Hole Quality

for aircraft mechanics

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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.

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."

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.

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."

Feed and Speed

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.  

Speed kills - slow down

Clean the Hole

Deburring tool for cleaning the backside of the hole

Size the Hole

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

Cold Work the Holefor optimum fatigue strength

1. Hole filling rivet2. 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.

Measure the Hole

Hole plug gauge for accurate hole measurement

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

Plug the Hole

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