Some CAD programs, like Silkworms can make true threads, UT still file size balloons and performance suffers. Do it In the Flat A AD representation of a screw is usually sufficient to convey its use in an assembly. A AD depiction of a screw thread can look quite real. The time spent on creating a realistic AD 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 AD. Method 1: Not very realistic. Fast. Just arrayed lines. Method 2: Semi-realistic Arrayed lines and gig-gag.
Method 3: Realistic Teeth offset, then arrayed lines Method 4: Real Splices and overlaps. Lots of time. Really real Actual model for comparison My personal preference for representing threads in AD is method 2 or 3. The first example Just doesn’t look like threads. It’ll be a cold day when I use method 4 and use splices! Showing Threads in Isometric Views The standard flat drawings aren’t appropriate all the time. Perspectives, assembly manuals, and presentations are a some of those times. One firm covered most of their bases by including an isometric view in each of their block drawings.
Just the woo isometric views when rotated or flipped can account for many different perspectives. But there are other views than Just isometric, right? Then make a solid model. There are thousands of times when a AD drawing isn’t appropriate. By time you draw two isometric views, or Just one real projection, you can make a solid model that can be viewed from an angle. Solids: Stretching the CPU Budget So if you absolutely insist on creating a solid model to represent threads, I’ll show you how. However, please do as little detail as you can get away with. Table 2: Several methods of making AD models of screws.
Method 1: Not very realistic Fast, Just two cylinders. This is passable in many drawings. Makes for small file size that renders and shades very fast. Detail rendering looks poor. Chamfer and socket. The head detail adds more to clarity and recognition than the threads. Method 3: A little more realistic (preferred) Same as before, but with AD thread line drawn. My favorite. Always recognizable, but small file size. The shank is the tooth root diameter, and display. Lisp is used to draw a helical line around it. Remember to block both or you’ll “lose” the threads.
Method 4: Almost there Revolved half-sections with teeth. Looks more realistic than #3 in details, close-ups, and side views. File size is doubles compared to #3 Method 5: Really real CPU killer. Solid threads made with multiples of half the intersection of two offset solid triangles. See next note. ‘True’ screw threads in Autocrat. The technically correct answer is that a perfect screw thread cannot be modeled in Autocrat. The figure above left picture shows that shapes extruded along pipelines ‘rotate around themselves’ and don’t keep a constant relationship to the extrude tat.
So you can’t extrude screw threads. But all is not lost, you can make an approximation. If accuracy of is close enough for you, then you can make half of one screw-thread with the offset intersection of two revolved triangles. Two halves intoned make a whole (see picture below) and so on and so forth until you have the amount of thread you want. The Autocrat users at Burros Optical wrote the procedure into a lisp that does almost the entire operation, but you’ll still have to construct the heads. The final product, real within 0. 01%