Is 89 degrees square

lizardhead · Mar 23, 2012

First of all - let me say I've heard all the argument before, And I agree "only square is square" So don't mount your high horse on me.
I have seen articles that date many years ago of the importance of maintaining a good square. Well I just seen another, and frankly I am just a teensy bit put off about it. The current issue of Woodcraft magazine is where you can read this article. It may appear to you that this guy works for Starret, or possibly for Woodcraft. Furthermore it may appear that he is selling Starret square's, you can make your own judgement about that.
I say that while there are squares that are not perfectly square, the ones that are not square are off less than .250 degrees. That amount (especially in my old age-and with my eye) are not noticeably detected until you get to about 20" from the focal point. The cost of some of these squares can reach a hundred $ mark. My squares like the framing square, combination square, speed square, and engineers square, were all purchased from my local hardware store, these are the ones that are being warned against. So I took to my shop and put these squares to the test. I first sharpened a #2 pencil to a very fine point, and fixed a 24" x 24" sheet of poster board to a table and began marking out a square then a second square, on the first I drew a line with my framing square and checked it by flipping and redrawing a second line in 24" it was dead on, wow I never expected that!! I then preformed the same test on my other squares and the results of all were the same as the first. On the second I drew out squares on top of each other with all my squares-sharpening my pencil as needed. The results of that test were within 1/2 of the thickness of a very sharp pencil. Possibly an error on my part. which in the end I conclude that for at least the squares that I brought home were in fact square. Now I know that this test of mine is not scientifically sound, but give me a break who are these annal people that want me to go out and buy a square that cost six times more than mine simply because it says Starrett on the face. Oh yeah did I mention that I have a Starrett and I used it to measure the square on other squares they were square. I'm square-You square???

dbray45 · Mar 23, 2012

When dealing with a square, the first three angles will be 90 degrees, the fourth usually isn't.

When working with one or two 90 degree angles if the straight edges are 1", 89 degrees works, if the straight edges are a foot or longer, probably not.

TrBlu · Mar 23, 2012

"When dealing with a square, the first three angles will be 90 degrees, the fourth usually isn't."

How is that possible? The sum of the angles of any quadrilateral must equal 360 degrees. If three angles are 90 degrees, the fourth must be 90 degrees. For one of the angles to be 89 degrees, the 1 degree must be made up in one or more of the remaining angles. Granted, 90 1/3 degrees is difficult to measure. You eyes may not recognize that a quadrilaterial with three 90 1/3 angles and one 89 degree angle is not square. But, it is not geometrically possible to have a quadrilateral with three 90 degree angles and one 89 degree angle.

Maybe I am reading this too literal.

JoeyG · Mar 23, 2012

IMHO we are working with wood here, not steel. I will be the first to say that the closer to 45 you are the better your corner, etc. I also know that no matter how perfect it is when I mark it or cut a piece of wood, it is going to move. That's what wood does. Just my opinion, Some people like expensive tools, personally I like expensive wood. In my world I can't have both.

Manitario · Mar 23, 2012

I'm not too sure what the limit of error in a square that is detectable by the human eye, but I know that an error of 0.5 degrees results in a gap on my mitres or a gap between the rail and stile on a raised panel frame. On my jointer, if the fence is not set to 90o the edge joints don't come together perfectly.
I have a number of squares, some cheap, some not. Finding a perfectly 90o square from a big box store is hit and miss, or having said cheap square stay 90o is also hit and miss. When I pay more for eg. Starrett, it is because I know that it will be 90o out of the box and will likely stay 90o for many, many years.

Loren · Mar 23, 2012

I imagine new squares would tend to be more accurate at lower
cost than in the past due to computerized manufacturing and
quality control.

BobM001 · Mar 23, 2012

The funny thing about "small errors" when building anything. They tend to "compound" as you move forward. The truer you stay, the better the end results.

canadianchips · Mar 23, 2012

I'm going out on a limb here:
Squares are over rated !
You can put finishing trim on a door without using a square. As long as the reveal is uniform, the naked eye will see a crooked reveal sooner than a miter that might be 44 1/2 ! (Old crooked homes are perfect examples of finishing tricks to make it LOOK good.
Building things "Square" is an easy way to continue any project without measuring to death every move !
The first NEW house I finished , the footings were 6" higher at one end than the other. The lower level concrete walls were 1 1/2" thicker at bottom than top _The rest of the house followed along (the person that started the mess was fired_). By the time I was called in…..........Yikes….....

