The shaft is the most important element in my machine, so i rather prefer forging for production technology, the circumscribed circle of the shaft is about 140 mm and the length is about 1400 mm.

What kind of dimensions should i specify on my drawing to help the operator to manufacture it ? The diameter of a circumscribed circle here does't help.

  • $\begingroup$ The final dimensions with a relevant tolerance. $\endgroup$
    – Solar Mike
    May 19, 2018 at 19:31
  • $\begingroup$ @SolarMike tolerance principal IT14 $\endgroup$
    – user14407
    May 19, 2018 at 19:42
  • $\begingroup$ why is the shaft so important? does it need to be strong? a specific toleranced dimension? What if it's not the same across flats in each direction? What if two opposing sides aren't perfectly parallel? If these things matter to the function of the machine, they must specified on the drawing. We can't help further without much more information. $\endgroup$ May 19, 2018 at 20:56
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    $\begingroup$ Why would you not give the AF (across-flats) dimension and tolerance? $\endgroup$
    – Transistor
    May 19, 2018 at 23:03
  • $\begingroup$ @Transistor Is it actually very good idea, why i did't ? because i'm still a nube, thanks $\endgroup$
    – user14407
    May 19, 2018 at 23:29

1 Answer 1


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Figure 1. Hex AF (across-flats) dimensioning.

That's how I'd do it (but I'm an electrical engineer so what would I know!).


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