Grades for wooden patterns denoted with H 1 a, H 1, H 2 and H 3.
Class H 1 a meets the highest design requirements; the patterns are to be made of hardwood (maple, pear, cherry, walnut and elm wood) or equivalent veneer panels (maple, beech) glued with AW 100 and are used for series production in hand and machine mold making (see Molding process). Reference values for the number of castings: 1000 with favorable, 500 with unfavorable pattern shapes (no large-sized patterns).
Class H 1 concerns patterns intended for the production of high quantities in hand and machine molding with high design requirements. The pattern material is the same as for grade H 1 a, but pine wood may also be used for large patterns. Reference values for the number of castings: 500 with favorable, 200 with unfavorable pattern shapes and 15 with large-sized patterns.
Grade H 2 is intended for small batches and repeated single castings in hand molding. The pattern materials used here are alder and pine wood or equivalent wood materials. Reference values for the number of castings: 50 with small- and 15 with large-sized patterns of favorable shapes or 30 with small- and 5 with large-sized patterns of unfavorable shapes.
Grade H 3 is meant for single castings in hand molding. For this grade, softwoods (spruce, pine, alder, lime wood and fir wood) are used as fillers, and sometimes even chipboard. Reference values for the number of castings: 1 to 5 with small- or 1 to 2 with medium- and large-sized patterns.
The admissible dimensional variations are the same for grades H 1 a and H 1, but more closely tolerated than for grades H 2 and H 3. For the group of the two latter grades, the admissible dimensional variations are also the same.
Moreover, information on butt joints, frame spacing and clearances, fiber direction, reference surfaces and guides as wells as fillets and loose pieces is included. Varnish should be applied in three layers for grades H 1 a and H 1, in two layers for H 2 and in one layer for H 3 (see Pattern coating). If possible, the pattern wood should be dry, a moisture content of 10 to 14 % by weight is desirable.