Measuring coins
saltlydog4
Posts: 180 ✭✭✭
Hey everyone,
What do you all use to measure coin lengths? Like, say, the width between CC's - is it 1.1 mm or 1.2 mm? How can you measure it that distinctly? props for answers to an ebay post to purchase said tool.
Thanks,
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Comments
Harbor Freight tools sells a Vernier Caliper that is adequate for most needs. Very inexpensive.
Will photograph mine and then post photo.
This is supposed to be able to get down to 0.05 mm, but I never need that degree of precision.
There is a digital version of these calipers that I use all the time. I bought mine of ebay, comes with a hard case.
@AUandAG oh, that's pretty neat.
When I'm trying to downsize a little bit, new toys pop out of the woodwork!
The digital section will show you down to .01mm. The trick is being able to properly determine the edges of the mintmarks to line up with the caliper opening for a proper reading... without scratching your coin.
The digital vernier is usually quite accurate, though the user can affect that as well. I use one for fine measurements. Cheers, RickO
Ordinary calipers are of limited utility when directly measuring the distance between "C" & "C" or other short spans.
A more useful technique is:
1. Photograph the coin's area of interest at high resolution.
2. Calculate the amount of image magnification.
3. Adjust net magnification to some whole number value.
4. Use calipers to measure the desired distance.
5. Divide by the calculated magnification to obtain the actual distance between two points.
The above assumes you have previously defined start and end points and that you will use these every time measurements are made.
Yeah, I know this is an inconvenient process, but absent a dissecting 'scope with calibrated reticle, it is workable and reasonably accurate.
This seems like a much better way than trying to line up an instrument on a coins surface.
RogerB said:
" ...absent a dissecting 'scope with calibrated reticle, it is workable and reasonably accurate."
True. There is no sense arguing the virtues of various precision calipers if you are going to throw away that precision using unscientific, or potentially dangerous (to the coin), methods to accomplish those measurements. I am fortunate to have a very nice Bausch & Lomb adjustable zoom stereo microscope, and I have fitted one of the eyepieces with a measurement reticle to make precise measurements. Of course, with an adjustable zoom microscope, the measuring reticle (in the eyepiece) is only accurate for one setting of the zoom, but this can quickly be determined, and then that setting of the zoom can always be used for accurate measurements without risking placing any measurement device on the subject coin's surface. I use this method routinely for measuring the size of various mint marks, date numerals, and the placement and spacing of same relative to the devices. If accuracy is important, then this is the only method to be used.
@BillDugan1959 said: "Harbor Freight tools sells a Vernier Caliper that is adequate for most needs. Very inexpensive."
I guess it all depends on the word "most." IMO, no professional numismatist would be caught dead using a plastic toy as this. Better to spend a little more and get a "real" caliper made of metal.
When measuring a coin, do it in several places as coins are not perfectly round or thick!
Edit: A very nice dial or electronic caliper can be had for under $50 and they are faster than using a scope and reticle scale. I've seen two of the ones on AMAZON in a TPGS.
PS @MrHalfDime will you please explain how you measure the edge thickness of a dollar and its diameter (quickly and accurately) if the magnification needs to stay the same. The barrel of the scope needs to be raised to view the edge and lowered to measure the cross-section and the edges of the coin may go off the field of the eyepiece. Perhaps if you instruct me as to your method I will try to see if I can count those tiny little lines at my age.
Calipers made from dimensionally stable materials are available but they are expensive. The ones I use for gross measurement - diameter, thickness, etc. but never touching the coin faces - were more than $300. But --- you'll get better results for details with a cheap student-grade 'scope and reticle.
Insider2 asked:
"PS @MrHalfDime will you please explain how you measure the edge thickness of a dollar and its diameter (quickly and accurately) if the magnification needs to stay the same."
In my many years of numismatic researching, collecting, and writing I have never had to measure the thickness of a dollar. Of course, that is likely due to the fact that I collect half dimes, and not dollars (although I have never had to measure the thickness of a half dime, either). As for measuring diameters, I use a MAX-CAL digital electronic caliper, much like the one recommended by AUandAG. I never stated that I had just one tool to measure coin dimensions. As I clearly stated in my response, I use the stereo microscope and measuring reticle " ... for measuring the size of various mint marks, date numerals, and the placement and spacing of same relative to the devices." It would be folly to use any microscope to try to measure the diameter of any coin as large as a dollar. I don't even use the microscope to measure the diameter of the tiny half dimes. Any numismatist worth his salt must have many tools at his disposal, and know how to effectively use all of them.
Along with the proper measuring tools, good, consistent techniques are also required.
A basic example:
Q - When measuring the diameter of a Seated Liberty dollar should the caliper blades be perpendicular or horizontal to the coin's face?
A - Neither. Measurements on reeded edge coins should be taken diagonal to the reed angle. If measured perpendicularly, the caliper blades can slip between raised reeds, and if measured horizontally they can sit on the top of reeds. Diagonal measurement is more consistent. (But -- be award that most US reeded edge coin diameters were planned from top of reed to top of reed. Use of knurling tools for cutting collar reeds often resulted in inconsistent diameters. Further, collars were deliberately cut with the upper side opening very slightly wider than the bottom - this facilitated coin ejection. )
Another example:
Each dimensional measurement should be repeated a minimum of 12 times. Discard the high and low values, and average the remaining 10. Since most tools hobbyists will use have only 2 significant digits right of the decimal point, the result must be rounded to the nearest 0.01. (MS Excel will do this for you.)