How Do You Measure Your Holes?

The only way to measure a bore accurately is with a Bowers Bore gauge.

Really, and what do you base that pearl of wisdom on?

Tony

I know in the British motorcycle industry pneumatic gauges were used to measure the bore of a cylinder. I can guess how they worked but would not like to put my guess into print without a lot of thought.

JA

I made myself some tapered parallels in various sizes to the same angle with a rounded edge on the straight side and use them in pairs in the bore and measure the projected end of the parallels with a mike.I have found them invaluable for measuring deep bores and for finding how much taper there is in the bore which you can then rectify.For small holes I use all of the previous methods posted.

Frank

Do all the Hondas and Toyotas of this world use Bowers Bore gauges? Perhaps they should be told.

Edited By vintagengineer on 17/12/2016 00:15:29

Bowers Bore gauges are very accurate, but like others have said a mass prod manufacturer would more than likely use a CMM. There is no guarantee that they would use a Mitutoyo though, there are many other makes including the worlds most accurate CMM's made by Zeiss.

For most holes I use vernier calipers but I have a set of Coventry Guage and tool company Matrix bore gauges which range in bore size from 1/2" up to 8" diameter.

I believe they are ex RAE (Royal Aircraft Establishment). Unfortunately I am not sure of the correct procedure for use, Maybe someone can educate me.

As far as I can tell they are capable of measuring to an accuracy of .0002" and work by exchanging various tapered inserts that act upon three legs that expand to to measure the bore within a very small range of about .025" There are 10 of these taper inserts to each size of measuring tool. They are fiddly to set up but again I only use them as a comparator rather than an exact diameter measuring device because I am not sure if my method of use is correct.

They are beautifully made and are in wooden cases complete with the specialist pliers, spanners and setting rings.

.

Sorry to have to say this to a new-ish member, but, with statements like "The only way to measure a bore accurately is with a Bowers Bore gauge."

... from here it's you that comes across as the 'smart Alec'

MichaelG.

Edited By Michael Gilligan on 17/12/2016 09:27:23

I have a couple of bore micrometers bought cheaply. One is a bit duff and would like one other size so periodically look around on ebay.

I couldn't resist buying a dti type bore gauge when arceuro started selling them. They are sort of 3 point but the 2 pointed end is rather narrow really. I believe it's possible to set these up with a micrometer and keep intending to make a jig to do that. Set carefully on a ring gauge these can be pretty accurate. The ring gauges in sufficient size ranges are probably rather expensive.

I do use telescopic guages at times. During training I found that these need to be a pretty tight fit across the true diameter to get accurate readings. Some care is needed measuring them with a mic.

One day when something suitable is being made I will try measuring OD and the wall thickness with a mic. Some mic's come with a ball end attachment. Some mic's are made for the job. Those can be pretty cheap as there isn't much call for them.

John

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Edited By Ajohnw on 17/12/2016 14:03:00

With a Bowers bore gauge you get a true and accurate reading, if you over tighten the gauge it won't come out of the hole and they are accurate to .0001". Also less skilled operators will find them easier to use than an inside mic, telescopic gauges or calipers, as these all rely on a degree of skill to take accurate readings,

The only other tool that gives the same result is CNC CMM.

Edited By vintagengineer on 17/12/2016 15:00:21

What people really need is one of these. Lots of decimal places and easy to use.

**LINK**

John

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I'd best order a couple then, I'm bound to lose one.

A useful but brief synopsis of methods published some while ago on David Carpenter's website:-

**LINK**

Not exactly true.

I have run a precision engineering shop ( 35 yrs ) manufacturing precision plain and white metal lined bearings where measuring bores is critical. Bowers, Tesa and Mititoyo 3 point internal gauges are in fact still used used on the smaller ranges of bearing bores. They are easy to use for operators and consistantly give accurate results to some extent. However they have their drawbacks. The main one in that they take no account of the holes roundness. We do in fact have operators who can measure bores equally as well using inside micrometers that are then verified over with an outside micrometer. This is down to operator skill levels and experience though.

Given roundness issues, it means measuring has to be further verified by a precision CMM, which is also demanded by those customers that will not accept 2 or 3 point micrometer results.

The issue with all micrometers is that 2 and 3 point measurement will never be as accurate as as a good precision CMM such as the Zeis models for the reason highlighted. The CMM will give a very accurate plot of the hole, its roundness, its cylindricity, taper, its best fit minimum, maximum and mean diameters. A Bowers or similar just cannot do this.

Micrometers ( 2 or 3 point ) do not in fact have guaranteed uncertainty of measurent figures that go down to 0.0001" as there are in fact too many variables in the tool itself, the process of using and interpretating it to achieve the end result required.

The Bowers type micrometers are far too expensive and each has a limited range such that will normally take them well out of the scope of the home engineer. Good results of bore/hole measurement can be achieved by using standard inside micrometers and cross verifying over with an external micrometer, you just need to practise getting the feel right and consistant.

For the home engineer, smaller holes a good pair of toolmakers inside calipers with micrometer over can get you pretty close to final sizing, again with practise on the feel. Telescopic bore gauges can give similar. Final sizing usually done with pins, be it drill shanks, drill blanks, precision dowels, silver steel, homemade plug gauge etc.

Edited By MalcB on 17/12/2016 17:37:57

Thank you MalcB ... That carries an air of authority

MichaelG.

Exactly, a three point measurement will give a 'precise' result on the inside of an equilateral triangle, although it is anything but round.

Andrew

And if not careful you will see a few of those after releasing a bearing that has been finish bored in a 3 jaw chuck.