# How Square is Your Square: A dial indicator method

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• posted on January 3, 2013, 9:58 pm
Let me know what you guys think.
I've been working on a new method (new?) for checking the squareness of a square using a dial indicator. The method works in theory. I've tried it and it seems to work in practice. A caveat is that the square needs a thick edge to support a stylus.
I am going to work on a video demonstrating the process.
http://www.garagewoodworks.com/square_a_square.php
Thoughts?

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• posted on January 3, 2013, 11:24 pm

Seems totally unnecessary. A pencil and a straight edge (a la sheet good cutoff) is all you need to check if it's actually square. And it's fast to set up.
--
Outside of a dog, a book is man's best friend. Inside a dog, it's too dark to

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• posted on January 3, 2013, 11:30 pm
On Thursday, January 3, 2013 6:24:52 PM UTC-5, Dave Balderstone wrote:

A minor caveat to this method is that it can be difficult to discern small gaps between the two pencil lines (especially with a thick pencil lead). The most you might be able to detect is a 0.010" difference which equates to a minimum detection of 0.036 degrees with an 8" square. Another caveat is that the edge you place your square against must be perfectly flat, otherwise you will not get an accurate calculation of your square's angle error.
The dial indicator method is 10X more accurate.

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• posted on January 4, 2013, 12:41 am
On 1/3/2013 6:21 PM, snipped-for-privacy@garagewoodworks.com wrote: ...

What difference does it make what the numeric value is?
If it's enough to detect that way, it's enough that for really precise layouts it's off.
So, what you gonna' do at that point, anyway even if you do know _precisely_ how much that is? Eggs-ackly the same thing as if you only know it's off---either ignore it and go on, go get a new Starrett, or adjust it until it does pass (the peen method works a charm for that).
If it passes the pencil test, it's plenty close enough for woodworking; even fine woodworking. The wood itself moves more than that.
--

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• posted on January 4, 2013, 12:45 am
On Thursday, January 3, 2013 7:41:36 PM UTC-5, dpb wrote:

If you don't know how much it's off you can't make a call either way.
So why bother checking?

What is a "pass" on the pencil test?

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• posted on January 4, 2013, 3:26 am
On 1/3/2013 6:45 PM, snipped-for-privacy@garagewoodworks.com wrote: ...

...
I'm sure you're clever enough to figure it out...
--

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<%-name%>
• posted on January 4, 2013, 1:17 am

Did.
--
Outside of a dog, a book is man's best friend. Inside a dog, it's too dark to

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• posted on January 4, 2013, 1:41 am

What are we building here, bookcases or space shuttles? 10X more accurate is not necessary for woodworking.
--
Make it as simple as possible, but not simpler. (Albert Einstein)

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org

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• posted on January 4, 2013, 1:45 am
On Thursday, January 3, 2013 8:41:23 PM UTC-5, Larry W wrote:

Scenario: You make it out to the woodshop after a hard night of drinking. As the acetaldehyde takes it's effect on you, you drop your Starrett square on the concrete floor. What do you do? Continue to use it and hope for the best or check to see if it's still of 'Starrett Quality'? How do you check?

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• posted on January 4, 2013, 1:55 am

I'm by no means a teetotaler, but I haven't had a "hard night of drinking" in over 20 years. And if or when I did, I sure wouldn't head to the wood shop afterwards. And if I did, I probably wouldn't use one of my Starret squares. And if I did use the Starret, probaly wouldn't drop it. And if I did happen to drop it, after a hard night of drinking, I probably wouldn't care enough to check it.
What was the question again?
--
Make it as simple as possible, but not simpler. (Albert Einstein)

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org

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• posted on January 4, 2013, 1:57 am
On Thursday, January 3, 2013 8:55:20 PM UTC-5, Larry W wrote:

Then why did you buy a Starret? :)

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• posted on January 4, 2013, 2:54 am
snipped-for-privacy@garagewoodworks.com wrote in

Doesn't happen in my shop. That's a hard and fast safety rule here: if I drink, I stay out of the shop until after a full night's sleep.
That doesn't mean I can't or won't ever drop the square, of course -- just means that if I do, it will be the result of my own innate clumsiness, not of inebriation.

Your imagination is lacking, Brian <g>. I can think of at least half a dozen things I could check it against: -- angle between the jointer fence and bed (previously set using the same Starrett square) -- angle between the fence of the Incra 3000 miter gauge, and the miter bar (ditto) -- angle between the Incra 3000 and the table saw blade (ditto) -- one of my Jevons 3D squares <http://www.jevonstoolco.com/ -- I have no connection with the company, except as a *totally* satisfied customer -- these are great products, and as close to dead-on-perfect as a woodworking tool needs to be (within 0.002" in 6", according to the manufacturer) -- my crosscut sled -- any corner of at least seven pieces of furniture in my home that I've made using some or all of the above

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• posted on January 4, 2013, 3:01 am
On Thursday, January 3, 2013 9:54:35 PM UTC-5, Doug Miller wrote:

How can you be sure it's still square to the level of accuracy required?

ibid
ibid
ibid
I hope you're joking.

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• posted on January 4, 2013, 3:43 am
snipped-for-privacy@garagewoodworks.com wrote in

I check it periodically, using both the Starrett and the Jevons squares. Don't you?

Why would you think that?
Just for giggles and grins, I just checked a corner of an end table that I made about 12 years ago -- put the head of the Starrett square against a corner of the tabletop, and tried to slip a 0.002" feeler gauge between the blade and the tabletop. It won't fit, anywhere within 7 1/2 inches of the corner.
I'm satisfied with 99.97%.

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• posted on January 4, 2013, 3:54 am
On Thursday, January 3, 2013 10:43:22 PM UTC-5, Doug Miller wrote:

I periodically check my jointer fence with a dial indicator (Powermatic) and it's always off by +/- 0.003". I shim the pos stop w/ paper when needed.
I wouldn't square anything against it as a reference.

Same goes for my Osborne EB3 that hangs on a wall. It needs periodic adjusting.

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• posted on January 4, 2013, 3:58 am
snipped-for-privacy@garagewoodworks.com wrote in

+/- 0.003". I shim the pos stop w/ paper when needed.

It is at least close enough to tell you if you've damaged a precision square by dropping it on the floor...

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• posted on January 4, 2013, 3:19 am

----------------------------------------------------------- A slow night in the Carolinas.
Lew

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• posted on January 4, 2013, 3:27 am
On Thursday, January 3, 2013 10:19:46 PM UTC-5, Lew Hodgett wrote:

Then go out and get a drink Lew! Get off yer butt! :)

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• posted on January 4, 2013, 3:42 am
I wrote:

---------------------------------------------

------------------------------------------------------ You must be kidding, it's 50F and dropping tonight.
Time to throw another log on the fire and enjoy a toddy.
Lew

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<%-name%>
• posted on January 4, 2013, 3:56 am
On Thursday, January 3, 2013 10:42:05 PM UTC-5, Lew Hodgett wrote:

Man I wish we had a log fireplace. The fake gas log variety just doesn't cut it.