Acme Screw Thread Views
The trapezoidal metric thread form is similar to the Acme thread form, except the thread angle is 30°.[5][6][7] It is codified by DIN 103.[8] Although metric screw threads are generally more prevalent worldwide than nonmetric threads, the Acme thread is very common worldwide, and may be more widely used than the trapezoidal metric thread. This is not surprising, as manufacturers today are usually capable of making whichever threads (metric or nonmetric) are best for any given application (based on customer expectations or tooling availability). It may be that the tooling for Acme threads has been so dominant (compared to trapezoidal metric) that customers tend to want Acme threads for power screws regardless of metric standards used elsewhere in the product.
The Acme thread form has a 29° thread angle with a thread height half of the pitch; the apex and valley are flat. This shape is easier to machine (faster cutting, longer tool life) than is a square thread. The tooth shape also has a wider base which means it is stronger (thus, the screw can carry a greater load) than a similarly sized square thread. This thread form also allows for the use of a split nut, which can compensate for nut wear.[9]
When created prior to 1895, Acme screw threads were intended to replace square threads and a variety of threads of other forms used chiefly for the purpose of traversing motion on machines, tools, etc. Acme screw threads are now extensively used for a variety of purposes. Long-length Acme threads are used for controlled movements on machine tools, testing machines, jacks, aircraft flaps, and conveyors. Short-length threads are used on valve stems, hose connectors, bonnets on pressure cylinders, steering mechanisms, and camera lens movement.[10]
When compared to general-purpose thread forms, centralizing threads are manufactured with tighter tolerances and limited clearance on the major diameter. When an acme nut is side loaded, a d“G ” class acme nut will .“wedgea” when both of the nut thread flanks come in contact with the screw thread flanks. To prevent wedging, less clearance and tighter tolerances are allowed between the major diameter of the nut and the major diameter of the screw.
Acme Screw Thread Images
