Digital Calipers

[Walter Deitzler]

After looking around CD, it seems that digital calipers are important and useful for CAD. My team is getting a pair, but we want to know which brand is the best (most accurate, reliability, etc.) so that we can make a good purchase.

Thanks!

[MrForbes]

Starrett.

But you'll probably buy something else....

[Tristan Lall]

Could also be Mitutoyo.

But just buy two cheap ones for the price of one Mitutoyo or Starrett. You'll get 99.9% of the accuracy, 85% of the build quality and > 150% of the utility. (In fact, if you find a sale on digital calipers, they can be cheaper still, down to $15 each.)

[msimon785]

I sincerely suggest you back away from digital calipers. Your money would be much better invested in a pair of Starett, Mitutoyo or Brown & Sharpe dial calipers.
I find dial calipers provide both more accuracy and reliability. Digital calipers often have calibration problems.

[MrForbes]

Or if you want to really do it right, use vernier calipers, they last longer around students who are still learning to take care of tools. And they give good practice in your math skilz

[DonRotolo]

Yeah, digital calipers leave much to be desired. Using a good vernier caliper is a skill that will help you elsewhere in life. Plus they are more accurate (if not more precise) for a lot less money. My daily caliper is a mitutoyo dial caliper good to a thousandth, but I have a micrometer that direct-reads to a ten-thousandth and verniers to a hundredth. Only useful in a temperature-controlled environment, though.

That being said, you do know that the idea of CAD is to design the parts and make them work in software, then build them, right?

[Tristan Lall]

The value proposition for dial calipers isn't fantastic, because they're more susceptible to miscalibration and damage than digital or vernier models.

With a vernier, there's nothing to adjust; hopefully it's correct (you get good precision, but no control over accuracy). With a digital, if you screw up by touching the zero button, it's usually obvious that you need to recalibrate it (except with very thin features). However, you do need to be careful about where your zero is in the first place. But with dial calipers, if the dial shifts by half a degree, will you notice? (Note that this is independent of feature size.) You still have to be careful about your zero.

Besides, if you drop them, the dial sticks out and is relatively easy to break on a set of dial calipers. The LCDs on digital calipers don't like direct application of force, but are usually recessed and reasonably durable. Also, the racks and pinions inside of dial calipers are not particularly tolerant of grime (such as abrasive dust from grinding stones). This can lead to backlash problems, which make switching from inside to outside measurements a bit unintuitive. Vernier and digital calipers aren't immune, but their sliding ways are inherently smooth, and there's no backlash.

The nice thing about dial calipers is that you get a readout in thousandths of an inch, with some idea of ten-thousandths due to the position of the needle between the gradations. Of course, those ten-thousandths are pretty much meaningless unless you've got a top-quality instrument under controlled conditions. (In other words, not relevant to the typical FRC application.)

Ordinary digital calipers enforce the inherent uncertainty of the measurement by refusing to allow you to believe in any measurement more granular than 5 ten-thousandths of an inch. That could be good or bad depending on your perspective, but it's probably moot either way, for the same reasons that dial calipers aren't much use past thousandths.

In any event, if you do need ten-thousandths of an inch, a micrometer (and perhaps a set of expanding gauges) makes more sense, because of its inherent rigidity and (typically) finer scale.

Originally Posted by DonRotolo

Using a good vernier caliper is a skill that will help you elsewhere in life.

Other than facility with mental addition, what skill, useful elsewhere in life, do you learn by using vernier calipers, that you wouldn't also learn using dial or digital calipers?

Originally Posted by squirrel

And they give good practice in your math skilz

Doesn't that imply that if their math skills aren't up to par, they're more likely to introduce error into the measurement? (Not a problem with digital calipers.) In this regard, there's probably a (weak) correlation between good mental math skills, and a higher rate of parts that don't fit.

[MrForbes]

Tristan, I think Don and I both understand that the odds of a team buying and regularly using vernier calipers is pretty darn slim....

Lately I've been using a cheap imported 6" dial caliper for general measuring. Either a dial or digital caliper will suffice for most of what an FRC team needs to measure.

