What is the best equipmenbt to gauge an ID bore; what gauge will give accurate Gage R & R studies as the best possible gauge? Is a Sunnen Gauge better than the CMM for ID's when there are problems with roundness?

Can you tell me where I can get a 3-point bore gauge and how much?
Thanks, Dawn

DAWN,
THE FOLLOWING ARE ONLY MY VIEW POINTS FROM MY PERSONAL EXPERIENCE.
1) THE CMM WILL PREFORM ROUNDNESS BETTER
2) THE SUNNEN GAUGE IS NOT AS GOOD AS A 3-POINT BORE GAUGE.
HOWEVER THE BORE GAUGE WILL SHOW YOU WHERE YOU ARE OUT OF ROUND. IF YOUR CMM DISPLAYS GRAPHICS ON MULTIPLE POINT FEATURES. IT WILL ALSO SHOW YOU WHERE YOU ARE OUT OF ROUND.
3) THE BORE GAUGE SHOULD GIVE A BETTER R&R BECAUSE YOU CAN CONTROL THE POINT OF MEASURE EASIER.

DAWN,
MOST ALL OF THE MAJOR MANUFACTURERS CARRY 3-POINT GAUGING. BEFORE YOU RUSH OUT AND BUY REQUEST INFORMATION FROM SEVERAL OF THEM. DEPENDING ON YOUR PROCESS THERE ARE DIFFERENT TYPES OF 3-POINT MEASURE. DO YOU HAVE A MANUAL OR CNC-CMM? IF IT IS CNC YOU CAN CONTROL WHERE YOU MEASURE AND COULD DO SOME SAMPLING BEFORE INVESTING IN A GAUGE THAT MAY NOT BE NESSARY. CHECK ALL YOUR OPTIONS AND PRICING CAN BE DONE THROUGH YOUR LOCAL INDUSTRIAL SUPPLY HOUSE.

Sunnen gages have 3 prongs and can measure tenths. Why would a bore gage be more accurate?

WHAT MODEL # SUNNEN ARE YOU USING?

What is the best equipment to gauge an ID bore;
The first reply question is what is the tolerance of the bore? Product can be over measured. Given enough tolerance, GO/NOGO plug gages may be sufficient.
what gauge will give accurate Gage R & R studies as the best possible gauge?
Again the tolerance of the bore plays a part in determining "best" for this application. A CMM should not be used to measure a counterbore for a cap screw.
Is a Sunnen Gauge better than the CMM for ID's when there are problems with roundness?
Remember that not all out of roundness problems are bilobal. Some are tirlobal and others are multilobal. More than one measurement tool may be needed to determine the lobality pattern of the product. Once established, a tool designed to detect that specific defect can be chosen.

Remember that not all out of roundness problems are bilobal. Some are tirlobal and others are multilobal. More than one measurement tool may be needed to determine the lobality pattern of the product. Once established, a tool designed to detect that specific defect can be chosen.Very good advice, and I'll add the fact that the best way to avoid roundness issues in bores is to fix the process. Often there's an easy fix, as roundness issues can usually be traced to fixturing and/or tool wear problems.

Several things to keep in mind when deciding the 'best' method of measuring an ID.

1) What is the tolerance of the feature?
2) What is the function of the feature?
3) What are you REALLY trying to determine (i.e. minimum diameter, maximum diameter, roundness, etc)
4) What does the customer need/want/expect?

I have used a variety of measuring equipment over the years, and find that anything that takes a discrete number of points (CMM, Shadowgraph, etc) will yield different results (sometimes significantly different) depending on which points you take, and how many. This is due to the software configuration for circle interpolation (least squares, best fit, etc)

A Sunnen gauge (and to lesser extent a bore micrometer) can be used to measure the entire diameter, and find the least diameter (but not always the greatest diameter, unless lobes are opposed by 120°). The Sunnen gauge has a further limitation of only checking to a very shallow depth.

The most common method that I use for verifiying diameter is a gauge pin. Most holes are designed to accept a mating component (bolt, shaft, etc) and you are generally interested in determining the minimum functional size of the hole.

Hope this is of some help.

Another possibility would be to use an air gage, these are paticularly usefull when you need to make many repeated measurements with a very high accuracy requirement . There is a good explination at www.edmundsgages.com

Agree with the above that a go/no go plug gauge is probably the best method of determining if a bore is acceptable or not, as it mimics the actual application of the bore, and measures the entire bore surface from front to back. A CMM or bore mic only measure points on the surface.

Agree with the above that a go/no go plug gauge is probably the best method of determining if a bore is acceptable or not, as it mimics the actual application of the bore, and measures the entire bore surface from front to back. A CMM or bore mic only measure points on the surface.

OK Gang. . . another opportunity to jog The Taz's memory bank of "Believe It Or Not" rediculous situations. . .

Once upon a time in a galaxy far far away. . . I was a VP of QA for a fastener manufacturer. . . in that capacity I had alot of practice explaining the many intricacies of fastener gaging to customers.

One of the special fasteners had a .062" diameter in the point end of it. Two gentlemen from a customer called and stated, "The hole measures .00205" undersize on our new $120,000 CMM."

I had one of the parts they had returned and went to my trusty Pin Gage Set and selected a .0620" +.0002" GO Pin and checked the part. It dropped in and I told the gentleman so. They then, in their infinite scientific wisdom, decided to get the (Lady) boss on the line to settle the dispute. They explained how they checked the parts with their new $120,000 CMM, and I explained how I checked the part with my $1.75 Pin Gage. She was very quiet for a moment. . . she then thanked me politely and requested that her two "scientists" join her in her office.

Simple wins! :agree1: :applause: