PIVOT FRAME JIG
-16-
ADVANCED APPLICATION
Mini Pivot Mode - Off-Centre Work
For decorative applications, the scope of the
Pivot Frame Jig may be considerably extended.
By mounting the workpiece in various positions
on the main disc and using the mini-pivot facility
to cut circles or parts of circles many designs
can be achieved.
A highly-versatile arrangement may be created
by machining a 6mm slot in the disc (referred to
from now on as the ‘primary disc’). The slot is
used to mount a ‘secondary disc’, preferably in
birch plywood, of about half the diameter of the
primary disc and about 9mm thick on to the
latter, via a central 6mm bolt, nut and washer.
Thus, the secondary disc may be rotated on the
primary disc to any desired angular position
relative to the mini-pivot centre and may also be
offset from this centre by any desired amount.
The secondary disc may be marked out with the
aid of rule and compasses into any number of
equal angular divisions, 24 being fairly versatile
since it allows the disc to be divided into 2, 3, 4,
6, 8, 12 or 24 equal sectors.
From these divisions, the disc may be drilled on
its edge with a series of holes of equal depth (it
is very easy to set up the router to do work of
this kind). The holes may be used in conjunction
with a simple stop block and metal rod. Exactly
the same idea may be applied to beam trammel
work. In this case, the trammel pivot is mounted
on a flat worktop and the secondary disc run in a
slot on the same worktop, a suitable distance
away from the trammel pivot. The workpiece is
mounted on the secondary disc by any preferred
means.
It is a simple matter to cut tubes (or parts of
tubes), of a depth limited only by the reach of
the cutter, for inlay purposes. For example,
imagine that a tube of contrasting timber is
required to be glued precisely into an aperture
which has been machined by a 3.2mm (1/8")
diameter cutter eg. Trend Ref. C001 or
3/10X1/4TCT. This can be done by fixing a
suitable offcut of timber to the centre of the MDF
disc and setting the Mini-Pivot system to two
positions in succession, to machine the outer
and inner diameters in turn.
Note that, if the same 3.2mm (1/8") dia. cutter is
used, the router will need to be moved along the
rods by 6.35mm (1/4") or in fact just slightly less,
to allow a little gluing clearance.
The work discussed thus far in this section is
obviously limited by the size of the primary disc,
since the top flanges of the mini-pivot shoes
must be allowed sufficient clearance to do their
job. It may seem at first sight that this
represents a limitation of the system, but in fact
it doesn’t.
EXAMPLES
SECONDARY
DISC
6mm.SLOT
STOP
BLOCK
WORKPIECE
PRIMARY
DISC
INDEXING
HOLES
INDEXING
BLOCK
SLOTTED WORKTOP
TRAMMEL
PIVOT
CUTTER
PATH
WORKPIECE
SECONDARY
DISC
Summary of Contents for PFJ/SET/1
Page 1: ...PIVOT FRAME JIG...
