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    You wouldn't'a thought that those "Rare Earth" magnets would have been quite as "rare" clear back then eh?


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    Ox

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    Quote Originally Posted by Ox View Post
    You wouldn't'a thought that those "Rare Earth" magnets would have been quite as "rare" clear back then eh?


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    Ox
    Didja ever try to find one of them when dropped into the chip pan ?

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    Well, I Shirley wouldn't expect it to be on the bottom!

    Maybe that's why they're so rare now?


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    Ox

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    Quote Originally Posted by Ox View Post
    Well, I Shirley wouldn't expect it to be on the bottom!

    Maybe that's why they're so rare now?


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    Ox
    Most of the times, they went right for the plate in my head.....

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    I Googled "accurately measuring large diameters" and the first one it came up with was this. I know nothing about it other than what I can read.

    ARCHIMEDE large diameter measuring instrument - AR

    I'm guessing it isn't "cheap" but have no idea what it costs. Apparently can measure diameters up to 6m / 236". Even looks "easy" to hold.

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    been my experience whatever gage type you get you need to check it or zero it to gage blocks. larger sizes of gages can vary quite a bit from temperature and measuring pressure. indicating gages are often used cause they can vary as you square up gage and or show taper or waviness 10x faster
    .
    also calibration can vary depending on gage orientation. that is if held vertical or horizontal. and also how gage is supported that is by one point or by holding ends. airy points or gage sag does become a factor with bigger gages
    .
    and obviously different metals expand at different rates. a part measured at 80F and at 60F can be quite different in size. literally some parts if measured at 10 different temperatures can give 10 different sizes. i often measure large part size changes 10 minutes after coolant touched one end of a large part the one end of the part can easily get smaller or bigger than the other end of the same large part

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    Quote Originally Posted by Gordon B. Clarke View Post
    I Googled "accurately measuring large diameters" and the first one it came up with was this. I know nothing about it other than what I can read.

    ARCHIMEDE large diameter measuring instrument - AR

    I'm guessing it isn't "cheap" but have no idea what it costs. Apparently can measure diameters up to 6m / 236". Even looks "easy" to hold.
    I didn't watch the video all the way through first time but I did second time. Still no idea what it costs but is made in Italy. Italy can make some good fast cars so why not that? Even surprised me it can also measure large internal diameters.

    Also wondered about accuracy and it gets shown here.
    https://www.microplan-group.com/images/pdf/ar.pdf

    It shows metric but I'll be surprised if it can't switch to inches.

    At the diameter Ox is dealing with accuracy is given as ±0.043mm = ±0.0017".

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    Yeah, I thought that it seemed to be REALLY accurate = for it's design.
    Still, not quite good enough for my normal work.


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    Ox

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    I'm in the Pi tape camp. Big range, they fit in a small
    drawer,Easily read to +-.001 similar to a vernier. A 38"
    mike is pretty hard to handle and a small bonk could knock
    it out of adjustment. A little practice may be needed to go around the part and pull it tight but they work well.
    spaeth

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    Quote Originally Posted by spaeth View Post
    I'm in the Pi tape camp. Big range, they fit in a small
    drawer,Easily read to +-.001 similar to a vernier. A 38"
    mike is pretty hard to handle and a small bonk could knock
    it out of adjustment. A little practice may be needed to go around the part and pull it tight but they work well.
    spaeth
    Maybe easy to read to ±0.001" but I'm not getting ±0.001 accuracy from "pull tight" and a 38" diameter.

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    Ox was saying +-.005 on a 38" OD. Pi tape new 36"-40" range price about 250.00. Anything else way more expensive. Plenty of choices for sure but for the buck the Pi tape will do the job. No issues with flex or temp either. Easy to check your reading by simply doing it several times and see what you get. Worst case another set of hands & eyes on the back side to get aligned.
    spaeth

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    Quote Originally Posted by spaeth View Post
    Ox was saying +-.005 on a 38" OD. Pi tape new 36"-40" range price about 250.00. Anything else way more expensive. Plenty of choices for sure but for the buck the Pi tape will do the job. No issues with flex or temp either. Easy to check your reading by simply doing it several times and see what you get. Worst case another set of hands & eyes on the back side to get aligned.
    spaeth
    I'm curious about this subject also. It looks like a different tape is needed for ID measurements vs OD? It seems that a PI tape is the way to go on large OD measurements, is that also the case for ID measurements say 36-72"?

    What is the best way to measure square parts over 60" in length up to at least 140"? +/-.005-.010"

    Various steel alloys in this size only, I'm aware of the thermal expansion issues.

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    I have never seen an ID Pi tape. Can you really measure IDs with a floppy tape that needs to be in compression? Won’t it just buckle? Pi tapes are good for measuring average OD, but you cannot pick up out-of-round. On the other hand, that’s exactly why they are good for soft plastic pipe, because it wants to go out of round from the squeeze of a micrometer.


