Holes in Plates, Stronger?
Country: United States
Date: March 2007
Does drilling holes in metal make it stronger?
Please explain how this works.
Removing metal (by drilling or any other means) never adds
strength to a part. This is an old wife's tale that is
This is something that probably started when someone noticed
a high strength part that had parts of it machined away, and
assumed that the high strength had something to do with the
metal that had been machined away. One might well ask that if
removal of SOME of the metal makes the part stronger, then it
must be true that if you remove ALL the metal, a part will be
even stronger! No, we both know that is nonsense!
It is certainly common for a part to have some of its metal
removed that is not contributing anything to its strength.
This is done generally to make the part lighter, and if done
correctly does not significantly weaken the part. But under
no circumstances does removing or drilling out metal actually
increase its strength. At best, it just makes it no weaker.
Let me give you a simple example of this. The drive shaft of a
car or truck is a long tube that connects the end of the
transmission to the gears in the rear end that drive the rear
wheels. All drive shafts are hollow tubes, as if someone took
a long rod that was perhaps 4" in diameter and drilled out
all the metal in the center. Now, a drive shaft is subjected
to strong torque, because the transmission is twisting one
end, causing the drive shaft to rotate and twist the gears in
the rear end of the vehicle. If you analyze the stresses in a
solid (not hollow) drive shaft, you will see that the stress
is carried mainly by the outer periphery. The center has
very little stress on it, and carries almost no load. It just
adds useless weight. So drilling out the center to turn the
drive shaft into a tube, has almost no effect on its ability
to carry the torque load, and it has the benefit of cutting
its weight dramatically. So what we have is much reduced
weight, and the use of much less material, with no
significant reduction in its strength.
Hope the above example is helpful.
No, drilling holes does not make a piece of metal stronger. But putting
holes in metal in the right places can make the piece lighter without
losing much strength. This is important on airplanes. Airplane frames
often have many round holes.
When someone goes about designing or making a structure, such as the frame
of an airplane, a bridge, or a car, that person usually starts with flat
or round pieces metal. The pieces are bent and cut to make the parts.
It turns out that it is possible to make holes in some locations (and
lighten the part) and not lose much strength. This is because the part
is not stressed uniformly, and places of little stress can be eliminated.
Round holes are often cut into the parts. The edges of parts are usually
carrying the most stress, so you put the holes away from the edges of the
In addition to cutting holes, it is possible to improve structures using
parts of varying size. For example, bicycle frames need to be light and
strong. They can be made strong by using thick material, but this makes
them heavy. Instead, hollow tubing is chosen. No holes are drilled in
bicycle frames for lightness, instead, the walls of the tubes are made
thicker in places with a lot of stress, and thinner where there is less
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Update: June 2012