North40 · Mar 23, 2012

I guess the thing to consider is that any error will compound with multiple joints. If you rip a piece for a shelf with an 89 degree edge, no one will notice. But if you rip 180 strips with an 89 degree edge on each side, you can make a cylinder.

As for Starret vs. anything else … well, Starret's probably the best. But you can correct a square if it's not true. And one drop on the floor and it probably won't be true, regardless of the name stamped on it. That's why the couple of Starret tools I own almost never see the light of day … I drop things.

Doss · Mar 23, 2012

We have rules in engineering about tolerances… how accurate can you afford?

Yes tolerances due stack, but not if you make adjustments as you go along.

To put it in perspective, let's build a square frame (like a picture frame) using 10' long by 1/16" wide strips of wood (just helping with a visualization of lines).

First piece of wood down. Measure 90°. Put second piece down. Measure 90° again. Put third piece down.

This time though, we get sloppy and lay the piece at 89.75° relative to inside angles. The result? Instead of closing your perfect square, you are now roughly 1/2" (0.5235971141695884") from perpendicular to the inside of the square. At 89° the gap grows to a little over 2" from perpendicular.

The question is, is 89.75 or 89° close enough for you and can you make the adjustment?

Yes, this is not a compounding problem where the slightly off angle will definitely bite you when building a square, but it helps in visualizing an error in measurement and how significant it can be. I'd say if you build things with long straight runs, long sides that need to appear square to each other, or need really tight miters, then I'd try to get as accurate a measuring device as possible.

This does not stop you from making a mistake when cutting or attaching though or even as the wood moves due to changing conditions.

Sawkerf · Mar 23, 2012

A big +1 to Canadianchips!! I can't remember ever casing out a door or window with a level or square. I eyeball it and nail it. Nobody has ever mentioned a problem.

I once used a laser level to install a chair rail and it looked terrible. It was dead level, but the 2" difference in the wall made it look goofy. I put the laser away and just made it look right.

lieutenantdan · Mar 23, 2012

Well, then there is the other extreme. A square that reads 91 degrees instead of 89 degrees. Life can suck if you let it. I used to be a perfectionist. My doctor says I am getting better every day.

Sawkerf · Mar 23, 2012

A square that is 1* off introduces a 1.1% error in your measurement. Is that ok? Probably not a biggie in rough framing, but bothersome for a nice cabinet. - ol

MrRon · Mar 23, 2012

A Starrett square is a precision tool intended for machinist accuracy. It wasn't intended for woodworking or framing a house, although it could be used for such. The garden variety square that you can buy at your home building supply store or Ace Hardware will not be as precise as the Starrett, nor does it need to be. For one thing, doing layouts with a pencil, no matter how sharp, will never get you a precise line. Even marking of metals with layout dye and needle pointed scribers are never 100% precise. Wood changes with temperature, humidity and internal stress and there isn't much you can do to compensate for it. The goal is to use whatever tools you have and be as precise with what you have. Using a Starrett square to draw a line will still not be precise due to the pencil point which has thickness to it, so there's no good reason not to use the generic brand square, as long as it is "reasonably" square. I have a Starrett square that I use only to check the squareness of generic squares and for metalworking. When not in use, it stays hidden away. It's never used for general woodworking. The square I use for woodworking is a Stanley. It checks out pretty good by the Starrett; good enough for woodworking.
Just think about this for a moment; layout for a 45° miter,(2 possible errors); set the miter gauge on the saw to 45°, (1 possible error); the miter gauge has a sloppy fit in the slot, (1 possible error); make the cut with the saw, (1 possible error) due to blade or arbor runout. Add up the errors, (5) and your 45° miter is no more. I may go out on a limb and say "it is impossible to cut a perfect 45° miter". If you do, it's an accident and not intentional. So don't beat yourself up trying to get perfection. We should always strive for it even if we know it can never be achieved. I'm certain if I was to lay out a 45° miter, one with the Starrett, and another with the Stanley, the final result would be the same. Just my 2¢ worth.

