updated
12/03/11
Direct and Indirect Dividing
Attachment with Tailstock
Cutting wheels on the milling machine
or working-on facets on workpieces require a solidly based dividing
head with a tailstock. I happened to be able acquire cheaply some
WW-lathe parts salvaged from the scrap bin. I gather the parts spend
their earlier life in a clock factory, considering the modifications
made to them. The central part is a short lathe bed. The other
important part was a collet-holding tailstock that at some time had a
bracket for a depth-stop(?) fitted to it. Then I had a simple tailstock
for solid runners, or runners for various centres.
The dividing head was meant to be arranged for three different types of
dividing operations: direct dividing with a small number of simple
divisions (2,3,4,5,6,8,10) on a drum, more exotic divisions using a
large CNC-drilled dividing disc that I had bought some time ago, and
finally I wanted to use on it the geared drive from the other dividing head I had made.
The depth-stop was easily modified to take the sprung stop for the
simple dividing drum. A dividing drum was made, drilling the wholes in
situ on the milling machine using the large dividing disc. A commercial
worm-wheel was bored out for the collet-holding tailstock runner and
keyed to the dividing drum. The dividing drum in turn is clamped to the
runner by a compression ring with three screws, as is done for similar
parts on lathe spindles. The large dividing disc is fitted to the
runner in the same way. The sprung stop for the large dividing disc is
inspired by original products from Lorch or Boley and utilises the
tapped hole in the tailstock for the hand-lever.
Having made a ball-turning
attachment, I decided to fix all parts to the dividing head by
lever-actuated cams. The levers reproduce those commonly found on
watchmakers' lathes. This arrangement looks much neater than set-screws
and also follows the style of the WW-lathes.
The bed of the WW-lathes for good reasons is rather thick and so I was
loosing a lot of clearance under the milling head. In order to regain
some of it, I milled down part of the bed by about 12 mm. I would have
liked to have even more - and it would have been quite possible withou
loosing rigidity for this application, but after milling down layer
after layer every evening over one week I lost patience with my small
milling machine.
The tailstock is basically original, but I had to replace the missing
compression ring that locks the runner in place. Someone had drilled
and tapped a hole for a locking screw at some time. Runners with 8 mm
diametre, as needed for the WW-lathes, are surprisingly difficult to
find. In the end I manufactured one myself for taking the various male
and female centres from the lathe. The most difficult difficult
operation was to drill a concentric hole of 100 mm length for the
ejector. I still have to make a knob from black bakelite.
The collet-holding tailstock runner was rather worn. It was tidied up a
bit, but its nose is not suitable for taking up ring-collets, beeing to
thin in diameter and there not being enough 'meat' to turn on the
spindle-nose cone. Eventually, it will be replaced by a home-made
spindle. The drawbar was missing the knob, which was replaced by a
brass one.
One of the applications of the dividing attachment is for work on long,
slender pieces, such as masts or spars of ship models. These often have
octogonal sections to be milled on, or need cross-drilling a prescribed
angles. The springiness of the workpieces requires a support near the
place where the tool is applied. I constructed a rather luxurious
version of a steady that prevents the workpiece from being bent
downward and from moving sideways under the tool pressure. Essentially
it is miniature V-block that can raised and lowered to accomodate the
diameter of the workpiece and a little clamp that can be screwed down.
The device is held to the bed of the dividing attachment by a pair of
neodynium magnets. The base unit doubles as a base for a miniature
steady rest for turning.
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