Using Calibrated OD mic over non-Calibrated ID mic for final dimension

[Michael_M]

[Michael M] - I don't understand your statement. No matter how you approach it, you ARE using the inside micrometer as the actual measurement device. You're just choosing to obtain your readout from another separate device.

You are correct. I never trusted an inside micrometer for the reading itself. The more I thought about this (after posting), the more I think I used the OD micrometer because we did not have anything to qualify an inside micrometer properly. I think I would still use the OD micrometer to check the actual diameter but fortunately, I don't check parts that are that big anymore.

However the (accurate?) measurement is obtained, unless there is a reason to restrict the measurement method (PO clause, quality issue, etc.) I don't see any reason to force a change.

 

[BradM]

So I understand....

They are manufacturing a product for you, where they are creating a hole in something. They are using device A to measure the inside diameter of that hole. Let's say they measure 1.0 inch

They then take device B to measure device A in the same position where it measured device A. Device B then yields 1.0 inch. They then accept the values given by device B for product acceptance.

If that is accurate,

1. That seems like an odd way to go from point A to point B. I don't understand why they have such a convoluted process.
2. More importantly, have they done any kind of gauge analysis/ uncertainty estimation of how good this process is? It sounds to me like there is quite a bit of error in that. Have they had a lot of failures?
3. Umm... last time I checked, you're the customer. I find it sad customer service on their part that they don't at least listen to the customer better and possibly see if there is a better way of doing their measurements.

They have the responsibility to not only assure their processes are "compliant" but more importantly, that they are satisfying the customer. I know that sounds hokey; but to me, is important. They need to win your confidence that they are producing quality product for you. If they want your long term business, they need to go the extra mile for that. Otherwise, it's worth your time and effort to search for other potential vendors, IMO.

 

[Eredhel]

It also sounds like they are sending all their tools out to be calibrated. I wonder if you could suggest they send out standards and then calibrate in house.

 

[Scott.Hilton]

Using an inside micrometer and then transferring it to an OD micrometer is the typical practice I followed for years (when I made parts big enough to use an ID micrometer). I never trusted the inside micrometer enough to use it as the actual measurement device. On a hole size with a tolerance of .003-.005 (total tolerance I assume not +/- .003-.005) I would be willing to accept the transfer. I might tighten up the tolerance a bit (and if I was performing the measurement I would tighten up).

Are you having quality issues with the supplier? Do you have any specific purchase order clauses that restrict this type of measurement? If no to these questions, I would not pursue it. If yes to these question then you have someplace to start.

-we are having some issues with the supplier and some of them even involve ID's. However, I am "politically" stuck now on it. We don't have clauses that restrict the usage.

 

[Scott.Hilton]

So I understand....

They are manufacturing a product for you, where they are creating a hole in something. They are using device A to measure the inside diameter of that hole. Let's say they measure 1.0 inch

They then take device B to measure device A in the same position where it measured device A. Device B then yields 1.0 inch. They then accept the values given by device B for product acceptance.

If that is accurate,

1. That seems like an odd way to go from point A to point B. I don't understand why they have such a convoluted process.
2. More importantly, have they done any kind of gauge analysis/ uncertainty estimation of how good this process is? It sounds to me like there is quite a bit of error in that. Have they had a lot of failures?
3. Umm... last time I checked, you're the customer. I find it sad customer service on their part that they don't at least listen to the customer better and possibly see if there is a better way of doing their measurements.

They have the responsibility to not only assure their processes are "compliant" but more importantly, that they are satisfying the customer. I know that sounds hokey; but to me, is important. They need to win your confidence that they are producing quality product for you. If they want your long term business, they need to go the extra mile for that. Otherwise, it's worth your time and effort to search for other potential vendors, IMO.

You pretty much stated exactly all the thoughts that went through my head. I would love to request a Gage R&R.............but it is now out of my hands.

 

[iamtroll]

We use transfer gaging for all dimensions over 4" on a routine basis since our Mitutoyo borematics only go up to 4" max. So we are very comfortable using a micrometer to set up our bore gages for over 4". The borematics are three point contact so you can't use them to transfer to a micrometer. But if we had two point gages that we were not confident in the indicators, we would probably consider using them as transfer gages rather than buy new ones at least in the short to medium term (maybe even long term). I'm sure that some of our customers might object, but making measuring decisions are an internal business decision unless you are contractually obligated to a methodology. In cases where we have been contractually obliged or found that we could not measure parts accurately to our own or our customers satisfaction, we have even leased some higher end measuring devices. Another alternative we have pursued is sharing gaging with the customer. It all depends on the confidence that you have in your measuring capabilities and the relationship you have with your customer. Customers have to understand that for suppliers, particularly in a job shop environment, the best measuring devices are not always available and management is probably not going to allow the quality department the spend the money unless there is obvious payback and justifiably so.

 

[normzone]

Yeah, I remember the first time I saw a gage travel with a product from department to department, then to a customer and back again.

Now here's a fun idea - somebody buy a pi tape.

 

[Michael_M]

Now here's a fun idea - somebody buy a pi tape.

I have not used (or even seen) one of those in 20+ years. I used one to measure a 61 inch diameter. It took 3 of us to keep the tape 'straight' and 'remove' gravity from the equation (Vertical lathe). I remember those days, and not fondly.