Other Dimensions: Special Equipment and You

March 30, 2010
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Remember that you cannot give your supplier too much information if you want custom-designed and built equipment that meets your expectations.



As I mentioned in last month’s column, selecting a specially made instrument is much easier if you ask the right questions. In this case, there’s no such thing as too much information. After asking who, what and why, it’s now time for when and where.



When?

When do you need the quotation? Forget about yesterday as an answer-practically speaking, what is a realistic deadline? Bear in mind that if you need pricing for a multidimension gaging fixture interfaced with someone else’s computers, you’re unlikely to see a quotation within a couple of days. Unrealistic requirements on this question will mean a lot of folks will “no quote” it.

When do you need the special gage, instrument or fixture? If you are quoting on a job and are not ready to buy now, you should be honest and upfront about this with the supplier. The supplier could be slow right now, but six months down the road when you get the go-ahead on the project, they may be jammed up with work and extend the delivery time.

When a family of parts with the same features is involved and a fixture is in the cards, do you want interchangeable tooling on it for the different parts or adjustable tooling, assuming both choices are practical?

When will sample parts be available? A drawing may be worth a thousand words, but a sample part can be worth a thousand drawings.

Where?

Where will this equipment be used? If the answer is in the shop as opposed to a temperature-controlled room, don’t expect millionths of an inch or parts of a micron performance.

Where will the work to be measured be located? Does it have to be checked while in place on the machine or will it be on a bench for easier measurements? If the product is on the machine, will it be in a chuck-mechanical or magnetic-or on centers?

Where are the datum surfaces on the work? Are they clearly defined and readily accessible? Or are they literally in space?

Where do those measurements have to be taken on each feature? Sometimes this is obvious or there are no choices. But often a “single” feature has to be measured in several places to ensure all of it is within tolerance.

When All Else Fails

If you are machining parts for someone else, it is worthwhile to find out what method your customer will be using to qualify the parts. There are two reasons for this. The first is that your customer may be using poor technology, but when you use the right equipment for the job, arguments will ensue. And you know who will automatically assume they are right and you are wrong. One way out of this is to duplicate what your customer is doing. You’ll both be wrong, but you’ll agree on dimensions. This works until someone else gets involved who knows what he is doing.

The other reason for checking your customer’s gaging for the job is in case they’ve got it right, but you don’t. You’ll end up in lengthy discussions under this scenario as well.

If you anticipate future discussions over dimensions due to different gaging methods, your quotation to the customer should indicate how you will be measuring or gaging the parts. This will give them a heads up so discussions-if needed-begin before the chips start flying.

As you can see from this brief list, a lot of answers are needed to properly quote special equipment. The point to remember is that you cannot give your supplier too much information if you want custom-designed and built equipment that meets your expectations. And don’t be offended if your supplier indicates that your expectations are not realistic-they are gagemakers, not miracle workers.



In a recent column, I misstated NIST’s uncertainty for a PD measurement. The correct value should have been 50 microinches.



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