A jointer is a stationary woodworking machine serving a limited but vitally important purpose: putting straight flat edges onto boards so that they can be edge glued together into panel. This article discusses the maintenance and operation of this machine and gives you the knowlege you will need when you go to shop for one.
While a jointer can be used as a planer for smaller pieces of wood, the most important function of this stationary machine is to put a straight, smooth, level edge or edges on wood to ready it for edge-to-edge glue-up. Rabbeting can be accomplished on some jointers but I prefer to use the table saw for this job. Chamfering, or making angled cuts, can be done by tilting the fence.
Accurate jointing or chamfering calls for that the cutter head knives be adjusted precisely with reference to the out feed table. The edge of each cutter head knife must precisely at the level of the out feed table: Not above or below it. In most cases, sharpening the cutter knives requires that they be detached completely from the cutter head and then replaced and aligned after sharpening. This is why I urge the use of solid carbide instead of high speed steel knives: Carbide knives stay sharp a lot longer and that means less time and effort has to go into detaching, putting back and aligning knives. Buy two sets. That way, you can keep using your machine while the dull set is out for sharpening and you will always have a sharp set waiting. Always unplug your jointer from electric power before commencing any knife adjustments. In my jointer, an 8” Rockwell/Delta classic, the knives are detached and re-inserted by using a flat wrench that came with the tool. This wrench is used to tighten the hex head machine screws that contact the knives and hold them in place in the cutter head. It is very easy to round over the hex heads, so I am very careful not to do so. I purchased a gadget that helps me align the knives with reference to the out feed table. It magnetically sticks itself to the surface of the out feed table and magnetically pulls the knives vertically and retains them in position, exactly aligned with the outfeed table, while I tighten the hex bolts. Each knife (there are 3 in my machine) must be in the extreme vertical head position before it can be suitably adjusted and tightened. When all 3 knives have been set properly, they should just touch, but not lift, a flat board laid on the outfeed table, extending over the cutter head. They must do this across their entire length of each knife. Jointer capacity is most commonly expressed by stating the full width of the knives (knives). A 6” jointer makes a maximum 6”-wide cut. An 8” jointer makes a maximum 8” cut and so on. It would be rare to use the entire width of even a 6” knife set at once, so the real advantage of wide knives is that you can move the fence to use a sharper place on the knife when the knife becomes dull. The wider your knives, the more use you will get out of them before it is time to re-sharpen. I usually start with a sharp knife set and the fence all the way to the right end of the cutter head and move the fence, in increments, a bit wider than the maximum board thicknesses, to the left until the knives are all used up. Sometimes, with curly or wavy grain structure, you will experience tear-out from the lumber edge even with sharp knives. Sometimes you can turn the board around and run it through again in reverse with very shallow cuts until the edge is fully jointed and the tear-out is gone. At other times, you may have to settle for a sawn joint made on the table saw. Usually you can make fairly good glue joints this way, if you have to, but a jointed edge is always my first choice because there is a more consistent (smooth) gluing surface and, thus, a better bond.
The depth of cut is determined by the height of the in feed table with reference to the out feed table. The lower the in feed table, the more wood is removed with each pass over the jointer. It is not a good idea to take off too much wood with a single pass. The chances of blow-out increase with the depth of cut and you may end up removing more precious wood than you really needed to, to get your perfect joint. After all, the idea of jointing is always to remove just enough lumber to create a straight, flat board edge. Removing any more than that is just a waste of wood.
Bob GillespieWoodworker
JOINTER REVIEWS:http://www.perfectwoodworking.com/jointerreviews/
WOODWORKING TOOL REVIEWS:http:www.//perfectwoodworking.com/woodworkingtoolreviews/
© 2010 Robert M. Gillespie, Jr.
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