Hole Preparation, Installation, and Inspection

Hole Preparation
Drill sizes should be chosen to generate holes within the diameter ranges recommended in the table below.  If holes are drilled at the low limit, or if sealant is used in assembly, spindles sometimes break low and installations are not complete.  An easy remedy is to drill the hole slightly larger (within the recommended limits).  This provides a little extra space for sealant trapped in the hole.

Rivet Diameter

Nominal Diameter Rivets

Oversize Diameter Rivets

Countersink Diameter

Recommended
Hole Limits

Recommended
Drill Sizes

Recommended
Hole Limits

Recommended
Drill Sizes

Recommended
C'sink Dia.(1)

-4
.129/.132
#30: 3,3mm
.143/.146
#27: 3,7mm
.222/.228
-5
.160/.164
#20: 4,1mm
.176/.180
#16: 4,5mm
.283/.289
-6
.192/.196
#10: 4,9mm
.205/.209
#5: 5,25mm
.350/.356
(1)  For best head flushness results, a rivet can be used to adjust countersink depth


Suggestions on Good Hole Preparation Practice
Clean round holes within tolerance and with minimal burrs are fundamental to good rivet performance.  Below are a few suggestions, which should help achieve good installations:
  • Drills should be sharp.  Optimized drill point geometry has surprising benefits for hole quality, productivity, and minimizing operator fatigue.
  • Drill speeds are critical to achieve hole quality and productivity.  In the case of aluminum structure, drill speeds of 4,000 to 6,000 RPM are recommended.
  • Excessive "push" on the drill motor can create sheet separation and burrs.
  • Hole normality is important.  Angularity beyond 2┬░ should be avoided.
  • Clamping of the structure with temporary devices is very helpful.
  • Countersink concentricity is important.  Undersize pilots are a common cause of eccentricity problems and cosmetic issues.
  • A relief radius at the base of the countersink helps achieve proper head seating.
  • The rivet installation gun should be properly aligned and firmly pushed against the structure.  This helps to avoid minor sheet gapping due to misalignment and presence of sealant.
  • The tool trigger must be depressed until pin break indicates completion of the installation.
  • Worn and dirty tools can cause bad installations.  Of particular importance are the gripping jaws (worn and dirty jaws can cause slipping of the jaws and breaking in the pin tails).

Inspection of Installed Fasteners
The positions of the spindle break and the lock ring provide important information about the quality of the installation.  The table below shows the spindle flushness limits published in the applicable specifications.  Spindle flushness per this table indicates good installations, which meet mechanical performance requirements of NAS1686, NAS1687, and relevant OEM specifications.

Rivet Dia.

"A" Dimension
Pin above head

"B" Dimension
Pin below head

Lock collar position

-4
+.010
-.015
Due to the installation principle, the collars are flush with the top of the head
-5
+.010
-.020
-6
+.010
-.020