Demystifying the AutoCAD Insertion Scale

[The CAD Geek]

The AutoCAD Insertion Scale is a mystical creature. Get it right, and the results are magical. Get it wrong, and you’re cursed with a riddle of why AutoCAD objects scale to seemingly random sizes when inserted into a drawing. Though it may seem like a curse, the good news is the counter-spell is an easy fix.

Understanding the Issue

Veteran AutoCAD users likely recall a time when there was no such thing as Insertion Scale. Using AutoCAD 2000, I remember struggling to figure out what scale to insert the first civil drawing I received into the MEP drawing I was working on. At that stage of my career, I had not yet learned civil engineering drawings (in the US) are typically prepared in decimal feet whereby building plans are usually developed in inches. Though each is a form of Imperial measurements, a scale factor of 12 or 1/12th is necessary to exchange drawings inside or outside the building.

Unscaled, an object measuring 2 feet, or 24 inches in an architectural or MEP drawing will measure 24 decimal feet in a civil or survey drawing – that’s twelve times the intended size. Conversely, unscaled, an object measuring 2 decimal feet in a civil/survey drawing would measure just 2 inches in an architectural/MEP drawing – one-twelfth the intended size. A scale factor is necessary when these two worlds collide since one unit in architectural drawings equal one-inch, but equals one-foot in civil/survey drawings.

Getting it Right From the Start

Is your head hurting as you try to make sense of when to scale objects by a factor of 12, and when to scale objects by a factor of 1/12th? You’re not alone; this is a concept that’s confused some of the savviest AutoCAD users I’ve known. And that my friend is why we can now set an Insertion Scale in AutoCAD. When correctly configured, AutoCAD will automatically figure out the proper scale when going from inches to feet, Imperial to Metric, or just about anything in between.

Three variables control how Insertion Units behave, or misbehaves, in your drawing. I’ll break each of these down in a moment, but the rule of thumb is to set Insertion Units to whatever the units are in your drawing. Generally speaking, that means drawings whose Length Type is set to Architectural should have an Insertion Scale of Inches, and civil engineering drawings whose Length Type is set to Decimal should have an Insertion Scale of Feet (or US Survey Feet).

To configure Insertion Units in your AutoCAD Drawing:

1. Select Units from the Application Menu > Drawing Utilities. The Drawing Units dialog box opens.Choosing Drawing Units from the AutoCAD Application Menu
   
2. From the Drawing Units dialog box, select the Units To Scale Inserted Content drop-down menu within the Insertion Units group.
3. Choose the units for the drawing you’re working with. Typical settings by plan type include:
   • Architectural & Building Plans: Inches
     

     Recommended Insertion Scale for Architectural drawings

   • Civil & Survey Plans: Feet or US Survey Feet

     Recommended Insertion Scale for Civil and Survey drawings

4. Click OK to set Insertion Units and close the Drawing Units dialog box.

Fixing The Issue for Existing Drawings

Like most configuration-related AutoCAD topics, spending the time to correctly configure your drawing from the start will pay dividends in the long run. Though that may be the case, we don’t always control the drawings we inherit. Thus the question remains, what is the best way to manage such drawings that are not properly configured?

When managing Insertion Units, there are three variables to know about and manage. These Include:

INSUNITS

The INSUNITS setting is a drawing variable. That means this is a setting that’s stored within your individual drawings. In fact, this is the setting you’re changing when changing the Insertion Scale within the Drawing Units dialog box (discussed above).

Though more time consuming, the best practice for managing Insertion Units is to configure this setting for each drawing in your project. Using a tool like ScriptPro is a way to automate the process of updating a large batch of existing drawings. Configuring individual drawings will allow you to insert drawings in any direction necessary. In other words, you could insert an architectural drawing into a civil/survey drawing, or a civil/survey drawing into an architectural drawing. AutoCAD will correctly scale drawings regardless of which is the source and which is the target.

INSDEFSOURCE

Unlike INSUNITS, INSDEFSOURCE is a system variable. Stored inside the Windows registry, AutoCAD uses this variable when INSUNITS for the source drawing is 0, the numeric value for Unitless.

This variable sets a systemwide default for Insertion Units for the source drawing. The source drawing is the drawing you’re inserting/referencing into a target drawing.

INSDEFTARGET

The INSDEFTARGET system variable is the INSDEFSOURCE system variable counterpart. Counter to the INSDEFSOURCE system variable, the INSDEFTARGET system variable applied when INSUNITS within the current (target) drawing is 0, the numeric value for Unitless.

This variable sets a systemwide default for Insertion Units of the target drawing. The target drawing is the drawing your inserting a source drawing into.

Bringing it All Together

Although the INSDEFSOURCE and the INSDEFTARGET system variables provide a workaround to configuring individual drawings, it’s just that – a workaround. The recommended practice is to set INSUNITS within each drawing to ensure Insertion Units function as designed. While some veteran AutoCAD users may prefer disabling INSUNITS altogether, I would suggest shying away from such a draconian action. Properly configured, INSUNITS is a wonderful AutoCAD function that dramatically simplifies the process of working with varied units.

What secrets and insights do you have about AutoCAD Insertion Units? Sound off in the comments section below.

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