Cam out (also cam-out or camming out) is a process by which a

screwdriver A screwdriver is a tool, manual or powered, used for turning screws. Description A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. This form of the screwdriver ...

slips out of the head of a

screw A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the screw head, head. The most common uses of screws are to hold objects together and there are many forms for a variety ...

being driven once the

torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...

required to turn the screw exceeds a certain amount. Repeatedly camming out damages the screw, and possibly also the screwdriver, and should normally be avoided.

Phillips screwdriver

The Phillips screwdriver design has a tendency to cam out during operation due to angled contact surfaces, which create an axial force pushing the driver out of the recess as torque is applied. Despite popular belief, there is no clear evidence that this was a deliberate design feature. When the original patent application was filed in 1933, the inventors described the key objectives as providing a screw head recess that (a) may be produced by a simple punching operation and which (b) is adapted for firm engagement with a driving tool with "no tendency of the driver to cam out". Nevertheless, the tendency of the Phillips screw to easily cam out was found to be an advantage when driven by power tools of that time which had relatively unreliable

torque limiter A torque limiter is an automatic device that protects mechanical equipment, or its work, from damage by mechanical overload. A torque limiter may limit the torque by slipping (as in a friction plate slip-clutch), or uncouple the load entirely (as ...

clutches, as cam-out protected the screw, threads, and driving bit from damage due to excessive torque. A follow-up patent refining the Phillips screw design in 1942 describes this feature and further argues that if screw drive clutches were perfect, a screw recess with zero vertical contact angles (and thus no axial cam-out force) could be utilized, but claims that where these have been tried, unsatisfactory results on assembly lines have prevailed since the driving bits would not cam out in time to prevent damage. Several later designs derived from Phillips, like Pozidriv and Supadriv were designed to reduce or eliminate the propensity to cam-out. In recent years, power tools can more accurately control fastener torque, and it is typical for precision engineered products to be assembled with

Torx Torx (pronounced ) is a trademark for a type of screw drive characterized by a 6-point star-shaped pattern, developed in 1967, Bernard F. Reiland, "Coupling arrangement and tools for same", filed 1967-03-21 by Camcar Textron. A popular gener ...

or Pozidriv head screws, which have been specifically designed not to cam out.

Robertson head screws

Robertson Robertson may refer to: People * Robertson (surname) (includes a list of people with this name) * Robertson (given name) * Clan Robertson, a Scottish clan * Robertson, stage name of Belgian magician Étienne-Gaspard Robert (1763–1837) Plac ...

screws are commonplace in Canada, and significantly reduce cam-out when compared to Phillips screws.

References

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External links

When a Phillips is not a Phillips!
at Instructables.com Screws

Phillips screwdriver

Robertson head screws

See also

References

External links