PLYWOOD
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Page 49
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Classes That are Available and Uses to Which They Can Be Put.
By a TIMBER SALESMAN. ALTHOUGH plywood now enters very largely into the construction of commercial-vehicle bodies (especially those of the passenger type), it is surprising how little the average woodworker knows about that valuable and most adaptable commodity. Possibly it is because some of the old erroneous prejudice against all veneered products still clings to plywood, and the woodworker, always a very conservative individual, will not open his heart and mind to it. The result of this is that vehicle owners often pay excessively for their bodywork repairs.
Only those in the trade know the value of timber, or so it wOuld seem by the nonchalant way in which some consumers order the most expensive material for the commonest class of work. This is specially
e26 noticeable in the motor trade with regard to plywood.
I have seen first-quality plywood panels, such as cabinet-makers use for the highest-class polished work, bought for purposes where they are not seen gild even where they are to be upholstered—a wanton waste of money. Surely this is due to ignorance. A little information on the subject, and a few hints on buying, will, therefore, be of interest to all concerned with the construction and maintenance of bodies.
Lack of knowledge often causes much waste of time, which means a waste of money, when ordering plywood. For instance, many buyers will write an order as
follows :—" One dozen sheets 60-in. by 48-in, five-ply," no thickness being specified. As a consequence the order is delayed until the merchant has time to enquire the thickness required. Then, more often than not, the reply is, "Fiveply." That conveys nothing to the timber dealer, for plywood is made in all thicknesses from in. to 1 in. and over, and in any number of plies. The number of plies has no bearing whatever on the thickness. Few people seem to appreciate this point.
At the present time there are five types of plywood readily obtainable. these being as follow :— Three-ply.—Panels made from three veneers, manufactured in thicknesses mostly from I in. to in. and in some woods up to gin.
Multi-ply.—Panels of any aumber
of veneers, or plies, varying in thickness between in and 1 in. and over.
Laminboard.—Panels with a core of multi-ply veneers, made into a solid block and recut edgeways, with thick outside veneers. These are obtainable, in thicknesses from j in.
up to 2 ins, and over. •
Battenboarti.—These panels resemble laminboard in construction, but have the core made from sawn lumber of from in. to 1" in. thick. Thicknesses available are as supplied in laminboard.
Veneered Plywood.—This coin, Prises all the above types, veneered on one or both sides with some kind of decorative plywood.
Three-ply and multi-ply boards are not always made with plies, or veneers, of equal thickness. A threeply board with the centre ply a little stouter than the two outside plies will be more rigid than one 'having plies of equal thickness. However, an equal-ply board is better foi. bending purposes.
Plywood is produced in the following woods as standard products:—
Birch.—This plywood is imported in tremendous quantities from Russia, Finland and the Baltic States. it is the most reliable of the standard qualities.
Abler.—Frorn Russia and Poland ; light in weight, less firm than birch. and not suitable for decorative work ; should -be used for painted and covered work.
Gaboon.—A mahogany of very light colour. Panels of large dimensions can be obtained.
Oregon Pine.—Ilgually without a blemish and having a beautiful grain; very attractive as panelling.
Ash.—This plywood comes from the Continent, Siberia, China and Japan. It Is very strong and can
• often be mistaken for plain oak;
Oak.—Mostly from the Continent ; it can be obtained figured and plain.
Plywood can also be obtained in the better kinds of mahogany, walnut, etc., but these are not as yet. considered standard products. •
Whenever possible plywood should be inspected before purchase; as the grading sometimes varies enormously. It is usually sold in first, second and third qualities, but often the "first quality" of one merchant will only equal the " second quality" of another.
-The merchant must not be blamed for this, as plywood is graded by the manufacturer at the mills in the different countries from whence it conies, and it will be understood that, timber being a natural product, the quality of material used varies . greatly. For example, birch will grow in one country much cleaner and larger than in another. It will vary even in different districts in the same country. However, the
quality signifies the relative absence of knots and has nothing to do with the strength of the panels.
First-quality panels should not be purchased for work which is to be covered, and it should be remembered that the price goes up with the thickness, irrespective of the number of plies.
It will ,be found cheaper to purchase plywood at so much per 100 feet super than at so much per panel.
Plywood is less likely to warp than solid timber, but all wood will absorb a certain amount of moisture until the pores have been closed up by polishing or paint. Plywood should, therefore, be stored in a perfectly dry place, and the panels must be laid flat on top of each other. Stood on end in a heated workshop they will quickly warp.
One often hears it said that plywood panelling on a finished job will warp. When this happens it is because, although elaborate attention is given to the polishing or painting of the face, the back is left untouched, and is, consequently, exposed to moisture, which quickly causes the panel to warp.
To avoid this state of affairs both sides of a panel should be treated. The reverse or hidden side should be given a rough protective coat or two, whilst the front is properly finished,