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  1. #1
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    Default good quality micrometers +/- 0.0001" really and truly ?

    Hello,

    Was feeling pretty proud this afternoon - adjusting tailstock and slowly getting turning between centres to cut a cylinder instead of a taper.

    Got it down to 0.01mm taper over 150mm and feeling happy about nailing it tomorrow

    Prior to the tailstock work I had the two collar test on the chuck working as well as could be measured by a micrometer graduated in 0.01mm

    Tonight I saw an ad for a Mitutoyo micrometer that is +/- 0.0001" is that way down at approx micron accuracy ?

    Ive seen a few people talking about their Mitutoyos on this forum, Is that the sort of accuracy that serious hobbyists aim for ?

    Would you try to do a two collar test off the chuck and a turning between centres to +/- .00001"

    Bill

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    Quote Originally Posted by steamingbill View Post
    Hello,

    Was feeling pretty proud this afternoon - adjusting tailstock and slowly getting turning between centres to cut a cylinder instead of a taper.

    Got it down to 0.01mm taper over 150mm and feeling happy about nailing it tomorrow

    Prior to the tailstock work I had the two collar test on the chuck working as well as could be measured by a micrometer graduated in 0.01mm

    Tonight I saw an ad for a Mitutoyo micrometer that is +/- 0.0001" is that way down at approx micron accuracy ?

    Ive seen a few people talking about their Mitutoyos on this forum, Is that the sort of accuracy that serious hobbyists aim for ?

    Would you try to do a two collar test off the chuck and a turning between centres to +/- .00001"

    Bill
    I would be quite content with a thou "1/1000" over that length.
    Best Regards:
    Baron J.

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    Quote Originally Posted by steamingbill View Post
    Tonight I saw an ad for a Mitutoyo micrometer that is +/- 0.0001" is that way down at approx micron accuracy ?

    Ive seen a few people talking about their Mitutoyos on this forum, Is that the sort of accuracy that serious hobbyists aim for ?
    Most serious micrometer manufacturers make a unit that will measure to that level, and if you are buying second hand getting a micrometer that measures to tenth's is probably not that more expensive.

    For the majority of us it's not necessary but the ability to work to "tenth's" (2.5 micron) has long been prized as a measure of how skilled someone is as when you start achieving that sort of accuracy consistently you really need to know your stuff. Sadly on some forums that has been perverted by some to claim superiority over others and their methods/ opinions. Of course, there is a world of difference between being able to get to within a few tenth once and hitting that regularly.

    It's a target to aim for.

    Michael

  4. #4
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    > Tonight I saw an ad for a Mitutoyo micrometer that is +/- 0.0001" is that way down at approx micron accuracy ?

    0.0001" is 2.54 um (um also known as micrometer or micron)

    All reputable micrometer screw makers sell two classes of micrometers. The ones mostly used in a workshop have a graduation of 0.01mm (or 0.001" for the imperial version).

    Then there are those with 0.001mm (or 0.0001" for the imp version) resolution. These are subject to considerable reading errors if not used in a tightly temperature controlled room. You should not handle these with bare fingers because it warms the micrometer up... do not breathe onto it...... You commonly use these in a metrology room wearing gloves or in a micrometer stand. Sometimes you have to use these on a machine, but it takes some precautions. For example do not store close to a window where the sun can heat it up. Do not handle directly with fingers, use gloves or rags. Let the workpiece temperature settle before taking the reading. And be aware that used on a machine, the real reading accuracy of the micrometer needs to be degraded (unless your workshop is airconditioned and hospital clean - such workshops do exist in precision industry but not usually at home).



    > Ive seen a few people talking about their Mitutoyos on this forum, Is that the sort of accuracy that serious hobbyists aim for ?

    Mitutoyo is just one brand of many. They make a whole range of micrometers from cheap to midrange and expensive. You choose what you need, and you get what you pay for. Mitutoyo's are very popular because they usually cost less than other top brands. But beware, there are inferior copies around that are almost indistinguishable from the real thing.

