Digital caliper

[fyrstormer]

I have a steel digital caliper I bought for $30 from Garrett Wade. It has a ruler on the side, and the LCD will display decimal inches, fractional inches, and metric units down to 0.01mm. It consistently measures the same thickness for the same sheet of paper, and different thicknesses for different sheets. It's super useful; I'd definitely buy it again.

EDIT: Specifically relating to the original post, I have used the caliper I mentioned in several projects involving my old Pro-Flex bike and my new Christini AWD bike. The caliper came in especially handy when buying an entire new set of (titanium!) bolts for the Pro-Flex.

ANOTHER EDIT: Link for the lazy. http://www.garrettwade.com/combination-fractional-display-digital-calipers/p/96T01.06/

 

[will]

I'd bet that 99% of the work out there is +- .001 or more. Heck, I'd bet a lot of work has .005 or more...

From what I remember - A lot of 'square' dimensions were + or - .005.

diameters would tend be be a closer tolerance - fitted into bearing and the like. Screw holes would tend to be -.000 but plus .005.

Of course - it would depend on the use of the object being machined.

 

[precisionworks]

I'd bet that 99% of the work out there is +- .001 or more.

Why are you never close by when I need money? I'll bet a fist full of Franklin's that the number is far less than 99%. How about it

Things that slide by each other are most often called out in tenths of thousandths - the wrist pin bore in an automotive piston is a good example. The pin does not want to even start in the bore unless it is 90.000° to the bore axis ... although it might start at 89.999° more or less. Bores on the racing engines around here are honed with a $100k Sunnen automatic honing machine & that machine can easily split a tenth of a thousandth into ten more parts.

Press fits are similar. Small bores (electric motor bearings 500hp & smaller) have the smallest allowable tolerance band you can imagine, often plus & minus three or four tenths.

Pins can be close call out or very wide call out. I've made dozens of small pins roughly 2"x12" & the call out was +0.000" & -0.062" (plus nothing & minus 1/16"). Probably would have been customer accepted at minus 1/8" & worked just as well. Not my call so we made the part to print.

It all depends on how good the fit needs to be or how bad the fit can be & still work. Look at some less costly titanium flashlights - external thread is +0.00mm & -0.20mm, internal thread is -0.00mm and + 0.20mm. Best case is that the head screws nicely onto the body, worst case is that the head screws on & doesn't fall off, either one meets the generous QC standards established by the maker.

If I had to guess the number might be 75% non critical, 15% somewhat critical, 8% pretty darned close & 2% so close that it's scary. All bets are off in third world & developing economies.

 

[will]

The shop I worked at was a small prototype shop. We had one job I will never forget. It was for Brookhaven National Lab. It was for a roller screw, think something like a automotive steering box. The screw part had very large rounded threads and was 10 inches long. We had to cut a diameter on each end that was within .0001 concentric to the bottom of the rounded screw thread. I have no idea how this worked or what it was going to be used for. They supplied the screw. If I remember correctly, we spent the better part of the day setting this up.

We also make component parts for the Grumman Lunar Excursion Module (LEM) These were mostly brackets and for the most part had tolerances of + or - .005, if you will - square tolerances, maybe a couple of screw holes, locations within + or - .005.

I was in my youth at that time and learned a lot from the shop forman. He still had all his fingers and I thought he was best to learn from...

 

[OCD]

My dad was a machinist for about 18 or 20 years, with about half that working for a shop that was a sub-contractor of (at the time) McDonald Douglas. I never got to see any of his prints or really knew what his typical tolerances were, but I can tell you his tool box has 2 sets of calipers...a set of 0-6" dial Mito's and a set of 0-10" dial Fowlers. He doesn't have any vernier calipers. The rest of his measuring tools consist of all mics....all shape, all sizes, just no digitals.

Most of the parts he made went into F-18's and F-15's. On a tour of McDonald Douglas his shop got to take their family's on in the late 80's, we stopped and he pointed out some parts on a table and said his shop made those. As he leaned closer and looked at the inspection stamp on them, he said "...Actually, I made those". As a kid that was just awesome!

Another similar instance was at an airshow back when you could literally walk up and touch and airplanes, we were looking at the front landing gear of an F-15 and he pointed out a part he routinely made and said there was a good chance he made that particular one. Makes a kid free real proud!

Sorry to get O.T.....I was lucky enough that my dad passed along to me his 0-6" dial Mito's he used at home once he retired as a machinist and brought his tools home along with a nice vintage 0-2" Brown & Sharpe micrometer and a vintage 0-4" Brown & Sharpe depth mic that he never used....and I don't even own a drill press, much less any machining tools....yet!

 

[precisionworks]

Cool story, thanks for sharing

... his tool box has 2 sets of calipers...a set of 0-6" dial Mito's and a set of 0-10" dial Fowlers. He doesn't have any vernier calipers. The rest of his measuring tools consist of all mics....all shape, all sizes, just no digitals.

I worked in one factory where the machine shop foreman hated all things digital. He put up with the two axis DRO on the Bridgeport & the three axis DRO's on the boring mills but that was the extent of his participation in "modern" technology. The first mistake I made there was pulling out a 9" Mitu Absolute for a critical bore job. Just as the jaws were touching the bore he walked over & asked WTF was going on. Tried to explain (in my best rookie voice) but he was hearing none of that. He handed me a well used Brown & Sharpe heavy frame master vernier caliper & a 5X magnifier glass. Last thing he muttered when walking away was "Don't f*** up this bore or you'll be sweeping floors instead of running machines". He certainly had a way with words.

Bought my own heavy frame master vernier, a Starrett 123-12. Added a Mitu copy 18" long. Both were eBay items that sold for not much more than a Happy Meal at McDonalds. Still have both, still use them.

Took the 9" Mitu Absolute home that day & it never went back to that shop :nana:

 

[350xfire]

lol! I am taking a machine shop class at the local comm college and the instructor is an old tool and die maker. We have 5-14" machines and 5-pretty nice mills. They are all Taiwanese units equipped with DROs. He pretty much told us he didn't trust the DROs and we should use vernier calipers...

 

[KC2IXE]

Why are you never close by when I need money? I'll bet a fist full of Franklin's that the number is far less than 99%. How about it

...snip...

Maybe the work you and I do - but remember, I was thinking by the part count. How many millions of PC board standoffs, candlesticks, drawer pulls etc are done for every wrist pin out there? Seriously, there are things you have to laugh at - for instance, I think I saw that 75% of all work is 1/2 diameter or less (which is why the old 3C/3AT etc collet sizes were popular - along with all the screw machines that took some sort of small collets) and something like 95% of all work fits through a 5C collet.

There are a LOT of parts made by the mile, cut off by the yard

 

[KC2IXE]

Will - RE BNL and the LEM - I know/knew people at both places, and I see you are in NY - still on the Island? Love to get together (I'm in Queens)

 

[will]

Will - RE BNL and the LEM - I know/knew people at both places, and I see you are in NY - still on the Island? Love to get together (I'm in Queens)

I was a mere child at the time, right before I went into the Navy on active duty. I did not know anyone at either BNL or Grumman. The owner of the shop had the contacts with the purchasing departments there.

I spend my time between NY and Florida, getting ready to head back to Florida soon.