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Building Materials - Engineering

Q1:

Pick up the correct statement from the following: Method of sawing timber

A tangentially to annual rings, is known as tangential method.

B in four quarters such that each board cuts annual rings at angles not less than 45°, is known as quarter sawing method.

C cut out of quarter logs, parallel to the medullary rays and perpendicular to annual rings, is known as radial sawing.

D all the above.

ANS:D - all the above.

Ordinary Sawing.

It is the most economical, cheapest and is widely used method of sawing. In it only long parallel planks are cut. Because the inner portion is heartwood which is hard and outer portion is sapwood which is soft thus after dryness there will be unequal shrinkage, thus the planks are liable to wrap and twist.

In Quarter sawing, the logs are cut or sawn in a quarter and is then cut in such a way so as to bend in a transverse direction. This method is adopted when no distinct medullary rays are present and gives very fine figure wood.

In this method, logs are sawn parallel to modular rays and perpendicular to annual rings. This method gives the least shrinkage but most wasteful. This method gives most decorative works in which medullary rays are marked, and least shrinkage is because of the property of medullary rays to resist shrinkage.

Tangential Sawing.

If annual rings are well formed and medullary rays are not well formed than tangential sawing is used. In this method, cuts are made tangent to the annual rings. Planks obtained by this method wraps too much and must not be used for costly works. Such planks are not suitable for flooring.