How Does GD&T Reduce Your Costs?

How does GD&T (Geometric Dimensioning and Tolerancing) reduce your costs? I will try to explain this with an example in this article.

Instead of using the location symbol for the hole on the sheet metal part, the designer mistakenly used the concentricity symbol and gave the tolerance as 1.

When the production team receives the technical drawing and sees the concentricity symbol, they do not think it is wrong. (Although an experienced manufacturer knows that concentricity is not required in a hole on a sheet metal part.)

The manufacturer probably thinks that concentricity is required between the two hole surfaces of the sheet metal, even if it is a bit difficult. He has no difficulty in providing concentricity in a part with a sheet metal thickness of around 1 mm and a tolerance of 1.

He produces the part and sends it to the quality team to measure. The quality team receives the technical drawing and sees that the hole is concentric, so they measure the hole as concentric and approve it.

When the part moves on to the stage of joining with another part, the error is realized because the hole does not match the hole of the other part and the assembly cannot be done. The hole concentricity is correct but the position is out of place.

Now the costs begin;

• Repeat measurement of mismatched parts (measuring device capacity cost, man/hour cost)

• Cost of production stoppage, risk of product not being delivered on time, and overtime costs

• No error found in repeat measurements (Because they are still measuring concentricity)

• Forming teams, making diagnoses, holding meetings one after another to solve the problem. (The cost of engineers leaving their regular jobs)

• The inability to resolve this error and the cost of hiring an external consultant

• Cost of the consultant finding the error and scanning activities

• Rework costs

• Scrap costs

This scenario was a scenario that explained the cost of the designer's mistake, and from here we understand that first of all, the designer must know and apply GD&T well.

Well, the designer used the location symbol, which is the GD&T symbol, correctly. However, since the manufacturer did not master the GD&T symbols, he worked on concentricity instead of providing the location. The part went to measurement and since the quality unit did not master GD&T, he measured the hole as concentricity and approved it.

The costs listed above also occur in this scenario. Perhaps the designer may have misunderstood the symbol of production and quality in a meeting he attended. This may eliminate only the consultant cost.

Let's come to the quality unit;

The designer used the position symbol correctly, the manufacturer worked according to the position symbol and sent the part for measurement. However, the quality symbol thought it was concentricity, measured it and approved it. In this case, if the manufacturer missed the position, the quality could not catch it and some of the costs written above would still be experienced.

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The scenario written here actually happened! However, an experienced manufacturer who was familiar with GD&T noticed the designer's mistake and updated the design before production started!

Therefore, it is not enough for the designer to know GD&T. If the production and quality employees also know GD&T well, they can get rid of most of the costs written above by giving feedback to each other. I even think that the purchasing department should know GD&T for part costing.