Regardless, Its waaaaaay overkill for what I do... Im not building Space X rocket parts in my garage [big grin] As mentioned I was right on the money at 2.940 after calibrating off of my fat max with 95" of travel not sure if I just got lucky but Ill take it. I will do some more validating while waiting for the class 1 but at this point not sure I need it. However I still want it for double checking not only parts but other tapes as well.
Class (1) one tape measure
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mino
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Calibration in case of measuring instruments is not what we normally (incorrectly) refer to as "calibration" when thinking of a tool.Bob D. said:
The point of calibration there is NOT to change/adjust the measuring instrument but to compare it to a known-good reference to see how far off the instrument we are calibrating is. The word "calibration" actually comes from this. It means, literally, "comparing to a caliber" where caliber is the name for "a known-good reference".
Result of a calibration is a calibration report which is then stored with the instrument. The calibration report can be used two ways:
A) if the accuracy of the instrument is found to be "within a range needed for the task" then it provides a sign-off on using it for the task
B) if the accuracy is found to be too-much off for the task, the differences from te calibration report can be marked on/with the instrument and applied as a corrective factor each time the instrument is used
The B) approach is actually very common for very-precise work as a way to save costs by buying a lower precision class than needed and using the calibration results to allow using the instrument "above its specification". When a "0" class straight edge can be $1000 and a "1" class one is $200 it makes sense to do so if the instrument is not used too often.
I will upload here the one I got for my tape measure, hopefully I will find it still.
mino
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Practically speaking, the shop I use it in is whole-year stable between 18-22C. So in -my- case that is moot. Yeah, lucky me!Svar said:
But that is not the point.
The points are
- i now know the actual variance and I know it is gradual - i.e. I can count on 600mm times 4 when put together will be 2400 as measure by the same tape, measurement errors notwithstanding
- that any error is additive, so if mine is almost exact, I have the "budget" for the thermal variance (in practive I do not use the tape above 5C variance so up to 2m total lenghts I am well within
Cheese
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Several years ago this same subject/discussion came up on the FOG so I contacted Starrett and had a nice discussion. They said there were actually 3 classes...Class I & Class II which must fall within their respective Class specifications and Class III which follows no specifications what so ever. So the take-away here is if the Accuracy Class is not stated, don't just assume that it has to be Class II.
Starrett says all the tapes they offer are officially Class II, yet if you look at the Starrett specs they maintain, their specs are more like Class I.5.
Here's the EC Specifications and the Starrett Specifications.
[attachimg=1]
[attachimg=2]
Starrett says all the tapes they offer are officially Class II, yet if you look at the Starrett specs they maintain, their specs are more like Class I.5.
Here's the EC Specifications and the Starrett Specifications.
[attachimg=1]
[attachimg=2]
Attachments
I am thinking back over when I need real accuracy in the woodshop and none of those instances required a tape measure. They required a ruler or combination square.
In any event, the added accuracy of a quality tape measure cannot be bad; it has to be good. It is part of a total attitude towards measurement. This article shows some of the other aspects that are required to up your accuracy in the shop.
It entails a good pencil sharpener, a marking knife, and some attitude.
https://www.woodmagazine.com/woodworking-tips/techniques/layout-measuring-marking/accuracy
When I had my picture framing business, I would clean both sides of the glass twice with glass cleaner and once with distilled water. That ensured that all the residue was removed. Was this required? No. But it slowed me down and put me in a "careful craftsman" frame of mind.
I do think that is the most important aspect of measurement. If having a highly accurate tape measure puts you in the "careful craftsman" frame of mind, then it is certainly worthwhile.
In any event, the added accuracy of a quality tape measure cannot be bad; it has to be good. It is part of a total attitude towards measurement. This article shows some of the other aspects that are required to up your accuracy in the shop.
It entails a good pencil sharpener, a marking knife, and some attitude.
https://www.woodmagazine.com/woodworking-tips/techniques/layout-measuring-marking/accuracy
When I had my picture framing business, I would clean both sides of the glass twice with glass cleaner and once with distilled water. That ensured that all the residue was removed. Was this required? No. But it slowed me down and put me in a "careful craftsman" frame of mind.
I do think that is the most important aspect of measurement. If having a highly accurate tape measure puts you in the "careful craftsman" frame of mind, then it is certainly worthwhile.
