Quality Magazine

Other Dimensions: Reject!

May 1, 2006
Before contacting your gage maker about a problem gage, follow a few steps to help determine the problem as quickly as possible.

In my last column I dealt with the subject of wear on gages. Being a faithful reader you'll recall that I also wrote that the word "reject" is another gage-user complaint that strikes terror in the hearts of all those who produce gages. Being a simple guy, I thought that would be the topic for my next rant. So here we are.

The ritual is the same and is played out around the world, as every gage maker will attest. The gage rejects the parts. Everyone knows the parts must be good so the gage must be wrong. I believe that's what is called critical thinking in some circles.

I had an example of this recently. The customer advised that the no go plug gage was entering the parts and his engineer wanted to know what the specs for the no go gage should be. Since we had calibrated the gage when purchased a couple of years ago I suggested they look up the report, which would have the specs for the no go gage.

When I hinted that it is unlikely the no go gage had worn much since they swore they hardly ever used it, I was asked why I thought the no go gage was entering the part. I hinted that my answer might sound a bit radical, but it was probably because the parts were oversize and should be rejected.

Being the wide-eyed radical that I am, I also suggested they measure the parts to see if the measurements confirmed what I was saying and the gage was showing. Since they didn't call back, I presume they followed my advice.

To save time-and possible embarrassment-I recommend checking out a few things if your gage is suspect before bringing out the reject forms:

n If you have another set of the same gages in the plant that are calibrated, see if they tell the same story. Bear in mind that a difference of a few millionths of an inch or parts of a micron between gages can mean one gage may accept while the other rejects the work.

n Check that you ordered the right sizes for the part being checked.

n Verify that the gage members in the handle have the same designation that is marked on the handle.

n When all else fails, measure some parts to see if the gage is telling the right story. But be careful. If you're measuring diameters with a two-point device, out-of-roundness conditions that are causing the gage to reject the part may not be detected.

n Another option is to have the gage calibrated by a competent laboratory.

n When thread ring gages are suspect, get the setting plug out and check them again, as they may have been dropped since their setting was last checked.

If you're dealing with threaded parts, measuring their pitch diameter may show they're OK, but the angle and overall form could be wrong, none of which will be found with a simple pitch diameter reading.

One or more of these steps may indicate that the gage is doing its job. If that's not the case, it's time to call the gage maker for help. Threats of lawsuits or a biker gang that will be sent to straighten out the gage maker won't help much.

Reputable gage makers want to know if a gage they have made is in error for a wide range of reasons. Doing your homework before you call will help get the problem resolved one way or another as quickly as possible. Some gage makers may ask you to return some sample parts with the suspect gage. If their calibration of the gage shows it to be within specifications, they may be able to do some checks on the parts for a modest fee or in some cases for free.

Rejects happen in the best of companies no matter what quality program they work with. The real problem is people. Maybe we should teach gorillas how to make gages. I'm confident this can be done because, given the condition of some of the gages received for calibration, those are the critters that must have been using them. But then we'd be plagued with banana skins and people slipping and sliding all over the place. Some days you just can't win.