263,580. Williams, E. Oct. 29, 1925. Trephining-appliances.-In a portable machine for performing annular cuts in any material, of the kind comprising positively rotated cutters constrained to move in a circular path and mounted on a rotary body which may be removably attached to the work being operated upon, the cutters are rotated by means of bevelled toothed or friction gearing, or other toothed gearing, driven from a central driving gear mounted on the machine. The machine comprises a central support 3, Fig. 1, which may be stationary or rotary, a rotary body 2 carrying the cutters 28, and a driving sleeve 33. The support 3 has a platform 6 which may be attached to the work by pins 7 or by studs engaging tapped holes 8, or may rotate together with the body 2 .on a detachable centre secured in a recess 8<A>. The centre may be protruded by a spring and may be mounted on a slide laterally adjustable by a screw on a guide secured to the platform 6 so that the machine may rotate about an adjustable centre other than that of the support 3, one cutter only being then used. The same result may be achieved bv detachable centres secured in recesses 8 which are differently spaced from the centre of the machine. The top of the support 3 may be steadied by a stationary tripod 4, Fig. 16, attached to the work outside the radius of the cutters by screws &c. entering bushes 56. In order to relieve the central portion of the work from the weight of the machine a guide having arms 60, Fig. 1, may be used, the lower ends of the arms carrying flanged rollers 61 which travel in the path of the cutters and the upper ends being adjustable on the body 2 by means of a hand-operated nut 63 or by a spring 62. The shafts 29 on which the cutters 28 are mounted may be adjusted angularly as shown' in Fig. 1 or may be parallel to the axis of the machine. The axes of the shafts 29 are normally radial but may be adjusted at other angles in a horizontal plane so that the cutters are not exactly tangential to their path of travel. The apparatus in a simplified form is stated to be useful for surgical operations. The toothed cutters 28, Figs. 1 and 11, are adjustahly mounted on their shafts 29 by means of nuts 32 and may produce the desired form of groove in the work in a single operation or by means of a series of differently shaped cuts. In the latter case a series of cutters, Fig. 12, have teeth of different sections and operate in sequence to produce a groove of rectangular section. Alternatively, a single cutter may have successive teeth of the shapes shown or a series of cutters may be mounted on the same shaft and the teeth located by a keyway in the central hole of the cutter. The cutter shafts 29 are driven through spur and bevel gearing from a central gear 33A attached to the sleeve 33, the latter being rotated by one or more electric motors such as 10, 10<A> or by hand or by a flexible shaft terminating in a bush surrounding the support 3 and having a coupling engaging the end 33<B> of the sleeve. A further bevel gear 14 slidably keyed at 13 to the support 3, may be provided for imparting a rotation to the body 2 simultaneously with a rotation of the cutters on their own axes, or this gear may be dispensed with and the body 2 rotated by hand, in which case a ratchet hand-grip is provided on the body to prevent reverse rotation when the cutters engage the work. When the shafts 29 are inclined, skew gearing 75 is provided. The direction of rotation of all or some of the cutters may be reversed by the provision of additional gearing. The power for the motor may be supplied through brushes 57, Fig. 16, on the stationary support 4. When the machine is attached to the work an automatic feed is provided in which a gear 44 secured to the sleeve 33 engages pinions 45 freely rotatable on a frame 45<A> splined to the support 3, the pinions meshing with an internal gear 46 which transmits rotation, through a friction clutch 70 hand controlled at 69, to a nut 71 screwing on the support 3 and thus feeding the body 2 relatively to the support. In an alternative feed motion the members 44, 45, 71 are removed and a cap is screwed on the support 3 so that on rotating the cap a spring may be compressed between the cap and the top of the body 2. When the machine is not attached to the work the feed is imparted by hand pressure directly applied to the body 2. The depth of cut may be limited by the rollers 61, Fig. 1, on the guide arms 60 or by rollers 64 mounted in spring-pressed holders 23 or on the body 2 and running in or adjacent to the path of the cutters. Alternatively, interchangeable discs 40 may be attached to the faces of the cutters to contact with the surface of the work and limit the feed. Rotary brushes may be attached to the shafts 29 to sweep cuttings away from the path of the cutters and stationary brushes may be attached to the body 2 in holders interchangeable with the holders 23. Guards 43 with internal vanes may be placed over the cutters to deflect the cuttings. According to one of the Provisional Specifications suction pipes and fans may be provided for collecting cuttings. The cutters 28, Fig. 11, have radial passages or grooves communicating with hollow shafts on which they are mounted for supplying cooling fluid during operation, the fluid being deflected from the peripheries of the cutters by the guards 43, Fig. 1. The hollow shafts communicate through passages 20 in the body and a pump 17 with a tank 16 on the body 2. the tank being supplied if necesary through the support 3 by a flexible connection on the centre of the platform 6. An alternative form of lubrication is provided by blocks of solid lubricant such as soap which are mounted in holders 19 and are pressed into contact with the work by springs in the holders. The bearings of the cutter shafts and gearing are lubricated by passages such as 20, Fig. 1, supplied by a pump 17<a> from a tank 15 mounted on the body 2.