Balancing the cutters
Balance of the finger joint head is extremely critical to a good finger joint.  Even a very slight amount of imbalance or improper setup may produce a joint that will fail.  All cutter stacks should be assembled so that they will keep the head in dynamic balance during operation.

The best way to ensure cutterhead balance is to weigh each stack of cutters, and then install stacks that weigh the same across from each other.  If there is more than one tenth of a gram difference between stacks installed directly across from each other, the heavier stack should be lightened by grinding material off the flat area on the back of the cutter.

Balance of cutter bolts is just as  important as the cutter balance. If you are replacing bolts or reassembling  a cutterhead, bolts that are straight across from each other must be balanced to within one tenth of a gram.  Be certain to use care when pressing bolts in or removing them from the head.  Always use an arbor press and be sure that both the bolts and the head are completely free from dirt or debris.  Bolts that are worn and scored should be replaced.

All WKW cutterheads are balanced to extremely tight specifications before they are shipped. The careless practice of not maintaining cutter balance will contribute to head imbalance, vibration, run out and a poor joint. If there is any reason to suspect that your head is out of balance, or if it has been dropped, or if it has hit any foreign object, please contact the plant for authorization to return it for possible re-balancing.

Grinding Cutters
Grinding the cutters correctly is a very important factor in obtaining a good finger joint.  The cutters must always be ground so the face bevel of the cutter matches the grinding template.  If the cutters are ground to the incorrect face bevel, the joint will not fit correctly. Always be sure to wear eye protection as well as a proper breathing apparatus.

The grinding wheel you select will have a great influence on cutter performance. An 80 grit wheel at 1700 RPM will usually give excellent results on HSS and OPTI cutters.  Depending upon your own grinding technique, you may have better success with a 120 to 150 grit wheel.  Dress the wheel so it will produce a smooth radius at the gullet of the cutter.  A cutter gullet that has a sharp corner, rough finish, or too small of a radius will allow a stress point to develop. This area may allow for the development of minute cracks that could eventually be subject to breakage.  A smooth radius will also help to prevent chip buildup and plugging of the cutters.

Once the head is mounted on the tool grinder, mark the faces of the cutters with a felt marker.  This will indicate whether you are making full contact with all cutters in a stack.  Be sure to remove only .001 or less in each pass and always be sure to grind enough to remove all of the wear and any chipped areas.  It is very important to grind until the top corners of the cutters show a clean sharp edge.

It is possible to have a cutter that appears to be sharp but upon closer inspection shows wear at the top corners.  This condition will prevent a good clean cut and may contribute to a poor joint.  Allow the wheel to "spark out" after the wear line is removed or after every .006 is removed from the cutters if you will be grinding more than .006.  Always let the last cutter in a stack go past the center of the grinding wheel.  With a manual face grinder, be sure to feed at a slow steady rate and only advance the wheel into the cutters while the wheel is in contact with the cutters. A micro finish of 50 RMS or better will give the best results. Although you may get several sharpenings before you need to reset the cutters, best results will be obtained with more frequent set ups.

Grinding Opti^® Cutters
Opti cutters are ground exactly like high speed steel except that extra care should be used when grinding OPTI finger joint cutters.  The extra hard surface may chip if too much material is ground off per pass. Careful grinding will produce an extremely durable and sharp surface that will give very long tool life.

The Set Up Fixture (Single Post)
The set up fixture  is perhaps one of the most important tools for guaranteeing a good joint. Once the fixture is mounted securely in a vise, carefully slide the cutterhead onto the arbor. Note that there are three locating holes for the "L" pin. Locate the "L" pin into one of the side holes that will hold the cutters away from the locating post. The center hole should not be used for loosening or tightening the nuts. Loosen the nut, and relocate the "L" pin to the center hole.

Rotate each cutter in that stack up to the locating post so that all cutters are flush with the post.  You may want to check with a feeler gage no more than .002 thick to be sure that all cutters are rotated completely to the post. Snug the nut up by hand and continue the same procedure until all stacks have been re-set to the post and hand tightened. Never use a wrench to loosen or tighten the nuts with the "L" pin in the center hole as this hole is for locating only and torque applied to it could disturb its accuracy.

After the cutters have been relocated away from the post, by placing the "L" pin in one of the side holes, use a torque wrench and begin to tighten the bolts in a diagonal or alternating pattern. It is important to gradually tighten the head in this criss-cross method to ensure you do not bind the flange on the bolts and to ensure that all cutter stacks are equally tightened. Torque each stack in 50 foot pound increments until you have attained 250 foot pounds (175 foot pounds may be used to prevent cutter breakage in extremely difficult applications.) On WKW laminated beam finger joint heads equipped with 1-1/8" diameter bolts, torque to 450 foot pounds.

Multi-post fixtures
Set up fixtures are available in multi-post design. This fixture enables all the wings of the head to be set up at one time and greatly reduces the overall set up time involved. Other sizes and configurations are also available.  Follow the same recommendations as above.

Fixtures for laminated beam heads
Laminated beam finger joints are strictly regulated and undergo regular strength testing and certification.  The fixtures for these heads usually consist of a precision ground plate that fits to the head by a series of exact locating holes. For more information on these heads, please contact the factory.

Problems from improper cutter bevel
The incorrect bevel on your cutter face is indicated by the grinding template. Great care must be taken to be sure that the correct cutter angle is maintained as the incorrect angle may produce the problems.

Cutters ground too sharp
If the bevel on the cutters is ground too sharp, the joint produced may be characterized by fingers that are concave. This situation will produce a joint that will either not glue up correctly, or one that will be visibly loose.

Cutters ground too blunt
If the bevel on the cutters is ground too blunt, the joint produced may be characterized by fingers that are concave.  This situation will produce a joint that is very tight or difficult to assemble.

Cutters ground correctly
If the bevel on the cutters is ground correctly, a good fitting joint will be the result as long as the trim saws are correctly set up.

Problems from mis-alignment of cut off saw
Correct setting of the cut off saw is crucial for a good fitting finger joint.  The overall length of the fingers is extremely critical as well as whether the saw is running true and cutting a good square end.  Following are some common problems and how the joint will be affected.

Fingers trimmed too short
When the trim saw removes too much material from the end of the stock, the joint will be tight at the sides of the fingers before the fingers are able to reach the bottom of the joint.  The saw must be adjusted so that the resulting fingers are longer.

Fingers trimmed too long
When the trim saw is set so that it leaves too much material, the resulting joint "bottoms out" before the sides of the fingers are in contact with each other.  Remember, unless you are using a special head equipped with trim knives, the fingers themselves are not cut on the ends by the heads. The trim saw must be set accurately to ensure the perfect fit.

Fingers trimmed correctly
When the trim saw is set so that it leaves the correct length finger, a good fitting joint is possible.  Always be sure that the cutters themselves are correctly ground or a poor joint will result.

Chip Load per cutter
In order to get both a good finish on the wood and to prevent burning of the cutters, it is important to remove the correct amount of material with each cutter.  The measurement that must be monitored is "chip load per cutter." Extremely high temperatures are generated at the cutting surface of the knife, and the wood serves as the coolant.  Too small of a chip load will result in too much heat and will either glaze the wood, burn the cutters, or both. The target range to shoot for in finger jointing is approximately .020" for the actual chip, but chip loads of .018 - .031 are commonly used depending on the application and material being cut. The important factors are whether you are getting a good cut and if you are getting good life between sharpenings without blackening or burning the cutters.