Thin Cutting Frame Saws - Dry or Fresh?

Frame Saws

Dry or Fresh?

Opinions differ, however, problems remain. Thin slats (lamellas), of course, can be dried up faster but deformations which occur as a result of this procedure significantly influence further processing of slats. Drying of sawn wood of greater thickness brings high demands for quality of driers and elongates markedly a period of time for which your money stay entrapped in the raw material. On the contrary, method of fresh slats production offers reduction in this period, however, the problems caused by this method cannot be omitted.

Saw Kerf: when processing a green / fresh wood on thin cutting frame saw, a substantially greater saw kerf must be taken into account. Fresh wood fibers are of significantly higher elasticity than dry wood fibers, therefore very sharp cutting edge is needed for their sawing. With a slight dulling of the edge which may not show up yet with dry wood the wood fibers stretch being literally torn apart with a tool. A result of this process is "shaggy" tool marks. The torn fibers rub against saw blade body thus causing its heating and later tension loss. A marked saw kerf increase will put this dulling limit off by several hours but the economy effect of thin cut dwindles away.

Saw Dust: fresh saw dust forming when slats are cut stick to the surfaces being cut or they crowd between saw blades with especially thin slats. Troubles occur also with exhaustion of fresh saw dust irrespective of the fact that machine steel parts as feed rollers, inserts between saw blades, clamps, etc. are stained with corrosion. Don't forget that height of the material to be cut is near the saw frame stroke which results in relative difficult pushing of saw dust out of saw kerf.

Kind of Wood: oak contains great quantity of tanning material. Presence of tanning material, water, and steel saw blade cause saw blade sticking already after very short time. The time in question ranges from 30 minutes through 3-4 hours of operation, depending upon the wood humidity. Larch contains great quantity of resin. Processing fresh without applying other auxiliary systems - nebula spraying upon saw blades - is nearly impossible.

Processing of wood using fine-cutting gang saws presupposes that the wood is worked using certain method. 3 - 4 sided working is a condition for reliable cutting. Accurate semi-product at the entry into the machine is guarantee of saw blades´ service life and first quality cutting result. Curved and twisted material puts saw blades under lateral stress which results in tension loss and saw blade run-out. Handling of fresh wood within heated halls leads to its very quick deterioration - cracking on ends, twisting, powdery mildews.

Most of the manufacturers prefer the dry method

Wood is living matter and therefore it must be handled correspondingly. It is recommended that freshly cut wood remain on cold deck properly stored for certain period of time. The wood partially air-dried and eased is best for further processing. Well dried wood is an essence of success. Drying quality remains guaranteed in the chamber and vacuum driers of up-to-date construction. For parquet and furniture-making products the final wood humidity values ranging from 6-8% or 8-10% alternatively, are recommended. The final drying stage is conditioning. Conditioning is treatment and preservation of dried wood status, that is, its final humidity and inner tension so that it suits best the utilization conditions. Wood is conditioned in driers at the close of the drying process or in air-conditioned rooms.

Dry wood, 3 or 4 sided worked is best to be processed on fine-cutting gang saws. It is recommended that wood dimensions be prepared with regard to the final slat number, that is that all the saw blades should stay under permanent cut. Well worked wood blocks with a minimum error tolerance are presupposition for precise wood guidance in the machine. Smoothly worked surfaces and trimmed balk ends are the basic presupposition for long service life of saw blade cutting edges. Depending upon the wood type and cutting height, application of stellite-tipped saw blades puts the edge dulling limit off to a range of 20 - 100 hours.

Saw kerf with a dry material can, at many instances, be designed as far as the lower limit of the tool capabilities, i.e. 1.0 - 1.25 mm. Dry wood is really cut off with the tool and the worked surface is clean. The economy selection of the saw kerf should be performed with regards to the tool sharpening number. That means, the lesser the saw kerf, the lower the total number of the saw blade sharpening. In the final consequence it means that it is possible to sharpen 2-5 times with a minimum saw kerf. The economy saw kerf should allow for at least 7-10 saw blade sharpenings.

A saw kerf size is selected with respect to the cut height. For the purpose of orientation, it is possible to start from the following data:

Cutting Height to 80 mm to 120 mm to 150 mm to 200 mm to 250 mm
Saw Kerf 0.9 - 1.25 mm 1.00 - 1.4 mm 1.05 - 1.4 mm 1.10 - 1.4 mm 1.15 - 1.4 mm

Kind of Wood: oak belongs to the hard deciduous trees. When cutting a dry oak with fine-cutting gang saws, the best cutting edge life results at cutting hard wood species are obtained. Beech, maple - these wood species are tougher when compared to the oak, especially when a maple is cut it is recommended to decrease a number of saw blades by about 15-20% or to reduce the feed rate in the same proportion. In general, the soft wood species can be cut without problems. Too thin slats (2 mm) are prone to fiber cracking and tearing. Reduction in the feed rate often solves the occurring problem.

Result: lamellas cut dry have precise geometrical shapes. Providing they are stored in a suitable environment they do not change further their dimensions and shape. Work surface is clean, lamellas can be used in the next production process without further necessary working.

Careful preparation of Wood and Machine: thin slats are always very sensitive to mechanical damage. Pay attention that the machine is always properly set for the corresponding material. Slats beyond the saw blades must be carries away conveniently so that they are not deformed or otherwise put under mechanical stress. Simultaneously, they must be, however, firmly gripped between squeezing rollers. The saw frame and saw blades must be suspended in perfect vertical position. Parallel suspension of saw blades in the frame can be carried out correctly in an assembly jig. Saw blades in the machine must not knock away! Knocking of saw blades reduces their service life, leading sometimes to their damage. Carefulness in the material preparation as well as carefulness paid to the preparation of tools and maintaining the machine in a good technical state are always rewarding.

Ogden Group RfsProtech