130 PATTERN MAKING 



and before removing from the Lithe, a circiilar line must be drawn 

 on the ends of the blocks, on both sides of the rim, indicating the 

 whole depth of the teeth. The use of this line will be explained 

 later; it is the only circular line needed for laying out, or for 

 working out the teeth. When the teeth are large, a tooth block 

 is first fitted on and screwed from the inside of the rim as shown 

 in Fig. 237, one edge of the block touching, but not covering its 

 line on the face of the rim. The thin strip is next fitted, glned 

 and braded against the block with the opposite edge of the strip 

 reaching just to, but not covering the next line. A second tooth 

 block is fitted and screwed in place, then a second strip, and this 

 alternate placing of blocks and strips continued until the surface 

 of the rim is covered, having a block and strip for each tooth 

 required. 



Care must be taken not to allow any glue to get between the 

 blocks and the strips when gluing and nailing the strips on. a^ 

 each block must be taken off, one at a time, after being laid out, to 

 work the tooth to shape. When all the blocks and strips are in 

 place, the wheel must be returned to the lathe and the face of 

 the blocks turned to the diameter required for the addendum or 

 outer ends of the teeth, and the ends of the blocks also turned 

 even with the rim. 



The whole depth circles are marked, one on each side, while 

 revolving in the lathe, as explained for a wheel with smaller teeth. 

 All parts of the rim should now be made perfectly smooth with 

 fine sand paper using a holder or block, to prevent rounding the 

 corners or angles of the tooth blocks. 



Beginning at the middle of a block, space the required number 

 of teeth on the periphery of the tooth blocks, and should the first 

 trial not result in even spaces, the trial spacing must be continued 

 until the greatest accuracy has been obtained, that is, until all 

 distances from point to point are exactly equal. Through each 

 spacing point, found as above, very sharp but light lines are drawn 

 across the face of the block*, as was shown for tin 1 wheel rim in 

 Fig. 240. When drawing these lines it will be found best to draw 

 along the tn^'ulc edge of the try square blade instead of the outside 

 as is usual. The reason for this is that on small or medium sized 

 wheels, a much firmer base will be given for holding the square. 



