. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . Fig. 67B Fig. 67A Fig. 67A—Pattern drawn from sandFig. 67B—Parted pattern with core print clearly in mind, we will now take up the question of^^ draft. ^*Draft refers to the tapering of the sides of a pat-tern so that it may be easily ^^drawn from the mouldwithout breaking out the sand. In Fig. 70A is showna section of a plain flange pattern in position upon themoulding board ready to be covered with sand. Thesides of the pattern are tapered off in
. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . Fig. 67B Fig. 67A Fig. 67A—Pattern drawn from sandFig. 67B—Parted pattern with core print clearly in mind, we will now take up the question of^^ draft. ^*Draft refers to the tapering of the sides of a pat-tern so that it may be easily ^^drawn from the mouldwithout breaking out the sand. In Fig. 70A is showna section of a plain flange pattern in position upon themoulding board ready to be covered with sand. Thesides of the pattern are tapered off in order to facilitateits being ^Mrawn, as shoA\Ti in Fig. 70B. It will beseen that if the sides Avere tapered in the opposite direc-tions the pattern could not be withdrawn without pulling 106 Model Engineering the sand np \^^.tll it and spoiling tlie monld, and that ifthe sides were made perpendicular difficnlty would alsobe experienced. Note that this pattern is made with ahole in the center, and that the sides of the hole are sotapered that upon drawing, a column of sand will be left. Fig. 68—Typical one-piece patterns standing in the center of the mould, so that the moltenmetal running around it will form the hole in the a column of sand formed directly by the pattern isknown as a ^^green sand core. The subject of cores willbe taken up later. Every side of a pattern which in the original designor drawing is sho^^m as perpendicular to the plane uponwhich the pattern will be moulded, or, in other words,every side which must slide through the sand in draAvingfrom the mould, must he tapered or given draft, and thistaper must he in the right direction. In Fig. 70A theamount of draft is purposely exaggerated; one-eighth ofan inch to the foot is usually allowed for small articles, Pattern Making 107 but the amateur could well provide a greater amount, atleast enough to make the taper easily discernible to theeye, for this would mean less work for the moulder andbe
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