Dial Bore Gages Worth Buying?

[Harold_V]

Harold--

How do you use them properly? I saw a video about their use and have followed that method for some time: Stick the gage in the hole at an angle, snug the lock, push the gage past the point where the spindle of the gage is aligned with the axis of the hole and pull it out. Mic it.

I cannot claim to know if that is the correct method. How do you do it?

--Bill

Pretty much the same way, although I do NOT mic the telescoping gauge without going back in the hole, and that is the precise thing that many speak against. Their position in the matter is that you risk changing the reading. My position in the matter is that their thought is true and correct, but it also guarantees that your feel was on center (a proper reading). So then, once the gauge has been dragged past center, it is then reintroduced to the hole, then carefully moved side to side (seeking center) in the bore as it is dragged past center. If one achieves the same feel as was created with the original pass, the gauge measured the centerline. If one does not, the reading would have no value. For small diameter holes, this isn't much of an issue, as the gauge tends to seek center, but larger holes offer far greater chance for error.

If, after passing the gauge through the bore for a second time, you get the same feel, the gauge should then be measured with a micrometer, seeking center, once again, and achieving the same feel as the gauge passes through the micrometer. This technique will yield measurements that are reliable to .0002" or less.

I speak against the idea of taking several measurements, then taking an average. I'm not too interested in averaging a bunch of wrong measurements.

Harold

[Harold_V]

Do you guys prefer the style with two telescoping arms or the style with one fixed arm? Why?

My choice is, and has always been, two telescoping arms. If for no other reason, it keeps the handle near center, but I find they are far easier to use. In fact, I find the single variety difficult to use, especially for large bores. Also, pay attention to my admonition to have quality gauges. Price may or may not be a measure, so don't judge by cost alone. If the telescoping members don't move smoothly when the lock is snugged, or if the lock setting changes in use, you'll struggle endlessly trying to measure accurately.

Harold

[seal killer]

Harold--

How do you use them properly? I saw a video about their use and have followed that method for some time: Stick the gage in the hole at an angle, snug the lock, push the gage past the point where the spindle of the gage is aligned with the axis of the hole and pull it out. Mic it.

I cannot claim to know if that is the correct method. How do you do it?

--Bill

Pretty much the same way, although I do NOT mic the telescoping gauge without going back in the hole, and that is the precise thing that many speak against. Their position in the matter is that you risk changing the reading. My position in the matter is that their thought is true and correct, but it also guarantees that your feel was on center (a proper reading). So then, once the gauge has been dragged past center, it is then reintroduced to the hole, then carefully moved side to side (seeking center) in the bore as it is dragged past center. If one achieves the same feel as was created with the original pass, the gauge measured the centerline. If one does not, the reading would have no value. For small diameter holes, this isn't much of an issue, as the gauge tends to seek center, but larger holes offer far greater chance for error.

If, after passing the gauge through the bore for a second time, you get the same feel, the gauge should then be measured with a micrometer, seeking center, once again, and achieving the same feel as the gauge passes through the micrometer. This technique will yield measurements that are reliable to .0002" or less.

I speak against the idea of taking several measurements, then taking an average. I'm not too interested in averaging a bunch of wrong measurements.

Harold

Harold--

Thanks. I will add the second "feel" to my technique.

--Bill

[f350ca]

Harold, for some of us ham fisted fellows that don't do this every day and develop and maintain the feel of setting the telescopic gauges, wouldn't the bore gauge give the same results with the dial doing the feeling for us.
Why would sweeping the mic with a bore gauge not give good readings but the telescopic gauge would.

Greg

[DavidF]

Depends on the type of dial bore gauge, the ones I have you set with a micrometer.

Set to what? As I said, using anything less than a ring doesn't guarantee you've set the gauge properly. You will get consistent readings, but they may or may not represent true size. If you happen to hit the correct setting, it's more by chance than skill, and in many cases, that's a recipe for failure. All depends on how critical the dimension is. Using a micrometer is no exception, and I don't care how much experience you may think you have. This has been proven to more than my satisfaction by working in conjunction with a secondary standards lab. Highly skilled workers often missed a setting by a couple tenths or more. In their line of work, the error was greater than the tolerance.

Harold

Im not following you here. You state you will get consistent readings but they may not represent true size. I set my micrometer (verified with a standard) to the desired bore size. Then I set my dial bore gauge to read zero when it is swept thru the micrometer in which zero indicates the finished bore size. I have done this for slip fits, press fits, and clearanced holes and have never noticed a problem.
So why would teloscopic gauges be any better when you still have to measure them with a micrometer???

I agree. They are faster and better than telescoping gauges, especially for making comparative readings, such as checking a cylinder for roundness and taper, but the reading you see may or may not represent the size. Setting with a ring instead of gauge blocks or other methods tends to eliminate that problem. That's the only point I've been trying to make. Been there, done that, got the T shirt.

Never mind, I think I see where you are at. Although I would love to see just how much of a difference the setting rings make. Then again whos to say the setting rings are 100% accurate? Most of the time we are looking for either press fits or clearance fits so using the micrometer to measure the shaft or piston, then setting the bore gauge to read zero at this setting and boring the hole to how ever many thou over or under you need it for proper clearance could easily be registered on the bore gauge.
Im not against telescopic gauges, I use them too, but my first go to is the bore gauge for reasons that may only be apparent to myself.

[SteveHGraham]

If I had a dial device that would get me within two thousandths, I'd be the happiest man alive.

