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Thread: Getting a good square piece of ply

  1. #1
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    Default Getting a good square piece of ply

    Is there a better way to get a biggish piece of sheet material square than using a tape measure on the diagonals? With the fatness of the tape, and the rough approximation of grabbing the corner, it seems like it can be off by 1/8 to 1/4 easily. Factory edges not always available.

    I am hoping for a method that can be used on sawhorses. I donít have a big table saw.

    Thanks
    Tom

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    Default Re: Getting a good square piece of ply

    Just an idea.
    If you have some staight stock around, you could build a giant square first. There are some pictures of such framing squares in the Gougen Brothers book.

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    Default Re: Getting a good square piece of ply

    If you have the funds but not the space, a tracksaw is a great alternative to a big tablesaw. Cutting large squares is simple with an accessory like this https://tsoproducts.com/tso-parallel-guide-system/

    The go-anywhere aspect of a tracksaw makes it superior in some ways to a table saw.

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    Default Re: Getting a good square piece of ply

    Assuming you have one straight side and can cut reasonable accurately all you need is a carpenters square and a straight edge....Oh yea and a pencil

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    Default Getting a good square piece of ply

    3-4-5 right triangle. Don't need no square.

    Mark out 3 units on one edge, 4 units on the other edge. The diagonal should be 5 units.

    Adjust the edges as needed to dial in the diagonal to 5 units.

    And the bigger the unit and the triangle, the more accurate you are.
    Last edited by Nicholas Carey; 02-21-2021 at 02:57 AM.
    You would not enjoy Nietzsche, sir. He is fundamentally unsound. ó P.G. Wodehouse (Carry On, Jeeves)

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    Default

    Also, this hack to make your tape work better for measuring outside diagonals. http://woodworkingtips.com/etips/etip092200ws.html





    Also this handy little gadget.

    https://www.leevalley.com/en-gb/shop...p?item=50K5801

    You would not enjoy Nietzsche, sir. He is fundamentally unsound. ó P.G. Wodehouse (Carry On, Jeeves)

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    Default Re: Getting a good square piece of ply

    Good stuff. Thanks all!

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    Default Re: Getting a good square piece of ply

    I’m a fan of tracksaws and TSOs products but a 4’ drywall square could help with layout, too.

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    Default Re: Getting a good square piece of ply

    I just bought one of these for my Makita track saw. Love it.

    71F87C83-D939-4C91-90F6-B7DF6B8B23DA.jpg

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    Default Re: Getting a good square piece of ply

    An eighth to a quarter off?
    Have you tightened down the tape measure rivets ?
    (don't)

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    Default Re: Getting a good square piece of ply

    I have that one, too, Ron. It works great with a 39” section of track for cross cutting sheet goods. I usually get my cabinet grade plywood ripped to width at the hardwood shop. So if I’m building cabinets 18” or 20” or 24” deep I get my plywood ripped and just use the tracksaw to precisely cut to length.

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    Default Re: Getting a good square piece of ply

    Tablesaw's of no help with full sheets unless you have the room and extra support to slide the sheet over the table.

    Maybe a helper too....

    I bought a length of 1/4" x 4" 6061 40 years ago for a straight edge. Cut to 9-1/2' & 6-1/2' for cabinetry stuff w/ circular saw & router before track saws ever appeared. Can use it pretty much anywhere.tract

    3-4-5 will always work for you if you bother to check diagonals from both sides of your perpendicular if possible.

    'Nother method's using a makeshift compass (straight stick w/ three holes - two near one end, third near other end) to first divide a straight line into halves, then strike two points equidistant from center using two holes closest together. Then use holes farthest apart to strike two intersecting arcs from the two equidistant points you found. From that intersection, draw a line to that centerpoint you first established.

    Done carefully, with a sharp pencil line, you don't need any other tools but that straight stick and the pencil.

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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by bluedog225
    With the fatness of the tape, and the rough approximation of grabbing the corner, it seems like it can be off by 1/8 to 1/4 easily.
    It made me curious how far off you'd be if you measured as inaccurately as possible. Assume you're measuring the diagonal of a 4' x 4' square of plywood and your tape measure is 1.25" wide. Hook the corner with the left side of the hook and then measure with both the left and right sides of the tape. The difference is .035" or about 1/32". In actual use you're way more likely to hook near the center of the hook so the error will go down considerably.

