Calipers, Digital, Vernier or Dial?

[precisionworks]

That is not a bad set. All the blocks that are 1 inch and under are guaranteed to 50 millionths. The listing does not state the accuracy of blocks that are over 1 inch, Meaning that the larger blocks probably do not meet the accuracy specification.

Unless you need to build a stack of gage blocks for setting a jig or fixture, or to set a height gage, a few individual blocks are the best bet.

The 81 piece Starrett set is $314 at MSC in Grade B. Those you can trust

 

[jtr1962]

Unless you need to build a stack of gage blocks for setting a jig or fixture, or to set a height gage, a few individual blocks are the best bet.

I might want to build a stack to check my calipers for accuracy on a critical dimension. Yeah, I looked at individual blocks. Not much on eBay, and elsewhere it seems a few blocks cost as much as a set. I'll probably just order the set I linked to for now. If I need higher accuracy later (say to calibrate a mic, assuming I purchase one down the road), I can always order an individual AA block or two.

Yeah, I'm sure the Starrett set is better, but I'm on a pretty tight budget here. If money were no object, I'd get a set of AAA ceramic blocks.

Thanks for the help! With so many options out there, it's confusing for a novice like me to decide what's decent and what isn't.

I'll report back when the blocks arrive, and also how my el cheapo DX caliper fares. As I said earlier, so far nothing I've done even requires 0.01" absolute accuracy, so I should be good. To give you some idea of what I do, my drill press, bench grinder, and Dremel are what I use for metalworking. Obviously not precision instruments. I'm really in awe at you guys who make parts to the ten thousanths. I don't even have tools capable of that kind of precision.

I'm actually kind of proud of this GPS bracket I made out of a solid chunk of aluminum after the plastic one broke:

Sure, it's not pretty, but keep in mind that I used only my dremel, drill press, vise, and calipers. It's a nice tight fit in the bike mount which is all I care about. And it won't break next time I hit a pothole.

 

[precisionworks]

Very nice job on the gps bracket

Gage blocks are a peculiar type of measuring tool. Everytime 2 or more blocks are wrung together, There is some measurable amount of wear. Probably in the neighborhood of 1/50th of one millionth of an inch. After 50 wringings, a block is one millionths smaller than it was to start with. For that reason alone used blocks are always a gamble.

 

[jtr1962]

From the HF web site: http://www.harborfreight.com/4-inch-digital-caliper-47256.html

# Resolution: 0.0005" (0.01mm)
# Accurate to ± 0.001" (0.03mm)

So it will display to .0005 what it thinks is correct, but what it thinks is correct will only be within .001 (plus or minus) of the real length.

If my thinking is correct....

Actual length .1012
It can think it's between .1002 and .1022. ,
It will round to the nearest .0005, so it will display between .100 and .102. That's off by more than the claimed accuracy. The question is... do you take off .002 more when it reads .102 ?

Add any inaccuracies in your measuring technique, and you easily add another .0005 Then you have up to .0015 that you can be off.

Personally, I use the cheap China calipers a lot. I realize that they are best when used as a comparator and for getting in the ball park. Since I almost never need to get down to really precise parts, it's not been a problem.

I found some interesting reading on how these low cost calipers work. Although they only display to the nearest 0.0005" or 0.01mm, internally they calculate the measurement to 20,480 positions per inch. That equates to an internal resolution roughly ten times the smallest displayed resolution if using inches, or eight times if using mm. And this makes sense. Many digital instruments internally calculate the value to roughly an order of magnitude more than the displayed value in order to keep quantization error low, and insure reliable repeatability.

Going by the example you gave, the displayed value might still be more than 0.001" more or less than the actual value even though the accuracy is as claimed (i.e. within 0.001"). With digital instruments, the maximum the reading can be off is the accuracy plus or minus one count before any rounding. Suppose the true measurement is .10125". Since the device internally measures to the nearest 0.00005", the caliper will think this is anywhere from 0.10020" to 0.10230" (i.e. +- 0.001" plus 0.00005"). Rounding off to the nearest 0.0005", you could end up with anything from 0.1000 to 0.1025. Worst case you're reading 0.00125" off the true value but are still within the 0.001" accuracy spec. Note however that this greater discrepancy from the true reading than indicated by the accuracy spec is simply an artifact of the instrument rounding to the nearest 0.0005". This adds a maximum discrepancy of 0.00025", or half the rounding increment. If the instrument displayed to the same value it used internally, the reading would be at most 0.00105" off. Obviously this isn't done because the physical design of the caliper precludes making measurements with 0.00005" repeatability. Quantizing internally to 0.00005" also ensures repeatability to 0.0005", whereas quantizing to 0.0005" wouldn't (it would only give 0.001" repeatability).

 

[jtr1962]

Very nice job on the gps bracket

Thanks! It took a good 4 hours to make, mostly because I lacked the proper tools.

Gage blocks are a peculiar type of measuring tool. Everytime 2 or more blocks are wrung together, There is some measurable amount of wear. Probably in the neighborhood of 1/50th of one millionth of an inch. After 50 wringings, a block is one millionths smaller than it was to start with. For that reason alone used blocks are always a gamble.

Well, that set I linked to is new. I'll have to remember not to wring them too many times, although I can certainly live with a 1 millionth of an inch error. That's only a fraction of a visible light wavelength.

 

[KC2IXE]

Nice job on that GPS mount

Now, remember that you know someone with a lathe and mill who lives what, a mile from you....

