sketch offset

[jezek.jaroslav]

Hello, can someone explain to me, why there is this strange number in offset function in sketch?

I just draw a rectangle, select offset --> leave the default value 1 --> double click the value 1 and see it's actually not 1

why is the number like 1.0000000149 mm and not 1.0 ???

Is it something I have somewhere in my settings ?

thanks for any explanations..

JJ

[SaeedHamza]

Could you provide the .f3d file?
Go to File > export > .f3d and attach it here.

[jezek.jaroslav]

here you go...

JJ

[SaeedHamza]

I've check the offset value and retyped 1 mm, and it only gave me 1 mm (see screenshot below):

Could you please check the values in your prefrences for the Unit and Value display, similar to the screenshot below, and please note that these are the values in my preferences, check them and compare them you yours :

[jezek.jaroslav]

If I retype "1" than I do have 1mm exactly. No problem here.

But my point is If I don't change the value once I select the contour I want to offset (that is set to 1mm by default) and double click it, it's not 1mm, but 1.0000000149 mm.

So I always have to retype 1  to have exact 1mm even if 1mm is default value for offset - if you know what I mean.

So I'm just curious why there is no exact 1mm as the default value.

I have the same setup just lower precision.

JJ  

[laughingcreek]

I doubt there is a "reason", other than it got programmed this way unintentionally initially, and never noticed.  @Phil.E ? 

[jeff_strater]

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@jezek.jaroslav wrote:

If I retype "1" than I do have 1mm exactly. No problem here.

But my point is If I don't change the value once I select the contour I want to offset (that is set to 1mm by default) and double click it, it's not 1mm, but 1.0000000149 mm.

So I always have to retype 1  to have exact 1mm even if 1mm is default value for offset - if you know what I mean.

So I'm just curious why there is no exact 1mm as the default value.

I have the same setup just lower precision.

JJ  

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The answer has to do with how the sketch solver works.  If you are offsetting a simple rectangle, all alone in its own sketch, yes, 1mm gets you 1mm (I hope).  But, in the context of a more complex sketch, with other geometries, constraints, and dimensions, the entire sketch is solved as a single system of geometries and constraints.  This solve process is complex, and involves iterating through geometry changes to try to find a solution.  In order for that process to be assured to terminate in a reasonable amount of time, there is a tolerance applied.  If I remember correctly, that tolerance is about 1.0E-6 CM.  So, yes, you can get these very small deviations in asked-for dimensions, and results.  The result you show is well within that tolerance.  In the real world of objects that will be manufactured, that difference is irrelevant.  That is a very tiny distance.

[laughingcreek]

@jeff_strater - waaaaaay over thinking your answer.  nothings being solved.  it's just the initial default value that is auto populating the offset dialog.  yes, it's small and inconsequential, but why man?  

[jezek.jaroslav]

that's the point. Very simple rectangle in it's sketch gives me 1.0000000149 mm as default instead of 1mm.

I could imagine some complex sketch, where this can be some workaround. But still don't get, why 1mm is not 1mm.

I know for machining process it's nothing... But if you measure a distance later in the model and you see something, that's not exact number (as it should be) you start to worry about the entire model and don't know, where this difference comes from... That's just silly

JJ

[jezek.jaroslav]

here is what I'm talking about. If I draw a simple rectangle 50x50mm and just put offset, the default value is 1.0000000149 mm instead of 1mm. Why is that ? Why do I have to retype 1 to get 1mm ?

[jeffescott]

Yup happens all the time.   

[HughesTooling]

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@jeff_strater wrote:

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The answer has to do with how the sketch solver works.  If you are offsetting a simple rectangle, all alone in its own sketch, yes, 1mm gets you 1mm (I hope). 

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@jeff_strater It's not a rounding error, Fusion seems to have a default of 1.0000000149 mm.

If you offset a curve and just accept the default 1.00mm then edit the dimension, the dimension is 1.0000000149 mm. If at the time of creation or later you edit and enter 1mm it will be 1mm.