Accuracy and precision are an ongoing topic with woodworkers as we know, much like sharpening. How many flip stops/sliding stops/fences have you got in the workshop and have you got a way to ensure all cut to the same dimension as the measuring devices you use and each other? If you measure a piece of wood and then the fence does not cut to the same dimension there does not seem much point unless you like extra work.
The problem with marketing Class1 tape measures apparently is that all the current popular tapes except one is dead accurate. So it is a tough sell marketing a much more expensive series of tapes.
See: https://www.protoolreviews.com/best-tape-measure/
The technology for producing the tapes is the same across the board, though I would assume that the class 1 rated tapes are subject to more stringent quality control testing.
But do like they did in the link I provided. They compared the tapes with a reference grade ruler. They only checked at 6 feet, but if you have a highly accurate ruler it will take a minute or two to compare the tape with the ruler at several data points.
See: https://www.protoolreviews.com/best-tape-measure/
The technology for producing the tapes is the same across the board, though I would assume that the class 1 rated tapes are subject to more stringent quality control testing.
But do like they did in the link I provided. They compared the tapes with a reference grade ruler. They only checked at 6 feet, but if you have a highly accurate ruler it will take a minute or two to compare the tape with the ruler at several data points.
Packard said:
not sure what review you are talking about. The review you linked, I only see that they tested to 6" not 6'. IMO 6" is hardy enough to test a tapes accuracy. plus they didnt test a single class 1 tape. I stopped reading after that. Pretty much crap review IMO. I have seen tapes that are off only in a couple foot section and then a few feet down are back on track again. So 6" is kind of a joke. I have plenty of accurate measuring tools including a starrett combo with 12&24 blade. However, I was looking for a quick and reasonably accurate and somewhat more trustworthy way to measure and verify other scales out to 8 feet or so. Spending 30-40 bucks on a class 1 tape seems like the best option still without spending thousands on class 0 laser engraved, certified rules and maintaining temperature controlled shop.
mino
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This. 100 times.afish said:
BTW, you made the exact same call I did. A Class 1 tape is an obvious choice as one can take advantage of it also on regular work. A (long) engineer's rule is the next step which may or may not be necessary down the line and it really needs reasonably stable temperature (like 15C - 25C tops) to make sense.
[member=73094]afish[/member] Do you know anyone with a good sliding table saw in your area? My digital crosscut fence is 6' long and has a resolution of 0.001". I can extend that resolution to 10.5' using stop blocks. Rather than using a ruler, you could get some reference strips cut (formica laminated MDF) and use them for calibration. I would think with a dial indicator mounted to the spindle, you would get better results over aligning a v bit to a line on a tape. Just a thought.
No I dont. But its all good, The tape measure and a very fine v bit (the one im using is 3mm bit and 20° the things needle sharp and never used for cutting) actually works surprisingly well believe it or not. I can really pin point that v bit to the center on the line on the tape very accurately. The biggest variable at that point is the tape not my eye. The class 1 tape specs out to +-.3mm at 2 meters. +-.4 at 3M So Ill call it .35mm or total possible error of .7mm which =.0275" If I call it .030 depending on my eye then divided by 96" of travel is .00003" of possible error per inch. Most R&P machines wont come close to that tolerance anyway. Not to mention wood movement, temperature, humidity etc. At some point the accuracy is just overkill. At what point do you draw the line building furniture and cabinetry? The class 1 tape isnt only for the cnc but to quickly check/verify other tapes and rules with "reasonable" certainty. For 30-40 bucks Im game. Much more than that and I really need to start questioning my OCD. This all started because when I checked with this method using my stanley tape I was .040" out over 95" using the steps per inch from the R&P specs. So, this got me wondering if the steps per inch was wrong or was my tape off and prompted the class 1 tape purchase. I was actually more than happy with the overall accuracy of the cnc before getting into this but I was recently working on making some vacuum fixtures for the DDF40 to end bore holes for dowels to match the cnc face bored dowels and had an issue that one side was off .008" while the other was perfect. Turns out after further investigation part of the issue was the ddf40 fence is not Perfect either. This is the big benefit of the domino over the Dowler but the domino also puts in a little to much slop for me. If festool ever updates the Domino a infinite slop dial would be awesome instead of just having 3 settings. Being able to dial in the amount of slop you need or want would be really nice. In the end nothing is perfect everything has some type of tolerance/error including the material and dowel itself. I think the best/easiest thing is to build my fixture with an extra .010" of play so I can plunge once then slide over the .010" and plunge again with the DDF40. This will give me a very slight oblong hole in one axis only and provide me a little wiggle room for final assembly to keep the front (edge banded edges) perfectly flush while still maintaining tight hole in the other axis. It will require 2 plunges per pair of dowels but the second plunge is taking off so little it should only take a couple of seconds. Opposed to just drilling an oversized hole. Where it will be bigger all around.
