Cad Basics
Start a new drawing
In a "NEW" drawing, type tilemode, then 0. You are now in a blank paperspace drawing. Set your "units" to architectural, and be sure to set denominator for smallest fraction to display to at least 1/64". The current layer should be 0. In most cases you will next reference (Xref) in a border and/or a title block. If we are doing a drawing that will be in paperspace only (diagrams, schedules, cover sheets, etc.) then we are ready to start work at this point. If we are doing a drawing that will require external references, then we will need to create a viewport. In paperspace (tilemode 0) set current layer to "defpoints" or create it if necessary. This layer never plots, so don't waste time turning it off, freezing or locking it Ypu can change its color for visual purposes if you like but it still won't plot. Type MV (mview) and draw your viewport box. Now change to modelspace (MS). We now need to create if necessary and make current the layer we want the Xref to reside on. This is important, because we don't want to inadvertently freeze or turn off the Xref, and this also makes manipulating all the layers, (lock, freeze etc.) easier. Examples of this layer name are: XARCH, XELEC, etc. Type the command "Xref" and reference the drawing file needed. Coordinates are always 0,0. In sheet drawings we need only insert as "overlay"*. Be sure the entire directory path for that "Xref" drawing is included. The next step for plan drawings that we eventually want to plot to scale, we must first zoom (while in modelspace) to a scale factor. If we need a 1/4"=1'0" scale, then we would type the command: Zoom (Z),then enter 1/48XP. We are then able to pan (in modelspace) to center the view. Sometimes it's easier to zoom in roughly on the area you need first, then do the zoom factor.
*Overlay as described in AutoCad "Help":Overlaying is similar to attaching, except that when a drawing is attached or overlaid, any other overlays nested in it are ignored and, therefore, not displayed. In other words, nested overlays are not read in. It is recommended that you use overlaying when you are referencing geometry that is not useful for other users to see when they reference your drawing. For example, you may have created a wiring plan for a house and need to reference the floor plan of the house. If you have chosen to overlay (rather than attach) the floor plan, then another user, who doesn't need to see the floor plan, could Xref your wiring plan without the floor plan attached. Overlaid Xrefs are designed for data sharing. By overlaying an Xref, you can see how your drawing relates to other drawings. Also, overlaying an Xref reduces the possibility that you might create self-referencing drawings (circular Xrefs).
To Attach an Overlay:
From the Insert menu, choose External Reference,or type "xref". The first time you attach an xref, the Select File dialog box is displayed. After you select a file to attach, the Attach Xref dialog box is displayed.
In the External Reference dialog box, select an xref and then choose Attach.
In the Attach Xref dialog box under Reference Type, select Overlay.
Specify an insertion point.
Specify parameters, scaling factors, and rotation angle, or select Specify On-screen.
Click OK.
Create an Xref Drawing file.
A reference file such as an architectural plan is a drawing created in modelspace (tilemode 1). If you were to change to tilemode 0 you would see a blank drawing. Do not draw in tilemode 0 of an Xref. (Background or base drawing.) When doing a background or Xref drawing, everything is drawn at full scale (1'-0"=1'-0").
Example 1-(Best for larger projects): Arch.dwg is a reference drawing (base) that other disciplines will use for the building background. If I create an "electrical base" drawing for Electrical Lighting called Elec.dwg, I can reference (Xref) the Arch.dwg drawing into it as an "overlay" for reference purposes. Since Arch.dwg is an "overlay" it won't affect anyone else that may be simultaneously "referencing" Elec.dwg. The Elect.dwg that I do all the lighting and circuiting work on is then referenced (Xrefed) into my "sheet drawing" as an "overlay" or as an "Xref". This "sheet drawing" is usually applicable to just one particular project, therefore the "annotation" concerning that project is placed in paperspace and not in the reference file (Xref). That is good practice anyway because it keeps "base" drawings from becoming too cluttered.
Example 2-(Smaller and single sheet jobs):Open your "sheet drawing" and change to modelspace. (You have already created your viewport(s), and the reference layer is current.) Type Xref and "overlay" or "insert" Arch.dwg. Set your zoom factor for the desired scale and center the drawing in the viewport. Change back to paperspace; your drawing is ready. To do your work directly on the reference plan, it's best to change to tilemode 1, rather than toggling between paper and model spaces.(Fewer zoom mistakes will happen!)
Plotting (HP Design Jet type plotter)
When plotting an architectural plan drawing that has a referenced (Xref) drawing attached to the "sheet drawing", first make sure you are in paperspace. (The "sheet drawing" is the drawing where the viewport, border, titleblock, notes etc. are located.) Also check the Ltscale. 0.5 or 1.0 give the best results for 1/4" or 1/8"=1'0" scale plots. Type plot. Choose device to plot to by clicking on Device and Default Selection. Assign pen weights if needed. In Additional Parameters, click the Extents box. (Be sure there are no entities outside the area you want to plot.) Next choose the paper size, rotation (0) and plotting scale. (This should always be 1=1 for plan drawings, as scale is actually set by the zoom factor in the viewport.) Preview if desired, then click Ok.