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    Default Re: Getting a good square piece of ply

    3-4-5 triangle. Use the side of the tape measure that is the top or bottom edge for diagonals
    Elect a clown expect a circus

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    Default Getting a good square piece of ply

    Quote Originally Posted by sp_clark View Post
    Tablesaw's of no help with full sheets unless you have the room and extra support to slide the sheet over the table.

    Maybe a helper too....
    These "helpers" are worth your weight in gold if you're cutting big plywood. 2 or 3 of them - you can use them as infeed, outfeed, or side support. For outfeed use, set the height and pull the pin to put in flip top mode - the the work piece droops as it comes off the saw, it will ride up the ramp until the flip top flips horizontal.

    The top is made of some slippery plastic. Unlike a roller stand, that means alignment isn't critical. You can be way off square from the line of feed and it won't try to skew the workpiece.

    https://www.ridgid.com/us/en/flip-to...e-work-support





    Available at the Big Orange Box and Amazon (at the very least). I think I paid about $30 each for mine. Cheap!

    I bought a length of 1/4" x 4" 6061 40 years ago for a straight edge. Cut to 9-1/2' & 6-1/2' for cabinetry stuff w/ circular saw & router before track saws ever appeared. Can use it pretty much anywhere.
    I made a zero-clearance cutting guide fixture for my circular saw from Masonite. Cut an 8 foot long x 6 inch wide piece of Masonite. Affix a straight edge like a MDF 1x2 or an 8-foot drywall straightedge.

    Put the blade you're going to use with this fixture on the circular saw, square it up to the sole and run the saw down the straight edge. Voila! Set that edge on the cut line, clamp it down and you've got about 80% of a tracksaw.

    Make a knock-down cutting grid like this, and with that saw guide, you can break down a sheet of plywood a whole lot easier than trying to wrestle it through the table saw.

    Last edited by Nicholas Carey; 02-21-2021 at 01:27 PM.
    You would not enjoy Nietzsche, sir. He is fundamentally unsound. ó P.G. Wodehouse (Carry On, Jeeves)

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    Default Re: Getting a good square piece of ply

    I always measure from a convenient measurement point away from the hook on the end of the tape.Might be 1" might be 100mm depending on the flavour of the job.

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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by John Meachen View Post
    I always measure from a convenient measurement point away from the hook on the end of the tape.Might be 1" might be 100mm depending on the flavour of the job.
    I do also, removes a potential cause of error. Couple of those Pony hand spring clamps helps on sheet goods; one holds the short end in place while I run the long end out to t’other corner. Need another clamp there too so’s I can get back to the short’n, make sure it’s still on 1” / 10.00 cm, hasn’t moved.

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    Default Re: Getting a good square piece of ply

    “Hold me on the two!” Inch that is. / Jim

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    Default Re: Getting a good square piece of ply

    Another thing about the table saw is you really need a straight edge to run against the fence. I cringe on job sites when I see someone running a long piece of ply though a table saw that had a hand cut wavy edge on it. Just crying out for binding and a kickback.

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    Default Re: Getting a good square piece of ply

    When you take things for granted..... for nearly 30 years I ran a nice big old school panel saw with full sheet and more rip and sliding table for the dock/cut off, it was squared.
    Now I don't have it operating anymore mundane jobs like a squared board with dead straight edges can become time consuming. But what I do have is some 3mm sheets of various sizes that came off it and they help a lot as squares without much /any setup.
    In other words, a pattern .

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    Default Re: Getting a good square piece of ply

    I suppose its not as accurate as other methods, but it works 90% of the time for me. I just use a four foot drywall square. Another trick, when getting out a new full sheet of ply, I start-out by determining which of the 4 corners is square (one of them typically is close enough) and mark that. Then I try to cut opposite sides first, so I always have a two sides on the left-over that are square.

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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by peb View Post
    I just use a four foot drywall square.
    I just bought one, yeah. Figured it'd be handy for doing some lofting from plans for a new tangent I've taken.

    Seems sturdy enough yet with its being made of 100% aluminum I've got it in my head that I really need to treat it kindly if I expect to trust it later on, even if I can get myself to do a check-for-square once in awhile.

  23. #23
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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by sp_clark View Post
    I just bought one, yeah. Figured it'd be handy for doing some lofting from plans for a new tangent I've taken.

