Some of those things youd think theres no way to mess up, but anywhere that a corner can be, it will be.


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## woodnthings (Jan 24, 2009)

*"square" is relative to the application ...*



kwoodhands said:


> Scott, your miter gauge can be made dead square with the following method. All machined tables , cabinet, contractor or band saws have the miter slots accurately machined to 90°. First flip the zero stop out of the way and loosen the lock knob. Turn the gauge upside down, slide the bar in the slot til the head hits the table edge and is flush to the table edge. Lock the knob, the gauge is dead square to the slots. If the stop is adjustable, move it to zero.
> My saws have the fence in the way, I made a jig from MDF with the 90 & 45 ° slots routed into the MDF. I have a table from an old Craftsmen contractor saw that is bolted to the right of my cabinet saw. Sometimes I use the miter slots in this table if I don't have to move a bunch of stuff to get at it.
> 
> mike



I use the same method for squaring my miter gauges, mike. :smile2:

The machine/milled slots in the table that are 90 degrees to the front edge and parallel to the sides, are "good enough" for me. I can't measure down to minutes of angle anyway and the old standby scribe and flip test will show any "glaring" errors, like a degree or two off. I promise you that that amount of error would not be possible with the kind of production machines at the factory, whether made in China or USA. It would not be "cost effective" to run a production line with any significant amount of error at the miter slot to front edge.
:vs_cool:


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