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How Square is Your Square, Really?

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Blog entry by GarageWoodworks posted 596 days ago 2215 reads 2 times favorited 27 comments Add to Favorites Watch

How Square is Your Square?

A common question that comes up in woodworking forums is “How do I know if my square is really square?”. Without access to an equipped metrology lab, this question can be rather difficult to answer with great accuracy, but we can come close enough to know if we have a serious problem with a square.

The most common method for checking if a square is a true 90 degrees involves using, what I call, the Pencil-Line-And-Flip Method.

An alternate way that I am proposing (if anyone finds a reference elsewhere to this procedure I’d appreciate you letting me know) involves using a dial indicator and a miter gauge at your table saw.

Dial Indicator Method

See it here (easier than re-posting everything)

-- Subscribe on YouTube: http://www.youtube.com/user/GarageWoodworks?feature=guide



27 comments so far

View Bogeyguy's profile

Bogeyguy

465 posts in 695 days


#1 posted 596 days ago

I’ve been working wood for nearly 44 years and have never had a square that was not square.

-- Art, Pittsburgh.

View GarageWoodworks's profile (online now)

GarageWoodworks

424 posts in 783 days


#2 posted 596 days ago

Or you’ve never noticed. I’ve got a BORG square that’s off by a degree.

-- Subscribe on YouTube: http://www.youtube.com/user/GarageWoodworks?feature=guide

View Greg..the Cajun  Box Sculptor's profile (online now)

Greg..the Cajun Box Sculptor

4994 posts in 1935 days


#3 posted 596 days ago

I buy starrett and woodpecker squares and always find their accuracy to be dead on accurate.
I Never heard of a BORG square before…who makes it and where does it come from? I did a google search and nothing came up for borg squares.

-- If retiring is having the time to be able to do what you enjoy then I have always been retired.

View GarageWoodworks's profile (online now)

GarageWoodworks

424 posts in 783 days


#4 posted 596 days ago

BORG: http://www.urbandictionary.com/define.php?term=borg&defid=1282013

If you ever drop your square (cringe) or bang it on something, you need a method to determine if it’s useable after the mishap with gravity. It’s useful to know how to check for when the time comes (it will).

-- Subscribe on YouTube: http://www.youtube.com/user/GarageWoodworks?feature=guide

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1742 days


#5 posted 596 days ago

to check a square you can use the CD covers I´m not sure who made it
but can be seen either here or on You-tube
as well as you can use plastic layout triangles that can be bought at any bookshop/officesuply stores
that our children use in the schools they are pretty much dead on most of them

Dennis

View RobertT's profile

RobertT

67 posts in 1408 days


#6 posted 596 days ago

I enjoy your tips do you have a video of this one. I don’t understand. But then again I have really been struggling with my daughters 8th grade math

View Grandpa's profile

Grandpa

3078 posts in 1302 days


#7 posted 596 days ago

I took my square to a machine shop with a coordinates machineand had it checked….juct for grins. They didn’t charge me for this because they thought it was interesting and it only took a few minutes. My old square is off .0003” in 2 ft. Closer than we can make a pencil line and I don’t have too worry about having a straight edge or lining up marks. This is the best method available.

I worked in our local tech school about 30 years ago. There were 2 aluminum squares (16×24) in the shop. neither had any apparent damage. You could stand them up on the 16 inch end with the 24 inch blade pointing upward. One of the squares was off an eighth inch or more in the 2 feet. Now the problem is to decide which one or are they both off in opposite directions.

View Greg..the Cajun  Box Sculptor's profile (online now)

Greg..the Cajun Box Sculptor

4994 posts in 1935 days


#8 posted 596 days ago

GarageWoodworks…A race of cybernetically enhanced beings that makes squares?
You really need to buy an American made square..

-- If retiring is having the time to be able to do what you enjoy then I have always been retired.

View GarageWoodworks's profile (online now)

GarageWoodworks

424 posts in 783 days


#9 posted 596 days ago

@Greg – I have more than one square – but it’s not made in the USA. And it’s accurate to 90.000 +/- 0.005 degrees. Ask me how I know. :)

-- Subscribe on YouTube: http://www.youtube.com/user/GarageWoodworks?feature=guide

View NiteWalker's profile

NiteWalker

2709 posts in 1204 days


#10 posted 596 days ago

Nothing against your method, but I do disagree with one aspect; the most a human eye can detect. It’s a lot closer than .01.

I’ve been using the parallel line technique for a while now and it works fine. There’s no need for anything closer that that can tell you.

-- He who dies with the most tools... dies with the emptiest wallet.

View crashn's profile

crashn

518 posts in 1092 days


#11 posted 596 days ago

I don’t understand the process. I understand the first step, measurement and calculation of the delta. And then the flip the square over. But, it looks like, from the diagram, that you have relocated the dial indicator and are measuring from a different point. Is that true?

-- Crashn - the only thing I make more of than sawdust is mistakes

View derosa's profile

derosa

1533 posts in 1463 days


#12 posted 596 days ago

All but my small craftsman combination square is accurate. I checked my one 12” combination square just to the other 12” combination square and it said it was square, then I reversed the check and the second square showed the first to be square. As the final check I stood each one up on my tablesaw top and lined them up to each other. They came out flush to each other which meant that the uprights had to be at 90 degrees. The final check was just to test that the two weren’t out of square the same amount but opposite each other. Once done I checked my framing square and it wasn’t far enough out at 12” to be worth worrying about.

-- --Rev. Russ in NY-- A posse ad esse

View GarageWoodworks's profile (online now)

GarageWoodworks

424 posts in 783 days


#13 posted 596 days ago

@NiteWalker We are talking about detecting (and measuring) that distance between two pencil lines. The thickness of the line in each is enough to throw you off.

Edit:
@NiteWalker At what point do you consider parallel line test a ‘fail’ or ‘not pass’?

-- Subscribe on YouTube: http://www.youtube.com/user/GarageWoodworks?feature=guide

View Straightbowed's profile

Straightbowed

717 posts in 925 days


#14 posted 596 days ago

I have used a cmm at work to check mine, a buddy made up a program and we just set a square in the jig and take off, most squares are off a few minutes I have one thats just off 4 sec so its my go to square but really even with the best machines you have to be good at covering mistakes or leaving them for character. I leave my mistakes for character cause usually Im the only one that knows

-- Stevo, work in tha city woodshop in the country

View Straightbowed's profile

Straightbowed

717 posts in 925 days


#15 posted 596 days ago

CMM is acurrate to within 0.000001

-- Stevo, work in tha city woodshop in the country

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