Franklin Adhesives & Polymers has a number of different types of finger jointing adhesives, each designed for a particular end-use requirement. If water resistance is desired, Multibond EZ-1 and EZ-2, one-part cross-linking PVAs, are commonly used. For exterior joints requiring ASTM D-5572, wet-use performance, Multibond X-016 with Catalyst A is recommended.
The preparation of joints as well as the adhesive play a critical role in the quality of finger jointed products. Most failures of finger jointed lumber are caused by poorly machined and poorly fitted dry joints. The adhesive plays a role in heat and water resistance. However, even the best adhesive available cannot make up for a poorly fitting joint. The fit of the dry finger joint should be checked before gluing begins. The following tips may help you in reaching a properly fitting finger joint or trouble shooting finger jointing problems in your operation.
For best results in using our adhesives in finger joint applications, please follow the below guidelines.
- Knife-set - Are all knives measured? New knives and shims should be balanced and dialed in with a micrometer.
- Knife Stack - Be sure to check overall knife stack for accuracy. Keep cutter-heads in pairs and properly cleaned. Cutter-heads should be sharpened as a set. Knife set should cut only 0.25 mm to 0.75 mm of wood.
- Knives should be sharpened after preparing approximately 70 cubic meters or 30,000 board feet of gluing stock (Wood species may cause this to vary).
- 0.08 mm to 0.10 mm should be ground off upon each sharpening. No more than 0.0013 mm of metal should be taken off on the final cut.
- The hook angle is important in the finger profile, and knives should be fitted to templates after three to four grindings.
- The set-up post should be used for realignment.
- The head should be balanced every three to six grindings.
- Make sure cutter-head spindle is set vertically with no wear or play in the bearings.
- Chain carrier lugs should be squared with the trim saws and cutter-heads. These should be checked periodically.
- Make sure trim saws are set true. Check bed rails for wear on a regular basis.
- Check hold-down pressure to provide sufficient pressure to prevent movement of stock while cutting the joint.
- Pressure should be held constant until joint is cured.
- End pressure should be set to provide 10.5 kg/cm2 – 14.0 kg/cm2 pressure for non-structural joints and 24.5 – 28.0 kg/cm2 for structural joints.
- Crowder wheels should be aligned to match fingers accurately.
- Sufficient adhesive spread will provide a uniform coverage that should cover one-half to two-thirds the length of the finger on both sides in a thin continuous film. Make sure fingers aren't skipped and that the adhesive is applied to the whole joint, not just the tips of the fingers.
- If the adhesive is a two-component system, make sure the ingredients are properly mixed.
- Excess adhesive squeeze-out can cause arcing in a high frequency tunnel. It also causes adhesive build-up and adhesive waste. Too much adhesive can cause a hydraulic effect in finger joint back off.
Additional information on finger joint gluing can be found in the full version of our Finger Joint Gluing Guide or by contacting our technical support team. For more information about gluing equipment, please refer to our resources link.
Advantage FJ-1 - has the highest water-resistance of any one-component PVA, meets ASTM D-5572-95 (2012) Wet Use for finger joints, has a low minimum use temperature, and a shear thinning rheology making it compatible for finger jointing and extrusion applications
Multibond X-016 - highly water-resistant adhesive ideal for finger jointing, cold press, radio-frequency and hot-press applications
Multibond EZ-2 - designed for cold press applications including finger jointing but can also be used for radio frequency, assembly and hot press gluing
Multibond FJ-3 – designed for finger jointing of interior stock, and applications requiring high heat resistance and easy extrusion
Woodbond 1910 - ideal for finger jointing of interior stock and has excellent handling properties, high heat resistance and easy extrusion capabilities
Woodbond X-338 – used in finger jointing of interior stock and capable of passing the ASTM-5572 3 cycle water soak while maintaining a high level of heat resistance