Mass property calculations could not match requested accuracy?

[todd_cannon]

I'm using IV 2008 and got the following error message when trying to save this part. It's a simple part, a hollow cylinder (extruded) and 4 odd shaped holes cut 90 deg apart from each other (cut extruded). I have tried to accomplish the holes a couple of ways always with the same result. The first hole extrusion works fine and when I save the part I get no error message, but when I try to get the rest of the holes when I save I get the error message "Mass property calculations could not match requested accuracy." I have tried to use circular pattern, Made 4 identical sketches at each 90 degree position. As soon as I try more than 1 extrusion, I get the error. The hole sketch is made from a closed spline and the dimensions came right off a production drawing, to explain the odd shape. Can somebody take a look, please.

Todd Edited by: todd.cannon@ngc.com on Nov 5, 2009 5:43 PM

[karthur1]

Change the extrude direction to "Both ways" and increase the depth to say "12in". Works now for me. I am using 2010 or I would post the file back.

[todd_cannon]

Thanks, I will try that. It's interesting though, in my first attempt, I placed the sketch at the origin and extruded both ways to achieve 2 holes at once. Then I rotated 90 degrees and did the same thing to get the other 2 holes. When that didn't work, that's when I moved the sketch out the tangent point on the cylinder. If you post the part in 2010 it probably won't help me much though. Thanks anyway and I'll let you know how I make out.

Todd

[todd_cannon]

Well, I tried to edit the feature to extrude both ways and it didn't work. Maybe it's a bug with IV 2008? Does anybody else have a idea what's going on with this part. Autodesk??? The mass properties are sort of what I'm looking for with the assembly it belongs to. Thanks.

Todd

[Anonymous]

I was able to update your part to high accuracy in a later version
without problem.

Have you installed all of the 2008 service packs?
--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[todd_cannon]

Thanks Dennis, I have SP 3 installed. Maybe it's just 2008 misbehaving. I have to wait till next year sometime before we switch to 2010. 😞

Todd

[jakefowler]

Hi Todd,

Many thanks for posting this issue. By unchecking the “Update Physical Properties on save” checkbox (inside “Applications Options”;”General”), you can avoid this dialog popping-up when you save your part. Also note that this dialog is just a warning message, and will not affect the Save in any way.

As for the mass properties issue itself; unfortunately the accuracy calculation can give erroneous results in certain circumstances, and it seems this model might fit into the category. What I can tell you is that the actual mass property calculations are more reliable than the accuracy calculation, so for a model such as this you can ignore this warning, since the volume, mass, etc. calculations themselves are likely to be accurate.

I don't think the problem is isolated to Inventor 2008; with "Update Physical Properties on save" checked, I can reproduce the same thing in Inventor 2010 SP1. However, work has been done recently to resolve some of these issues, and in my current development build the problem is now fixed on your model.

Apologies for the problems you are experiencing, and thanks again for submitting this.

Jake Fowler
QA Engineer
Autodesk Shape Manager

[todd_cannon]

Jake,
Thanks for the reply and explaination. I'm sure a few more users will be interested in your response. Thanks again!

Todd

[Anonymous]

> {quote:title=Dennis Jeffrey wrote:}{quote}
> I was able to update your part to high accuracy in a later version
> without problem.

Did you change his part at all ?

We (used to ?) run into this all the time with complex, curvy cast parts.

[Anonymous]

I opened the file and went directly to iProperties physical. I changed
it from low to high accuracy, then picked update
--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com