PhilFo 

This is true.
​​​​​​​
I got my Mitutoyo vernier caliper while on patrol in the city of Fallujah, Iraq two days after we began "the Push", and the day after my unit entered the city behind the Marines. I had just taken this photo of the most surreal scene I could think of.

The caliper was sitting on the ground, amidst a bunch of other metal junk, just outside the wall of Jolan Park. I picked it up, looked to see if it was straight, stuck them in my camera bag (I was a combat photographer with the Seabees) and went back to work.

mdarnton

I use calipers daily at work. Be warned that if you buy a cheap electronic caliper you might be replacing the battery every time you use it. I was getting about 30 days per battery on a $15 electronic caliper, which means a lot of people will be putting in a new one every time they take it out. Before that I had a Mitotoyo and the battery lasted forever, but it wasn't cheap and the plastic face got messed up just as easily as a cheap one (maybe they use gorilla glass now?--they should). I went back to a Mitotoyo plain vernier, though a GOOD dial caliper is always a temptation.

For brakes, the mentioned C-frame micrometer is probably the best tool. https://www.amazon.com/General-Tools.../dp/B00004T7UD

awac

I read somewhere that Mitotoyo have a patent on the battery system and that is why it lasts so long and others don’t.

mschwett 

so this definitely seems like the right tool for the job - very easy to position the point of measurement on any one section or the perforated / patterned rotor. also about $30 delivered.

assuming the thing isn’t total junk (doesn’t seem to be, although i have nothing of absolutely definitive thickness other than some valve feeler gauges) my rear rotor has a lot of variance, with many “spokes” at 1.60-1.65 but then a few at 1.48-1.51. can’t really imagine why that would be on a spinning disc, I guess wear subsequent to mild warping would thin out spots?

braking performance is still excellent, smooth, quiet, powerful, so I’m not going to replace them until the majority of the surface is at 1.50.

Keefusb

I have an old Swiss-made vernier scale caliper that was a hand-me-down from my dad that I have no idea where it came from. I also have a cheap $10 digital caliper from China that I believe came from Lidl. Between the two of them I should have the accuracy and convenience sides covered.

Sy Reene

For speed of use, the spring actuated ones seem would suffice
https://www.amazon.com/Neoteck-Digit.../dp/B07D1JCPWM

mpetry912 

somebody sent me this measurement one time. What's wrong with this picture?

/markp

ralphs

Judging by the condition of the inside jaws, a lot.

mschwett 

jaws? jaw? wut

Iride01 

They shouldn't be used to clamp a seat post! <grin>

Though if you have to do that I suppose it's better to mess up the outer part of the inside measuring jaws as are they.

mpetry912 

had prolly been used as a crescent wrench previously

/markp

mschwett 

any thoughts on whether a .1mm variation in thickness across the rotor (at the same distance from edge) is particularly unusual?

mpetry912 

as somebody said above, a disk rotor is best measured with a micrometer

the swept area of the rotor probably has a shoulder at the periphery of the wear area

so, hard to say

/markp

mschwett 

yes - as noted, the micrometer (pictured above!) made it pretty easy to zero in on a particular section of the braking track of the rotor. the variation is from one section to the next, e.g. on two sides of a perforation.

these are the rotors (when they were newer)

mpetry912 

so is there any pulsing or odd behavior under braking ? or noted in lever pressure ?

if your measurements are correct there should be !

if not I would not worry

/markp

mschwett 

nope, braking is smooth, quiet, reliable, powerful. easy to lock it up or not. i did feel some chattering yesterday on a 25% downgrade with very rough pavement, but i’m pretty sure that was the tire locking up super easily in a situation i’d normally avoid. i do a decent amount of very fast descending and the brakes are smooth and confidence inspiring.

maybe i’ll make a little video measuring, i suppose it’s possible i’m doing something wrong.

mschwett 

i think i can say that when used properly the tool is accurate. tried a few different feeler gauges and all within .001




the range on one quarter of the rotor seems to be about 1.42 to 1.57. i guess i do in fact need a new rotor. distressingly short life - 2400 miles!! the .15mm variance doesn’t seem to affect the actual braking.

boring video - which does illustrate how much the measurement varies if the 1/8” diameter (approx) flat head of the micrometer isn’t completely true and flush on both sides. the tool has a very soft clutch, so cranking it with the dial doesn’t exert enough force to square it up.

https://imgur.com/a/X2KJHNk

jccaclimber

The other name brand calipers all have similar battery life to the Mitutoyos. The cheap imports use cheaper batteries when new, and have substantially higher power consumption when turned off. There’s a write up online somewhere about what’s different in the circuit of the imports that makes it cheaper to produce but uses more power. The result is way shorter battery life. That’s actually the easiest way I’ve found to separate real digital Mitutoyo calipers from the massive number of fakes for sale.

sweeks

Why would anyone use the *inside* measuring jaws for an *outside* measurement?

Camilo

I just bought a couple of cheap ones at IIRC, Home Depot or Lowes, maybe eBay. Before that I had a Verneer, and an analog dial type. I think the dial type would work fine, if it were in mm, but it's in inches.

Both of my very cheap ones (I'm thinking <$25) work fine. I really wish the dial type was in mm because I think it's cool.

I also have a micrometer I inherited from my grandpa in the 80s, probably from the 40s or so. I have used it and enjoy every time I do. But never on a bike so far. I might use it when I measure my disc rotors to get past the edge and compare to what I get from the digital caliper.

Too bad. I've had my cheapos for many years and never changed a battery.

awac

You was a lucky person that it wasn’t attached to an IED, a very tempting thing to pick up. I don’t think many on this forum could have resisted either for what it is worth!

PhilFo 

Naa, it was in a heap which used to be an old handyman’s repair shop, from what I gathered. Not every shiny is booby trapped; they had other less savory tactics. There was a LOT of UXO there, which is one of the things we were taking care of. I have a photo somewhere of an uncapped RPG HEAT round not too far from my foot.
Anyway, the simple vernier calipers survived heavy urban combat, the trip home in 2005, and very frequent use ever since.

awac

You are right, not every one…….you should post a thread of some of your photos, make/find a thread link with “Are you a cyclist and ex-services” probably already exists, I have not looked. Interesting to know how much cycling helps with issues derived from service.

mschwett 

i replaced that rotor, and just for kicks weighed it compared to the new one. perhaps the weight isn't precise enough, or there is a few grams of variation in new rotors, but theoretically, on average, it should only be .14mm thinner than new, but was reading more like .25 with all available methods of measuring thickness!

drlogik 

I would go with a mechanical micrometer, preferably Mitutoyo or Starrett. One thing to know is that with digital calipers, even the good ones, the tolerance of those "could" exceed the variance on disc rotor thickness. That results in variable readings. With analog (mechanical) calipers you can typically get a closer reading because you can read in-between hashes.

The other thing to know is that the slight variance in the flatness of the rotor "may" give weird readings with a caliper versus a micrometer because the caliper reads across a long distance.

I'm not a machinist but I have another hobby that requires absolute precision with measurements (or bad things can happen) and there are two camps in that hobby as well: mechanical versus digital, for the reasons I stated above. The cool thing about digital, and I own two actually, is the quickness of the reading and the no "interpretation" of incremental (in-between) measurements on a mechanical tool make a digital much easier to use for the average joe. That's one of the reasons digitals are so popular. My wife uses my digital tools for her hobby and loves them.

If all you're going to do is measure bike rotors or other bike parts, a digital micrometer may be your best choice. If you plan to use it on other precision measuring, a mechanical micrometer would be the better choice, in my opinion.