A well-established and popular machine - with many exported world-wide and still in use - the Cawi-Spiral twist drill grinder was manufactured in Berlin by Cawi & Co. at Teltowkanalstra▀e 1-4 in the south-west of Berlin, Germany.
The grinder could be had in either dry or wet grinding forms; the standard models - with a capacity of 1/16" to 1" - were the S2 for dry grinding and the N2 for wet, this latter type having the coolant supply fed through the main spindle. Sub-models included the dry S3 and wet N3, these being of the same basic form as standard S2 and N2 types but with the ability to grind both two and three lip twist drills. If the suffix "60" was appended to a model this indicated that, in addition to grinding the usual included lip angles of 90░ to 150░, angles from 60░ to 180░ could be accommodated.
With the suffix "O" added to the Type N (as in NO) this indicated that an oscillating motion was fitted to the movement of the grinding wheel to assist with the pointing of carbide twist drills - though this specification removed the ability of the machine to hand thin the web with a small wheel. A number of special versions were also offered, the N4-90 for example being able to grind 4-lip tools and having an enlarged chip pan that allowed especially long or flat-pointed drills to be dealt with; this machine was provided with two auxiliary scales at the rear side of the pan, their use being clearly explained in the comprehensive instruction manual.
In a busy machine shop - indeed, in any place where drills are used - keeping them correctly sharpened not only improves the ease, speed and accuracy of drilling, but makes the drill bits last longer per grind and gives drilling spindles, their bearings and motors an easier, longer life.
Drill bits were held in twist-and-open-by-hand, quick-acting chucks with no need for a set of collets or adapter bushings being necessary; originally just two chucks covered the range of sizes from 1/16" to 5/16" (1.5 mm to 8 mm) and 5/16" to 1" (8mm to 25 mm) and could be swapped over in under one minute. In later years four chucks were available, these taking, respectively, drills from 1" to 15/64" (25.5 to 27 mm); 5/16" to 1" (8 to 25.5 mm); 13/64" to 33/64" (4 to 13 mm) and 1/32" to 5/16" (1.5 to 8 mm). Accurate Alignment of the drill bit was assured by a patented guiding system that guaranteed concentricity with the jaws (like all other parts of the machine) of precision manufacture and made from hardened and ground steel.
Using a patented planetary gear system, the drive brought the lips of the drills in contact with the grinding wheel in such a way that with each revolution of the head, the drill turned around its axis 11/2 times for two-lipped drills, and 11/3 times for three-lipped. The result was that lips were always ground alternately, one after the other and because they revolved automatically, they were always exactly alike and concentric with the axis of the drill body.
A change in the point angle (from 90░ to 150░, or from 60░ to 180░ as previously descried depending upon the model) was achieved in seconds by just pivoting the drive head into the position desired and then locked in position by the levers set at the edge of the table.
The lip relief angle could be adjusted within the normal range by a lever on the left side of the drive head, the setting being read on a visual scale.
In its working position, the drive head was locked by a clamping lever on its right-hand side and for changing drill bits was backed away from the grinding wheel - and returned to its work position - by a second hand-lever. On the other side of the grinding spindle, a small grinding wheel was provided for hand thinning of the web.
Dressing of grinding wheels was provided by a diamond fitted to a unit, the sliding action of which was controlled by a long lever that gave sensitive control; also, as the complete headstock was moved within its prismatic guide-ways against the dresser by a handwheel , the diamond point of the dresser could thus be located exactly at the point at which the grinding wheel touched the drill. As an option - but once fitted as standard on the Model NL2-60 - a special dresser was available that could be mounted in addition to the main diamond. This unit was designed to dress the wheel obliquely and so increase the range of angle points able to be ground.
Being completely enclosed, dust from the grinding wheel collected at the bottom of the guard and from there fell into a removable cloth dust collector within the pedestal. As an extra-cost option, a central vacuum dust collector could be provided, a bayonet-locking connector on the dust collector providing a handy hook up to this.
Like any well-made machine tool, the Cawi-spiral was designed to absorb its own vibration, this being assisted by the use of a heavy, cast-iron pedestal stand that offered storage for holding a selection of grinding wheels fitted to their special carriers with built-in, adjustable balance weights. When wheels were changed, a push-pin on top of the wheel housing was provided to lock the spindle.
Mounted inside the stand, the 1.5 h.p., 3-phase motor was bolted to an adjustable hinged plate for adjusting the tension of the direct-drive, twin A-section V-belts, the spindle turning at 2040 r.p.m. on a 60 Hz supply, or 20% slower on a 50 Hz. At the wheel end, the grinding wheel spindle ran in a precision double-roller bearing and at the drive end in a pair of ball races, these being preloaded against each other. As the roller bearing was formed on its inside with a taper, this provided a means of adjusting the end float.
Electrical control of the wheel was by push-buttons - these being duplicated at each side of the stand - with fuses and relays housed in a separate drawer.
Supplied with each machine were the following: a work lamp with a built in switch and magnifying glass for close examination of the work; a hardened and ground wheel balancing shaft; two chucks; two grinding wheel mounts; three keys; one twist drill support; a support for other tools; three wheel-mount plates for thinning wheels; one spare wheel-dresser mount - and a cleaning brush. When ordered with an electric-pump driven coolant system for wet grinding - with feed through the spindle - the set-up was comprehensive with separate main and setting tanks (separated by screen filters inside one housing) and, in the feed line, a full-flow cylindrical filter..