# How would you measure this accurately?



## Reddinr (Aug 24, 2021)

What is a method of getting precise x-y measurements on the electrical pins of the assembly below?  I don't have anything other than a caliper, ruler and micrometer.  I can be off by about 10% of the pin diameter or about +/- 0.06mm.   Seems like every time I try to measure it by hand I get a different answer that is too far off.

Some information:

This is a lens extender for a Canon RF mount camera.  It includes 12 control pins to control the lens by the camera.  Canon does not share any details about these signals or the mechanics of the lens mount as far as I can tell.  I need to make a test fixture that enables the application of test signals to the pins.  I need accurate measurements of the pin centers and to figure out the bolt circle of the pins.  They appear to be concentric with the bayonet mount.

For scale, the OD of the barrel is 68.6mm.  The bolt circle is roughly 45mm in diameter.  The pin spacing is roughly 2.5mm c-c, except one group of four pins is a little further away from the others. maybe 3.5mm.  The two groups are not in the same vertical plane.  The pins are about 1.1mm diameter and are down inside the body about 8mm.

I've tried scanning / enlarging to get better accuracy but my flatbed scanner seems to add some sort of perspective which makes the scaled measurements difficult.  Seems like every time I measure it comes out different...


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## Shootymacshootface (Aug 24, 2021)

Would it be easier to take the measurements off the back of the lense? I would try to get the spacing in degrees with a rotary table.
Thats a tuff one.


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## pontiac428 (Aug 25, 2021)

The pattern would be fully defined if you find the number of pins, the radius of the pattern, and the distance between pins (in two groups, one for each set of pins you identified).  Then relate two of the pins to the corner edge of the bayonet fitting by measuring the three legs of the triangle formed by the corner and any two pins.  I think it can all be done with calipers and your favorite cad program.


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## hman (Aug 25, 2021)

If you have a milling machine with a DRO, you might want to cobble up something like post #10 at 








						Portable Optical Comparator
					

Has anyone had any experience with these cheap LED portable optical comparator like the ones from fowler or iGaging.  skipd1




					www.hobby-machinist.com


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## graham-xrf (Aug 25, 2021)

The suggestion from @pontiac428 has it all! John is right about getting at the thing from it's pattern.

The flatbed scanner may not be showing you the exact measures because of parallax and scanner optics, but it will have a symmetrical center.
A chord line from the first pin to the last, bisected will pass through that center.
Unless the designer was totally nuts, the pins are on the arc of a circle, and you know any regular group will have a measurable chord.

1. Eight of the pins are in a regular group.
2. The remaining four are in their own group. Their pins are spaced as two pairs, separated by smaller gap.
3. The image may be good enough as is, but if you want to reduce the distortion, you can try a regular SLR camera and put some distance in. A zoom lens will give a narrow angle view. I think the circular symmetry, proportions, and one real measurement could be enough.
4. For the one real measurement, you can get a caliper around the outer rim. Possibly, using a telescopic T inside diameter transfer gauge, you can get an additional measure on the bore inside of the screws

From the above, you should be able to get at these, or at least discover if the assumptions were OK.
*
The most direct way*
3. Laid on it's back under a mill with a DRO, one can get a small round point over a pin. Get a set of coordinates.

The image posted seems not "square-on". Unless I be looking at a shadow, I can see part of the inner surface bore to the top left, and not on the bottom right. It gives the impression the pins are on a spiral of their own. The leftmost pin seems further from the bore than the last one on the right.
It would help to know if the arc the pins are on has the same center as the lens.

My FreeCAD program allows to import an image into the design, and draw stuff (circles, axes, angles, etc.) right over it. It also allows to select two points, and state the dimension, which instantly scales all else to comply. From that point on, you can measure at will.

Try posting the diameters - let's see what this image has.


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## BornToDrink (Aug 25, 2021)

Found this image:
	

		
			
		

		
	




Which should give you a good starting point for the pins positions.
You can measure the pin diameter, then 2 pins together, remove one diameter and you have ~"center to center".



PS - if you need some more info about the RF bayonet, you can check in ThingiVerse this item: thing:4621075 (can't post the full link due to spam restrictions..).


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## SLK001 (Aug 25, 2021)

Cut a piece of paper the radius of the inside cavity.  Put the paper in the cavity and press it into the pins.  Using the paper as a template, you should be able to now find the info you need.  Once you get your PCB designed, print out a 1:1 Gerber and check it against your template.


