If you are seeing
Machine Doubling, it is very common on the 1968-1972 cents.
Machine Doubling is a common striking event on that years coins. (For all three mints) Even the doubled dies show
Machine Doubling. But
Machine Doubling never creates a doubled die. A doubled die is created from a doubled die. So you can find examples of both on the same coin:

Note the doubled digits on the date? Now note the yellow arrows? That is where you will see the
Machine Doubling. Note all are showing the mahcine doubling on the mintmarks? On a doubled die, the mintmark will not be doubled on the mintmark. The die is created in one process, the mintmark is added in a different process. So when you see this
Machine Doubling on the date and the mintmark, it is
Machine Doubling. So it is a doubled die with
Machine Doubling (caused during the striking process). Normal dies with
Machine Doubling are very common to see on the 1968-1972 cents from all three mints. So if you are seeing an alteration on the devices/mintmark it is probably
Machine Doubling on these years.
Machine Doubling can happen on normal dies and doubled dies, as mentioned earlier, because of the looseness of the machines. You can have
Machine Doubling on a doubled die coin, but
Machine Doubling is never considered a doubled die. It is
Machine Doubling on a doubled die coin.
Machine Doubling can alter from strike to strike:

Note the same markers on these images? They were all from the same run of that die/machine. Thus the MD is different on each one. It just depends on the movement of the strike. (Looseness of the machine will cause other areas affected/more or less.
So if you are seeing MD, it is a common event. So if it looks like the examples below, it is
Machine Doubling:
The affected areas for
Machine Doubling is on the outside/inside edges of devices.
1. On raised devices the they will be reduced in size because of the contour reduction of the devices by the machine.
2. A doubled die will show an enlargement of the devices seen on the center areas of the devices increasing the size. The more spread that is present the wider/taller the devices will be.
3. Note the examples below, how the
Machine Doubling is reducing the center areas of the raised devices.
Click on the images to enlarge the images to see the Machine Doubling even easier to see.



CoopHome:
What is the difference between a doubled die and Machine Doubling? look for spread on the devices on the centers of the devices making the devices wider/taller in size than normal. if they are reduced, it is not a doubled die, but
Machine Doubling.