 |
The joint that we developed is based on the many natural characteristics of Bambusa affinis (locally Kanakais) and based on its fantastic strength and general straightness and it can however be made straight by heating over a fire and making straight on a wooden V block. It is almost solid when grown in Tripura farms and the diameter is more or less uniform and round between 15 mm for the fishing pole bamboos and upto 30 to 50 mm for the pole vault pole bamboos. The joint is called DDP (Drill, Dowel and Pin) after the process used which is drill, dowel and pin. Three sizes of drill bits are used in the following sequence.
First the 'T' junction is drilled with a "Fostner bit" which gives a flat bottomed hole on the top of the 'T' and the hole depth is controlled to be precisely upto half the diameter of the top member and equal to the diameter of the vertical member which is inserted into the top member to get a perfect fit. This is when both members are of the same diameter. In some cases we use the vertical in a slightly smaller diameter and even in this case the hole depth is max upto the half diameter of the top horizontal (see picture above)
The vertical member is then inserted after the end is shaped if necessary to fit the hole (in case of irregular size or shape) and another hole is drilled from the top of the 'T" well into the vertical member which is almost 6 to 8 cm deep using a thick twist drill bit of about 12 to 15 mm diameter. The diameter of this bit depends on the size of the hollow lumen in the vertical bamboo member and the diameter taken is always larger than that of the diameter of the lumen so as to ensure a full fit when a dowel of the bit diameter is inserted from the top. The dowel is longer than the hole and protrudes out of the top before glueing. The extra portions are cut only after the glue has dried and set.
The third set of holes are drilled perpendicular to both dowel and member of the "T" joint with a thin twist drill of about 4 or 5 mm bit by keeping the "T' joint flat on the ground and the new holes pass through each of the main members fully through and through as well as the centreline of the dowel in both cases, at the top and the bottom of the joint, thereby locking all members in place and it therefore works quite well even without glue, but we recommend epoxy adhesive to make it waterproof and insect proof for furniture use.
The "T" joint is then used on all four sides of a frame and on any intermediate housed members as per the design and these frames are assembled using the RPG (Ready to Pin and Glue) strategy since these items need to be air-lifted to Kolkatta (45 minutes away by air but 3000 kms by rough road otherwise) or another destination and the final assembly can be done there to save on transport costs. In some cases we have made the items fully stackable so these dont need to be in knock-down condition and can be fully finished at the farm production unit itself. For example the school furniture benches and tables are stackable and can be offered in finished form at a very low cost to local schools in a cash-less economy of the village where materials and labour are donated for community good or through a cash based economy (GDP based) to schools across the country in packs of ten or twenty since these can be easily lifted by two persons while cargo handling is done. No metal hardware is needed in any of these and this is a big advantage for the producer groups since the region has no producer of such hardware and these need to be sourced at great cost and on unreliable supply schedules from Kolkatta.
|
|
