# How do I indicate in something SQUARE?



## ErichKeane (Oct 22, 2021)

So a while back, I picked up a pair of the Windy Hill Foundry 6" machinist square castings (https://windyhillfoundry.com/) to play around with.  I finally got around to starting to machine them.  

I started by milling, the 'sides' on a pallet plate, then am working on surface grinding the sides.  

For the 'faces' I'm going to use the same plate, then use my X and Y axis to mill the sides, which should get me as accurate as my machine is for 'square'.  However, I'm wondering how to grind the 2nd face?  For the 1st, I can indicate across the face and just grind it that way. 

I'm not sure if I should just do the same for the 2nd face.  That would make it out-of-square up to 2x the error in indicating it in.  I thought about indicating the 1st ground face using the spindle-up/down, however that would only get me as accurate as the surface grinder spindle squareness.  AND considering that the 'head' up/down doesn't necessarily have to be accurate in that dimension, I'm scared that would be worse than the mill.

Every one of the youtube videos I've seen seem to use some giant 'machinist cube' and just bolt it to that, and rotate the cube.  However, I can't seem to 1- find one of those available, 2- convince myself this job is worth whatever-many-hundreds/thousands one of those would cost.

Is there something I'm missing here?  Does anyone have an idea?

Currently, I'm planning on mounting it to an angle plate that I'll indicate in at 90 degrees somehow or another


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## jwmelvin (Oct 22, 2021)

ErichKeane said:


> Currently, I'm planning on mounting it to an angle plate that I'll indicate in at 90 degrees somehow or another


If you trust your angle plate (you can check it on a surface plate?), then you should be able to use that and you'd just have to indicate the surface to be ground so that it is true in the pitch direction. I guess if you don't trust it, you'd indicate the mounted square true in both longitudinal and cross-feed directions on the surface grinder; that approach would be relying on the milled angle as a reference. 

If you are using the mill axes for the 90° reference, then is surface grinding just to improve the finish?


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## Lo-Fi (Oct 22, 2021)

I don't think I've seen a good cheat for this. If you use an angle anything, your grind is only as good as the accuracy of your fixture. Indicating and adjusting or shimming may be your best bet if you've not for a precision doodad.


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## Shootymacshootface (Oct 22, 2021)

I'm sure that you have already watched it, but This old Tony has an excellent vid on squaring a block on the milling machine. He demonstrates how difficult perfection really is to achieve. His measuring techniques are also excellent. It's definitely worth a refresher before working on a straight edge.


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## ErichKeane (Oct 22, 2021)

I've squared up blocks before (and have vises and stuff to do that), but the issue is basically the shape of these.  There is no 'opposite' face I can make it square to.  

I wasn't particularly worried about the angle plate, since it could only introduce a 'tilt' in the short-dimension, so I figured indicating it square-ish would be close enough.

But the problem is with the square bolted to the angle plate, I have to set the 'twist' correctly.



jwmelvin said:


> If you trust your angle plate (you can check it on a surface plate?), then you should be able to use that and you'd just have to indicate the surface to be ground so that it is true in the pitch direction. I guess if you don't trust it, you'd indicate the mounted square true in both longitudinal and cross-feed directions on the surface grinder; that approach would be relying on the milled angle as a reference.
> 
> If you are using the mill axes for the 90° reference, then is surface grinding just to improve the finish?



I had a couple of ideas how to set the angle plate to as-close-to-90 as possible, but I am not AS concerned, as that is a minor-direction.  I AM using the mill to set the 90 degrees, but I was hoping there was a way to make that more accurate.  My mill is about as good as I could guess, but I was hoping to use this as a particularly-precision square for my surface plate.


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## RJSakowski (Oct 22, 2021)

I made a "precision" square using my rotary table.  I edge milled one side and rotated the table 90º.  My RT is capable of resolving to 5 seconds of arc.  If one can believe the readings, this should provide an angular error of .0005" over 10".  Believing the readings is the rub though.  Trust but verify.  

It is possible to check a 1/2/3 or 2/4/6 block for squareness.  The sum of the four included angles are equal to exactly 360º.  A squareness indicator as used by TOT referenced in post #4 above normally has to be zeroed with a known good reference square.  Not having a reference square at hand, one side of the block can be used as the defacto square.  All four sides are measured and the deviations recorded.  The block is flipped  and the measurements repeated.  If the sides are labeled 1, 2, 3, 4, you want the angles created by side 1 & 2, 2 & 3, 3 & 4, and 4 & 1.  From the deviations from zero, and the length of the face, the included angle can be calculated. adding the four included angles, the original zero error can be calculated and corrected for in the squareness indicator setting.


