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# Need help with calculating the whole surface area of elements depicted on technical drawings

## Need help with calculating the whole surface area of elements depicted on technical drawings

(OP)

### RE: Need help with calculating the whole surface area of elements depicted on technical drawings

The second sketch shows a 3-dimensional, circular plate with diameter and thickness indicated. However, the horizontal portion of the sketch is a 2-dimensional piece with length given but no width or thickness given. This sketch makes no sense to me.

www.PeirceEngineering.com

### RE: Need help with calculating the whole surface area of elements depicted on technical drawings

Well, if that is the case, the object looks like the sketch below. The dimensions are approximate. The blue area represents a flange with thickness 0.049" in a cylindrical configuration.

To calculate surface area:
1. Calculate perimeter using Section A-A.
2. Find the radius R to the center of gravity of the perimeter.
3. Multiply the perimeter from 1. by 2*pi*R.
Similarly, if you want to find the volume of material, find cross sectional area from Section A-A, calculate R', where R' is the radius to c.g. of area, then V = A*2pi*R'.

### RE: Need help with calculating the whole surface area of elements depicted on technical drawings

It occurred to me that you may wish to record the stipulated area as well as the minimum and maximum area. In the sketch below, metric dimensions are shown without any allowance for fabrication error. Outside diameter at b or c is 149.95mm; inside diameter at a or f is 127.00, but it could be as large as 127.15 or as small as 126.85.

Face ab is a circular ring with width (149.95-127.00)/2 = 11.475mm and an average diameter of (149.95+127.00)/2 or 138.475mm. It would have an area of 11.475*pi*138.475 = 4,992mm^2 if built precisely to the targeted dimension. But with an allowance of plus or minus 0.15mm in inside diameter, the width and diameter of the ring changes slightly.

Similarly, the other faces will have a targeted, minimum and maximum area which you should be able to calculate.

### RE: Need help with calculating the whole surface area of elements depicted on technical drawings

@Krzysziek, are you still alive? If so, please respond. If not, R.I.P.

### RE: Need help with calculating the whole surface area of elements depicted on technical drawings

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