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Dimensions changing

Discussion in 'General Discussion' started by Jake_Steidy, Jan 16, 2020.

  1. Jake_Steidy

    Jake_Steidy Member

    Hello all,

    I have been working with some parts and then have been putting them into an assembly. One thing I have noticed with some of my parts is that dimension values are changing or displaying differently than I had just inputted. I have seen this showing up as diameters of 3.499 42.999" repeating instead of 43". It is a bit frustrating as I try to constrain parts to find that the dimensions are thousandths of an inch off when there is no reason I would have inputted a dimension like that. Has anyone else seen anything like this lately working with any of their files? I have been able to identify the problem, which is if I using the trim/extend tool on lines you will have an undefined line of magnitude and position. So then when I click the DOF callout to input that dimension, instead of doing the current exact dimension which would give me the proper dimensions, it auto rounds the value and inputs the incorrect dimension. This would be like the line being 0.1875" and instead of the line being 0.1875" when the DOF callout is clicked and saved it changes to 0.188". Do I have a setting that is causing this or is this an error with how the DOF callouts is supposed to work?

    Thanks for your time,
    Jacob S.
  2. DavidJ

    DavidJ Alibre Super User Staff Member

    May relate to your selected precision setting for dimensions for the file - are precision setting consistent across parts and assembly?

    Can you share an example?
  3. Jake_Steidy

    Jake_Steidy Member

    Yes the attached file is the one I was having difficulty with. The dimension is the 1.75" dimension that is listed twice, one off of the incorrect line and then the correct dimension off of a reference line. I would replace that reference line with a drawn line trim the ends then remove the wrong lines. Then when I use the DOF callout on the lines at 45 degrees it reverts to the incorrect position. Which it is saved at. Where do I access that precision setting?

    Attached Files:

  4. JST

    JST Alibre Super User

    I have seen things that appear to be what you describe. I know the precision is set maximum, because the differences were in the 6th decimal in a couple cases. Dimension entered as a whole number, like 46 inches, and dimension to 6 places actually reads out as 46.000002 inches, or some such. Just not possible that I "accidentally" put in the number in that form.

    I have suspected a problem with "numbers" for quite some time. I have seen, with several past versions, cases where two dimensions that measure to be the same to 6 places, will not actually align, apparently due to differences in dimension which are in the hidden decimal range.
    Jake_Steidy likes this.
  5. DavidJ

    DavidJ Alibre Super User Staff Member

    Open the dimension in 2D sketch mode, type in 1.750 and hit Enter - that will set it to 1.750000 rather than the 1.749684" it is currently set to.

    That will not work for the Reference dimension (in brackets).
  6. Lew_Merrick

    Lew_Merrick Guest

    Hi Jake -- One thing is that if your Sketches are not fully Constrained "pulling" on components of the Parts can "stretch" things (or "pushing" on components of the Parts may "shrink" things). -- Lew
  7. Jake_Steidy

    Jake_Steidy Member

    Yeah I get that David, what I was having trouble with was the Diagonal DOF lines that would change sizes because the precision wasn't fine enough. It would display .354" automatically, but that dimension, 0.354", wasn't the actual dimension of that diagonal line, so then it would give me that 1.749684" instead of the 1.75" I wanted. Let me know if that helps clarify the problem.

    Nevermind the error is just going to opposite and now it is giving me a value of 1.750244 and this is because the DOF line is now giving me a length of 0.353" instead of the exact value. This is also with all my lines defined but it just auto changes the dimensions.

    Hey Lew thanks for that tip!
    Last edited: Jan 16, 2020
  8. DavidJ

    DavidJ Alibre Super User Staff Member

    As an aside - it's generally much easier to model the pulley in 2 steps.

    First a disc, the add the groove with a cut - both sketches are much simpler that way. You can further simplify if you use symmetry to help.
    Jake_Steidy likes this.
  9. Jake_Steidy

    Jake_Steidy Member

    Thank you for that David, I am always appreciative of new ways to streamline my design process.

    I just wanted to bring this up because if I am having this problem creating a simple pulley then this rounding error must be replicating itself with parts of high levels of intricacy.

    Thanks for your help and time!
  10. idslk

    idslk Alibre Super User

    Hello Jacob,

    there are a lot of ways to do a design...i couldn't resist, i have to do one, that is other than normal, but might be interesting...:D



    Attached Files:

    Jake_Steidy likes this.

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