A poor quality hole will fail the aircraft joint. It does not matter how strong the rivet or bolt is if the hole is of poor quality. A poor hole can cause a loose fastener or metal fatigue and lead to joint failure at stress levels below specifications. Ensuring proper hole preparation, drilling speed and feed rate, cleaning, sizing, cold working, measuring, and plugging holes is important for maintaining optimal joint strength. The Mechanic's Toolbox software website provides tools and information to help mechanics efficiently produce quality holes.

1. Hole Quality
for aircraft mechanics
brought to you by Mechanic's Toolbox Software - makes your job easier.
www.mechanicsupport.com

2. A poor quality hole will fail the joint
It's not how strong the rivet or bolt that matters - it's
how strong the joint is. A poor hole will fail the joint and
leave the fastener loose.

3. A poor quality hole will fail the joint
Smoking Rivet -
the rivet hasn't failed - but the hole has!
"With a loose rivet, all we have is a hole in the airplane
with some trash rattling around in it, and it always
enlarges the hole."

4. A poor quality hole will fail the joint
Joint failed at a stress far below published strength
data due to metal fatigue. Proper hole preparation
retains strength.

5. A poor quality hole will fail the joint
"You can calculate stress all you want but if the hole is
shaped like an hour glass or a pear it won't perform like
you expect it to."

6. Feed and Speed
Speed kills - slow down
Feed is the feed rate, or when hand drilling, how much
pressure you put on the drill. Speed is the spindle speed
or how fast the drill bit is rotating. Too much feed and
speed dulls your drill bit and makes holes like the one
above.

7. Clean the Hole
Deburring tool for cleaning the backside of the hole

8. Size the Hole
Drill slightly undersize and ream to proper size.
Reaming cleans the hole surface.

9. Cold Work the Hole
for optimum fatigue strength
1. Hole filling rivet
2. Mandrel Expansion - http://www.fatiguetech.com
Cold working the hole improves the surface finish and
places the hole boundary under compression. Aircraft
grade rivets are designed to expand against the hole
boundary and compress the surfaces.

10. Measure the Hole
Hole plug gauge for accurate hole measurement

11. Plug the Hole
Open Holes Increase Stress by 3 times. Plugging holes
only increase the stress 2 times. 1/3 less stress!

12. Mechanic's Toolbox
Software for the Mechanic
Saves you time and money
www.mechanicsupport.com