Preparation of specimen : Green logs of Gamar (Gmelina arborea), Silkoroi (Albizia procera), Nageshwar (Mesua ferrea), Gutguttya (Protium serratum), Dhakijam (Syzygium grande), Pitraj (Aphanamixis polystachya), Jarul (Lagerstroemia speciosa), Chickrassi (Chuckrassia velutina), Telsur (Hopea odorata), Kamdev (Calophllym polyanthum), Garjan (Dipterocarpus alatus), Haldu (Adina cordifolia), Chapalish (Artocarpus chaplasha), Teak (Tectona grandis), Banderhola (Duabanga sonneratioides), Mahogany (Swietenia macrophylla), Bakroom (Mitragyna parvifolia), Lali (Amoora wallichii), Civit (Swintonia floribunda) and Uriam (Mangifera sylyatica) were procured from BFIDC timber depot at Kaptai and were converted into 1.9 cm ´ 20 cm ´ 100 cm planks. The sawn material was airdried to about 25 percent moisture content. The dried planks were resawn and dressed to prepare 1.27 cm ´ 3.81 cm ´ 91.4 cm strips.
Softening process: For successful bending timber needs to be softened by either steaming or boiling in water for a suitable period. For this purpose a steam chest was designed and constructed with M.S. sheet. Arrangements were made for spraying live steam in the chest. The specimens were subjected to exposure in saturated steam at atmospheric pressure at about 1000C for periods of 30 and 60 minutes prior to bending operation.
Bending device: The bending was done by the hand bending method similar to the one developed by Rehman, Kishan and Kukreti (1956). Two wooden forms with varying radius of curvature were made of Jam (Syzygium grande) timber. One form was prepared with 10 cm to 20 cm and the other with 5 cm to 10 cm radii of curvature.
A flexible steel strap was used to counter the tensile forces on the convex face of bent timber. The supporting strap was made with 32 gauge M.S. sheet of 4 cm ´ 96 cm dimension.
Bending operation: Immediately after steaming, each specimen was put in the wooden form and clamped properly in the bending appratus. The actual bending operation was carried out manually.
Setting : After maximum acceptable bends were obtained in the bending forms, the specimens were maintained in the bent position by means of G. I. wire. The bent pieces were then removed from the forms and kept in that position for 24 hours in order to set the bends.
Data collection: After the completion of setting, the binding wires were removed and the observations on the bending behaviour of the bent pieces were recorded. Any piece showing even the least of rupture on the convex face was considered to have failed. A piece having compression wrinkles upto 0.10 cm across the thickness in the concave face was accepted. The minimum radius of curvature at which breakage during bending operation did not exceed 5 percent of the total bent pieces was recorded. Characteristics with respect to ease of bending, retention of shape and any peculiarity of timber during tests were noted. The specific gravity of wood of each species was also determined on the basis of green volume and oven dry weight.