MSA and Gage R&R for Measuring Microscope

[abrnidgrl]

Hello,

I'm trying to perform a gauge R&R on a measuring microscope. I have 10 parts (which are my only available parts), and all are on the low side of the tolerance. Please see attached results. What I'm trying to figure out from the numbers is:
1) is the gauge acceptable to use for this measurement?
2) is the problem more related to operator issues?

Any help would be appreciated. Also, any thoughts on how to make a measuring microscope more repeatable would be great.

 

[bobdoering]

You are dealing with a difficult GR&R. First of all, chamfers can be tough because often under magnification the end in either a rounded corner or a series of tool marks (if really magnified). So, the operator has to choose an endpoint, generating some error.

Also, you may be picking up irrelevant part error if you do not look at exactly the same point on the part being measured for each part by each operator. This can be minimized by carefully marking the part and fixturing the part to measure the same location each time.

You do not have the full range of variation, which can skew your results.

The final questions are: What can you do to minimize the errors? Are there any other measuring systems that would be more accurate? How critical is the feature? If you can not get satisfactory variable data, would attribute be acceptable?

I will say this, I have seen vision system CMMs choke on chamfers for much the same reasons a measuring microscope would. They are tough little buggers for GR&R.

 

[Miner]

What will the microscope be used for, inspection or process control?

If inspection, it looks like the microscope is acceptable. If process control, how reflective are the parts of the actual process variation? The study appears unacceptable for pocess control, but might be misleading if the parts do not represent the process variation.

 

[abrnidgrl]

The microscope is only used for inspection. We do not manufacture the parts here. I realize that these parts were all within the low side of the tolerance, however these are the last 10 pieces we have in house and we wanted to perform a gauge R&R prior to a new supplier shipping parts in order to verify/correlate our measurements with theirs.

 

[bobdoering]

Good idea! If this is a particularly troublesome characteristic, it is often handy to do a lab-to-lab verification of the same set of parts to check measurement system comparison. We did that with a customer's air gage, only to find their gage had worn, and we did not duplicate their results with our newer gage.

You never know....

 

[Miner]

The microscope is only used for inspection. We do not manufacture the parts here. I realize that these parts were all within the low side of the tolerance, however these are the last 10 pieces we have in house and we wanted to perform a gauge R&R prior to a new supplier shipping parts in order to verify/correlate our measurements with theirs.

When you are assessing the suitability of the gauge for inspection, you will use P/T Ratio as the metric. The product variation is not part of the formula, so part selection is not critical.

Many people will recommend that you select parts from the full range of the tolerance, but this is not really necessary.