Why Isn't It Square

[dusty]

As a review of my learnings in geometry class, I would like to ask a question or two.

If I am building what amounts to a box (actually it is the first in a set of drawers), the opposing sides are equal and one of the corners is perfectly square - should I not expect the drawer to be square?

What am I doing wrong, if all of the above is true but when I finish gluing and clamping the box is not perfectly square?

It is reasonably square but the other corners are not as square as the first. I do this repeatedly. This is certainly one of those factors that separates the true craftsman from the wantabe.

I watch Norm, et al., do this all the time and their results are always perfect.

[edflorence]

Hi Dusty-

Very common problem you are posing, I believe.

A box or drawer can have opposite sides exactly equal in length and no square corners, creating a parallelogram. Unbraced squares are notorious for "wracking" into parallelograms. But to have equal sides and one "for sure" 90 degree corner is more of a puzzle. It seems to me that the corner opposite the square corner must be trying to pull itself into a parallelogram and taking the corners adjacent to it along for the ride. You might be able to verify this more accurately by measuring diagonals rather than by putting a square into each corner.

What has helped me is to assemble a box or drawer in opposite halves, using internal squares clamped in place while glue sets. I got a pair of heavy black plastic squares from Rockler a few years ago designed for this. You clamp them into the inside corner. Work great. After the two opposite halves are glued up, remove the interior squaring devices and re-use on the other two corners while gluing the box halves together.

[cowboyplus]

...
I watch Norm, et al., do this all the time and their results are always perfect.

You only get to see Norm’s acceptable for TV result ... They don’t (he doesn’t) always get a presentation result the first time.

After clamping, but before the glue has set, make sure the diagonals measure the same with the project on a flat surface (equal clamp distance from a flat surface). You might need another clamp to square (reduce) the longer diagonal. You need to verify both the top and bottom.

Another method I use as well, is use an angle piece of plastic that glue does not adhere for each corner (I sliced plastic electrical boxes) and cut calculated diagonal pieces chamfered to form a 90º angle on the tips and place in both directions, top and bottom, and band clamp to hold.
.

[Nick]

I watch Norm, et al., do this all the time and their results are always perfect.

I assure you that they aren't. They have precisely the same problems that you do. It's just that a produced television show can wrap up drawers, projects, even life-threatening situations in a nice, neat, edited package with a happy ending.

That said, there is more to making a square drawer than meets the eye. Here are several tips I give my students.

1. Geometry doesn't lie -- except in the shop. Wood is a cantankerous substance with a perverse sense of humor. A slight bow, warp, twist, or cup in a single board can make a drawer
[INDENT]a. Appear square when it isn't.
b. Appear out-of-square when it isn't.
c. Appear square when it is.
d. Appear out-of-square when it is.[/INDENT]
2. Check the length of the pieces. The two sides must be of equal lengths and the drawewr font and back must be the proper lengths depending on the construction of the drawer.
3. Check the joinery. A dado, rabbet, groove, dovetail, or box joint that's out of position by a tiny amount will effect squareness. So will a joint that is not cut to the proper depth.
4. Check the wood. If two adjoining boards are not perfectly straight and flat, the joint between them may appear something other than 90 degrees when you lay a square in the inside corner. This situation may also make a corner appear square when it isn't.
5. Check the clamps. About 80% of the time, this is the culprit. Woodworkers tend to put too much pressure on clamps when they draw wooden parts together. When a drawer part is under too much pressure, it will bend or bow. If you allow the glue to dry with the wood distorted, it may hold this distortion when you release the clamps (depending on the construction).

To avoid these problems, check the drawer squareness twice during assembly -- once when you dry-clamp the parts without glue and again when you clamp the parts together with glue. You must make the second check within the working time of the glue, before it begins to set.

You may also want to watch http://www.shopsmithacademy.com/Tips_Ar ... quares.htm

With all good wishes,

[edflorence]

Nick wrote:
"You may also want to watch http://www.shopsmithacademy.com/Tips_Ar ... quares.htm"




Nick...

Many thanks for the link to the Tip re the inside and outside corner squares. The inside squares are exactly what I was trying to tell Dusty about. After watching the Tip I decided I would like to make a set like the ones you demonstrated. Have you got any tricks for machining these tools exactly square?

Thanks for all your help

[beeg]

Dusty

Take the drawer frame amd set it up against your rip fence, then check the corners. And report back here.

When building the covered wagon toy box. I had the same problem and boy was I disappointed. After awhile I final found the problem, each end was not at 90°(Ed's parallelogram). All I had to do was line up one end with a straight edge, push/pull the other end inline, then it was ok.

[beeg]

Ed

Did you go to the blackboard and see the corner squares plans?

[edflorence]

Bob...

Oops...No I didn't. I will check there. Thanks for the help!

Ed

[dusty]

Dusty

Take the drawer frame amd set it up against your rip fence, then check the corners. And report back here.

beeg; I have an aluminum straight edge (2" angle) that I use as a fence for some routing. I also use this same straight edge as a clamp point for some gluing.

Does this do the same thing that you are suggesting using the rip fence for. If it does, not all my corners are square. Which just confirms what all my shop squares tell me.

If it does not - please explain.

I understand the principle of measuring the diagonal but even then I sometimes can't get everything as accurate as I think it should be. Furthermore, when a diagonal measurement shows me an out-of-square condition, I usually can also measure that with a square.

What I have always thought the "diagonal measurement method" was for was to test large items like door casings, window openings, etc. Where a measurement with a shop square might seem OK but is not when the error is extended for feet rather than inches.

I am particularly interested in improving my skills in this area because I am about to begin construction on a piece of furniture for one of the grand kids. A legacy item that I would like her to be really proud of rather than just "we still have this because grandpa built it" sort of thing.

I've got bookcases that I built in high school that are still here for that reason but in this case my wife won't part with them because I built them way back when we were dating.

The one thing I'm pleased with - the glue joints are all still strong. The virtue to hot animal hide glue I think.

[jg300da]

Dusty,
Your high school geometry has not failed you. If the diagonals (hypotenuse)are equal, then the sides are square (Pythagorean theory).
When I first started constructing drawers I discovered early on that clamp pressure could make square drawers flex out of square. Easily.
And don't place too much weight in what you see Norm do and say. He's a carpenter, not a fine furniture craftsman or artisan. Craftsman do not use nails or brads in the construction of their pieces, nor do they use speed squares.
If you are entering the realm of heirloom quality pieces I recommend you invest in some high quality measuring and marking tools, and practice their use.
Here's a recommendation; http://www.garrettwade.com/sdx/H35764.jsp

Joe