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3rd September 2019, 01:37 PM #16GOLD MEMBER
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I thought I'd add that I haven't changed the supplied battery in my Digi gauge since purchase a couple years ago.
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3rd September 2019 01:37 PM # ADSGoogle Adsense Advertisement
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3rd September 2019, 02:05 PM #17
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3rd September 2019, 06:43 PM #18
Wow, that thread developed a life today!
At the heart of this discussion, when it's all boiled down is the difference between accuracy & precision & where each is required. In woodworking, where you are making one thing at a time, what you most need is accuracy. The parts have to fit neatly, but whether a rail is 1mm longer or shorter than the plan says is neither here nor there. As long as all the matching rails are the same, and the fit is neat, no-one is ever going to know or care. Apart from a few initial measurements, I prefer to avoid all those things with lines & numbers on them & do the rest with gauges and a 'story-stick', or simply marking one part off another. Not only does this antiquated way of working reduce my errors, it saves me an awful lot of time looking for that blasted tape-measure or ruler I had in my hand a minute ago!
And Chris, yes, I own a decent set of digital calipers & I use them a lot, when working with metal. Here precision is often required. A good example is when you are aiming for either a press-fit or a sliding fit, and the diameters have to be a precise x or y. I do also use a couple of cheap old-fashioned verniers for woodworking, particularly on the wood lathe, for their convenience as outside/inside/outside gauges. In those situations, I usually don't bother with the numbers & lines - they are simply for transferring or checking dimensions directly. Occasionally I do measure wood, but I certainly don't bother with the second decimal point (in mm, that is, of course 0.625 inches has some meaning.. )
As others have noted, one of the major advantages of any instrument with a digital readout is ease of reading! Until a few years ago, I still used a good-quality genuine 'vernier' (no batteries needed!) for precision work, but it lost me about the specs upgrade before last..
Anyway, I wouldn't castigate anyone for over-doing precision - that's far better than the other way round, for sure. But I would whisper in your ear that excessive precision really isn't necessary in most cabinetmaking procedures.....
Cheers,IW
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3rd September 2019, 06:50 PM #19Taking a break
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I think you've got accuracy and precision backwards Ian; accuracy is how close the measurement is to the true value, precision is how close multiple measurements are to each other (aka repeatability).
If all your rails are 1mm off the required size, but all the same as each other, they're inaccurate, but precise.
The number of decimal places you can read is, effectively, your precision (ok it's technically the resolution, but for the sake of the argument we'll go with it), but an uncalibrated tool will just give you a 3 decimal place inaccurate number.
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3rd September 2019, 07:37 PM #20
Elan, I'm going by the definitions we were given in Physics 1B - I may have gotten them bass-ackwrads; it was more than 50 years ago...
What I was driving at is that if all my rails are 1mm over or under what's specified, the fit will still be accurate. But the rails are neither accurate nor precise
An inaccurate gauge may still allow precise work - as long as it's consistently inaccurate.
I think I will run for cover at this point..
Cheers,IW
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3rd September 2019, 07:48 PM #21Taking a break
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Yep. I was told to make sure I use the same tape measure throughout a job for that exact reason (after I got caught out once )
Now that I've moved to the engineering field making medical and aerospace parts, I get to have both precision and accuracy; all our calipers and micrometers are calibrated annually
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3rd September 2019, 09:00 PM #22GOLD MEMBER
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This could become something resembling a sharpening thread, I will get my slippers and a warm drink of milk.
CHRIS
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3rd September 2019, 10:05 PM #23
As a surveyor through out my working career we had an obligation to maintain "legal traceability of measurement" for all forms of measurement, be it a steel rule, tape measure, steel band (chain) or electronic distance measurement (EDME) so it did not matter which surveyor, company, tape, EDME etc was used - accuracy & precision.
In the past all steel bands were standardized / calibrated against a "regional subsidiary standard" steel band or a certified measurement baseline, the accuracy of which could be verified (traced) back to the National Measurement Standard …...
