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Information about the use of “Berliner Dendro-Bohrer”
- the borers for dendro sampling by the manufacturer PFUNDT-Schneidwerkzeugmechanik:
The borers were developed in cooperation with the dendro laboratory of the Deutsches Archäologisches Institut Berlin (the German Archaeological Institute, Dr. Karl-Uwe Heußner DAI, Ref. Naturwiss, Im Dol 2-6, Haus IV,D-14195 Berlin) to be able to carry out samplings with minimal side effects. They are suitable for dendrochronological examinations especially at historical construction timber and are conceived for the use in solid dry wood. Fresh wood can be bored more or less well depending on its nature. Boring into wet wood causes problems with the chip removal. Moreover, the wood core can become wedged in the borer by the swollen condition.
It is optimal to extract a core as big as possible from a drill hole as little as possible. That implies that the cutting geometry lies in the limits and is corresponding to proceed.
Two diameters are offered at present:
· Nominal size 5 mm of wood core (4.8 mm.)
· Nominal size 7 mm of wood core (6.5 mm.)
The length of the wood cores is about 240 mm- 290mm by default. Little longer or shorter borers are deliverable on demand.
Problems in the wood conservation by fungal attack, pest infection etc. lead to useless cores regarding the relatively small core diameters. Soft early wood zones or tensions appear in the wood occasionally so that the borer transports merely wood chips of the late wood. In this case it is helpful to execute a greater core diameter (for example standard borer 15 mm wood core) or to use the saw. A closed core only has to be expected if the wood offers sufficient stability. Foreign materials like nails, stones etc. in the wood lead to serious damages or total loss of the borer very quickly and have to be avoided by all means.
The dendro laboratory of the Deutsches Archäologisches Institut uses these special borers in addition to the standard borers in particularly sensitive areas as:
· woods in the visibility range,
· inside ceilings,
· door leafs,
· at particularly weak beam dimensions,
· square planks,
· boring without an available current source and similar.
Unlike the increment corers no splitting up lengthwise has to be feared at the use of these special borers even when drilling planks or the like as only little strength impacts on the sampling. The effectiveness of the borers’ cutting geometry makes this possible.
The borers are executed for the use with heavy accumulator drills, which are equipped with a direct electronic speed control.
The optimum rotational speed is 850 - 1400 1/min (rpm) depending on the type of wood and its condition. Net machines also can be used, but lead quickly to an overload of the borer. A manual operation is not sufficient.
When boring most important is patience, patience and patience again. Each wood is different and puts a new challenge to the drill. Oak is not oak at once. If the annual rings lie more narrowly oak is softer than at higher increase distances. The boring behaviour of the drill also changes with that. If at first boring goes fast, it does not seem to go in the harder part any more. It is most important that no additional pressure on the drill be put now. This will result in bending and breaking. Let the drill bore and be patient. Easy pressure and a constant speed are sufficient.
With the new generation of drills pulling out is made easier if the direction of rotation is changed at the drill (left-hand motion).
The thermal load is very large at hard conifer wood since you pass resin rich regions in the wood and with the result that a sticking together may occur.
The conditions in the dendro laboratory can surely not be compared with a work outside where you must work over head or stand on unsteady ladders.
Therefore, you should drill straight through if possible, keep the pressure constantly and try out the speed at adverse circumstances.
So much energy as for spudding is almost needed for the reverse turn of the borer from the hole. Therefore, the accumulator must be fully charged or an additional charged accumulator should be available. A core should not be drawn with reduced strength. A little grease or beeswax can have a favorable effect on the drilling behavior. Depending on the situation a higher rotational speed can be advisable.
After putting on it must be drilled off the reel with slight pressure. The core sampling with the 7-mm-model can be made easier when the chips are removed regularly. This concerns the reverse turn particularly and requires some skill. It should be bored as evenly as possible. Otherwise, the core mostly remains in the borer concerning borings above the pith area. If this is not the case a little wire hook helps concerning the 7-mm-model. It becomes more difficult regarding the 5-mm-cores. The hook of an increment borer can be helpful. The same applies to a pipe with a small sampling hook at the tip, which corresponds to that one of the borer (without cutting head).
The core must be pushed backwards after boring. Possible stuck-out pieces can completely be pressed into the borer by pressing the wood surface. Usually it does not work to pull out the cores. The core is, then, to be pushed behind the cutting edges with a match or the like and backwards with a 4-mm-diameter-stick. This helps saving the cutting edges. Caution: Do not damage the sensitive cutting edges! Small pipes (long straw) or prism holders are useful to save and store the cores.
The shank diameter of the borer of 12 x 40 mm for the chuck is connected to an industrial adhering at the pipe. It is a little sensitive to heat and must be cooled down at multiple use. In difficult cases gluing in once more with superglue or epoxy resin adhesive becomes necessary.
Careful re-sharpening is possible in case of smaller damages at the cutting head. Proceed as sparingly as possible and strictly pay attention to the compliance with the angular ratios. A fine diamond three-square file with the granulation D 46 is suited for the field survey.
All precautions and work protective measures usual for machine tools have to be taken into account. Unlike full steel drills a substantially higher danger of breakage exists with hollow-walled core borers. Idle rotation at high speed without working in a drill hole has to be avoided. There is a danger for the eyes when boring overhead. Wear safety goggles!
And now: Enjoy your borers.