# How Square is Your Square: A dial indicator method

snipped-for-privacy@garagewoodworks.com wrote:
> There is no need to "try again"
Then who is being arrogant?
and I appreciate your veiled > arrogance.
> Where are you having trouble with the math?
Your identifiers are poorly chosen making your "work" difficult to read. From your words/diagram, it looks like delta1, delta2, and L are all the same. I don't see the 5-degrees you mentioned (in your diagram).
Doing math is like doing design: Do-over, and do-over, and do-over. One should get quite humble about the process!
Bill
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On Thursday, January 3, 2013 8:43:05 PM UTC-5, Bill wrote:

Not at all. The red d2 is above the red line. d denotes distance.
The passage "take a reading at the bottom of the square (d2 in Figure 1)" should have clued you in that d was a distance. We are, after all, discussing a dial indicator method. Dial indicators measure distances.

" Tilt your miter gauge to approximately 5 degrees." You can't tell that the miter gauge and square are tilted in Figure 1?

Point out what you think needs a do over. If you have other questions let me know.

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snipped-for-privacy@garagewoodworks.com wrote:

should have clued you in that d was a distance. We are, after all, discussing a dial indicator method. Dial indicators measure distances.

I guess that we never had a "meeting of the minds" as to what your procedure was. More descriptive writing would probably help.
Sorry for any mix-up I may have contributed!
Bill
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snipped-for-privacy@garagewoodworks.com wrote in

Ummm.... Brian, you don't know Bill personally. I do.
He's not the sort of guy to toot his own horn, so without his consent, I'm not going to say why I'm so sure of it, but please trust me on this: the man *knows* math.
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On Thursday, January 3, 2013 10:01:36 PM UTC-5, Doug Miller wrote:

Good. The math is sound. Let's see something from Bill to the contrary.
I've checked it and rechecked it.
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snipped-for-privacy@garagewoodworks.com wrote:

Doug, Thank you for your support. Brian, Thank you for your indulgence, as I came into this confused about the details of the procedure/algorithm that was being proposed--and I apologize for any fuss that I may have created as a result of that. I think I may need to see a picture with a real dial indicator in it, or a drawing of one, to understand the procedure. There is so sense in me making any further comments, other than the request for clarification I have already made, until I understand the algorithm.
Brian, I know Doug well-enough to know that he has a lot to offer on this problem. If he understands what you are trying to do, than I'm sure that he can help you make it "first-rate" if that's your goal. We're all here to help and support each other, right?
Cheers, Bill
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On Friday, January 4, 2013 12:43:52 AM UTC-5, Bill wrote:

The procedure really couldn't be any simpler, I can only conclude that you have not read the procedure carefully enough. Procedure: As shown in Figure 1, position the dial indicator to the left of the square and miter gauge so that the stylus makes contact with the square to obtain reference distance d1. Push the square and miter gauge forward to obtain distance d2. If you zeroed the dial indicator at d1 then the Delta1 is determined directly (See equation 1). Flip the square over and repeat the same process with the dial indicator on the right side to obtain Delta2. Delta2 = abs(d3-d4). L is the length of the square. Because we rotated the square and miter gauge (to make the calculations work) there will be some error introduced into the equation that is very small. See Reference 2. L actually gets a little smaller because of the rotation. If you have access to CAD, draw an 8" square with an angle of 89.5 degrees (0.5 degree angle error). Create an isosceles trapezium to simulate the two squares coming together when flipped.
(With the 0.5 degree angle error, Figure1 creates an isosceles trapezoid) Rotate your trapezoid by 5 degrees to give a representation of Figure 1 in CAD. Measure your d1 - d4 and calculate the angle error per equation 2. You should calculate an angle error of 0.498 degrees. The 0.002 degrees that the calculation is off is explained in reference 2. I hope this helps.

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A commonly overlooked factor when using dial indicators that often interferes with obtaining accurate absolute measurements is accounting for the angle that the plunger makes with the surface it contacts. I'm a little rusty on trig & geometry, so I'll leave the calculation of that effect on this method as an exercise for some other reader...
--
Make it as simple as possible, but not simpler. (Albert Einstein)

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
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On Friday, January 4, 2013 12:43:52 AM UTC-5, Bill wrote:

I added a new Figure that might help:
http://www.garagewoodworks.com/pictures/unsquare_mitergauge_isos_small.jpg
see: http://www.garagewoodworks.com/square_a_square.php

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On Thursday, January 3, 2013 7:24:24 PM UTC-5, Bill wrote:

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.

For the same angle error, as L get longer so does abs(Delta1 - Delta2).

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On 1/3/2013 7:24 PM, Bill wrote:

As I understand his equations the L is not a variable in any given situation as it is the length of the square. How ever it would be different depending on whether one used the long or short arm of the square.
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I challenge anyone to find a flow in my math. :)
Good luck.
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On Thursday, January 3, 2013 8:30:56 PM UTC-5, snipped-for-privacy@garagewoodworks.com wrote:

Flaw Not flow. /that was intentional (grin)/
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On 1/3/2013 7:32 PM, snipped-for-privacy@garagewoodworks.com wrote:

Appears to be a matter of resolution. I'm of the camp that if you don't have perfection as a goal for every step of the process, you will never scratch that itch some of us are cursed with.
At the same time, I'm just as guilty as anyone of occasionally settling for less ... mainly due to time, circumstances, the medium (woodworking), and the need to 'git r' done'. ;)
That said, you are only as accurate as your tools allow ...
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
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On Thursday, January 3, 2013 8:44:17 PM UTC-5, Swingman wrote:

My sentiments exactly.

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Tools, and the material you are working. Context is a large part of it.
A couple of thousandths over two feet is out of context for woodworking joints. The material is going to move more than that simply due to weather variation.
I'd rather spend a few bucks on a quality square than putz around with a dial indicator.
--
Outside of a dog, a book is man's best friend. Inside a dog, it's too dark to
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On 1/4/2013 9:00 AM, Dave Balderstone wrote:

Here, let me put back in the part you conveniently left out:
"At the same time, I'm just as guilty as anyone of occasionally settling for less ... mainly due to time, circumstances, the medium (woodworking), and the need to 'git r' done'. "
Notice the mention of "woodworking"?
How does that not set the "context"?

Here, I'll say it again:
You are only as accurate as your tools allow.
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
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snipped-for-privacy@garagewoodworks.com writes:

I don't know why google groups double-spaces every one of your posts, but it is annoying.
Starrett is in business to supply precision tools to the metalworking and patternmaking industries, for which a much higher level of precision is required than for building furniture, where "within a 32nd" is usually more than sufficient.
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On Friday, January 4, 2013 12:26:27 PM UTC-5, Scott Lurndal wrote:

No. They are in business to sell their products to anyone that wants them. And I while I don't know the percentage, I am willing to bet that a significant percentage comes from woodworkers.
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On Friday, January 4, 2013 12:26:27 PM UTC-5, Scott Lurndal wrote:

I left out:

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