Panels & Furniture Asia Jul/Aug 2020

July / August 2020, Issue 4 | Panels & Furniture Asia 64 | WOOD CLINIC Hello Mr Shen, I am a reader of Panels & Furniture Asia. Recently, I am responsible for the manufacturing of solid wood furniture in an Indonesian carpenter’s shop, and was tasked to handle a batch of oval coffee tables made of Nyatoh wood which have been stored in the warehouse for a long time. After continuous sampling and reinspection of the coffee tables, it was found that these solid wood panel tables’ glue lines have cracked, and can be easily broken by hand (see Figure 1). I hope you can help analyse the potential causes, and provide suggestions for improvements and remediation. Yours sincerely, Mr Lin Mr Shim (Shen Yuxin) Reasons for cracked glue lines on coffee table made from Nyatoh wood (I) Analyse the cracks of the splicing glue line of the Nyatoh wood oval coffee table and propose improvement plans: 1. Wood moisture disequilibrium: The moisture content of Nyatoh wood is in the range of 12-25%, whereas the equilibrium moisture content in the warehouse is around 10-14%. This means that wood with high moisture content in the warehouse continues to lose moisture and shrink, leading to the defect of splice glue line cracks in Nyatoh wood furniture. Below is the analysis of the causes and improvement plans for wood moisture disequilibrium: a) Irregular operationof thedrying kiln: Inconsistent thickness of different wood species are dried in the same drying kiln. Due to the differences in wood species and timber thickness, the timbers are susceptible to uneven moisture content. b) Solution: When drying wood in a drying kiln, the timbers should be stacked properly and separately with 1-inch spacers. The thickness of the timber must be the same, and, if possible, of the same wood species. Prior to the drying operation in the kiln, ensure the boiler’s steam supply is stable, and the hot air circulation is uniform and free of short circuit. 2. Quality inconstancy of panels: The use of four-sided planing to prepare Nyatoh wood often results in unstable quality of solid wood panels, and impacts the adhesive force. Recommendations: a) Rough cutter mark: When preparing material with conventional four-sided planer at fast-feeding linear speed, the number of cutter marks has only 5-6 tool marks per foot inch, and the depth of the mark depth (arc depth) is greater than 0.07mm. As a result, there are many gaps in the splice plate’s glue lines, leading to poor adhesive force. It is recommended that the width of the cutter marks is kept at or below 2.0mm. The feeding linear speed of the four- sided planer is set between 10-12m/min so that the number of cutter marks are at 10-12 tool marks per foot inch, thereby improving the rough cutter mark issue of the panel. b) Snipping: There will be gaps in the glue line at snipping sites of the panel material, resulting in poor adhesive force. If the chip ring of the four-sided planer’s planing tool is higher than the outfeed table, snipping may appear at the ends of the timber. It is recommended to check with a ruler to confirm that the chip ring of the planing tool is at the same horizontal plane with the outfeed table. c) Hairy: When wood moisture content is too high, the four- sided planer is not sharp enough, and the sharpening angle is greater than 30o. The planed surface of the timber may be hairy because of cell damages, leading to defects such as glue line cracks or false gluing as shown in Figure 2 and 3. It is recommended that the operator regularly inspect