Easy Way to Round "Big" Fractions from Digital Calipers - Woodworking Talk - Woodworkers Forum
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post #1 of 17 Old 02-21-2018, 06:51 PM Thread Starter
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Easy Way to Round "Big" Fractions from Digital Calipers

I saw this thread...

http://www.woodworkingtalk.com/f2/calipers-194881/

... and it got me thinking about how to solve a minor annoyance with digital calipers:

I have an iGaging IP54 Electronic Digital Caliper. I like it very much. The one drawback is the way that it displays fractions. If your measurement rounds to 128ths, you see 128ths. You can't set it to round to the nearest 1/16, for example.

I have some small experience with math, but rounding quickly from 128ths is not my best skill. Sometimes I want to round the reading to what I think is the "real" or "intended" value, and not the exact measure. That's because I may accidentally tilt the caliper jaws when measuring, for example.

When I see "113/128" on the caliper display, I am not super fast at figuring out that the "actual value" or "rounded value" is 7/8 inch. It turns out that 113/128 is only 1/128th of an inch above 7/8 inch. The actual value is probably 7/8ths, but I angled the caliper jaws when I made the measurement.

To deal with that, I just made a quick and dirty spreadsheet in Excel. When you get a "large fraction", use the table in the spreadsheet to scan for a nearby row with a "longer line" to round up or down to a "nicer" fraction in 16ths, 8ths, or whatever.

INSTRUCTIONS:
At the top of the chart, find the denominator (bottom) of your fraction on the caliper display. Slide your finger down the column until you find the numerator (top) of your fraction. Now look just above and just below it for a row that has more values to the right. You must decide how much you want to round up or down. (How far away from your reading that you want to stray.) It depends on whether you are looking for the nearest 16ths or 8ths or whatever, to get your "rounded" value.

The next time I go out to the garage, I will tape this printout inside one of the cabinets. I hope it helps others.
Attached Files
File Type: pdf Fractions Table for Digital Calipers.pdf (24.9 KB, 63 views)

Last edited by Tool Agnostic; 02-21-2018 at 06:53 PM.
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post #2 of 17 Old 02-21-2018, 07:08 PM
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simple math

It's taken quite a while, but over the years I've memorized some decimals from fractions. 1/4" = .250, 1/8" = .125, 1/16" =.0625 and so forth. You can get to all the others by adding those fractions together:
5/16" is 1/4" plus 1/16" so .250 + .062 = .312 etc..... no need to memorize them all, just the basic ones.

Going backwards from digital (decimals) to fractions means subtracting the big easy ones like .750 0r .500 and dealing with the remainders. Here's a good chart if this doesn't work for Ya:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #3 of 17 Old 02-21-2018, 07:10 PM
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Might have to get a calculator and covert it to decimals. 113/128 comes out to .8828125 which is a fuzz over 7/8". It's less than 1/64" so I would round it to 7/8". Unless you are figuring the openings of a number of shelf spacings there is no reason to get into 64ths in woodworking.
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post #4 of 17 Old 02-21-2018, 07:53 PM Thread Starter
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Quote:
Originally Posted by Steve Neul View Post
Might have to get a calculator and covert it to decimals. 113/128 comes out to .8828125 which is a fuzz over 7/8". It's less than 1/64" so I would round it to 7/8". Unless you are figuring the openings of a number of shelf spacings there is no reason to get into 64ths in woodworking.
Thanks. Your decimal method works well. I would want something like your chart, but out to 128ths, since that is what the digital calipers display.

For now, I'll give my home-brew chart a try first; I think it will be the fastest solution for me.
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post #5 of 17 Old 02-21-2018, 08:03 PM
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I have a drill graph similar to @woodnthings does drill size, fraction and decimal the 3 I usually need
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post #6 of 17 Old 02-21-2018, 08:12 PM
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Quote:
Originally Posted by Tool Agnostic View Post
Thanks. Your decimal method works well. I would want something like your chart, but out to 128ths, since that is what the digital calipers display.

For now, I'll give my home-brew chart a try first; I think it will be the fastest solution for me.
I don't know, I've never seen a tape measure with 128ths increments. The dimension wouldn't mean anything unless it translates into usable increments. You might be better off with a caliper which reads in decimal equivalencies. If you use it enough it doesn't take long to memorize the decimal equivalencies of at least the 1/16" increments on the tape measure. The decimal equivalence is then rounded off to a usable dimension.
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post #7 of 17 Old 02-21-2018, 08:32 PM
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I've never seen a tape measure that read to better than 1/16." I have a precision Starret scale that reads to 1/64" on one side and 1/100" on the other. My Wixey digital readout on my router table reads to 1/64, but I ignore everything beyond 1/32"

Someplace in my youth, I was require to memorize the decimal to fractional equivalents table to 1/64" and have never forgotten it. So my decimal-only dial calipers reads 1/1000's, and I still calculate in my mind to 1/64"

YMMV

<Chas>

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post #8 of 17 Old 02-21-2018, 08:33 PM
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I do so love a good millimeter. so simple . . .
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post #9 of 17 Old 02-21-2018, 10:16 PM
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The best way I know to handle a problem like that is to get rid of the offending caliper and buy one that reads the way you want it to read.

George
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post #10 of 17 Old 02-22-2018, 08:12 AM
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Guys the problem was solved in 1791 when the Metric system came into use.
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Measure twice, Cut once, Then force it to fit with a big hammer.
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post #11 of 17 Old 02-22-2018, 08:13 AM
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Quote:
Originally Posted by GeorgeC View Post
The best way I know to handle a problem like that is to get rid of the offending caliper and buy one that reads METRIC the way you want it to read.

George
Fixed that for you
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Measure twice, Cut once, Then force it to fit with a big hammer.
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post #12 of 17 Old 02-23-2018, 02:19 PM
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Most of time when using a caliper it's to transfer a measurement and I don't need to turn it on for that. If measuring to 1/8 or 1/16 then a rule should be good enough. I actually prefer working in tenths of an inch.
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post #13 of 17 Old 02-23-2018, 03:35 PM
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I don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
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post #14 of 17 Old 02-24-2018, 07:09 AM
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Quote:
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i don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
cost/price!!!
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post #15 of 17 Old 02-24-2018, 12:31 PM
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I printed this one up and have it in the shop.
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post #16 of 17 Old 02-24-2018, 01:44 PM
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Quote:
Originally Posted by Quickstep View Post
I don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
You can buy fractional dial calipers. Also those pocket calipers measure in fractions and metric.
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post #17 of 17 Old 02-24-2018, 02:02 PM
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Stick to the metric system. Common global language.

For dead stuff, wood moves.
You cannot measure it with any accuracy.
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