    Sent from my iPhone using Tapatalk

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    Quote Originally Posted by rklopp View Post
    I have never seen an ID Pi tape. Can you really measure IDs with a floppy tape that needs to be in compression? Won’t it just buckle? Pi tapes are good for measuring average OD, but you cannot pick up out-of-round. On the other hand, that’s exactly why they are good for soft plastic pipe, because it wants to go out of round from the squeeze of a micrometer.


    Sent from my iPhone using Tapatalk
    well that was my first reaction, so i did a quick search:

    Inch 1095 spring steel inside inside diameter measuring Tapes from PI Tape Texas, LLC are delivered with a Calibration Report traceable to the National Institute of Standards and Technology.

    they have linear stuff also, but im not convinced this is the best way to go for either ID or linear applications.

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    For context, I have an rfq with prints for parts ~135" long with +/-.010" dimensions, holes and OAL...and although the customer is going to check them with a generic tape measure, I'm curious what the right way is to inspect them with "normal" hand tools.

    ID mics aren't a big deal, just curious if they are still the preferred method over roughly 40".

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    Quote Originally Posted by Hillside Fab View Post
    well that was my first reaction, so i did a quick search:

    Inch 1095 spring steel inside inside diameter measuring Tapes from PI Tape Texas, LLC are delivered with a Calibration Report traceable to the National Institute of Standards and Technology.

    they have linear stuff also, but im not convinced this is the best way to go for either ID or linear applications.

    I think I'd haft'a see that go down once first....


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    Ox

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    Quote Originally Posted by Ox View Post
    I think I'd haft'a see that go down once first....


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    Ox
    I dont think it's pure snake oil. You can put decent pressure on a band inside a tube without buckling occurring. However, I would expect ID mics are the preferred method. I really dont know over 4 ft.

    I've never worked in a shop with oversized parts, and while the machines are pretty easy to figure out, the inspection for big stuff isnt very documented.

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    We have mic's up to 1200mm in the style in the first link. thermal expansion from handling is a big problem, i scrapped a part because i wasn't aware of it at the start. I would recommend using gloves, and only holding it by the plastic handles. they are also a lot easier to use with 2 people, one (usually the apprentice) holds the mic up and steady at the bottom, this leaves the operator to find the high spot.

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    Quote Originally Posted by snapatap View Post
    We have mic's up to 1200mm in the style in the first link. thermal expansion from handling is a big problem, i scrapped a part because i wasn't aware of it at the start. I would recommend using gloves, and only holding it by the plastic handles. they are also a lot easier to use with 2 people, one (usually the apprentice) holds the mic up and steady at the bottom, this leaves the operator to find the high spot.
    .
    i always have gage block or ring gage setup that was kept in cnc at same temperature as part preferable within 1 degree F and the mic is used to measure the gage block or ring gage to determine mic calibration error and compensate for it. extremely common for .0005" changes cause of slight temperature changes. and its possible for coolant touching only one end of a large part for that end to get .0005" bigger or smaller compared to dry end of a large part
    .
    large (10" to 30" dia) aluminum bodied boring bars are famous for changing size within minutes of coolant contact compared to a steel or cast iron part

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    Quote Originally Posted by Hillside Fab View Post
    I'm curious about this subject also. It looks like a different tape is needed for ID measurements vs OD? It seems that a PI tape is the way to go on large OD measurements, is that also the case for ID measurements say 36-72"?

    What is the best way to measure square parts over 60" in length up to at least 140"? +/-.005-.010"

    Various steel alloys in this size only, I'm aware of the thermal expansion issues.
    .
    Tram gages either mic or indicator type have been used to measure inside to inside or outside to outside dimensions compared to reference rod or gage block or ring gage for hundreds of years. originally used to set railroad tracks parallel. and printing press rollers parallel. the base is often wide enough to assist in squaring it
    .
    the swivel connecting type can be a curve that is go around a roller in between 2 other rollers. hard to describe. been used by millwrights for centuries although early ones just used a fine threaded screw instead of a micrometer or indicator
    .
    yes thats a trammel point end for fine adjustment on the one end. trammel points were adapted for Tram gages for centuries. obviously if 5 foot long repeatability is not less than .001"
    .
    most millwrights have made a few Tram gages. i have made dozen of varies types all different sizes. Telecoping type is often adapted from a snow brush. that is a tripod leg or something else using telescoping tubing that locks to different lengths. i have also adapted pipe tubing compression fittings to not stay permanently crimped on tubing when unlocked. most experienced millwrights can go to any hardware store in any city in the world and in 10 minutes adapt something to have a Tram gage
    Attached Thumbnails Attached Thumbnails tramindicator.jpg  

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