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AutoCAD Tutorial Features

How to Model Screw with AutoCAD If You Must

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(skroo) noun

Screw Picture

  1. A cylindrical rod incised with one or more helical or advancing spiral threads, as a lead screw or worm screw. 
  2. The tapped collar or socket that receives this rod.
  3. A metal pin with incised threads and a broad slotted head that can be driven as a fastener by turning with a screwdriver, especially:
  4. A tapered and pointed wood screw.
  5. A cylindrical and flat-tipped machine screw.
  6. A device having a helical form, such as a corkscrew.
  7. A propeller.
  8. A twist or turn of or as if of a screw. 

source: dictionary.com

A realistic screw thread is possible but comes at a cost of time and effort

By James Patrick

A recurring topic in CAD newsgroups is making 'real' screw threads. CAD users insist on modeling parts that are accurate to every detail down to thousandths of an inch. Hours may be spent on this endeavor. This can lead to much frustration. 

Don't Do It

My usual answer when asked how make real screws is "Don't do it!" Draw them in 2D. AutoCAD strains itself on solids. A realistically modeled length of thread can bogs down most computers. And when it gets right down to it, a true screw thread is impossible in AutoCAD. Some CAD programs, like SolidWorks can make true threads, but still file size balloons and performance suffers.

Do it In the Flat

A 2D representation of a screw is usually sufficient to convey its use in an assembly. A 2D depiction of a screw thread can look quite real. The time spent on creating a realistic 3D model as well as the time needed to then print it with hidden lines removed  is better spent on something productive. 

Table 1: Representing screw threads in 2D.

Method 1: Not very realistic.

  • Fast. Just arrayed lines.

Method 2: Semi-realistic

  • Arrayed lines and zig-zag.

Method 3: Realistic

  • Teeth offset, then arrayed lines

Method 4: Real

  • Splines and overlaps. Lots of time.

Really real

Actual model for comparison

My personal preference for representing threads in 2D is method 2 or 3. The first example just doesn't look like threads. It'll be a cold day when I make threads with splines!


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