# Verifying An Angle Plate



## PatMiles (Jun 17, 2015)

I have an angle plate that I want to verify the squareness and parallelism. Might any of the learned folks on this site care to tutor me on doing so? I figure that this might take some time and effort on my part (duh) so it will require a bit of time. Any help will be greatly appreciated.
Along the same lines, is there anybody that offers regrinding of an angle plate if needed?
Thanks,
Pat


----------



## RJSakowski (Jun 17, 2015)

Tom Lipton at OxTool did a You Tube video on measuring squareness.  

It depends upon your level of tolerance but you could probably do a reasonable check with a tenths reading test indicator and a known good square like 2-4-6 block.  I would set up a test indicator in the spindle of my mill and sweep the known good square to determine any deviation.  This is essentially measuring the tram of the mill spindle.  Clamp a reference edge to the table to ensure alignment to the same position each time.  Replace the reference square with your angle plate and sweep it. You should be able to detect a difference of a tenth or so over the height of the plate.  Parallelism could be checked with an appropriate mike or with an indicator sweeping a face while the opposite face is on a surface plate.


----------



## brino (Jun 18, 2015)

Hi Pat,

I remember one of the books in the Dave Gingery series had details on how he made some small angle plates for mounting things to the lathe faceplate. 
http://gingerybooks.com/
http://gingerybookstore.com/

Likely either the lathe book or the accessories book...maybe the mill book?. He had a method where he bolted one to the lathe faceplate and a second one to the first. That gave the ability to face-off the second one. There was a system of adding spacers and operations such that you ended up with a matched pair of guaranteed square angle plates. I believe he made them out of angle iron.

The exact steps elude me, but I know I could find them again. Let me know if you want me to dig it up and give some better details.

I don't know if yours would fit on a lathe faceplate (I do not know the size you are dealing with), but the concept should be similar.
If you had two and could find a way to mount them, you could put an indicator on them give them a manual spin and maybe get an idea how good/bad they are.

-brino


----------



## ronzo (Jun 19, 2015)

The most universally accepted method is with a cylinder square and squareness gage.


Sent from my iPad using Tapatalk


----------



## rdhem2 (Jun 20, 2015)

ronzo said:


> The most universally accepted method is with a cylinder square and squareness gage.
> 
> Anyone onboard who can explain how to use these instruments?  Although it sometimes frustrates me I love accuracy!


----------



## RJSakowski (Jun 20, 2015)

A cylinder square is a relatively easy gage to make because it can be made on a lathe in a single setup.  The cylindrical surface is turned and the end faced.  As long as you are not turning a taper (verify by miking the cylinder) and your lathe is not facing convex, you should have a perfect square relationship between the face and the cylindrical surface.  You can purposely face a concave surface or  cut a slight recess, leaving a thin raised ring on the perimeter of the face to prevent possible rocking.  Due to symmetry,  a cylinder made in this way is square to the face no matter where you approach it which is a useful feature.

I have not used a squareness gage but watched Tom Lipton (Ox Tool) use one in one of his Monday Night Meatloaf You Tube videos.  Others with actual experience may want to chime in.
A squareness gage is constructed similar to a height gage with a flat base and a vertical beam.  An indicator on the vertical beam is capable of sweeping a vertical surface.  The base has a reference edge that you bring your test piece up to.  You can adjust/calibrate the squareness gage to read true for a cylindrical square.  You the put your test piece in place of the square to verify its squareness or measure its deviation. A surface plate is used to ensure a reproducible flat for the square, the gage, and the test piece to rest on.


----------



## RJSakowski (Jun 20, 2015)

I should add that I would expect the a precision cylindrical square will ground rather than turned but the principle is the same.  It is possible to make a precision square using only a micrometer to verify its accuracy.  Additionally, it is fairly easy to verify the accuracy after the fact by rotating the square held to a reference edge (usually a Vee) and measuring runout.


----------



## Rex Walters (Jun 20, 2015)

Search the YouTube videos of "the tool and die guy" for "how to check a block for squareness". Here's the direct link: 





All you need is a small surface plate, a surface gauge with a fine adjust, and a dial test indicator (tenths preferably but 0.001" graduations will still get you pretty square). You also need to radius the front of the surface gauge somehow.

Easy once you see how it's done.
--
Rex


----------



## RJSakowski (Jun 20, 2015)

Rex Walters said:


> Search the YouTube videos of "the tool and die guy" for "how to check a block for squareness". Here's the direct link:
> 
> 
> 
> ...


What the "tool and die guy" is verifying is that the angles are the same.  In order to use properly, you need to go a step further and mike top and bottom to determine that the two faces being compared are parallel or you need to use a known good square (e.g. the cylindrical square) to set it gage up.  It also only works as shown if you have a block with parallel sides.  
However a good 1-2-3 block or better, 2-4-6 block should be fairly close to square , squareness to a tenth per inch or better.  You can easily mike the block to verify parallelism and check as demonstrated for equality of the angle, flipping it over to verify the same reading.  Once you are satisfied your block is true, you can zero the indicator and check your test piece.


