WOOD FOR AUTOMOBILE BODIES ¹ 240022

Shortage of the most desirable kinds of wood for automobile-body purposes has necessitated the substitution of second-choice woods having the essential required properties and the buying of stock for body parts in cut-up dimensions that conform in size with those now produced in the cutting-room. An investigation by the United States Forest Products Laboratory as to the species, kinds, grades, sizes and amounts used by the automotive industry shows that maple and elm comprise over one-half the total amount used and that ash and gum constitute one-half of the remainder. Although the quantity of ash used has not decreased, the increase in the production of medium and low-priced cars in the last few years bas caused a proportional increase in the demand for maple and elm. Classifying cars for purposes of analysis into four groups, small, medium, medium-large and large, the investigators found that the woods most used in small cars are hard and soft maple, elm, birch, beech, oak, gum and pine; that maple, elm and birch are used extensively in bodies of the medium and medium-large classes; and that ash predominates in the large cars, with hard maple as an alternative choice. Fifty-one per cent of the running-boards are made of pine, and 17 per cent are made of sound wormy oak. Oak, ash and elm are used for top-bows in the proportion of 92, 7 and 1. The grade of lumber used in bodies is very high, 40 per cent being firsts and seconds, and 49 per cent No. 1 common and selects. The problem of eliminating light or brash ash is important and, while there are no visual means by which tough and brash ash can be separated, the factors that afford a fairly reliable criterion of strength and toughness are density, rate of growth, proportion of summerwood and the original position of the wood in the tree. Seasoned ash that has good weight and is sound will have strength. Unseasoned ash, on the other hand, cannot be judged by weight.

Little or no uniformity in size of corresponding parts was found among the various makes of body, although the majority fall within very narrow limits. Charts have been prepared showing the range and grouping of the sizes of several of the main body parts, such as the body and door pillars of closed bodies, the main side sills, the side roof-rails, the front and rear roof-rails and the rear belt-rails. The stock used in the larger bodies is of very high quality; in open bodies a few small defects are allowed; in smaller and lighter bodies the requirements are not so severe, a mixture of woods is used, and some defects, such as small sound knots, are allowed; in soft maple, elm and gum, considerable amounts of stain and dote are admitted. When the requirements are not exacting it would be possible to utilize sound low-grades; the use of clear stock where sound stock is sufficient introduces unwarranted expense and wastes material that might serve higher purposes. As the waste in cutting ranges from 20 to 50 per cent, it is evident that careful work at the saws may result in considerable saving. Other ways in which saving may be effected are the gluing-up of stock to get required sizes and a more general use of ready-cut small-dimension stock. As automobile builders are much interested in finding woods that may be substituted for those now in use, a table is given showing the specific gravity, strength, stiffness, shock-resisting ability and hardness of the principal species as compared with those of forest-grown white ash; and the advantages and disadvantages of first and second-growth timber, and such woods as ash, hard and soft maple, rock and white elm, birch, red and sap gum, oak and the softwoods are discussed.