TopamaxSurvivor · Mar 23, 2012

I think for our purposes in wood working, if it is pleasing to the eye, it is square. For moon shots, you'd better be prefectly square with the earth when you launch or you'll miss ;-)

mtenterprises · Mar 23, 2012

Just my 2cents here, one day at HF they had orange plastic speed squares on sale for like $2.99. I said to myself, how good can a $2.99, PLASTIC, Made in China be? So on a lark I bought one. I've wasted more money on other items that I never used or that didn't work. I took it home and took out my machinist dial protractor and to my suprise it measures dead on nuts 90 deg. and 45 deg.. I proceeded to put a screw in my table saw frame, hung it thare and use it all the time. I guess it just comes down to trust. So, lizardhear after your testing do you trust your tools and your skills? Some people think they must have the very very best or the most most expensive.
Sign in my shop - It is not what your shop looks like nor the age or quality of its tools. It is the quality of work that you can produce there with them that is important. -
MIKE

lizardhead · Mar 23, 2012

I used to beat myself up every time I made a 12 segment ring for my segmented bowls, because they quite often did not have tight joints. A 12 segment ring has 24 miter cuts. 24 X's anything can be a lot, I'm talking about smidgeons here guys, maybe even half a smidgeon. Then I would have to go to the fix it stage. Now I just glue up 2 halves, then disk sand till flush the glue up the 2 halves. Ah perfection

ssnvet · Mar 23, 2012

My squarest square is an old Stanly…

I have a $75 Starrett combo square and it's been slightly off since day one. I recently got a set of small thin Swiss files and found that one of them will fit in the slot of the combo. square.

They (intentionally I think) cut a profile in the bottom of the slot, somewhat like an upside down "U" and just a swipe or two with that very fine file will make a noticeable adjustment over 12".

All that said. The guy who taught me the little bit I know about finish carpentry didn't carry a square in his tool belt. He carried a block plane.

Square or not, his joints are tight and look good.

:^)

ssnvet · Mar 23, 2012

OBTW, the only place a 'truely' square square exists is in your head.

If you think you square is perfectly square, you just need to get a reference with finer increments…. or in the OPs example, a sharper pencil.

It always comes down to what's "good enough"

RandyM68 · Mar 23, 2012

The only time it has to be perfect, is when you have an anally-retentive Q.C. inspector trying to check your work. They focus on crap like that and miss the important things like, does it work? and does it look like it fits right? If you are making bunches of interchangeable parts they have to be perfect. If you're building one cabinet, it just has to look good. The pieces don't have to match the blue-print, just each other. If you get caught up in perfection, you'll throw away a lot wood that is .015" too short. It just doesn't matter that much when laying out cuts. On the other hand, I bought two clamp-its from Rockler. I tried to use them to square up a face frame when I glued it up. The joints wouldn't close. I checked everything with speed,framing, combination, and machinist squares. Neither one of the clamp-its is square on the inside angle. That does matter. Good thing they were on sale.

lizardhead · Mar 23, 2012

In my particular case 99% of the time that I use a square is to check what I have already cut. The "square" is in my jigs or in my sliding miter guage. and if you want to do a little check on that get yourself 3 pieces of scrape pine about 10-12" long & cut 1 piece at both ends at 45 degrees, and the other 2 pieces at one end then friction glue the joints or otherwise attach them then measure the joints end to end. and then measure across the open end if they measure the same it is square if not-well you are not square

280305 · Mar 24, 2012

Don't forget to keep in mind the curvature of the earth, if not the curvature of space itself:

mtenterprises · Mar 24, 2012

Chuck yes!
Now is it possiable to have a triangle with 3 - 90 deg. corners? Yes it is! If you cannot figure this trick out I'll tell you later.
ALL IN FUN!!!!
MIKE

280305 · Mar 24, 2012

Imagine a triangle with vertices at the North Pole, 0 deg longitude at the equator and 90 deg W longitude at the equator.

mtenterprises · Mar 24, 2012

DAMN MAN YOU GOT IT ALREADY!!! Congrats! Look at that a 13 minute WINNER!
MIKE

miles125 · Mar 24, 2012

A 200 dollar trisquare for wood is like using diamond tooling to carve a bar of soap. It works, but what's the point?

Is 89 degrees square

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