----------



## RJSakowski (Jun 20, 2015)

OK, here is a way to answer the OP's question with tools we have available.  
1. Place an 8" faceplate from the lathe face down on a surface plate. 
2. Place a magnetic base test indicator on the hub of the face plate and lock it down.  
3. Adjust the position of the test indicator at the approximate height of the contact point of the tested object.
4. Adjust the test indicator to read zero when rocking a 1-2- 3 or 2-4-6  block around the circumference as per the video.  Check the opposite side for variation.  Flip the block end for end and note the difference.  If they measurements are all the same to your desired accuracy, you're good to go. Otherwise, averaging the four readings is going to be fairly close the the "square" reading.
5. Place your test piece in position and repeat the measurement to determine its squareness.

Any plate will work for the base.  The faceplate just has a convenient curved edge built in. Here is a picture of the setup. (Yeah, I know I need a bigger surface plate; it's on the list)


----------



## Rex Walters (Jun 21, 2015)

RJSakowski said:


> OK, here is a way to answer the OP's question with tools we have available.



Cool idea using a faceplate. I also like the hot-rod red paint on yours. <laugh>

Since the OP was about verifying an angle plate (of unknown size, but presumably 90 degree angle!) step 4 isn't really feasible. You would just compare your reading to one from a known square part (1-2-3 block or cylinder square as you originally suggested). I think your comment about turning a cylinder square vs. purchasing a precision (hardened, ground, and expensive!) commercial square was a great one. Guy Lautard also recommends building a cylinder square like this.


----------



## RJSakowski (Jun 21, 2015)

Rex Walters said:


> Cool idea using a faceplate. I also like the hot-rod red paint on yours. <laugh>
> 
> Since the OP was about verifying an angle plate (of unknown size, but presumably 90 degree angle!) step 4 isn't really feasible. You would just compare your reading to one from a known square part (1-2-3 block or cylinder square as you originally suggested). I think your comment about turning a cylinder square vs. purchasing a precision (hardened, ground, and expensive!) commercial square was a great one. Guy Lautard also recommends building a cylinder square like this.


The color is OEM Grizzly.  I think it is the primer they use.

It was unknown whether the OP was referring to a cast angle plate or to a precision angle plate.  Some of the precision angle plates are ground flat, parallel, and square ,much like stacked 1-2-3 blocks would be. 

A 1-2-3 block can be used to calibrate the setup in step 4.   The point in step 4 is that you need a test object that has parallel faces in order to do the calibration. That is the purpose of the cylindrical square mentioned in above posts.  The takeaway from this is that it is possible to get a reasonably accurate measure of squareness with commonly available and relatively low cost tools.


----------



## Rex Walters (Jun 21, 2015)

Ah. Sorry, I think I misread.

Please let me know if I've got it right (apologies for the pedantry, but I'm still learning and like to verify my understanding):

If I now understand you correctly, in step 4 you're basically verifying that the reference square is truly square. You're flipping the square in that step, not the part being tested (this is what caused my confusion).

My (possibly faulty) understanding is that the bearing point on the DTI simply establishes a straight line (two points) between the base (your faceplate) and the object-being-tested (the whole point of swinging a curved surface at the bottom to find maximum deflection is just to ensure you use the same point on the base surface each time you measure).

You want to know whether this imaginary line is truly perpendicular to the surface plate or not. One way to verify is to compare to the line produced to one known to be perpendicular (like a cylinder square). Another way, if the object has a flat top and bottom that are verified to be parallel (easily verified with the same DTI and surface gauge) is to flip the object upside down and re-measure. Any variation will be double the angle off of perpendicular.

Unless I'm missing something, the best way to verify an angle-plate-looking-object (possibly one that can't be flipped top-for-bottom) is truly square is to compare it to something known to be square.

My very slightly modified sequence (for clarity) would be something like the following. (DTI: dial test indicator, OUT: object under test):

Find or borrow a known true surface plate (doesn't need to be huge, but big enough to hold the OUT and gauge at the same time) and a DTI.
Create a squareness gauge with a dial test indicator on some form of curved base (either a mag-base on a faceplate, or a surface gauge with a curved base).
Find or make a precision square (a 1-2-3 block, for example, or a cylinder square).
Verify your precision square is truly square as follows:
Verify with the DTI and surface gauge that the top surface is the same distance from the surface plate at all points.
Place the point of the DTI on a vertical/side surface of the OUT, with the curved base of the gauge touching the OUT.
Swing the curved base to find the point of maximum deflection and zero the indicator.
Flip the square top-for-bottom, re-measure, and verify the dial is still zero (if not, it isn't a square)

Replace the square with the OUT and re-measure. If the dial doesn't read zero it isn't square.
I suppose if you were really anal, you would re-measure at multiple horizontally spaced points along the vertical surface of the OUT and 1-2-3 block (to test for wind in the vertical faces). The advantage of a cylinder square over a rectilinear square is that there is only one vertical line at each point around the cylinder, not a complete surface (potentially in wind).

