The Jointer - Canadian Woodworking Magazine


The Jointer

With any woodworking machinery you must keep your hands clear of moving parts that can hurt you. The jointer has a cutter head with three or more “knives” spinning at high speed to produce a smooth surface. Although push blocks are provided by the manufacturer to keep your hands away from the cutting action, it is virtually impossible to use a jointer properly using push blocks Most push blocks work by friction caused by pushing down on the board. However, you must avoid pushing down to flatten a bowed board. Pushing down flexes the board downward into the blade and it will never become flat.
Using your hands, however, doesn’t mean you must sacrifice safety. Your hands must stay clear of the cutter head area and preferably on top of the board you are jointing. If you must grip the edges of the board while jointing its wide surface, grip them well away from the cutter head and always remember where all ten of your fingers are.
As with the table saw, a kickback throws the board towards you. On a jointer, that means that the board will be thrown from the cutter head to the right along the infeed table. So never place your hands too close to the cutter head on the outfeed side. A sudden kickback would pull your hands backwards into the cutter head.
In reality, kickback rarely occurs on the jointer. The board will only be thrown if the knives hit something unusual. For example, a knot could fall out while you are jointing. Kickback might also occur if you hit a nail that is imbedded in the wood. For this reason, be very cautious with old wood like barn board. Don’t put anything questionable on the jointer unless you’ve done a thorough inspection and used a magnetic wand to check for foreign metal objects.
When jointing a board it can be difficult to make it perfectly flat, especially when jointing a wide surface instead of an edge. This is because a board will not flex easily on edge, but the wider surface will flex quite easily unless the board is very thick. As stated earlier, try to put as little downward pressure as possible on the board while jointing it.
The best test for flatness is to set your cutting depth to just a hair above 0 (like 1/128th of an inch) and see if your jointer cuts the board for its entire length. You can judge by sound because your jointer will become very quiet if it isn’t cutting part of the board. Only when the jointer cuts for the entire length when set at such a small cut can you be certain that the board is very flat.
Don’t put anything questionable on the jointer unless you’ve done a thorough inspection and used a magnetic wand to check for foreign metal objects.
If your board fails this test no matter what you do, there may be a problem with your knife settings. Knives that are set lower than the outfeed table will result in a tapered cut. The jointer will only cut for the first one third or so of the board and then stop cutting altogether at the back end. You must raise your knives or lower your outfeed table to get your jointer working properly again.
To get a really clean surface on the jointer, you have to feed the boards with the grain. In one direction, the wood fibres are severed cleanly. In the other direction, the fibres are raised and then torn. This is known as “tear-out” and looks like pits or craters on the finished surface.
To plane in the proper direction, imagine petting a cat. When you pet your cat from head to tail, its hairs smooth down nicely. When you pet from tail to head, the hairs ruffle up. This is exactly what happens with wood, except that the ruffled wood fibres are also torn out by the spinning jointer knives. So you must feed the “head” of your board into the jointer first and the “tail” last. The jointer will “pet” the board properly and leave a smooth surface behind.
Learning how to read the grain direction of a board isn’t as simple as you might think. I really can’t cover the issue properly in a few paragraphs, but suffice it to say that a rag will often tell you the story. If you rub a rag in one direction over a board, it will glide smoothly over the surface. If you rub in the other direction, you will feel and hear the rag getting pulled over the raised wood fibres. Once you have established that the smoother results are rubbing from end A to end B, consider end A to be the board’s head and end B to be the board’s tail. Then feed the board head-first into the jointer knives.
Next issue Hendrik gives three tips on using your thickness planer.

Hendrik Varju
HENDRIK VARJU is a fine furniture designer /builder who provides woodworking instruction and private seminars near Acton, Ontario.
(519) 853-2027

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