Sasha Ayers Jointers August 14th, 2018 - 03:27:42
Jointer size is most commonly determined by 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.
The jointer is a high-speed, stationary power tool. It has a table consisting of two adjustable surfaces: an infeed and an outfeed. Between these two horizontal surfaces (under a safety guard) is an opening below which are razor-sharp knives that rotate at a high speed. By adjusting the height of the infeed surface the knives will shave wood away from a board fed through the jointer.
Assessing the quality of a used jointer follows the same four-step process of evaluating other used woodworking machinery. First, you should avoid amateur sellers of used woodworking machinery (e.g. eBay merchants and company auctions) and buy from professional sellers that are capable of accurately assessing a machine's value. Second, you should avoid purchasing a used jointer from a seller that has unresolved customer complaints at the Better Business Bureau (BBB).
Always unplug your jointer from electrical current before attempting any knife adjustments. In my jointer, an 8" Rockwell/Delta classic, the knives are removed and replaced by using a flat wrench that came with the jointer. This wrench is used to loosen and tighten the hex head machine screws that press against 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 outfeed table. It magnetically attaches itself to the surface of the outfeed table and magnetically attracts the knives upwards and holds them in position, exactly level with the outfeed table, while I tighten the hex bolts. Each knife (there are 3 in my machine) must be in the extreme vertical position before it can be individually correctly adjusted and tightened. When all 3 knives have been set properly, they should just touch, but not lift, a flat piece of wood laid on the outfeed table, extending over the cutter head. They must do this across their entire length of each knife.
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 backwards 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.