    Seems sturdy enough yet with its being made of 100% aluminum I've got it in my head that I really need to treat it kindly if I expect to trust it later on, even if I can get myself to do a check-for-square once in awhile.
    I have had one for several years, and I suppose I could treat it more kindly. It seems to be accurate enough for the plywood problem in most cases. IIRC, I did not use it for lofting. Even if it is perfectly square, depending on the service on is lofting on, I suspect it might be hard to use accurately. I lofted on mylar sheets (which works great for transferring lines onto wood BTW) and did not worry about making sure the mylar was aligned perfectly with the edge of the table I was working on.

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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by Nicholas Carey View Post
    These "helpers" are worth your weight in gold if you're cutting big plywood. 2 or 3 of them - you can use them as infeed, outfeed, or side support. For outfeed use, set the height and pull the pin to put in flip top mode - the the work piece droops as it comes off the saw, it will ride up the ramp until the flip top flips horizontal.

    The top is made of some slippery plastic. Unlike a roller stand, that means alignment isn't critical. You can be way off square from the line of feed and it won't try to skew the workpiece.

    https://www.ridgid.com/us/en/flip-to...e-work-support





    Available at the Big Orange Box and Amazon (at the very least). I think I paid about $30 each for mine. Cheap!



    I made a zero-clearance cutting guide fixture for my circular saw from Masonite. Cut an 8 foot long x 6 inch wide piece of Masonite. Affix a straight edge like a MDF 1x2 or an 8-foot drywall straightedge.

    Put the blade you're going to use with this fixture on the circular saw, square it up to the sole and run the saw down the straight edge. Voila! Set that edge on the cut line, clamp it down and you've got about 80% of a tracksaw.

    Make a knock-down cutting grid like this, and with that saw guide, you can break down a sheet of plywood a whole lot easier than trying to wrestle it through the table saw.


    Much better than a roller as it is non directional and wont pull the work to one side or another. I took a 25LB barbell weight and slid it over the upright post. Makes it almost impossible to tip over and keeps it from moving when I'm ripping long, heavy stock. The top eventually got scratched up so I glued a piece of satin formica to it to make it slippery again.

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    Default Re: Getting a good square piece of ply

    Ok. One more question.

    I got some fresh new BC 3/4 ply today. And a big drywall square. The latter seems to be square.

    As far as I can tell, one end of the ply is not square. And one long side of the full sheet is 1/8 short (edit-1/8 on diagonal and 1/16 on the long edge)

    Up to this point in life, I had assumed that factory plywood was absolutely square. Do I need to adjust my thinking?

    The edges appear straight so I can get where I need to be but it never occurred to me that the ends would be off.
    Last edited by bluedog225; 02-25-2021 at 08:43 PM.

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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by bluedog225 View Post
    Ok. One more question.

    I got some fresh new BC 3/4 ply today. And a big drywall square. The latter seems to be square.

    As far as I can tell, one end of the ply is not square. And one long side of the full sheet is 1/8 short.

    Up to this point in life, I had assumed that factory plywood was absolutely square. Do I need to adjust my thinking?

    The edges appear straight so I can get where I need to be but it never occurred to me that the ends would be off.
    Yes, adjust your thinking, plywood from BOBS is often off-square by 1/8" or more. Also drywall squares can frequently be off by the same amount, drywall being a very inexact science. My drywall square is off by just a bit, and works fine for drywall, but I'd never use it for cabinetry. Get a good quality framing square and a good 4' straightedge.

    If it's boatbuilding accuracy you're after, then the only proper way to insure squareness is to erect a perpendicular using a beam compass.

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    Default Re: Getting a good square piece of ply

    Well shoot. Thanks. That explains some small part of my shoddy work.

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    Test your sheet metal framing or drywall square for square by butting it up against a known straight edge on something like a sheet of plywood or Masonite. Strike the line. Flip it 180 and strike the same line in the same place. If they diverge, the gap at the end is twice the error. You should be able see whether the square needs to be opened or closed.

    Open it by striking it with a mallet and punch on the inside of the corner; close it by striking with a mallet and punch at the outside corner.

    You would not enjoy Nietzsche, sir. He is fundamentally unsound. ó P.G. Wodehouse (Carry On, Jeeves)

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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by TerryLL View Post
    If it's boatbuilding accuracy you're after, then the only proper way to insure squareness is to erect a perpendicular using a beam compass.
    Yep, agreed. No arguments with geometry.

