I recently purchased a used Jet six inch cabinet jointer. The last time I used a jointer was decades ago in high school shop class. I don’t know if I have just forgotten, or if I was never taught the proper operation of the jointer. What I do remember, is coming out of high school thinking it was exclusively used for flattening the edge of a board, not also the face.
Through investigation, and experimentation, I have come to some ideas on how the jointer is to be set up and used. These are things that I believe are mentioned, but not in detail, and with no explanation as to why.
The two things I’m going to explain, are jointer blade height, and proper stock feeding.
Regarding jointer blade height, it is recommended that the height of the blade is at, or, preferably, just very slightly above the height of the outfeed table.
Observe what happens if the blade is below the height of the outfeed table. As stock is run across, some of the material is removed, but then the end of the board hits the outfeed table, and will go no farther. Getting the blade exactly at the same height as the outfeed table is difficult, and may not prevent all possibility for the stock to hit it.
This is why Jet recommends setting the blades to 1/16 of an inch above the outfeed table. Now, I think this is a bit (way) too high. Right now my blades are more like 1/32 of an inch, and can probably be a bit lower without an issue.
So let’s say your blades are just a tiny bit above the height of the outfeed table. This second image shows a bit of an exaggeration, but there will be a gap between the board and the outfeed table. In order to obtain the best possible cut, you need to smoothly transition downward force from the part of the stock that is riding on the infeed table to the part of the stock that is riding on the outfeed table, while maintaining a consistent feed rate.
I have heard this mentioned a few times, but with no explanation as to why. Instead, you just see some guy running boards through the jointer, and out pops a nice, smooth surface. When I started using my jointer, and was getting ridges and snipe, I assumed it was the machine. Now I know why I get that.
If you get a gouge or ridge in the middle of the board, it is because you have not smoothly transitioned from downward force on the infeed table to downward force on the outfeed table while maintaining a consistent feed rate. Imagine what happens in the second figure when an abrupt force is applied to the outfeed table. Since there is a gap, the board will tilt to meet the table, and the cutter will make a gouge.
If you get a snipe at the end of the board, it is probably because you haven’t transitioned force to the outfeed table before the end of the board passed the end of the infeed table. If you try to maintain pressure on the infeed side, after the end of the board passes the end of the table, it will both drop down suddenly from the gap still on the outfeed side, and, depending on the boards length and weight, may start to tilt up from the opposite end, much like any item cantilevered over the end of a table with pressure applied.
So, I think practice is in order to learn when and how quickly to transition force between the infeed and outfeed tables. Even with a very closely co-planar setup, our eyes and our fingers are able to sense minute snipe quite well. If that transition were to be made across a few inches of the board, it would be hardly noticeable.