In January to August 1976 a series of articles by T. D. Jacobs was published in the Model Engineer describing a gear hobbing machine designed to be within the capabilities of the home workshop. While the machine, of fabricated construction, was designed primarily to cut spur gears the author mentioned modifications to enable it to cut helical and bevel gears without giving a great deal of detail. However he did clearly state the engineering and geometric principles involved. It is possible to make hobs in the home workshop but the procedure to form relieve the teeth is not easy. The article by Giles Parkes (see ref 2 in part 1) describes this process and a tool for achieving it. Arc Euro Trade (ref 8) offer hobs at reasonable prices. They offer a 20DP 14.5deg. PA hob at 50mm diameter suitable for Myford change gears at ￡67. Metric hobs from Mod1.25 to Mod 0.3 20deg. PA at 25mm diameter are between ￡22 and ￡26 each. I have used these hobs and found them of good quality. Hobs for industrial use will be in most cases prohibitively expensive, however, many are offered on internet auction sites, usually used, at modest prices.
展开▼