On the cost/quality decision...there's a lot to it. You can buy several of the low cost calipers, for the price of one very high quality caliper. How many does your team need? how good is your team at taking care of delicate instruments? Are you planning to make stuff that needs very high precision?

[Cory]

Unless you are using CNC machine tools or otherwise working on high precision non-FRC projects Starrett, Mitutoyo, Brown and Sharpe, etc are a complete waste of money. Buy a cheapo set of digital calipers. Amazon currently has them on sale for $15 a pair. Buy 4 or 5.

Your kids are likely to abuse them anyways and drop them, get oil on them, use them to scribe lines, etc. Don't waste $150+ on name brand calipers that will get abused.

I prefer dial calipers to digital and I love all Brown and Sharpe measuring tools. We have a mixture of B&S, Mitutoyo, and Starrett calipers and inside/outside/depth micrometers we use for high precision work on the CNC. We have a variety of SPI and Fowler calipers and micrometers for oddball sizes we don't use often and less precise work. For infrequent use we don't notice any difference. The only real difference is that 25 years from now the cheap Chinese tools will be in the trash and the high quality tool will still be going strong if properly cared for.

The more people who will be using them the cheaper calipers I'd get. It's too easy for someone to destroy an expensive tool in seconds to make it worth spending a bunch on general use measuring tools.

[sanddrag]

Agreed on all points Cory said. I have a cheap import 6" digital that is actually my primary caliper. I got it about 5 years ago for less than $20 and other than batteries once or twice a year it's still doing great. But, I take care of it. I've purchased other import digital calipers more recently from Harbor Freight and I don't like the feel of how they slide, and I had a couple that were about a thousandth off on measuring half an inch. But, honestly you'll probably be just fine with any other sort of cheap import digital caliper, from VXB or Little Machine Shop or Amazon or wherever.

For quality, I too like Brown and Sharpe. Very very smooth and accurate, but expensive. Too easy for students to ruin expensive tools like that.

There are instances where a dial caliper is preferred, such as measuring to see if something is out of round, because the cheap digitals lack on display update speed. However, the digitals are easier to read.

I'd stay away from vernier calipers. Talk about an instant drop in work efficiency. I used them once and never again. I had a professor with a PhD that couldn't figure out the darn things.

[DonRotolo]

Originally Posted by Tristan Lall

Other than facility with mental addition, what skill, useful elsewhere in life, do you learn by using vernier calipers, that you wouldn't also learn using dial or digital calipers?

How to read a vernier scale, perhaps? Also see below.

Originally Posted by Cory

Buy a cheapo set of digital calipers. Amazon currently has them on sale for $15 a pair. Buy 4 or 5.

I guess for everyday team use it's not a bad thought.

Originally Posted by sanddrag

I'd stay away from vernier calipers. Talk about an instant drop in work efficiency. I used them once and never again. I had a professor with a PhD that couldn't figure out the darn things.

I guess it depends on what the PhD was in. But a vernier scale is a useful construct in the linear measurement world, as is the idea of indirect-reading scales.

No Tristan, it's not a huge life lesson, but just another bit of knowledge that could help some day. The difference between education and experience. And, if you get a PhD, you won't embarrass yourself by admitting you can't figure out a vernier scale.

[MrForbes]

A couple of my Starrett micrometers have a vernier scale to read tenths...it's really not that difficult to figure it out. Fortunately, technology has made cleverness obsolete.

[Ether]

Your kids are likely to abuse them anyways and drop them, get oil on them, use them to scribe lines...

... use them as clamps.

[EricH]

Originally Posted by Cory

Your kids are likely to abuse them anyways and drop them, get oil on them, use them to scribe lines, etc.

Actually, the bolded portion is one purpose of a set of calipers. You're just supposed to use that function with Dykem on the part, though--the calipers scratch that away easily.

I use dial calipers myself--that's what I have. They don't need batteries to run.

[Tristan Lall]

Originally Posted by DonRotolo

How to read a vernier scale, perhaps?
...
The difference between education and experience. And, if you get a PhD, you won't embarrass yourself by admitting you can't figure out a vernier scale.

Fair enough, I guess...it just doesn't seem like a skill that would be much help to learn now, rather than on Wikipedia, 5 minutes before you need it.