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## Shootymacshootface (Oct 22, 2021)

Joe Pie has another excellent vid where he takes advantage of the mills inherent accuracy between the X and Y axis movements. 
I know that your question was intended more towards the orientation of the straight edge, but to me it is kind of a moot point. I believe that there is always a way to indicate a peice, part, or tool of any shape to get things started.


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## petertha (Oct 22, 2021)

Edge Precision did a detailed 3 part series back in 2015 called Square Me Up. The method might be a bit over the top for most home shop applications, but he shows the underlying principles & logic in detail. One big takeaway point for me was to ascertain how perpendicular the fixed vise jaw is. We go through great lengths tram the mill head to table & dial in the fixed vise jaw laterally to X, but if the jaw itself is deviating from perpendicular for whatever reason, then then the successive part flip & rotate method likely results in a parallelogram section because it relies on this datum. Most jaws aren't very deep to begin with & using parallels reduces the contact area, so the collective tolerances can stack up. If you can count on your vise accuracy, it makes life so much easier.


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## woodchucker (Oct 22, 2021)

so you started with the small edge, which makes it difficult to square up. Since you can only rely on a very short distance indicating to know if you are square.

Consider that that small edge is not a finished side. use it to roughly aquire the square, and mill the bottom. That now has a longer face in the short direction now.  Then grind it. Now you can use that to re-tune your smallest face. When you are done, you can square to 45 or 60 your angled face.

Just my 2 cents, as that's all opinions are worth.


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## Dabbler (Oct 22, 2021)

You can put your square on a magnetic SIN plate and indicate the vertical side.  You then are free to grind the horizontal side and it will be square to tenths of a thounsandth.

Otherise you have to trust your angle plate.


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## rabler (Oct 22, 2021)

RJSakowski said:


> It is possible to check a 1/2/3 or 2/4/6 block for squareness. The sum of the four included angles are equal to exactly 360º. A squareness indicator as used by TOT referenced in post #4 above normally has to be zeroed with a known good reference square.


Another similar approach, if you have two matching size angle plates, you can check them against each other on a surface plate to see that they add to 180.  Then check both of them using a squareness indicator to see if they are both equal.  If both conditions are true to within whatever tolerance you use for your checks, than your angle plates are 90.


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## Janderso (Oct 22, 2021)

Kieth Rucker just did a video on this subject, FYI.
Same Windy Hill square too.


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## ErichKeane (Oct 22, 2021)

Janderso said:


> Kieth Rucker just did a video on this subject, FYI.
> Same Windy Hill square too.


He's the one I was talking about... he had one of those magic-already-square-blocks to bolt it to   I ended up using my sine-plate , indicated it at 90 degrees, then used the side of it as my reference (after a few false-starts), and it ended up reasonably square, at least as square as I have the ability to measure.


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## Janderso (Oct 22, 2021)

I was thinking about how I would do it. This usually incl a comedy of errors.
I do however have an accurate angle plate scraped in at Richard’s class and my B&S SG.
After milling, I would mount to the angle plate and put it on the mag chuck.
Verify it was clocked properly by either a machinists square or a dial test indicator.
2 cents worth.


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## ErichKeane (Oct 22, 2021)

Janderso said:


> I was thinking about how I would do it. This usually incl a comedy of errors.
> I do however have an accurate angle plate scraped in at Richard’s class and my B&S SG.
> After milling, I would mount to the angle plate and put it on the mag chuck.
> Verify it was clocked properly by either a machinists square or a dial test indicator.
> 2 cents worth.


The problem is that you have to get the angle right on 2 axes, right?  And the angle plate can only provide 1 of those.  I managed to bolt a 1-2-3 block to the side of my 'angle plate' and used it as my other axes of reference, but I was hoping there was some way of figuring out some level of 'true squareness' the way we can for parallelism.


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## Shootymacshootface (Oct 22, 2021)

When I made my jumbo angle plate, I borrowed a largish cast iron angle plate from my sons employer. They are a highly certified company that almost exclusively does government related work for electric, well they make electric boat parts, hint, hint.
The angle plate that I borrowed would not idicate in untill I put .003 shim under part of it. My angle plate came out square to the mill table and is perfect when it is clamped down. Their angle plate? Not so much, but I needed it to machine mine.


