This article was written by Tim Brown, of Mereen-Johnson Machine Company.
With the right equipment, you can achieve a joint suitable for edge gluing directly off the gang rip saw, saving time, yield, material handling, and boosting your productivity.
Properly prepared material is critical to successful glue line ripping. Material to be ripped must be properly kiln dried and stress relieved to industry standards and within a moisture content range of 6% to 8%. Material must also be surfaced (both faces) to assure that ripped edges will be perpendicular to the top/bottom surfaces. The industry standard practice of “Hit/Miss” or “Skip” planing is acceptable.
We define a glue joint finish as follows: Ripped strips must hold width tolerance of +/-.005” throughout the length of the piece. Width tolerance is best measured with a digital caliper on nominal 12” intervals.
Ripped strips should hold straightness tolerance of + or - .015” in 8’ of length. This tolerance does not include stress relieved in the material as a result of the ripping process.
In addition, the ripped edge finish must not have any variance exceeding +/.0025” (example: saw hatch marks) and must be perpendicular to the planed surface within a tolerance of +/-.0025”. This tolerance explains why, with thicker material, it is more difficult to maintain glue joint quality.
Although machine capabilities can be defined with dimensional tolerances, the true definition of a glue joint can be somewhat subjective to individual users. For example, what passes as an acceptable glue joint for an edge glued core material manufacturer may not be acceptable for a high end solid wood table top manufacturer.
Correcting problems with glue line production can typically be achieved by making subtle changes to variables such as feed speeds, tooling design, and gluing practices. The industry standard for the successful edge gluing is to glue material within 24 hours of the ripping process.
Typical feed speeds for glue joint production will vary between 80 – 200 feet per minute based on machine capability, saw blade design, type of material being processed, and other factors. A general rule of thumb is to increase feed speed when blade burnishing is present and decrease feed speed when saw hatch is too coarse.
Another factor contributing to successful edge gluing is the method of gluing. Clamp carriers are more forgiving than RF gluing. This is because Mechanical Carriers clamp panels individually and clamps center themselves on each panel, applying equal pressure from both sides. RF batch presses typically have cylinders on one side and push all boards against each other so there is more potential for accumulation of error.*
It is critical that the gang rip saw be in good condition and adjusted properly for successful glue joint production. Feed works must have a flat and true surface and the means for captivation (friction, spikes, knurling) must be suitable for proper material containment.
Other machine components such as hold downs, dip cams and chain way can also influence feed system accuracy.
Hold downs rolls must be set to rotate on a parallel elevation to the feed bed and perpendicular to the feed direction or the potential for “banana” cuts will occur. The means for providing hold down roll pressure and actuation (typically spring or air) must be smooth and consistent. Feed rolls set with excess yield (rolls set too far below the top of material) or excess force can influence cut quality.
Arbors must be set to be perpendicular to the feed direction with minimal runout and end play. An arbor, when set at acceptable perpendicular position, will deliver a trace crosshatching on ripped strips. Crosshatching marks result from equal “toe” and “heal” saw blade contact with the strip. When an arbor is not running in true perpendicular position, single directional hatching (“toe” or “heal”) will appear on the ripped strip.
Arbor runout can be measured with a dial indicator on the outboard horizontal surface of the arbor. It is recommended that runout not exceed .002”.
End play can be measured with a dial indicator positioned on the outboard vertical surface of the arbor shaft. It is recommended that end play not exceed .001”.
There are additional factors that can affect gluing success. Yearly seasonal changes can contribute to increased glue line failure rates. We typically will field most calls regarding glue line issues in the spring and fall seasons. We believe this to be a result of moisture and material stress issues.
Equipment such as feeding devices, infeed systems, and outfeed conveyors can also impact the glue line preparation success. Feed rolls or other feeding devices should be set to deactivate once material is contained by the rip saw feed mechanism. Any time two mechanical devices compete for containment, there is opportunity to not only negatively affect joint quality but also create unnecessary machine wear.
Feed rolls can be set to deactivate via timing devices or can be equipped with a slip clutch or other mechanisms allowing the rip saw feed works to override the feeding device. This principal also applies to any outfeed roll assemblies.
It is also important that the elevation of the infeed and outfeed systems match that of the rip saw feed works. Material should not change elevation within a distance equal to the maximum length of material to be processed, both on the infeed and outfeed ends of the rip saw.
A common symptom of improper feed system set-up is consistent flaws in the sawn edge at a similar area along the length of boards. Measuring the position of these flaws can facilitate troubleshooting by indicating where feed system interference may be occurring.
Manufacturers are a great resource for troubleshooting glue joint issues. Mereen-Johnson Machine Company has a full time staff of experienced customer service representatives and technicians available to assist their customers with helpful information.
Other resources for assistance are web based forums. Many manufacturers are willing to share their knowledge and experiences regarding processes, tips, and problem solving techniques.
*Information contributed by Michael Burdis – James L Taylor Company, Poughkeepsie, NY
This article was written by Tim Brown, of Mereen-Johnson Machine Company.
