Small Hole Gauge Differences
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  1. #1
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    Default Small Hole Gauge Differences

    Why are most of the small hole gauges that I see this style, with a plunger and formed metal sides.



    Instead of this style with a plunger and steel balls? This seems like a more precise method to me.


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    Half ball allows measuring to the bottom of a blind hole.
    The top one is most likely less costly.

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    I hadn't seen one like the 2nd picture. Seem like it would be more accurate but with a smaller range. Probably more expensive to make also.

    Dave

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    The small diameter balls of the Moore and Wright are highly succeptable to surface roughness in the hole. They are also more succeptable to an individual's feel, more of an expert's gage.

    The half ball you show is easier to use, and the full ball are easier still. The relatively much larger contact area with the hole is much more forgiving as surface roughness increases.

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    Quote Originally Posted by gbent View Post
    The small diameter balls of the Moore and Wright are highly succeptable to surface roughness in the hole. They are also more succeptable to an individual's feel, more of an expert's gage.

    The half ball you show is easier to use, and the full ball are easier still. The relatively much larger contact area with the hole is much more forgiving as surface roughness increases.
    Well if the M & W's are an expert's gauge, I guess I better sell mine. I understand what you mean about hole roughness, it's very easy to tell the difference in hole smoothness with them. As for the range, I have a set of 7 that goes from 1/8" to 1/2", Starrett's get there with 4 gauges.

    I have never felt that I've gotten repeatable results from the half ball gauges.

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    I think a lot of it depends on what sort of measuring accuracy you are requiring... I have a set of the half ball ones from Mitutoyo... They work to my tolerances OK...

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    I have both the Starrett styles, the short half-ball No.830 and the longer full ball No.829.

    I find they're both about the same repeatability, but the full ball style does have a better feel in a bore. I often get a .0005" difference between the small hole gauge measurement and a measurement made with a small telescopic gauge.

    Neither is good for anything closer than .001" accuracy, IMO. For smaller holes I'd rather use pins, for larger I'd rather use a dial bore gauge or in mid-size (too big for pins, under 2" for dial bore gauge), I like the three-pin hole micrometers from Brown & Sharpe, Mitutoyo, Starrett or others. Unfortunately, those are still out of my budget for home shop use.

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    I want to VERY respectfully disagree with Gordon, on the desirability of direct reading inside gages. When I am doing such precise work as I do relating to OD's and ID's that must fit, I always prefer to use only one micrometer that tells me the dimension,and an adjustable gage for the other measurement.

    If I read the OD of my shaft with an outside mike, and the ID of my bore with an inside mike, unless the two instruments are correctly calibrated to a common standard, I may easily be in trouble.

    If I mike my shaft, and gage my bore, and then read my bore-gage with the same mike with which I measured the shaft OD, then however out-of-cal my mike may be, my parts will fit as well as my technique in manipulating my tools allows.

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    I personally like small hole gauges but I believe their usefulness is limited. Holes +/-.005 they are accurate but holes like that can also be measured with calipers satisfactorily considering they're most likely bolt holes or other non critical ids. When it comes to precision hole making for small holes if I'm boring I start with an intrimik but rule it good or not with pins. Bigger holes are bore gauge territory. I'd like to think the tolerance threshold for small hole gauges starts at +/-.001 but even that is a bit risky

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    I think one of the reasons a lot of people don't think split ball hole gauges are very accurate is they fail to realize how critical a sensitive "touch" is needed in setting and measuring them. The best way I've found to develop that touch is to practice measuring an assortment of hole gauges. If they're used infrequently, a short practice session does much to re-establish that touch. After a brief practice session in a quiet environment I find I can measure hole gauges using a good micrometer with no discernible error - within the limit of the micrometer.

    Of course, few of the holes that get measured are as well-formed as those of a hole gauge. This means that because split ball and telescoping hole gauges essentially measure diameters between two points, the quality of the hole has much to do with the precision (repeatability) of the measurements. But in my opinion, that's not the fault of the hole gauge. It's our fault for failing to recognize their limitations.

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    A set of four split-ball gages is a lot less expensive than the equivalent spread of gage pins, and they will fit in one of the shallow drawers of your Gerstner, but there's no debate with a pin. Pins conclusively demonstrate effective hole diameter as no other method will. If you're working for fun and you enjoy measuring things, by all means transfer measurements with mikes or use calipers and trust your feel. But if you have to make a living depending on the production of operators your shop better have pins.

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    Quote Originally Posted by Oldwrench View Post
    Pins conclusively demonstrate effective hole diameter as no other method will.
    Didn't mean to imply that hole gauges did a better job of measuring the effective diameter of a hole. Just wanted to comment on my personal assessment of their accuracy in measuring what they can measure - whether you like to measure things or not.


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