Ingold Fraise
A pinion shaped cutter used for correcting inaccuracies in the shape of wheel teeth, invented by Ingold, a Swiss watchmaker. This consists really of a hardened pinion with square, sharp points. The fraise is gradually brought into depth, in a specially arranged depth tool, with a wheel whose teeth are incorrect, and rotated the while by means of a ferrule and bow. The fraises do not supercede the rounding up tool, but may often be used after it with advantage, for if a wheel contain any thick teeth they would not be corrected in the rounding up tool, which also of necessity leaves the teeth slightly hollow. The fraises cut the teeth in the direction they move on the pinion in working, and, therefore, leave a surface which works with the least friction.
A fraise for any particular wheel should be chosen so that, when placed upon the wheel, the fraise does not bottom, but just touches the sides and almost closes over the middle one of the teeth engaged, at the same time just making contact with the teeth right and left. If the fraise chosen is too large, it will cut a jagged and uneven tooth; and, if too small, will leave a ridge or shoulder on the tooth; in this, as in everything else, practice makes perfect. As a guide at first, it will be prudent to use the sector to ascertain the most suitable fraise for use; thus--place the wheel to be operated upon in the sector, and choose a fraise of such size as will correspond, not to the size indicated by the number of its teeth, but to two teeth less.