Anyone who has ever tried to drive a screw into a board, only to strip out the recess with the driver bit? The cause of this may be poor installation technique. But it may also stem from bad quality. According to experts at Wrentham Tool Group, Bellingham, MA, this can be traced to several things:
- Poor metallurgical properties of the recess or driver bit
- A recess that was not formed properly
- A gage that is out of specification and not conforming to the design
- A driver bit that is not formed properly.
Wrentham Tool Group, an expert in this area, says these failures can be prevented, by having the correct gaging calibrated to standards, by using them according to their design intent, and testing along the way. It lists some steps to prevent such failures:
Metallurgical failure can be identified by torsional strength testing, using a precision-made fixture for holding the driver and using a torque tester.
Gaging the Fastener Recess involves a number of varying requirements. In Cross Recess fasteners (such as slotted or Phillips screw, important gage requirements include recess penetration (the depth a driver bit enters the recess, not the total depth of a recess). The penetration depth is gaged differently depending on the recess type being manufactured.
Cross recess penetration gaging is done by using a penetration gage that has as its tip a gage element with a very precise geometry, one that is profile ground and duplicates the recess itself.