Cost effective thread gaging with ISO 9001

I need some expert opinions with some trouble we are having with determining the best way to manage the ISO requirement for measuring with calibrated instruments and the cost effectiveness in our situation. We are manufacturing components with Acme threads for valves purchased from our vendor in China. The problem is that we would need to purchase $500K worth of Go/NoGo gages to cover all of the threads that are being used. We are researching the highest use threads and will probably purchase gages for them, but this leaves many others without a gage. We have been gaging them with a mating component, but this does not meet the calibrated requirement. We have discussed using the 3-wire method, but we have limited employees that are trained or competent enough to be trained. This also would not solve the issue for female threads. Due to the low volumes of each thread type being manufactured, we would like to continue using mating parts, but I am struggling to find a justification or measurement method that will satisfy the ISO requirements.
One of the issue I can see with using a mating part is: What guaranties do you have that the mating part is good. Additionally, threads have a 'go' and a 'no-go'. A mating part just checks the go, meaning the thread can be under/over sized and still pass.

Do you have any type of comparator or vision system that can measure thread detail such as (for OD threads) the minor diameter, thread angle. If your comparator or vision system can measure this, it should be able to measure the pitch diameter.

I do not have any suggestions for ID threads that I think would effectively measure the part.


Quality Manager
Are you trying to meet ISO 9001 requirements, a customer's requirements, or your own in house requirements? Because a lot of this goes beyond what is actually required by the standard.

Are you all using Thread Disk for the 3 wire method or are you having them do the formula by hand/excel? Thread Disk software will give a machinist the information they need to make Go/NoGo gages as well as the actual thread/mated part and it will give an inspector the information they need to verify them (although I highly encourage using a comparator in tandem with 3 wires, including orange repro rubber for ID checks and OD checks that are too big to fit). You can also get the more expensive add on for Thread Disk that does all this for tapered threads as well.

Are you all willing to make your own in house plug gages? Have you ever made set gages with Thread Disk? Did you know you can get generic gaging from places like GageMaker where you can just buy different rollers for different sizes/threads?

Even if you do the 3 wire method I really suggest investing in a bench top comparator. There are some things 3 wire won't catch that a comparator will.

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