Projected Design Dims vs. Manually added Dims

[pottersfriend]

So, I don't post often and as a hobbyist I rarely use the drafting features, but today I needed something so I could build some parts and ran into some issues. I'm not sure if it's something I'm doing or what but it definitely doesn't look like it should behave this way no matter what.

I have a fully constrained part that I manually dimensioned in drafting and noticed that parallel lines were coming out at an angle, but off by .000001 degree. Though if I look at the sketch they are fine. So if I project the design dims they are obviously fine but off if I manually add dimensions. Seems to me they should be the same no matter what. I might be doing something wrong (the only thing I can think is the manually added line for the angle, but it's constrained to the center points so it should be fine). Also, the 19.999999 dim should be (and is) 20mm in my sketch.

Another funny thing is that while setting this up for a screen shot it changed. The manually added 29.999999 degree dimension was obviously non concentric initially, then I deleted and redimensioned it and now it's concentric. Also, the 19.999999 dim changed. I manually created it and at first it was 19.999999 then I just did it again and now it's 20mm. This inconsistent behaviour stuff is frustrating. How can anyone prove there are issues if it changes all the time?!

 

[DavidJ]

Difficult to comment without the files to examine. Might be linked to levels of precision selected for the relevant dimension style, but that's juts a guess.

 

[HaroldL]

There was another discussion on the forum a while ago about the same issue of Alibre being "off" at the sixth decimal place. That's a millionth of a degree.

You didn't say what version you are using and I am not sure if that was ever resolved with v21, I don't recall seeing it in my work. But thinking about it, I have never seen a drawing of a part, machined or not, dimensioned to more that four (4) decimal places, other than some thread callouts, mostly they are three (3) places. If you changed the dimensions to two (2) or three (3) places would you see an issue? Not saying that it is not an issue, but if I saw an error of .1 or .01 I'd certainly be more concerned.

 

[pottersfriend]

I've attached the package file, assuming I did it right. I created it from the drafting section so I assume it will package the 3D model along with it.

@HaroldL - Yes, a precision change seems to bring it back to an acceptable display, i.e. 29.999999 with a 2 decimal precision will then display as 30.00mm, but this all started because I was using 2 place precision and I noticed some obvious inconsistencies. 1) the angular dims from a common point were NOT concentric and 2) the 12mm parallel offset couldn't be dimensioned as anything other than an angle. From there I started playing with projected design dimensions and seeing how they compared to my manually added dimensions. Just seems wrong now matter how you slice it. The fact there are inconsistencies between how things are being displayed/dimensioned in 3D versus 2D is an issue.

 

[Lew_Merrick]

Hi Pottersfriend -- Dimension display setting are tied to the Drawing Format you use. I, being in the United States, tend to live in the inches world. Thus I have Dimension Styles such as 2_Place_Dim, 3_Place_Dim, 4_Place_Dim, BSC_Dim and the like. You RMB select a Dimension and then assign a Style to it. -- Lew

 

[HaroldL]

1) the angular dims from a common point were NOT concentric and 2) the 12mm parallel offset couldn't be dimensioned as anything other than an angle.

Take a look at the sketch for the large Tick Mark, there is something amiss with it that may have contributed to the dimensioning problem.



Something to watch out for is to make sure that the part feature sketches are fully constrained. I've seen issues on some of my models until I started to leave the sketch DOF colors displayed.

 

[pottersfriend]

I feel like maybe the point is being missed on this thread. If I model an object, fully constrained then bring it into drafting and manually add dimensions, then those dimension should be the same. In the example I submitted I can't manually add the parallel 12mm dimension without it coming in as an angular dimension. I accept that maybe I did something wrong but I'm not seeing it. Precision settings don't have anything to do with this. If I can't add a parallel dimension (which is how it was drawn in the sketch) then it's not working correctly. Please see the attached again, as I think people are missing the point. I'm sorry if this might sound combative, it is not meant to be, I just don't understand why if I model something a specific way then why can't I then manually dimension it the exact same way in drafting. I will be submitting this to support.

 

[DavidJ]

Look very carefully at your sketch 8. It is the edge of the Tick mark that you have aligned with the 30 degree reference line. NOT the centre.

If you are consistent with dimensions between drawing and sketch - they will agree. When I added new dimensions to edge of your mark I got the 30.0 deg and 12.15mm as shown.

 

[DavidJ]

The way the 0.000001 deg dimension was placed, forced it to be an angle. If instead it had been placed 'edge to centre' it would have given a linear measure.

 

[pottersfriend]

@DavidJ - Admittedly, I screwed up the tick marks, but I'm not seeing how the tick marks relate to the issue shown above. If you look at my sketch 1 compared to the screenshot above (post #7) you'll see that they should match. There is no reason why the manually created line, from center point to radial slot center point, should be different than what I created in sketch 1. Therefore when manually adding the dimensions, they should be the same as sketch 1, but as you can see the .000001 degree dimension should be 12mm parallel but isn't.

 

[DavidJ]

As per my second post on this, dimensioning from edge to your manually created line for some reason forces an angular measure (then it just 'does its best').

If instead you measure from edge of part to one of your centre marks, you'll get a linear dimension.

I'm not saying that all is perfect here. I'm not sure why your manually created line should be a tad off (I tried re-creating it and got the same behaviour myself).

 

[pottersfriend]

I realize I can make things work and there are always work arounds but I just wanted to mention that these issues exist and shouldn't. At least you were able to recreate the behavior, so I'm not completely crazy. Thanks again for everyone's input on this.

 

[DavidJ]

After deleting and replacing all your dissociated (red) dimensions, things work much better.