1. Field of the Invention
The present invention relates to fastener means for joining two metal panel frames and more particularly, to a quick-positioning captive screw, which consists of a mounting base member, a lock screw and a spring member, wherein the mounting base member has an outer thread extending around the periphery of the top flange thereof for the threading of an inner thread of the plastic cap of the lock screw to guide an inside stop edge of the plastic cap of the lock screw over the top flange into the space) member below the bottom edge of the top flange of the mounting base member.
2. Description of the Related Art
The power drive or speed-adjustment unit of a machine tool generally has a panel frame detachably attached to the casing thereof. This panel frame may be fastened to the casing by screw members. However, the screw members may fall from the panel frame and missed accidentally during dismounting due to user's negligence, affecting further re-installation operation. To avoid this problem, a captive crew formed of a knob, a barrel and a screw is created. During installation, the barrel is affixed to a mounting through hole on the panel frame, and then the knob is rotated to drive the screw into a mounting screw hole on the casing of the power drive or speed-adjustment unit of the machine tool. After disconnection of the screw from the mounting screw hole on the casing of the power drive or speed-adjustment unit of the machine tool for allowing removal of the panel frame from the casing of the power drive or speed-adjustment unit of the machine tool, the captive screw is kept secured to the panel frame, avoiding missing the component parts.
FIGS. 9 and 10 illustrate a captive screw D according to the prior art design. According to this design, the captive screw D comprises a cap A, a screw member A1 mounted in the cap A, a barrel C coupled to the cap A and a spring member B sleeved onto the screw member A1 and stopped between a head A11 of the screw member A1 and a part inside the barrel C. The cap A has a bottom coupling flange A2. The barrel C has a top coupling flange C1 that is movable with the barrel C relative to the screw member A1 between the head A11 of the screw member A1 and the bottom coupling flange A2 of the cap A, and a bottom mounting portion C2 bonded to a mounting through hole on a metal panel frame E. During installation, a hand tool is used to drive the screw member A1 into a mounting screw hole on the casing E1 of the power drive or speed-adjustment unit of a machine tool. Thus, the fastener is secured to the metal plate member E, and therefore the metal panel frame E is affixed to the casing E1.
According to the aforesaid prior art design, the cap A and barrel C of the captive screw D are rigid metal members, and the outer diameter of the head A11 of the screw member A1 and the outer diameter of the top coupling flange C1 of the barrel C are greater than the inner diameter of the bottom coupling flange A2 of the cap A. When installing the screw member A1 and the barrel C in the cap A, a high pressure must be employed to have the head A11 of the screw member A1 be affixed to the inside of the cap A and the top coupling flange C1 of the barrel C be forced over the bottom coupling flange A2 of the cap A into the inside of the cap A. This installation method is difficult to achieve. Further, the top coupling flange C1 of the barrel C or the bottom coupling flange A2 of the cap A may be forced to deform or to break during installation by pressure. If the top coupling flange C1 of the barrel C or the bottom coupling flange A2 of the cap A is damaged, the bottom coupling flange A2 of the cap A may not be accurately coupled to the top coupling flange C1 of the barrel C, and the cap A and the spring member B may fall from the barrel C accidentally.
Further, when forcing the top coupling flange C1 of the barrel C over the bottom coupling flange A2 of the cap A into the inside of the cap A, the applied pressure may be transferred to the barrel C against the metal panel frame E, causing the junction between the barrel C and the metal panel frame E to break.
Therefore, an improvement in this regard is necessary.