It is suggested that a few experimental cuts are
taken, with a small cutter (of more or less any
type, as long as it has a bottom-cut facility), on
scrap timber. This may be attached to a
sacrificial piece of hardboard, which is then
attached to the primary disc, with fillets of hot-
melt glue. The purpose of the hardboard is to
avoid possible damage to the surface of the disc
by over-depth cutting. A very good exercise in
this respect is to machine a full circular hole of
about 50mm diameter in one workpiece and then
machine another into a disc which fits it exactly.
Note that for operations of this kind, the mini-
pivot assembly may be removed from the disc
for the purpose of a trial fit, then replaced for
further machining, with no loss of accuracy. The
workpiece must of course, be left in its original
position on the disc.
If some means of accurate measurement of disc
diameter (eg. vernier caliper) is available, trial
fits are unnecessary, since the adjuster knob and
locking nut can be used in conjunction with
feeler gauges (available from most auto parts
suppliers) to adjust the router position directly.
PIVOT FRAME JIG
-12-
Setting-up the Mini-Pivot
Configuration
At this stage, the disc may be left attached to the
worktop for the moment in order to assemble
and get the general feel of the mini-pivot
configuration. For this purpose, the jig should be
re-assembled in accordance with the assembly
instructions, but (temporarily) without the lateral
adjuster stud and knob. This is because the
stud does impart a slight frictional resistance to
the movement of the pivot bars on the rod and it
is important, at least to begin with, that the user
gets the feel of the shoes against the disc.
The jig is placed over the disc such that the
flanges of the shoes rest on the top of the disc
and the smaller diameter of the shoes bears
against the edge of the disc. In this position, the
bars are locked on to the rods. It should be
possible to rotate the jig on the disc freely,
without any undue play in the system. Some
slight resistance to motion will be felt; this is
normal. The shoes must always be tight on the
pivot bars; they are not meant to rotate on their
threaded studs.
Of particular interest is the ability to cut a
complete circle without changing operator
position, i.e. there is no need to walk round the
work. This feature should be practiced
somewhat, since it is necessary to get used to
the idea of controlling the plunge locking knob at
the same time.
Please note that the router cable can
get in the way of the shoes, unless it
is held by an overhead mount.
If this standard is adhered to for all primary discs
made, it becomes a simple matter to fix any disc
to a worktop with matching holes. After initial
making of the disc, an excellent method of
subsequent fixing is to bore out and counterbore
the holes, to accept flat-topped bolts, which may
also be passed through the worktop. Accurate
router boring and counterboring may be
implemented with the jig.
WORKTOP
DETAIL
DISC
DISC
BATTEN