Cheese
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afish said:
Ya this review is indeed very strange, I really question why a magazine would even dedicate the necessary resources to produce this article?
The review starts off with "Before you worry about anything else, a tape measure has to be accurate. If it isn’t, nothing else matters." They then go on to introduce their "Lixer Master calibration tool" that's only 6" long. [blink] So as long as I only measure 6" long or shorter items I'm good to go? [huh] Very strange indeed.
afish said:
It’s probably worth 10x that to the right person in the right industry. But as woodworkers, I’d say a pair of digital calipers would be just as good and provide 100x the utility in other applications. I couldn’t live without mine in the shop.
egmiii said:
Well for the life of me I cant think of any industry or person that would need or use a tape measure for just the first 6" If the first 6" is all that matters then there are much more accurate tools to measure such small distance. Perhaps Im small minded but it seems completely ludicrous to me for anyone to buy such an item other than perhaps a lab that does certification for tapes such as Mimo was talking about.
Cheese
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The disconnect comes with the authors of the magazine article. The person that designed the testing procedure mistakenly assumed that just using the Lixer Master Calibration Tool would be the simple answer for accessing tape measure accuracy, never thinking the entire problem through and coming up with a complete solution. "If we test the hook push & the hook pull then we're golden."...ah not really. [jawdrop]
Lixer on the other hand understands the situation and they offer tape measures with a NIST certificate of traceability. They not only check for hook push & hook pull but also check the length against a standard. From the Lixer web page...
"Each tape measure has been carefully selected and verified for end hook push and pull accuracy at the 6" and/or 10 cm marks.
Tape measure blades, up to 100' long, are verified against NIST Traceable scales. Blade errors will be indicated on the Certificate of Traceability to NIST (The National Institute of Standards and Technology). Specific errors are indicated approximately every 5' on standard tape measures and every meter on metric tape measures."
Personally I think every 5' is too long of a span as a 12' tape would only have 2 data points. But that's better than 6" and DONE.
https://lixertools.com/collections/products-standard-tape-measures
Lixer on the other hand understands the situation and they offer tape measures with a NIST certificate of traceability. They not only check for hook push & hook pull but also check the length against a standard. From the Lixer web page...
"Each tape measure has been carefully selected and verified for end hook push and pull accuracy at the 6" and/or 10 cm marks.
Tape measure blades, up to 100' long, are verified against NIST Traceable scales. Blade errors will be indicated on the Certificate of Traceability to NIST (The National Institute of Standards and Technology). Specific errors are indicated approximately every 5' on standard tape measures and every meter on metric tape measures."
Personally I think every 5' is too long of a span as a 12' tape would only have 2 data points. But that's better than 6" and DONE.
https://lixertools.com/collections/products-standard-tape-measures
An ISO 9001 shop that uses tape measures as part of some certified process likely needs a calibration procedure to comply with whatever is written in their policy and procedures. NIST traceability is almost certainly part of that and is not cheap. What industries require an NIST certified tape measure is beyond my imagination, but clearly one exists. If you think about what could go wrong with your new Class 1 tape, it’s likely not going to get longer or shorter from 6” to it’s maximum length under normal operating conditions. But it is much more likely to get longer over the first 6” due to wear and tear/damage in the sliding hook. My assumption is that if the Lixer says it’s good at the 6” mark, then some standards body will say the tape is true to its calibration standard at manufacture.
I think Cheese and I responded at the same time, but ultimately agree on the same point. The Lixer isn’t for determining how accurate a tape measure is. That’s what the calibration at manufacture is for. It will only tell you if it remains true to that calibration, with the assumption that if the first 6” is true, then the remainder is also okay. I didn’t read that article, but it appears the authors picked the wrong tool for the job.
