7 Tooling
Jointers are capable of producing an extremely smooth, clean cut if the tooling is kept sharp and free of nicks. If the machine seems to not be cutting properly, for example the cut seems to taper slightly, or it is difficult to get two pieces cleanly edge jointed for glue-up, it may be time to change the tooling. Tracks on the surface indicate nicks in the knives, however it is not always possible nor desirable to change knives for every nick. The fence can be positioned to avoid them, especially for narrow pieces. The knives can also be laterally offset from each other a small amount by loosening the gibs and repositioning them. This ensures that the nick on each knife is in a different spot, the other knives will then remove the track left by the damaged knife.
To keep the tooling sharp and in good condition for as long as possible, observe these guidelines:
- Never place material to be machined on the floor. It will pick up grit that will dull and damage the cutters.
- Never joint plywood or composites such as MDF, or painted or finished wood.
- Trim the raw ends of boards before jointing. They often have metal staples from inventory tags. The ends of logs are usually sealed at the mill to help prevent drying defects, the sealer is abrasive and will prematurely wear the cutter.
- Inspect the edges of every board for staples.
There are three types of tooling commonly used for jointers, including straight knives, disposable, and carbide insert.
Standard straight knives
Straight knives are commonly found on many jointers, both smaller models and larger industrial machines. In recent years, helical cutterheads have begun to replace straight knives on higher end tools.
The knives are often available in either high speed steel (HSS) or carbide tipped. HSS is a good choice for most work, and will produce an excellent surface quality. Carbide tipped knives cost quite a bit more in comparison, but will last longer before requiring sharpening. They are recommended for use in production settings, and for used with extremely hard and abrasive woods.
HSS knives can be honed in the shop with regular sharpening stones. Care must be taken to keep the entire edge of the knife perfectly straight, and to prevent rounding over of the cutting edge. To achieve this, the knives can be honed while in position in the cutterhead. A strong paper or plastic can be wrapped around part of the stone to prevent it from cutting into the outfeed table. The cutterhead is rotated until the knife edge is horizontal but a little higher at the toe. The outfeed table may have to be adjusted to accommodate this. The cutterhead is then wedged in position and the knife edges honed in turn. Once the bevel is honed, a slip stone may be used to remove the wire edge. If using water stones, ensure no excess moisture may wick between the knife and the cutterhead where corrosion could occur.
While HSS can be touched up with sharpening stones, both HSS and carbide knives are commonl