    That said, hobbyists do not normally make parts to absolute accurate dimensions. Hobbyists FIT parts to each other, often to very highly accurate fits - but they do not care about the absolute dimension. Think of fitting the piston of a model engine to a cylinder. The task can be done with a good set of calipers, does not even need a micrometer. The end result is a fit to only few microns.
    In industry it would be different story, there they would make thousands of cylinders and pistons in a day, and it would be expected that each piston fits each cylinder so a customer can order a spare part years later and it will fit. Hence they cannot jut fit thing to match, they must work to absolute dimensions.



    > Would you try to do a two collar test off the chuck and a turning between centres to +/- .00001"

    you must mean 0.0001"?

    No, the two collar test is sensitive enough using a plain standard everydays use 0.01mm or 0.001" micrometer. Just pushing lightly with your small finger sideways onto the tailstock will cause a larger taper error than 0.01mm!!!

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    Default Thats good news !

    Thanks for the clarification. Am quite encouraged and relieved by your various comments.

    I will continue to rely upon the accuracy of the Tesa graduated at 0.01mm and not be too concerned about anything finer. Although some sort of estimating "between the lines" is possible.

    Given cba's explanation it sounds like a very fine 0.0001" instrument would be overkill and completely wasted in my shed.

    For a few hours I was thinking "Oh no ! Gotta do all this again with an more precise micrometer".

    I was concerned because that is the sort of accuracy Harold Hall often quotes in his books - although people have pointed out to me before on this forum that the figures in his books can be a bit too demanding sometimes i.e. in my current exercise he was quoting +/- 0.002mm on 150mm cylinder between centres.

    .............. and yes ............... have started "fitting" things together and just using the micrometer and caliper to tell me when I am getting close.

    Bill

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    Quote Originally Posted by steamingbill View Post
    ...I was concerned because that is the sort of accuracy Harold Hall often quotes in his books - although people have pointed out to me before on this forum that the figures in his books can be a bit too demanding sometimes i.e. in my current exercise he was quoting +/- 0.002mm on 150mm cylinder between centres...............
    Bill, is this maybe where Harold Hall explains how to make a "cylinder square"? (that is a precision square for milling, that can be home made in a lathe if one knows how to tweak lathe alignment). The idea would be, to measure both ends of the cylinder, and to "fine tweak" the adjuster screw that mounts the lathe to the base until the desired precision is achieved. For that one workpiece at that particular time that is.

    Personally, I do not think that a lathe can be adjusted to turn as low as 0.002mm (2um) taper over 150mm AND stay that way for any length of time. Not the sort of lathe used in home shops anyway. Maybe a small Schaublin bolted to a granite surface plate could. Chris

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    Hey Bill,

    I have a 0.001mm Tesa mic. An exquisite bit of gear. Allows me to measure my f... ups with high precision.

    Bob.

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    I'd agree Chris,
    In the last few days i have made a test bar so i can check the Mar's headstock alignment. One afternoon i had it within .0001" from one end to the other (250mm). The surface finish was a bit poor (for this purpose anyway) so i decided to skim it with a shear tool the next day. The result was the bar was .0003" out. This is on a lathe that weighs more than a ton. I have not been able to replicate that .0001", it is now .0002" out from end to end. The good thing is as long as i keep this in mind i can compensate for it when dialing in the head.

    The bar also took me a better part of a day to get that good-not something i would want to do every time i wanted to turn a part! I do use mics with the vernier markings to .0001" and .001mm but generally i just read between the main lines. It has also taken me about 8 years to get to this stage-i have made plenty of parts that are probably no better than +/- .1mm on the way!