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## graham-xrf (Aug 25, 2021)

Reddinr said:


> For scale, the OD of the barrel is 68.6mm.  The bolt circle is roughly 45mm in diameter.  The pin spacing is roughly 2.5mm c-c, except one group of four pins is a little further away from the others. maybe 3.5mm.  The two groups are not in the same vertical plane.  The pins are about 1.1mm diameter and are down inside the body about 8mm.



It is probably enough to know the 68.6mm OD.
It would help if you took another picture of it placed over the center of the scanner lens, or just use a camera, but this time, put a ruler scale somewhere in the image. What we need is an image where the view down the bore is symmetrical. We know, with thanks to @BornToDrink that the radius of the pins placement circle is 22.6mm. This too is a confirmatory thing to help scale the image. When one does this trick, every tiny distortion in the image becomes obvious when perfect CAD circles are matched to it, but that's OK. It does not stop us getting the dimensions.

Once we have the fit, we can then likely get at all other dimensions in the image.


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## Chewy (Aug 25, 2021)

Use a piece of soft plywood instead of paper. The 5mm whatever is passing for 1/4" plywood is soft. Can also use a piece of balsa wood.  Attach screw in center for lifting.  Put a thin sharpie line on center of pin or use layout dye.  Repeat over and over til the spacing repeats.  Paper and cardboard deflect. the wood doesn't.


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## RJSakowski (Aug 25, 2021)

The image in post #6 is a good place to start.  When using information like this, it is yseful to know whether it comes from original documentation from the manufacturer or it was derived by reverse engineering as you are trying to do.  By measuring the chordal distance between the dirst and last pins in the set of eight, as others have suggested, and knowing the radius of the circle, you can determine the pin to pin spacing. It will be more difficult to determine the start angle of the pattern.

For tasks such as this, I made a DIY optical comparator. https://www.hobby-machinist.com/thr...icroscope-aka-cheap-optical-comparator.38077/  It is capable of locating features down to a tenth of a thousandth (2.5 microns).  It still has to deal with issues like cosine error and odd reflections from physical parts but I found it to be an accurate way to reverse engineer part geometry.


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## BornToDrink (Aug 25, 2021)

Agree that it's good to know the source, and here it is (you need to refactor the link as I can't post urls yet):
dpreview DOT com/forums/post/61662975


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## Reddinr (Aug 25, 2021)

Excellent ideas everyone.  I think I'll look into an optical comparator setup for this/future use too.   

BornToDrink   Gaaah!  Where did you find that image?  I've been looking for days.  All I could find are non-dimensioned patent drawings.
Having that radius accurately, now it is easy.    (Asked w/o going to page 2 of the thread.   Thanks for the link!)

I think I'll do a combination of getting an impression with some soft material and scanning/enlarging.  With the now known radius, I should be home-free.

Also, for anyone interested in Canon cameras or camera tech. in general, the white paper that is linked in the dpreview forum post is very interesting!


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## RJSakowski (Aug 25, 2021)

The drawing appears in a link from the above link to a white paper by a Nikon employee so probably reliable dimensions.


			https://www.canonrumors.com/eosr/canon_eos_r_white_paper.pdf


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## RJSakowski (Aug 25, 2021)

BTW, ain't the internet great?  Everything you want to know and then some.


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## BornToDrink (Aug 25, 2021)

I was surprised there isn't detailed graph with all dimensions, but the mount is a bit new...
Interesting how the aftermarket manufacturers are doing all the adapters etc..


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## Reddinr (Aug 25, 2021)

Canon has always been tight with its information.  They like to sell lenses too and try to hold off the competition a bit.  I've found several attempts at reverse-engineering the communication protocol to the EF lenses.  It is basically a modified "SPI" serial communication plus a couple of sense pins.


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## graham-xrf (Aug 25, 2021)

The drawing from Canon at least gives the real radius, but the graphic of the drawing is not up to using that information to get at the very pixels of a real image. The yellow circle has a thickness, and it's all inside a black circle. The tip of the arrow goes through the yellow line.

Nevertheless, using the middle of the yellow circle thickness, and setting the diameter to 2 x 22.6 = 45.2mm, and then estimating the cursor between the pin pixels, we get the set of measurements shown in the image Between the 8-set of pins, it is about 2.2mm. The gap to the 4-set is about 3.43mm. The 4-set is two pairs separated by about 2.2mm, and the distance between the pins of a pair is the wider 2.55mm

The chord measures 24.8mm, and the angle over the chord casually measured 71.72 degrees, which probably meant 72 degrees. None of this is pixel-perfect. The drawing graphic is just an illustration, and most all calibration is messed by the thickness of the lines, and not having an accurate pixel distance to calibrate from. A real image, using a narrow angle telephoto zoom from a distance to make the image sphere near planar is needed. With also a scale in it somewhere, it could yield an accuracy that might challenge what you could do with most other imagers.




