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Shaft Generator....considerable inaccuracies! Watch out!

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Message 1 of 6
KEJay74
910 Views, 5 Replies

Shaft Generator....considerable inaccuracies! Watch out!

I normally operate in "Inches" for the majority of my design work.  So, when I needed to 're-create' a custom shaft which was done (originally) in metric I simply started out entering my dimensions in ##.## mm format and let "Inventor" do the math...right?  Not so good!  There appears to be a serious flaw with this approach within the Shaft Generator.  Especially when looking to put it in items concerning the lengths or distances along a shaft.  In particular, locating a retaining ring groove on a shaft.  If you call 12.65 mm for the distance 'x' from the end of the shaft, it is converted (AND TRUNCATED OR ROUNDED) to 0.498 inches.  Then, if you inspect the distance on the actual shaft model you will find it is placed at 12.6492 mm from the end of the shaft.  If you use 13.65 mm it becomes truncated to 0.537 which is 13.6398 mm.  I thought...OK...I will do the conversions meeself and put in about 10 or 12 units of precision....guess what....IT MAKES NO DIFFERENCE!  The shaft generator ONLY uses 3 units of decimal precision on it's lengths!!!

 

Anybody have any work-a-round for this?  The attached screenshot illustrates the 13.65 mm  entry in the Shaft Generator.

 

Best regards,

 

Ken

5 REPLIES 5
Message 2 of 6
blair
in reply to: KEJay74

Check the Units Setting within the Options>Document Settings>Units: this may be set to only 3 decimal places for your default IAM file. You may need to increase this for the IAM, and then do a "Save As Template" so the next IAM you create the desired number of decimal places will be present.

Inventor 2020, In-Cad, Simulation Mechanical

Just insert the picture rather than attaching it as a file
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Delta Tau Chi ΔΤΧ

Message 3 of 6
KEJay74
in reply to: blair

Thank you 'blair'! 

 

Now comes the really HARD question...  Why is a "Display" option tied into the performance of a math calculation?  I mean, didn't the 'Y2K' debacle teach anything about 'truncating' data?  Anyway, the changing of how data is "displayed" is limited in the Tools, Options, Document Settings menu to five decimal places.  This "does" get it closer....0.49803 Inches on the conversion and result is 12.64992 mm instead of 12.6492.  Obviously, this is an issue of symantics now, and not one of physical machining tolerances. 

 

Last of my 'rant'....If one asks for the cube root of 64, would you be happy with 3.98354???  Just sayin'....the computing power is "there"....USE IT!

Message 4 of 6
blair
in reply to: KEJay74

Inventor is only limited to the number of decimal places in the floating point processer used in the CPU. So it really comes down to how many decimal places you set in the Document settings. The CPU is working to around 13 decimal places and Inventor is only displaying and rounding up to what you set.


Inventor 2020, In-Cad, Simulation Mechanical

Just insert the picture rather than attaching it as a file
Did you find this reply helpful ? If so please use the Accept as Solution or Kudos button below.
Delta Tau Chi ΔΤΧ

Message 5 of 6
KEJay74
in reply to: blair

Yes.  I understand that Inventor is only limited by machine architecture....however, the Shaft Generator IS (apparently) being limited.  For some reason the setting of the number of decimal places to 'display' is affecting the accuracy of the calculation of the length to make a portion of the shaft.  Also, as far as the 'display' setting, it IS limited to five decimal places.  There is no setting for it to 'use all available decimals' here.  Now, if I open the 'shaft' IPT file, without changing ANY settings, make a single circular sketch and extrude it to a distance entered of 12.65 mm.  Then "inspect" the length of that extrusion, it IS EXACTLY 12.65 mm, NOT 12.649962, as it is within the Shaft Generator.

 

I am attaching  1) the shaft1 file that was created with the ring groove as 12.65 mm from end of shaft (which measures 12.649962 mm from end of shaft).  2) a copy of that shaft model as "shaft2" to which I have added a 'direct' extruded component also as 12.65 mm (which DOES measure 12.65 mm).  For whatever reason the posting software will NOT allow me to post the .IAM file that I started with for the shaft generator to work.

 

Before 'inspecting' the sizes I DO set the measure tool for "all decimals" and "dual units - mm".  Now, the question remains...Why use a conversion value which has been artificially "limited", "rounded" or "truncated"?  Inventor (natively) does NOT do this.  This is (IMHO) an effect of the coding within the Shaft Generator.  This probably occurs by converting the "formatted for display text" instead of using the actual numeric variable of the value to use.

 

Am I wrong?

 

Best regards to all,

 

Ken

 

Message 6 of 6
KEJay74
in reply to: KEJay74

Smiley Embarassed Ok!  Ok!  I stand now chastised!  This issue has been corrected in Inv 2015!!!  Until this afternoon I had been working ONLY in Inv 2014 Pro.  Upon installation of Inv 2015 Pro.....The issue is GONE!

 

THANK YOU Adesk!

 

Best regards to all,

 

Ken

 

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