Is 89 degrees square

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Forum topic by lizardhead posted 03-23-2012 03:03 PM 3098 views 1 time favorited 48 replies Add to Favorites Watch
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653 posts in 3901 days

03-23-2012 03:03 PM

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???

-- Good, Better, Best--Never let it rest---Always make your Good be Better & your Better Best

48 replies so far

View dbray45's profile


3408 posts in 3836 days

#1 posted 03-23-2012 03:20 PM

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.

-- David in Palm Bay, FL

View TrBlu's profile


386 posts in 3685 days

#2 posted 03-23-2012 03:33 PM

“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.

-- The more I work with wood the more I recognize only God can make something as beautiful as a tree. I hope my humble attempts at this craft do justice by His masterpiece. -- Tim

View JoeyG's profile


1275 posts in 3685 days

#3 posted 03-23-2012 03:36 PM

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.

-- JoeyG ~~~

View Manitario's profile


2818 posts in 3942 days

#4 posted 03-23-2012 03:50 PM

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.

-- Sometimes the creative process requires foul language. -- Charles Neil

View Loren's profile


11158 posts in 4707 days

#5 posted 03-23-2012 04:03 PM

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

View BobM001's profile


388 posts in 3390 days

#6 posted 03-23-2012 04:06 PM

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.

-- OK, who's the wise guy that shrunk the plywood?

View canadianchips's profile


2632 posts in 4056 days

#7 posted 03-23-2012 04:13 PM

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….....

-- "My mission in life - make everyone smile !"

View Peter Oxley's profile

Peter Oxley

1427 posts in 4934 days

#8 posted 03-23-2012 04:38 PM

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.

-- -- --

View Doss's profile


779 posts in 3324 days

#9 posted 03-23-2012 04:53 PM

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.

-- "Well, at least we can still use it as firewood... maybe." - Doss

View Sawkerf's profile


1730 posts in 4128 days

#10 posted 03-23-2012 06:37 PM

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.

-- Adversity doesn't build reveals it.

View lieutenantdan's profile


176 posts in 3365 days

#11 posted 03-23-2012 08:35 PM

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.

-- "Of all the things I have lost in life, I miss my mind the most."

View Sawkerf's profile


1730 posts in 4128 days

#12 posted 03-23-2012 09:25 PM

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

-- Adversity doesn't build reveals it.

View MrRon's profile


6006 posts in 4303 days

#13 posted 03-23-2012 09:57 PM

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.

View TopamaxSurvivor's profile


20655 posts in 4735 days

#14 posted 03-23-2012 10:02 PM

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 ;-)

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View mtenterprises's profile


933 posts in 3752 days

#15 posted 03-23-2012 10:29 PM

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. -

-- See pictures on Flickr -[email protected]/ And visit my Facebook page -

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