A perfect circle fitted onto the pins of the scan picture of the lens has a center in a different place as the circle of the rim. It is not usable to do this trick on.


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## pontiac428 (Aug 25, 2021)

Now you're cooking with gas!


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## SLK001 (Aug 25, 2021)

You could import the image in post #6 into AutoCad, scale it to 1:1, then proceed to get all the info you need.


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## Reddinr (Aug 25, 2021)

I changed my mind and ordered a cheap microscope with a reticle to mount to my mill.  I'll use the DRO method once I mount it up to the machine.
I'm sure it will come in handy from time to time.  I'll publish a drawing when done for any other photo people that are curious.


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## hman (Aug 25, 2021)

@RJSakowski - DURN!  I'd forgotten your thread on this far superior scope system.  Thanks for the memory refresher!


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## pontiac428 (Aug 25, 2021)

Reddinr said:


> I changed my mind and ordered a cheap microscope with a reticle to mount to my mill.


Is it a reticle, or a graticule?


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## Reddinr (Aug 25, 2021)

You are correct sir!  It was stuck in my brain as reticle.  I can look at the graticule through the reticle though!


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## hman (Aug 25, 2021)

OK, guys ... ya done glommed onto my igrunce here.  What's the difference?  I tried the built-in dictionary in my Mac, and they sound pretty much alike:

reticle | ˈredək(ə)l | noun    a series of fine lines or fibers in the eyepiece of an optical device, such as a telescope or microscope, or on the screen of an oscilloscope, used as a measuring scale or an aid in locating objects.

graticule | ˈɡradəˌkyo͞ol | noun technical    a network of lines representing meridians and parallels, on which a map or plan can be represented.

... or is it that a reticle is something "inside the optic" and the graticule is something like the background against which the unknown object can be compared???


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## graham-xrf (Aug 25, 2021)

hman said:


> OK, guys ... ya done glommed onto my igrunce here.  What's the difference?  I tried the built-in dictionary in my Mac, and they sound pretty much alike:
> 
> reticle | ˈredək(ə)l | noun    a series of fine lines or fibers in the eyepiece of an optical device, such as a telescope or microscope, or on the screen of an oscilloscope, used as a measuring scale or an aid in locating objects.
> 
> ...


All my life, they called those plastic windows with measuring grid lines engraved into them, as are fixed over oscilloscope screens, "graticules".
A "reticule" was a small drawstring bag, or a woman's purse. How crazy is it that such is now called a "clutch" to the total confusion of guys like me who think a clutch is the bit between the engine and the gearbox!

At some point, reticule also became etched lines or cross-hairs built into the focal plane of optics like weapon sights or theodolites.
The terms can be used interchangeably, although "graticule" is more commonly the term for marked grids or lines on stuff not actually inside optics.


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## RJSakowski (Aug 25, 2021)

Ah yes, the spoken vs. the written word.  There are numerous examples of how the spelling of the spoken word eventually gave rise to entirely new word.  It is quite prevalent in the U.S. with words of native American origin as at the time, there were few people who could read or write.

Some years ago, my British in-laws were giving me some static over Americans referring to "soccer" what the rest of the world calls "football" or "futbol".  I did a little research  and discovered that soccer or football originated in Britain in the nineteenth century.  Some time later, the other "football" aka "rugby" came about.  To distinguish between the two, the press started calling the original football "association football" which eventually was shortened to "soccer" by the British.  Since we had our own brand of football, we just adopted the British alternative.  

Now you know rest rest of the story.


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## graham-xrf (Aug 26, 2021)

RJSakowski said:


> Ah yes, the spoken vs. the written word.  There are numerous examples of how the spelling of the spoken word eventually gave rise to entirely new word.  It is quite prevalent in the U.S. with words of native American origin as at the time, there were few people who could read or write.
> 
> Some years ago, my British in-laws were giving me some static over Americans referring to "soccer" what the rest of the world calls "football" or "futbol".  I did a little research  and discovered that soccer or football originated in Britain in the nineteenth century.  Some time later, the other "football" aka "rugby" came about.  To distinguish between the two, the press started calling the original football "association football" which eventually was shortened to "soccer" by the British.  Since we had our own brand of football, we just adopted the British alternative.
> 
> Now you know rest rest of the story.


Of course, with the internet inevitably getting us more used to the norms in each other's countries, we now have a whole stack of examples where an expression in one place has a whole different meaning in another.
In Australia, "Durex" is cellulose sticky tape like "Sellotape".
In USA, mils are thousands of an inch, called "thou" in UK. Everywhere else, it means millimetres.