And if you really, really, really, want to start from first principles and only "stuff on hand" you'll need to  make three surface plates using the "principle of symmetrical distribution of errors" before step 1. You'll need to fabricate a scraper and find some marking medium (red-lead or hi-spot blue).

Wait.

First you'll need to make a blast furnace and to read up on refining iron ore....

The more I learn about metrology (and this entire hobby) the more I enjoy it. 
--
Rex


----------



## RJSakowski (Jun 21, 2015)

Rex Walters said:


> If I now understand you correctly, in step 4 you're basically verifying that the reference square is truly square. You're flipping the square in that step, not the part being tested (this is what caused my confusion).
> 
> My (possibly faulty) understanding is that the bearing point on the DTI simply establishes a straight line (two points) between the base (your faceplate) and the object-being-tested (the whole point of swinging a curved surface at the bottom to find maximum deflection is just to ensure you use the same point on the base surface each time you measure).
> 
> ...


Rex, I think you've got it! Almost anyway.  With the assumption that the 1-2-3- block has flat surfaces and a reasonably parallel (we gotta start somewhere, right); It is not necessary that the 1-2-3 block be perfectly square.  Let's label the 1 x2 faces A and C and the 1 x 3 faces B and D. 

With side A on the surface plate and side B in contact with the curved surface, adjust the DTI until you get a small deflection. Let's say that deflection is +3.1 thousandths. Now keeping side A on the plate, rotate the block 180 degrees and measure the deflection on side D.  Let's say it is+1.3 thousandths.  We now know that there is a difference between the angles AB and AD.  They could however be any angle.
Now flip the block over so side C is in contact with the plate and remeasure sides B and D. Let's say for side B we now measure 1.5 and for side A we measure 2.9 thousandths.
To summarize. we have: 
AB +3.1 thousandths
AD +1.3 thousandths
CB +1.5 thousandths
CD +2.9 thousandths
If we average these four readings, we get a value of 2.2 thousandths.  For any four sided polygon, the sum of the interior angle is 360 degrees, f the 1-2-3 block were perfectly square we would get four equal measurements of +2.2 thousandths for the four angles. What the measurements are showing is that angle AB is larger than 90 degrees by .9 thousandths over 3", angle AD is smaller by .9 thousandths, angle CB is smaller by .7 thousandths, and angle CD is larger by .7 thousandths.  Note that this indicates the 1 x 3 faces are reasonably close to parallel but that the 1 x 2 faces are at a slight angle to each other, causing the .2 thousandths difference. These are actual measurements of one of my blocks.

The point of the exercise is that it is possible to calibrate our gage even though the block isn't perfectly square.  There is the assumption of flatness of the surfaces and that there is no twist in the sides but I think that is reasonable if we are measuring to a tenth.  Once calibrated, we can then check any other objects for squareness.

The following illustrates the geometry of the 1-2-3 block. The angles were calculated by taking the arcsin of the deviations divided by the 3" separation and adding to or subtracting from 90  degrees.



Let us know when you get your blast furnace up and running.


----------



## Rex Walters (Jun 21, 2015)

Ah! Got it.

If I understand you correctly, your point is that even without an accurate perpendicular reference, you can calibrate the "squareness gauge" (DTI + curved base) to define two points "perfectly" (within your measuring limits) perpendicular to your surface plate by re-zeroing at the average of the measured deviations from a 6-faced block. Makes complete sense.

This week I hope to actually make a cylinder square and measure it as well as my various 1-2-3 blocks and engineers squares. I'm really curious now.

Thanks! (Blast furnace is on hold until the, uh, head office approves the strip mining operation in the back yard).
-- 
Rex


----------



## PatMiles (Jun 24, 2015)

Gentleman,
Thanks for the replies and info. I haven't posted here cause I thought I had received no other replies due to the fact that for some reason the site is not sending me email notifications for replies. Yes, I did opt for following my post but I guess I was opted out.
Regarding the angle plate, it is a precision angle plate that appears to be ground. I am just wanting to verify it for my own satisfaction.
I have all the equipment listed above, surface plate, surface gauge, .0005" DTI and a faceplate from my lathe so my time this evening will be occupied testing the angle plate.
Thanks again,
Pat


----------



## PatMiles (Jul 6, 2015)

I haven't had the time to measure my angle plate as suggested above but did have the time to order a Suburban Tools angle plat that I found in their "hot deals" section at half price. I received it, cleaned the preservative off of it and put both angle plates on my surface plate. Putting them back to back and aligning them, I found no visible gap when backlit with a flashlight. Yeah, there still could be a tiny gap so I started to remove them and measure them with a surface gauge and DTI. I found them difficult to separate  and finally figured why. They had wrung together when I was sliding them around aligning them. I'll take that as a good sign even though I still intend to put a DTI on the original angle plate. The Suburban is guaranteed to .0005" squareness.


----------

