Geometry Head Screw

[Anonymous]

Hi all,

I'm a new maker and generally figure out my own issues in Fusion, however this one is a head screw that I can't resolve (or find any clues on). Hoping someone can help.

Using the polygon tool in sketch, I create a hexagon, with perfect 120 degrees internal angles between faces (as pictured). Once extruded however, using the inspect/measure tool, I have internal angles between faces that are slightly over/under 120 degrees. I realise the precision setting here (0.123456) is wildly high, however this is really bothering me. How am I losing my perfect 120 degree angles?

Any ideas, help, explanations?

Thank you

[hamid.sh. · Accepted solution]

This is an interesting find. I checked your file and made my own and it seems to me it is just an artefact made when measure tool calculates and reports the angle between two faces. The reported angle changes every time you select the points (repeat the measurement between same faces and you'll see different numbers). Interestingly if you measure angle between edges it always report with much better precession (e.g. 120.0000000000002132°).

[TheCADWhisperer · Accepted solution]

What measuring instrument will you use in the real world?

Can you demonstrate where this causes an issue?

If you absolutely know that you have done it right and you cannot identify any downstream issue, I would ignore.

[jeff_strater · Accepted solution]

This comes up fairly often.  The short answer is:  all geometric math is done to a tolerance.  Some of the algorithms involved are iterative, and at some point, we have to say "good enough".  Otherwise, the modeling could take forever.  And, @TheCADWhisperer is right - I'm not sure that there is even an instrument in existence that could measure that kind of deviation on something the size of a screw head.  0.00002 degrees is an awfully small angle.

Because of concerns just like yours, we are planning to remove the "all decimals" option from Measure.  All it does is to create anxiety.

[Anonymous]

Thanks for your reply,

This has no real world application or practicality, just a mathematical curiosity. It’s a very simple angle and model after all. I suspect it’s actually perfectly 120 degrees as in the sketch, but the measure tool isn’t designed for this purpose. 

Cheers

[Anonymous]

That makes sense, thank you.

In checking my work, I thought I had perhaps made an error somewhere.

Again, a curiosity more than an issue.

Thank you for your time.

[Anonymous]

Thanks,

This seems to explain what I’m seeing, and interesting to note the values continue to change.

Of course, not an issue in the real world.

Thanks