    Cheers,
    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    Quote Originally Posted by cba_melbourne View Post
    Personally, I do not think that a lathe can be adjusted to turn as low as 0.002mm (2um) taper over 150mm AND stay that way for any length of time. Not the sort of lathe used in home shops anyway. Maybe a small Schaublin bolted to a granite surface plate could. Chris
    I would agree. I recently got my Colchester Chipmaster to turn parallel to 0.0002" over 6" machining an arbor between centres but I know full well that it won't *stay* at that point. Next time I need to work to that level I'll have to tweak the TS alignment again.

    This in a small work envelope machine with a 3 point base mounting and massing over 500 kg. IOW it is quite a heavy and stiff machine with a massive bed casting and designed so that there is no possibility of introducing twist from an uneven floor.

    PDW

  10. #10
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    Default extracts from book

    Quote Originally Posted by cba_melbourne View Post
    Bill, is this maybe where Harold Hall explains how to make a "cylinder square"? (that is a precision square for milling, that can be home made in a lathe if one knows how to tweak lathe alignment). The idea would be, to measure both ends of the cylinder, and to "fine tweak" the adjuster screw that mounts the lathe to the base until the desired precision is achieved. For that one workpiece at that particular time that is.

    Personally, I do not think that a lathe can be adjusted to turn as low as 0.002mm (2um) taper over 150mm AND stay that way for any length of time. Not the sort of lathe used in home shops anyway. Maybe a small Schaublin bolted to a granite surface plate could. Chris
    Chris,

    See attached extracts from relevant sections of book. It consists of a sequence of tasks to set up the lathe and make increasingly difficult items.

    He is recommending 0.002mm for the chuck test at 100mm length and also for the between centres test at 150mm length.

    He recommends doing the chuck test prior to making the cylinder square.

    Maybe I've misinterpreted whats been written ?

    Bill
    Attached Images Attached Images

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    Quote Originally Posted by steamingbill View Post
    Given cba's explanation it sounds like a very fine 0.0001" instrument would be overkill and completely wasted in my shed.
    Bill
    Hi Bill,

    Well, not wasted. I don't think Chris quite said that..

    The general rule is if you want to measure something accurately, you need an extra digit of precision more in the instrument doing the measurement.

    Then again most of us would routinely measure to micron resolution with DTI's, but that's a relative measurement... different story.

    Ray

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    Quote Originally Posted by steamingbill View Post
    Chris,

    See attached extracts from relevant sections of book. It consists of a sequence of tasks to set up the lathe and make increasingly difficult items.

    He is recommending 0.002mm for the chuck test at 100mm length and also for the between centres test at 150mm length.

    He recommends doing the chuck test prior to making the cylinder square.

    Maybe I've misinterpreted whats been written ?

    Bill
    Hi Bill,

    No, you are reading it correctly, but that sort of accuracy is pretty much the limit of what you can achieve, but you only fuss about tweaking things to do it for something like a cylindrical square.

    And don't forget this is still a relative measurement, still not absolute.

    Incidentally on a 24mm diameter cylindrical square, a temperature change of 3 degrees C will cause a 1 micron change in diameter.

    Ray

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    Hi Ray,

    This might sound a bit dumb but could you explain what you mean by relative vs absolute?

    Thanks,
    Joe

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    Quote Originally Posted by jmebgo View Post
    Hi Ray,

    This might sound a bit dumb but could you explain what you mean by relative vs absolute?

    Thanks,
    Joe
    Hi Joe,

    By relative measurement, I'm thinking of say, measuring run-out on a job in the lathe, not unusual to use a high resolution dial test indicator ( DTI ) and you spin the part measuring the deflection on the needle in microns or tenths, or whatever. So you are measuring to +-1 micron, but it's relative.

    Using a micrometer to measure the actual diameter of something, that's an absolute measurement, and very difficult to get +- 1 micron.

    Making a cylindrical square to +-0.002mm is a relative measurement, you don't really care what the actual diameter (in absolute terms) is, only that it's parallel.

    Hope that makes it clearer.

    Ray

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    Got it! Glad I asked, as I was thought you meant something completely different.

    Thanks,
    Joe

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