I did check into US-made gages. The cost was pretty insane. I seem to recall someone telling me I could buff the Chinese ones to make them work.

[tornitore45]

I seem to recall someone telling me I could buff the Chinese ones to make them work.

Tried that, did not work. There are several surfaces that rub together responsible for the feeling and smoothness.
The crux of the issue is that the locking piston is rigid. It works nearly as a vise, very little movement of the jaws equate to a huge change in the clamping force. The irregularities do not allow a smooth frictional movement.

In desperation I shortened the bar in the handle and inserted small stiff springs, the improvement was minimal.

I paid very little for them and chalked up the loss to education.

[Harold_V]

Harold, for some of us ham fisted fellows that don't do this every day and develop and maintain the feel of setting the telescopic gauges, wouldn't the bore gauge give the same results with the dial doing the feeling for us.
Why would sweeping the mic with a bore gauge not give good readings but the telescopic gauge would.

Greg

I didn't say a bore gauge wouldn't be different from a telescoping gauge. The same problem exists with either item, and that's why there's not much of a benefit to dial bore gauges (without setting rings), aside from rapid and easy use.

Please concentrate on what I said---that without rings to set them, they offer the same degree of error that one can get with telescoping gauges. That's especially true if one uses a micrometer to set them. The real danger is that once set, users tend to assume that the dial bore is correct, so the amount of error that is introduced becomes a constant. If you're working to tight tolerances, you may well target a scrap diameter, ensuring the everything that is machined has been targeted to be scrap.

Needless to say, if all you hope to glean from taking measurements is the amount of difference, a bore gauge beats a telescoping gauge, hands down, but without setting rings, they are no better----just faster.

Harold

[Harold_V]

Never mind, I think I see where you are at. Although I would love to see just how much of a difference the setting rings make.

More than you may think. What triggered my exploration was the time when I had to set a dial bore for a grinding job. There was no ring at my disposal (although the secondary standards lab had one). I set the dial bore with gauge blocks, but I had the lab verify my setting. I was off by more than .0002", which was greater than the tolerance of the job at hand. At this point in my life, I was more than capable of fine work, and had a wonderful work ethic. I gave the setting my best shot, it was not blindly set.

Then again whos to say the setting rings are 100% accurate?

Depends on your world, doesn't it? Mine, then, was one whereby I was working in a facility that manufactured missiles---and had a certified secondary standards lab. All gauges were certified to comply. That's all you can do---work against known (certified) standards.

Most of the time we are looking for either press fits or clearance fits so using the micrometer to measure the shaft or piston, then setting the bore gauge to read zero at this setting and boring the hole to how ever many thou over or under you need it for proper clearance could easily be registered on the bore gauge.

I understand, and I agree. The real point is that if you must work to a given dimension, setting the bore gauge by any means but a ring offers the risk of error. Once you've accepted the error as being correct, you now target all of your work to be scrap. The shop where there is little or no QC can get by this way indefinitely----I've not said it doesn't work---I only stated that there is risk of error when rings are not employed.

In regards to standards, my one negative experience was when I purchased my 1'-2" mic (Starret) back in '58. The standard provided was clearly marked as being 1", but it was .0002"off size. Needless to say, it was discarded.

Im not against telescopic gauges, I use them too, but my first go to is the bore gauge for reasons that may only be apparent to myself.

Nope--it's apparent to me, as well as most of the readers, I'm quite sure. Bore gauges are very nice (I own them, too), but they offer only speed as an advantage over telescoping gauges without having rings to make the settings.

In regards to telescoping gauges, I like to encourage readers to use them, as they are relatively inexpensive, yet offer quite precise measurements, assuming one learns to use them properly. The average home shop can't really justify the purchase of a wide range of bore gauges (unless the owner is Steve Graham, who is infinitely wealthy), which is why I make mention. Besides, the skills acquired in learning to use telescoping gauges properly will serve one for ever. It's like learning to grind proper lathe tools. A skill that is very useful.

No, I don't own rings. I wish I did.

Harold

[DavidF]

@ Harold, properly grinding lathe bits.....LOL. I won't touch that subject with a 100' pole. Some of my bits look more like discarded scrapnel LOL.

[Harold_V]

If I had a dial device that would get me within two thousandths, I'd be the happiest man alive.

Not if you had a need to make fits. If you can't measure to .0002" or less, your ability to create proper fits evaporates. That's why I constantly harp on NOT using calipers for fine work. Whether they display a size consistently, or not, isn't the issue. The issue is that the reading you assume to be correct often is not--so you target a reading that will be scrap.

I've commented on the subject of being able to measure properly some time in the past. Using a mic with tenths markings, those of us in the grinding department could measure within .000050" consistently, using a Sheffield Shadowgraph as a standard to verify our measurements. That, of course, wouldn't work well on a lathe, where surface finish wouldn't be as good---but you should still be able to measure within a tenth. Fits demand that you do.

So then, in order to achieve fits, you MUST be able to measure correctly, otherwise your target will be wrong, so you achieve your goal only by chance.

Harold

[Harold_V]

@ Harold, properly grinding lathe bits.....LOL. I won't touch that subject with a 100' pole. Some of my bits look more like discarded scrapnel LOL.

Spend more time, and learn to grind without a rest. Also, ensure that you're using the proper wheel. That makes a difference that is often lost on the individual, who thinks that what they have is adequate.

This I guarantee. If you use one of the gray wheels that come with the typical grinder, you will struggle.

Harold