A Geared Dividing Head

Making equal divisions on the circumference or on the face of a turned part is a frequent shop task. Think of drilling holes for the spokes of wheels, cutting a spur gear, milling flat-sided columns, cross-drilling etc. The watchmakers lathe usually has some simple diving capability built in as the pulley has 60 equally spaced holes drilled in one of the faces. Some lathes sport even two or three rows of holes. A spring-loaded stop is provided. This indentation capability, however, is meant to be used with the double filing rest. The milling and grinding attachment can also be used. If you have one on a vertical slide, almost every type of gear etc. can be cut that has the divisions of 2,4,6,10,12,15,20,30, and 60. A rotating headstock, as was available from some manufacturers, makes the arrangement more versatile (Figure 1). The ultimate would be a large dividing plate mounted either on the back of the headstock, or on the back of the milling spindle (Figure 2). These dividing plates fetch premium prices these days on the second-hand market.

I have been tossing about with the idea to make a miniature universal, geared divind head for some time. This was meant to take 6 mm collets and other work-holding devices, such as the 3- and 4-jaw chucks. This would be for use on the milling machines and could be used for exotic tasks like cutting microscopic bevel gears. Then I happened to acquire, together with some other lathe stuff, a not so-good-anymore 6 mm grinding attachment (LS&Co. No. 31a). Inspired by some exotic Lorch equipment (Figures 3 to 5), I designed a geared dividing attachment that fits onto the grinding attachment.

The intention was to alter the historic substance of the grinding attachment as little as possible. However, a previous owner had already used it for a similar purpose and drilled a hole for a spring-loaded stop. So in the end I became less concerned.

The divind head was to be used for direct dividing, using a drum with three rows of holes (6,8,10) allowing the most common simple divisions of 2,4,(5),6,8, and 10. A 40 teeth worm-wheel and worm together with a plate of 90 indentations would allow 3600 division steps, i.e in increments of 1/10 of a degree. In addition, the self-locking properties of of the worm would allow to carry out various circular milling operations. The indirect dividing attachment can be exchanged for the direct dividing stop by simply loosing one screw.

For the conversion I replaced the two-step pulley with the dividing drum and the worm-wheel coupled together with two pins. The original collar to tighten the pulley down on the spindle was retained, but the slot-head screws were replaced by M2.5 Allan screws, for which the head was turned down. A clamping bracket fits on the cylindrical part of the grinding attachment's body (Figure 18). In this way it can be turned around for fitting the attachment either parallel or perpendicular to the lathe axis. A stub arbor is used to mount the two types of indexing gear.

The indirect dividing gear (Figure 12 to 17) consists of a steel body that provides a simple cylindrical bearing for the spindle that carries the worm on one end and the divind drum at the other. The indexing wheel is a commercial brass 90 teeth spur gear. The zero-adjustable drum (with friction locking) was graduated on the milling machine using the spur gear as template. Numbers were stamped in with the help of a little gadget that kept the punches perpendicular to the bevel. The knurl was cut with a milling cutter. The locking pin is spring loaded as can be seen in the drawing (Figure 7). A crank allows easy turning for circular milling etc. By loosening one screw, the worm can be disengaged.

The dividing head fits onto the 6 mm D-bed lathe cross-slide directly. Since in the WW-lathe the centre-height above the cross-slide is higher by 1 mm, a spacer had to be made. On the Dixi mill it can be either mounted directly or on a raising block to provide clearance for the larger chucks (Figure 8 to 11).

In shipmodel building from time to time slender and tapered pieces (e.g. masts or yards) have to given facets or need to be cross-drilled. For this purpose a support at the outward end is necessary. Inspired by the diving head that fits onto Myford vertical slides (Figure 6), I also designed a tailstock support (Figures 8ff.). A 6 mm hole was drilled and reamed for a sliding bar to be clamped in place. The 'tailstock' has a short cylindrical runner that can be tightened by a screw and accepts the the standard LS&Co. or WJ&Co. centres. In this way I have the whole collection of hardened male, female, half etc. centres available.