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## Janderso (Oct 23, 2021)

ErichKeane said:


> The problem is that you have to get the angle right on 2 axes, right?  And the angle plate can only provide 1 of those.  I managed to bolt a 1-2-3 block to the side of my 'angle plate' and used it as my other axes of reference, but I was hoping there was some way of figuring out some level of 'true squareness' the way we can for parallelism.


I was thinking just like you said but run an indicator in the vertical position as you raise/lower the SG


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## WCraig (Oct 23, 2021)

Tom Lipton did a really good video on accurately measuring squareness using a surface plate and some not-too-crazy setups.  






Craig


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## ErichKeane (Oct 23, 2021)

Janderso said:


> I was thinking just like you said but run an indicator in the vertical position as you raise/lower the SG


That was my first thought too, but the 'squareness' of the travel of the spindle on the grinder is realatively unimportant to its operation, so I am/wasnt sure its trust-able.


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## addertooth (Oct 23, 2021)

I always love listening to these true/flat/square conversations.   There are so many nuances.  Almost all start with "find a true flat surface you can trust", and work from there.  I pity the poor fellah, back over a hundred years ago, who had to achieve this without the benefit of modern tools (and ultra-high quality references).  What shop tools he used, had far less precise bearings in the head of his equipment.  I suspect there was a lot of hand working of the metal after the last machine tool took it's final pass.


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## ErichKeane (Oct 25, 2021)

Huh, looks like Keith Rucker just released this video this morning! 




Watching now, but maybe it'll tell me the secret


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## ErichKeane (Oct 25, 2021)

Well shoot, he uses his magic precision-ground square from Solid Rock Machine Shop again.  So not much help on the setup.


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## Cadillac (Oct 25, 2021)

You need a trusted square, cube,or block to do this without a lot of indicating and trial/error. Also need a cylinder square to set your indicator to check for squareness after being ground. Of course their are other ways. 
 A grinders column should be pretty dam square to the machine. Grinding both surfaces in one setup should get you pretty close. Or at least you’ll see how square your column is.


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## WCraig (Oct 25, 2021)

Cadillac said:


> You need a trusted square, cube,or block to do this without a lot of indicating and trial/error. Also need a cylinder square to set your indicator to check for squareness after being ground. ...


The Tom Lipton video I linked to talks about determining square from a block that is close to square.  The sides do need to be parallel but that is relatively easy to do with a surface grinder.  He uses a tenths indicator to check for parallel and then by flipping the block you can measure the amount that it is non-square.  And thus splitting the difference shows the amount it is out of square.  Kind of an 'Aha' moment if you watch the video.  At least, it was for me.

Craig


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## RJSakowski (Oct 25, 2021)

addertooth said:


> I always love listening to these true/flat/square conversations.   There are so many nuances.  Almost all start with "find a true flat surface you can trust", and work from there.  I pity the poor fellah, back over a hundred years ago, who had to achieve this without the benefit of modern tools (and ultra-high quality references).  What shop tools he used, had far less precise bearings in the head of his equipment.  I suspect there was a lot of hand working of the metal after the last machine tool took it's final pass.


It is an interesting problem.  There used to be a game show, if you can call it that, where contestants were on an island and teams of two were given various tasks to complete, using whatever resources they found on the island.. Tasks were like make an accurate map of the island. etc.  The contestants did surprisingly well, considering their makeshift tools.

Making a straight edge or a square are simple tasks, being accomplished from geometric principles.  Making accurate straight edges or squares are more difficult.  Making instruments with high degree of accuracy is much more difficult.  As has been previously pointed out, it is possible to make a flat surface without the benefit of any modern metrology tools.  Once a flat surface is available, it is possible to make a straight edge without the metrology tools.  Making a square is a matter of bisecting an 180º angle  Two squares, along with a straight edge can be checked for squareness visually within a few thousandths of an inch. which was probably sufficient for most practical reasons.

There is evidence that these techniques were known in antiquity.  Any further precision would require more sophisticated metrological instruments.  The invention of the micrometer occurred in the eighteenth century, along with the movement to standardize measurements.  Optical methods came about near the end of the nineteenth century that would allow measurements to a tenth of a micron or 4 microinches.


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## ErichKeane (Oct 27, 2021)

So I've decided that grinding/indicating in these two is much harder than just doing a cube, so I'm going to make one of those fancy reference squares.

I have this big scrap block of A36 that I'm going to rough out on my shaper and try to do about a 5.75*5.75*2 setup block I can use to do this.

