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.

Wobble: for the cross recess there is also a gage that is used for identifying if the recess has the correct fit. Now, this can be done simply by taking a recess plug gage and inserting it into the recess and judge by feel that the fit is tight. But using a wobble gage quantifies that fit.  

Calibration of Gaging: the gages mentioned above need to be maintained and calibrated at a frequency defined by use. Very specialized measuring equipment needs to be used. Optimally, the manufacturer will use a laboratory that is accredited to ISO17025. This standard ensures the competency of the laboratory to perform a calibration that falls within a certain measurement uncertainty.  

Driver Bit Gage: The driver bit gage is used for ensuring that the profile is within specification of the size driver bit being manufactured. Again, this gage is precision made and matches the cross-recess profile of the geometry opposite the external plug gage.

Driver Bit Profile (Ring) Gage

Read more about recess gages at The Wrentham Tool Group.

About Wrentham Tool Group
Wrentham supplies not only the heading recess punches and pins but the recess gaging for each one. This gaging is manufactured on specialized equipment that can hold the tightest tolerances at its Bellingham, MA manufacturing facility, as well as an on-site a calibration laboratory accredited to ISO17025 and Z540.3 by A2LA. In 2004, Wrentham was purchased by Phillips Screw Company, original holders of the Phillips recess patent. In July 2010, WTG purchased RICO and ASTRO® from PCC Specialty Products Inc., known around the world for their high quality industrial, automotive, and aerospace punches and associated tooling.