In France, "soccer" is used as casual slang. The match with a round ball is just called "football" or "le foot".
When they mean the oval ball game as in USA leagues, it's " le football américain" (with a lower case "a")

Yet another kind - Australia Rules Football. This is the sort with an oval field, played without much body protection, wearing the too tight undersized shorts and minimal vests that the ladies just love. In France, they say "Il joue au football des Règles de l'Australie"

So get used to it! Pavements are sidewalks, lifts are elevators, jam is jello, fags are what smokers smoke, and in USA, jam is something traffic gets into!


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## pontiac428 (Aug 26, 2021)

I'll keep that in mind if someone with an English accent asks me for a cigarette and a roll of cellophane tape before it leads to unnecessary argie-bargie.


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## RJSakowski (Aug 26, 2021)

My first encounter with Britspeak/Amerispeak was when I first met my future wife.  I was to pick her up fro her hotel the next morning for a tour of the local countryside.  She asked me what time I was going to "knock her up" meaning to call on her. That phrase has a very different meaning here.  In the US, a fanny pack is a small pouch worn to the back around one's waist.  Quite a different connotation in the UK.  The first ten years of our marriage, the most common phrase was "meaning what".  Nowadays, it has been "say that again".  Old age


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## hman (Aug 26, 2021)

Anyway, it was nice of you to marry her after you knocked her up


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## graham-xrf (Aug 27, 2021)

@RJSakowski
Bob, in using your spindle mounted microscope+DRO, I get it that you can measure any point relative to another, even if the camera is mounted arbitrarily.  If cross-hairs aim are on the spindle axis, of course rotating the spindle will show the image rotating about a stationary point, but there is some calibration construction in moving either it, or the cross-hairs before it becomes something you can put in the collet, and move until it's over the round thing you want to centre on.

What did you do to get it on centre axis?

[ Edit: Umm - I guess the final tweak is with Jim's software image cross-hairs add-on. I use Linux, but I think both GIMP and FreeCAD have video plug-ins. This is something I definitely want to have. That said, I also like Stefan Gotteswinter's spindle mounted DTI project for getting to the centre of round things].


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## RJSakowski (Aug 27, 2021)

I did two things.  First, I put a positive lock on my spindle to prevent any rotational movement.  This allows me to make accurate point to point measurements.  Second, @Jim Dawson 's little program allows you to shift the graticule so you can align it with the spindle axis.  By rotating the spindle and observing the rotating image, I can center the graticule with the spindle axis to within a tenth of a thousandth.  It's a bit of work so I only do this when I need to center the spindle on a feature.

I mounted my microscope in a dedicated R8 end mill holder with the hope that it would retain calibration on reinsertion but that isn't the case so if I want to do any accurate location, I will go through the recalibration process.

Can you post a link to Stefan's project? Another tool that I have is a modified laser pointer which I mount in my boring head to provide an adjustable circle which I can align with a circular feature.  By being able to fairly closely match the laser circle to the feature, I can get the center to within a thousandth or two.
https://www.hobby-machinist.com/thr...did-you-do-in-your-shop-today.14637/page-1088 post 10872


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## graham-xrf (Aug 27, 2021)

RJSakowski said:


> Can you post a link to Stefan's project? Another tool that I have is a modified laser pointer which I mount in my boring head to provide an adjustable circle which I can align with a circular feature.  By being able to fairly closely match the laser circle to the feature, I can get the center to within a thousandth or two.


Stefan published the plans, and described the project on his website, but I am not sure he did a YouTube video.
I think there may be versions from several other YT machinists, but MachineNZ and Max Grant were the first I found.

Anyway - we can start with the plans - PDF attached.




*MachineNZ version from Stefan's plans.*
MachineNZ did then do a YT video of his take on it, using Stefan's plans.
There are 3 parts to it, but here is the link to Part 1. The other parts follow by themselves.
#60 - GTWR Indicator Holder Part 1 - Arm and Swivel Pins





*The Max Grant version series (up to Part 5 I think)*
We can start with Part 1
Building the GTWR Indicator Holder. Part 1





"GTWR" is, of course, a shortened reference to his name "Gotteswinter" for his website "gtwr.de"
https://gtwr.de/stefan-gotteswinter-prototyping-tools-and-machines/


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## RJSakowski (Aug 27, 2021)

Thanks Graham.  This functions pretty much the same as the Indicol articulated arm.  It works great if you have a cylindrical surface to sweep.


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