These days EDME is calibrated over a measurement base maintained and certified by DNRM (QLD) with the same traceability to the NMS etc, but they are still scratching their heads about how implement a system to calibrate measurements determined by GPS observations.Mobyturns
In An Instant Your Life CanChange Forever
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3rd September 2019, 10:24 PM #24
Oh and as a point of interest the most common measurement error with a steel tape or rule in wood working is the "offset / zero error." i.e. the unit does not measure zero when it should! This is because of wear or damage, or manufacturing errors which cause all measurements to be in error by the offset as the face of the tab is not correctly aligned as "zero."
A simple check for retractable steel tapes is to accurately & precisely measure and mark say a 200mm "baseline" using a mid section of the tape then remeasure it using the zero end (tab). If there is a discrepancy between the two then that is the zero / offset error which affects all measurements. The same can be done to compare / check other sections of the tape measure.
Carefully measuring the length of a board from both ends to a line marked anywhere mid board (sum of two measurements) then measuring the total length (single measurement) will also identify a "zero / offset error" as the sum of two measurements will also have two "zero / offset errors." So it always pays to measure the total length of any set of measurements taken in sections.
I would also be cautious using cheap vernier calipers as I found out the hard way why I was not getting a nice suction fit on lidded boxes when transferring measurements. We traced the problem to a manufacturing error in the verniers themselves by comparing against other vernier calipers. The inside and outside measurements on the set I was using varied by about 0.4mm i.e. they always were 0.4mm different.Mobyturns
In An Instant Your Life CanChange Forever
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3rd September 2019, 10:26 PM #25Taking a break
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Sounds the same as what we have to do for ISO9001 and AS9100.
We have our masters calibrated externally and we check the rest in-house against those masters, we also have a Mitutoyo super-micrometer (reads to 0.1 um) for checking plug gauges. Oh yeah, and we have to keep job inspection records for 30 years , so if something falls out of the sky we can find out who made it, who checked it, what equipment was used and what batch number the raw material was.
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4th September 2019, 12:48 AM #26GOLD MEMBER
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I use a retractable tape for landscaping because that is all most of them are good for. There are some which comply to a standard such as the BMI tapes but they are exy and not generally easily available in Oz. The quicky tapes from BMI do comply with a known standard but I see they have had a recent hefty price rise Pocket Tape Measure Retractable Stainless Steel 2 Metre BMI 4007368104957 | eBay
CHRIS
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5th September 2019, 01:50 PM #27rrich Guest
I got a laugh when "Surveyor" was mentioned.
Here in the US we use feet and hundredths of feet in surveying. An old and crusty party chief told me that the only people that use feet and inches are carpenters and ladies of the evening. (It is the most PC wording that I could use and not put the thread in the room with padded walls.)
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6th September 2019, 01:25 AM #28
Chris, this digital gauge looks good, and I may even purchase one ... it will be useful. However, there is more to the gauge than meets the eye.
Essentially, this is a power tool users gauge, and not one for hand tool users. I know this will appear strange at first, and I shall explain.
In hand tool work, an emphasis is given to working from a reference side. Everything is gauged from the reference side. The reason for this is that it is common that the non-reference side is left rough until a later time. This side may be not be parallel and not even flat. Anything gauged from the non-reference side is going to create errors ... unlike a board that is finished with a thicknesser.
When working from the reference side, an exact positioning of the gauge is unnecessary. For example, exactly 1/2" in from an edge, or exactly in the middle of the board. All that is necessary is that one gauge is dedicated to each set up, and then this is used to transfer lines between parts. Generally, there may be a few gauges for use as, once one is set up, it is unwise to risk altering the settings. I may use 4 or 5 gauges during a build.
What this means is that working to a number is unnecessary. One might never use a rule to determine the setting (other than the width of a chisel when marking mortice-and-tenon joints). Close enough is good enough. And quicker.
It is really only power tool users that work to measurements for repeatability. That is where this digital gauge excels. That is not a criticism of the gauge, just a recognition that it fits best with someone who does not use the hand tool method.
Regards from Perth
DerekVisit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.
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