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    Default Re: Getting a good square piece of ply

    It used to be that plywood from the factory was really 48" x 96" and it was square. When I was building in the late 70's, early 80's this was a given. We'd check a sheet every so often but always found it true. Nowadays, not so much. I'm not even convinced that the edges are straight on every sheet.

    Every time I've relied on a carpenter square to be accurate it's come back to bite me. No exceptions. I'll use the tool if it's not really got to be spot on, but not ever for a cabinet or similar. And anyone who relies on the accuracy of a drywall square is taking a huge risk in my experience. Those thing will go out of whack while your back's turned.

    Layout, usually by using a 3-4-5 triangle, is the only way to plot an accurate right angle corner. And while you do this, be sure that the surface you're laying it out on is one flat plane. The surface cannot have any sort of curvature.

    Jeff

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    Default Re: Getting a good square piece of ply

    Thanks everyone. I did some checking on the new stuff I bought and it is, in fact, 1/8” off on one end when comparing two new full sheets. I would think they could do better if they cared to check the machine on occassion.

    Knowing this, the quality of my carpentry has improved substantially.

    No doing cabinetry, just hacking out some shutters. The drywall square seems square through every method I’ve used to check it. But I will keep an eye on it. It is my only reliable 4 foot straight edge.

    I’m curious on laying out a 3x4x5 triangle. It seems difficult to do with a tape measure. Is clamping it down on your mark somewhere away from the end of the tape the way to go. I see the “pony hand springs” comment above. Or a longer straight edge? Like the alu channel.

  32. #32
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    Default Re: Getting a good square piece of ply

    There are lots of ways to make plywood square, but if you are working on a boat the saltest way is like you are lofting. One line down the center, (straight edge and string) use a compass (18" stick, pencil size hole on one side couple little holes along its length for brads) to mark the points for the 90 degree line. Any lofting book.
    this will be very accurate, and all you need to do is measure from those lines. The more you do it the faster it gets.

    Now if you use this method for anything besides boat building every carpenter out there will laugh their a__ off. But your lines will be square!

  33. #33
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    Default Re: Getting a good square piece of ply

    Quote Originally Posted by bluedog225 View Post
    Ok. One more question.

    I got some fresh new BC 3/4 ply today. And a big drywall square. The latter seems to be square.

    As far as I can tell, one end of the ply is not square. And one long side of the full sheet is 1/8 short (edit-1/8 on diagonal and 1/16 on the long edge)

    Up to this point in life, I had assumed that factory plywood was absolutely square. Do I need to adjust my thinking?

    The edges appear straight so I can get where I need to be but it never occurred to me that the ends would be off.
    I don't know how these things are regulated in your part of the world but I do know that we would expect sheet dimensions to conform to established standards.The standards relate to the overall size of the sheet and the deviation from square.Most are very close to square but it would be unwise to assume absolute perfection.

  34. #34
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    Quote Originally Posted by John Meachen View Post
    I don't know how these things are regulated in your part of the world but I do know that we would expect sheet dimensions to conform to established standards.The standards relate to the overall size of the sheet and the deviation from square.Most are very close to square but it would be unwise to assume absolute perfection.

    Yes... but here in the States, the standards are set by the lumber industry. And tolerances are... errr... loose.

    2x4 lumber is now 1-1/2 x 3-1/2. It used to be just 1/4 undersized, to account for shrinkage and planing. Sometime in the late 60s IIRC they took another quarter inch.

    Plywood is always undersized by about 1/32nd of an inch.

    Looks like youse guys across the pond have it good WRT square and straight: https://apawood-europe.org/official-...ards/en-324-2/
    You would not enjoy Nietzsche, sir. He is fundamentally unsound. ó P.G. Wodehouse (Carry On, Jeeves)

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    Default Re: Getting a good square piece of ply

    This pic makes it look worse than it is. But it's still pretty bad. These are the same 4' edge.

    IMG_20210226_100101792.jpg

    IMG_20210226_100129993.jpg

    I ended up cutting a 6 and 10 foot section out of an old tape measure. Works great for this purpose.

    I got to within 1/8 of square on a 6 foot diagonal which was a big improvement. Still chasing down little issues with my set up.

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