Charlie

 

[etard]

Ok, now I want a master vernier caliper! I saw these:

http://cgi.ebay.com/Starrett-Master...aultDomain_0&hash=item20b6448f81#ht_500wt_922

One has a sticker on it, saying, "do not use" I couldn't blow it up, but why would it say that? Does anybody recognize the sticker as some sort of inspection standard?

These are going for $125, and there are a few that can be had as low as $80 and as high as $500. Why the wide gap here?

Thanks guys, I have enjoyed this thread, I also use the HF calipers and have seen very little variations in measurements between 5 or 6 HF cheapos, a Mitu, and even a Starret digital height gauge. But, I've never worked in the industry, where the instrument is used dozens of times a day, that would make all the difference I'm sure.

 

[PEU]

Its a one way ride, now I do not trust my digital caliper

I saw many spotless 123s go for less than that in the many months I waited for my unit in mm, what you can do is name your price and start sniping until you succeed. If the engravings aren't very deep, you can remove them as I did


Pablo

 

[precisionworks]

A DNU (do not use) sticker is placed right over an expired calibration sticker. They are often bright red, while the "normal" cal sticker is black on white. Sometimes an out of cal instrument gets put into the box to be sent to the cal lab, and then someone needs that instrument (usually on 2nd or 3rd shift, when no one is around to open the instrument bin).

Get caught using one of those and it's a write up on the first offense, if luck is smiling upon you

 

[precisionworks]

many spotless 123's go for less than that in the many months I waited for my unit

+1

No dial, no digits, no flashing lights, no Gee Whiz ... who would want one of those dinosaurs? The answer, of course, is anyone who needs the capabilities that only a Starrett 123 (or the Mitu equivalent) can bring to the table. $75-$100 will often buy a pristine one if you aren't in a rush.

Sold for $100 and really clean: http://cgi.ebay.com/STARRETT-12-MAS...241?pt=LH_DefaultDomain_0&hash=item3f0a1231f1

Nice looking for $35: http://cgi.ebay.com/Starrett-Calipe...210?pt=LH_DefaultDomain_0&hash=item2310d28042

How about a 36" version for $99: http://cgi.ebay.com/Starrett-38-Hei...529?pt=LH_DefaultDomain_0&hash=item3367cc93d1

 

[PEU]

Nice mitu 160 24" for $75+Shipping http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250828299633


Pablo

 

[precisionworks]

I have the identical caliper in 18". It is very sturdy & comparable in quality to Starrett. The 18" and above have longer jaws that allow reaching farther into a recess to check a bore.

 

[metalbutcher]

What do you guys think of this 12" Mitu? Seems like a decent price.

http://cgi.ebay.com/130524849960?ru...49960&_sacat=See-All-Categories&_fvi=1&_rdc=1

Thanks,
Ed

 

[precisionworks]

That's a sweet looking Mitu 160. Because there is no "Starrett" in the listing, it may go for not much more than the starting bid. Easily worth $75.

 

[PEU]

another one but 6 days auction: http://cgi.ebay.com/Mitutoyo-long-jaw-caliper-24-/320707202893

None in mm, the only thing I envy about inches is the availability of cheap used tools, otherwise: go metric!


Pablo

 

[precisionworks]

the only thing I envy about inches is the availability of cheap used tools

There has to be the European equal to Starrett. Not sure who that is, but there must be at least one maker of best quality precision tools.

Everyone knows about the quality of the Kurt vises, but few people have heard of Eron, a Japanese company that's been casting iron since 1560. Nabeya Co., Ld of Gifu, Japan owns the Eron name. http://www.nabeya.co.jp/com_E/index.html

I bought two sets of their thick parallels on eBay, maybe $20 per set, easily equal to Starrett or Brown & Sharpe that cost $200. Same with a quick acting drill press vise, dead copy of the Henirich for 10% of what Heinrich costs. Angle plates, V-blocks, etc. Must have 100# of Eron iron that probably cost $100.

Someone in Europe makes (or has made) a nice Master Vernier Caliper. The Swiss Etalon brand, purchased by B&S, might be one to search for. Moore & Wright (from the UK) is one Starrett equal. Steinmeyer (German) made very nice mics, not sure about calipers. Also Tesa (Swiss).

Also, you can use a thousandth reading Master Vernier as a comparator gage with your metric reading mic (for ID and bore measurements). Measure the ID of the part with the Starrett or Mitu Master Vernier, lock the slides, and read with your mic.

 

[metalbutcher]

That's a sweet looking Mitu 160. Because there is no "Starrett" in the listing, it may go for not much more than the starting bid. Easily worth $75.

I like the fact the it's only 12". I don't need one longer than that. I sent the seller an email asking if they accept money orders as payment since I don't have a PayPal account.

Ed

 

[PEU]

Nice 123M http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270774039277

Offered the guy $60 and he accepted but insisted on shipping via flat rate box at $45 told him that I want a flat rate envelope $25, as I received my previous unit this way, but stubbornly he refused, insisted 3 times with no luck. Its not the $20 difference, a flat rate envelope clears customs automatically here, a box I need to spend at least 3 hours at customs plus customs duties...


Pablo

 

[precisionworks]

insisted on shipping via flat rate box at $45

I sell quite a few items on eBay, and would never use an envelope for anything larger than perhaps a package of carbide inserts. Damage is always the fault of the seller who does the packaging, as it should be, and shipping problems cause more negative feedback than any other category. Just like the seller of the metric mic, I would ship only in a box.

 

[PEU]

if you check the item photo it includes the wooden box and an extra cover over the wooden box, even if a fat ******* like myself (300lbs/6.2') steps over the envelope, the caliper inside the box would remain intact, I tried to explain this and seller declined, but hey! its a free world and a free market, another one will appear, its just a matter of time...


Pablo