This is a big round I used for a lathe chuck adapter plate at one point but never used the rest. It's a touch over 8" round and 2.5 thick.I probably should have started by squaring up one side on the lathe, but instead did it on the shaper in a pretty error prone setup. I didn't hold it tight enough the 1st time (despite flatting the copper wire a ton!), and had some troubles with the step over, but on the last pass with the 1st side right now!


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## Shootymacshootface (Oct 27, 2021)

ErichKeane said:


> So I've decided that grinding/indicating in these two is much harder than just doing a cube, so I'm going to make one of those fancy reference squares.
> 
> I have this big scrap block of A36 that I'm going to rough out on my shaper and try to do about a 5.75*5.75*2 setup block I can use to do this.
> 
> This is a big round I used for a lathe chuck adapter plate at one point but never used the rest. It's a touch over 8" round and 2.5 thick.I probably should have started by squaring up one side on the lathe, but instead did it on the shaper in a pretty error prone setup. I didn't hold it tight enough the 1st time (despite flatting the copper wire a ton!), and had some troubles with the step over, but on the last pass with the 1st side right now!


That is really sweet!


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## ErichKeane (Oct 27, 2021)

A little more progress today, but probably it! I finished the shaping of 1 side which appears really smooth and flat.

I blued up the opposite side and tried to come up with a way to lay it out, but couldn't come up with one. Instead, I just popped it into the bandsaw 4x to square it up 

I'll spend a bit of time in the shaper creating the first 2 90 degree sides because I'm sure my bandsaw isn't close, but a bit of shaping my next time in the shop should get me pretty well roughed out.


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## ErichKeane (Oct 28, 2021)

A little more progress today! I started by putting my "best" bandsaw side down, which was pretty out of wack. I finished a few cuts along that "top" to have as square of a side as I could get.

Annoyingly, as soon as I was ready for my last cut, my electric power feed stopped working! So I spent most of today working to fix that. Turns out someone in the machine's past replaced a 3" key with a 1" key that had a hole drilled down the middle!

There wasn't any set screw or anything that it could have been for, so I'm guessing they used something from a drawer!  The key ended up breaking into 2 pieces where the hole was drilled and each piece apparently walked themselves out and all I got was a whirr sound when using my power feed. A trip to Ace for key stock and some replacement bolts (swapped SHCS for hex, since there wasn't enough room around the motor to get to the heads!) and we were back in business.

Flipped the block over and hung it off the side of the vise. The idea is I should be able to use my up/down feed to cut the other side as well to get a 90.

Hopefully ill get much further tomorrow


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## ErichKeane (Oct 29, 2021)

I had time to do one of the 90 degree sides foday, and it went really wrong  I wasn't able to get a good grind on the tool considering the angle to the holder (it's just a lathe tool), so it kept digging in.

I managed to get a grind that did decently though, and got all but that top corner cleaned up.

Measuring with a square, the too corner is about as square as I'd think is possible, though the vise is apparently not perfectly trammed. I counted on that anyway, so the idea of this cut is to have a reference surface for the opposite side so I can cut it facing up, and I'll flip it 1x more to recut this side up.

So, SOME progress .


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## ErichKeane (Oct 31, 2021)

Wife and kid were away today so I got a lot more progress! 

I got it shaped down on all 4 sides, and it looked pretty good on all my squares! I popped it on the grinder, and found it wasn't grinding it as flat as it looked! It took me enough thay every corner was wrong before I figured out there was a chip embedded into my mag chuck! It took a minute with my flat stones to get rid of, but by that time it had screwed up all my squares surfaces 

Frustrated, I went to the mill to drill/tap the screw pattern. I got all but the tapping done tonight... Just 48 more to go!

In retrospect, I wish I'd done 1.5" on center instead of .75", but at least I know I'll have plenty of bolt down spots!

My next 2-3 days in the shop are likely just manually tapping these (I'm not brave enough to power tap steel, I did with my aluminum pallet, but this one scares me!).

After that, I'll probably regrind the big surfaces, then map out the squareness of each corner.


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## Parlo (Dec 4, 2022)

If you have no reference square - angle plate or dti, use both blocks to grind each other square. Once the blocks are ground parallel clamp them to each other and then rotate 180 degrees to see double the error. Shim one block until the other cleans up when clamped on opposing faces. A vertical face is now established etc....
Link to complete method -


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## ErichKeane (Dec 4, 2022)

Thats an interesting method!  I've seen a few folks use the a DTI to calculate how much of a 'step to leave, so I am probably going to do that... whenever I get back to this project, haha!


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