Proper use of gauge pins - Inspecting thru holes of plastic parts

[jaygolfpar4 - 2006]

We are having an issue at my work with the proper use of gauge pins when inspecting thru holes of our plastic parts.

Is there a standard out there that details the proper use of this type of inspection equipment or for all inspection equipment for that matter. We use calipers, micrometers, gauge pins, go nogo gauges, and optical scopes on a regular bases

Our main issue is; does the pin need to fall freely thru the Inner Diameter to make it a conforming product?

 

[Wes Bucey]

Concurrent engineering with customer

We are having an issue at my work with the proper use of gauge pins when inspecting thru holes of our plastic parts.

Is there a standard out there that details the proper use of this type of inspection equipment or for all inspection equipment for that matter. We use calipers, micrometers, gauge pins, go nogo gauges, and optical scopes on a regular bases

Our main issue is; does the pin need to fall freely thru the Inner Diameter to make it a conforming product?

The US government used to have Standards covering stuff like this, but they were all phased out.

Frankly, the best process is to create a Control Plan for performing inspection in conjunction with your customer to make the determination.

Simply stated, there are some thru-holes which function best for the overall product if they are "snug" while others function best if you can drop the "go" gage through like a marble through a basketball hoop.

Also to be considered is the ambient temperature (versus ambient temperature in function) at which you make the determination because of the different rates of thermal expansion between steel pins and plastic piece part.

I hope these two items alone (out of many I could envision) will help you in the discussion with your customer.

Does your "handle" (jaygolfpar4) indicate you ARE good at golf or that you ASPIRE to be good at golf? (which reminds me of an anecdote I may post in the humor section later this week)

 

[Al Rosen]

Jay:

Even simpler. If the go gage enters the hole and the no-go gage is unable to enter, the design specifications of the hole have been met.

 

[Marc]

Don't forget to consider cure time and related factors. Depending upon the material, there may be a time period between manufacture and measurement during which the material will shrink or expand. I have seen this as an issue - 15 years or so ago I went through a scenario where there was about a 1 year 'cure' issue. It was 'solved' by a design change. No - the company didn't wait a year to measure. Field failures brought to light the issue and the hole size was changed to account for material shrinkage. The original design engineers didn't account for material changes over time. It was a polybutylene terephthalate alloy if I remember correctly. Checks were made after molding but the items were kept for a week as WIP (work in progress) after which a sample was again measured to make sure there weren't any short term issues due to material 'cure' variation.

So much is made out of plastics now days that I am sure these factors are taken into account 'normally', but back then things were a bit less precise.

 

[Jen Kirley]

Jay:

Even simpler. If the go gage enters the hole and the no-go gage is unable to enter, the design specifications of the hole have been met.

This is correct as per all references I have seen, though none a government standard or anything...

 

[Wes Bucey]

This is correct as per all references I have seen, though none a government standard or anything...

OK I was reading between the lines here. Perhaps I'm wrong in this view, but my experience is when anyone asks questions like the original

Our main issue is; does the pin need to fall freely thru the Inner Diameter to make it a conforming product?

odds are the guy asking it wants someone to back up his point of view.

My further experience is this is rarely a cut-and-dried situation.

Therefore, since the overweaning Quality philosophy is "customer satisfaction" - why not inoculate the customer in advance by getting his buyoff on ANY method, rather than trying to ram your method down his throat?

When I am the customer - that is what I expect.

 

[Marc]

Therefore, since the overweaning Quality philosophy is "customer satisfaction" - why not inoculate the customer in advance by getting his buyoff on ANY method, rather than trying to ram your method down his throat?

When I am the customer - that is what I expect.

I have seen this consistently as a problem which often goes back as far as acceptance of a contract. 'Measureables' aren't really addressed - especially in situations of 'Visual' requirements. That's why I'm a BIG proponent of a serious, effective Contract Review process.

 

[Govind]

Jay,
I have not seen any standard on the usage.

But when I started with metrology , my ex boss use to say that the Pin gauge should never be forced through the hole. It should be dropped in freely on its own weight. This is tricky for very small diameters less than 3 mm. Weight of the pin is less and may not fall freely. You may have to guide the pin without excessive force.

I agree with all the other inputs provided by the members on part shrinkage, pin expansion, contraction, etc.Very good points. All to be taken into consideration. (even particularly when the hole tolerance is tight (< 25 microns)

For pins of smaller diameters also make sure the straightness of the pin is acceptable.
This will matter particularly for smaller holes with larger length.We use to roll the pin on a flat granite table to quickly look for air Gap and verify straigntness visually.

Other than that verify for flashes on the edges of the plastic part and any tapering of the holes.
Also take the mould and measure the pin size to make sure pin diameter is designed based on proper mould calculations.Glass filed plastic moulding can wear the mould pins faster. You may want to have a periodic maintenance check of the pin diameters.

Govind.

 

[Wes Bucey]

I have seen this consistently as a problem which often goes back as far as acceptance of a contract. 'Measureables' aren't really addressed - especially in situations of 'Visual' requirements. That's why I'm a BIG proponent of a serious, effective Contract Review process.

Yes! ISO9k2k (Section 7.2 Customer related processes) also stresses the importance of ironing everything out BEFORE accepting the contract, even to the extent where it states

Where the customer provides no documented statement of requirement, the customer requirements shall be confirmed by the organization before acceptance.

 

[Jen Kirley]

Yes! ISO9k2k (Section 7.2 Customer related processes) also stresses the importance of ironing everything out BEFORE accepting the contract, even to the extent where it states

Heh. I am reminded of Juran's description of Job Shop Quality. When I read that, I felt so much better after closely observing one.

I don't know how they've fared since registering for ISO, but I surmise from all the calls to customers asking for details or settling MRB, that they had a very appreciable phone bill. :mg: