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Free CAD drawing Viewer
All you need to view and print any drawing on this site with step by step instructions

Free PDF drawing Viewer
View, zoom in to detail, print in scale any PDF drawing on this site with step by step instructions.

What is a CAD program & do I need one?

The difference between a drawing done in CAD software, and software like, for example, Windows Paint or Photoshop, is that the cad software maintains a mathematical database of all the drawing information, and what you see on your computer screen is merely a visual translation of this database. The paint program, on the other hand, draws information on the screen directly, with no underlying information.

Thus two red lines on the screen in the paint program are just that, and if you zoom in closer, the pixels they are drawn with get bigger - the paint program does not "know" anything about the red lines - you can't, for example, pick one up and move it somewhere else. In the cad program, however, the lines have known lengths, angles, starting and end co-ordinates, and the cad program "knows" they are two different entities. As you zoom in, the program redraws the screen, so the pixels don't get bigger, and the file maintains resolution on screen.

Thus, drawings such as those on this site maintain their mathematical integrity no matter what cad program is used to read them, because it is the mathematical database that describes the drawing. If I draw a wall in a theatre 5.600m long, you will be able to measure it accurately in your cad program, plus print it out at whatever scale you wish!.

The drawings contain a number of layers with different information, views etc. on each. Typically, you turn the various layers on or off in different combinations to get the information you are interested in.
For this reason, software other than CAD programs will not be able to successfully resolve the drawings unless they have layer management, or the drawing is simple.

File formats

CAD files are presented on this site in either release 12 DWG format, or in release 12 DXF format. Larger files are zipped (i.e. compressed).

DXF is a file format developed by Autodesk (makers of the CAD program Autocad) specifically for the exchange of drawing information between different CAD [Computer Aided Drafting] packages.

DWG is the native Autocad file format, which has become accepted as a standard CAD format among many different CAD packages.

Although Autodesk keep updating the format, release 12 is a basic standard that all CAD programs should be able to read.

Depending on your CAD program, the drawings may be able to be opened directly via the file open dialog, or they may need to be imported - usually from an option on the file menu.

Viewing the drawings in your C.A.D program.

Many larger drawings on this site are zipped (i.e. compressed) to keep file size down, so must be unzipped (i.e. uncompressed) on your computer before you can use them. Windows XP has built-in support for uncompressing these files.

Once the drawing is imported or loaded into your CAD program, issue your appropriate "zoom all" or "zoom extents" command, so you can see the whole drawing.
Then "zoom window" into the scale , which will be visible along with revision and title information on layer 1. Measure this scale - (using snaps to ensure accuracy) - for example, measure the five metre points and observe what your package reports the measurement to be.
If it is 5.000 metres all well and good, but otherwise you need to do a little math, and scale the whole drawing (using 0,0 as the origin point) by the appropriate value to get the scale to measure 5 metres in your package.

For example, a likely scenario is that the 5 metres will be represented as 5000.000 units - you could just read this as 5000 mm, or you could scale the whole drawing by 0.001, to get the measurement to read 5.000.

If you are using imperial units, you will need to take this into account as well (1.000m = 3.281000 feet)

The thing here is not to sweat it - just scale the drawing and everything will be OK. Different programs handle units and measuring in different ways so it is impossible to be specific as to what to do.

Differences in CAD programs

CAD programs will differ in the way they interpret the exact same file, which often causes confusion. Usually the actual geometry will be OK (although it may need to be re-scaled), but often colours, text, dimensions, line weights, line types and symbols (or components or blocks) will screw up, lose their format, appear in different areas of the drawing etc.

For this reason, Adobe Acrobat's PDF format is becoming a good way to present CAD files, espically since Version 6 and above supports layers. Increasingly, CAD drawings on this site have only basic text and dimension info, and should be read in conjunction with a PDF version of the same drawing. - See PDF page.

CAD drawings on this site have had dimensions exploded (i.e. - the dimension is broken down into sub elements, and although it looks the same, it is no longer a dimension entity), and in this example file, symbols (blocks) have also been exploded, but there will still be noticeable differences.
For example, below is the exact same file as it appears in a number of different CAD programs. In each case the geometry is OK, but the file looks noticeably different. In most cases you can alter the offending elements within the program to something acceptable. Note that none of these examples below is "wrong" - they are presented just to illustrate the type of thing you may experience in opening a CAD file created in one program in another.

The file is a release 12 DWG file created in Rhino V2, Generic Cadd 6 and finally Visual Cadd 2. Click on the icons for full screen shots:

The file in Visual Cadd 2 before export - note font, line types etc.	A black and white gif image grabbed from Visual Cadd, - can be printed as is from the browser, but is not a CAD file - has no layers, not in vector format.
The file in the viewer recommended on this site. Note line types lost, different (but OK) font.	Visual Cadd V4 - colours changed, font changed.
Visual Cadd Viewer. Font change.	Voloview - Autodesk's viewer. Font change, linetypes gone.
Autocad LT95 (release 13) Font change, linetypes lost. Also arc smoothness lost - see notes below.	Autocad 2002. Font change, line types lost. Also arc smoothness lost - see notes below.
This is a close up of the area in the elevation where the roof beams are attached to building. In AutoCAD the arc smoothness on screen is lost.	In full AutoCAD you can adjust this setting with the "viewres" command, or in the preferences dialog. Set smoothness to about 1000 (up to a maximum of 20,000) to have arcs, circles etc. display well. In AutoCAD LT (at least in LT 95) there appears to be no way to set this.
Generic Cadd 6 (MS-DOS based product) Font change, line types lost.	General Cadd. Windows based revival of Generic Cadd. Font change, line types lost.
Rhino V2. Font change, line types lost completely - i.e. doesn't support line types.	TurboCad V8. Font change.