Forums >> General Discussion >> Revit Project Management >> What dimensioning tolerance do you use and why?

hyoctane

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I was just curious on what everyone uses as their drafting standards when drawing in Revit. We have differences of opinions in our office on whether to use 1/16" or 1/256" as a minimum dimension tolerance.

Reason for 1/16" tolerance: People in the field can't measure any more accurate than that. Why draw any different? It keeps quirky dimensions out of the dimension string (ie: 23/32".

Reason for 1/256": It keeps the drawing as accurate as possible and you can adjust anything you're dimensioning to be any dimension you want, whether it be 1/2", 1/4", etc. Why not draw as accurate as Revit allows?

What do you use and why?

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WWHub

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Our project units are 256... so that we draw accurately and don't have screw-ups.  If you see something with a 256 dimension then you screwed up or you traced a darn CAD file - They are always messed up!

If you don't draw accurately and use rounded, somewhere a string won't add up if someone checks it in the field... then ....

There are places where our dimension tolerances are set differently because we may not want units even at 1/8" but these dimension settings will never be used in a string.

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mgr2820

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Joined: Sat, Sep 1, 2007
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We have one dimension called "project standard". This is the default dimension for everything. It is not rounded off.

We have another to use when we need to superceed feet and only show inches...i.e. 5" instead of 0'-5". This is rounded off to 1/8", although we never use this dimension to place elements. It is only for graphics.

We do not round off, or override our dimensions.

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Bronsart

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Our tolerances is to the nearest 1/8".  Reasoning... thickness of a saw blade.  Out in the field, their heads start spinning when they are trying to figure out what 173/256" is closest to on their tape measure.  They know there might be an 1/8" bust in a string if I'm dimensioning angled walls.

We also use "EQ" a lot if a window is centered in a room or decorative beams are evenly spaced.  Our framers then need to field verify the size of the room before installing the windows, beams, etc.

 -Mike

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MARS1276

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We are a design-construction company and we use 1/8" tolerances for everything with one exception.  Most of our lengths we show are overall dimensions, so since our overall dimensions are usually to the nearest foot (and inches) that is why we use 1/8".  Someone else mentioned the width of a saw blade.  That is a very good point as well when considering dimensioning of saw-cut joints in concrete floors and sidewalks.

 The exception is when we do details of our anchor bolt layouts for the pier and footing details.  This needs to be precise so we use 1/16" for this.  Again, it makes it easier for the guys in the field to measure and I'm pretty sure when they start placing the tie-rods and anchor bolts into the concrete that the diameter alone will compensate for the difference.

 Besides that, we also do as-built measurements after the job is complete.  Any dimensions that are not accurate we change on the print and then subsequentially in the project file as well.

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JDAGEN

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 From the earlier post:

"If you see something with a 256 dimension then you screwed up or you traced a darn CAD file - They are always messed up!"

We have worked from a cad file and experience exactly what you are talking about. I spent hours trying to clean up the cad file... and still get /256" dimensions at some points in the Revit Model. What is the source of the problem AUTOAD or REVIT? I am assuming it is AUTOCAD. It seemed like Osnaps is the issue. Can it be avoided in Autocad? If not, we are using project units of /256" and rounding our graphic dimensions to 1/8" in REVIT: will we encounter roundering errors where the dimension strings won't close out?

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blake

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qabulin

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We will go to the nearest 1/8" (and actually 1/4" in a couple of RARE cases).

To solve for the issue of losing measurements, we double-check the overalls, and then be careful not to OVER dimension and use a few "V.I.F." to help ensure that the contractor is responsible for the final fitment.  We try to focus on the critical tolerances and primary controls... but we also do a lot of remodels and rarely a ground-up, which influences this.

Just my way of doing things. 

-----------------------------------

qab

^_^

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mgr2820

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Joined: Sat, Sep 1, 2007
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Autocad is an engineering software that allows for very precise dimensioning. Revit is based on a construction tolerence of 1/32". You cannot dimension or move anything less than 1/32".

If you notice there is a measure tool and a dimension tool. The measure tool will give you a percise measurement, the dimension tool will always rouud off to 1/32".  So, if you place two objects and set the distance to 20'-1/256", the dimension tool will show 20'-0", but the measure tool will read as 20' - 1/256".

 You will also notice that you cannot zoom and magnify an object beyond a specific magnification in Revit. Once you cross the 1/32" threshold, the graphic display does not function properly. Intersecting lines will fly apart in the view.

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