Woodhaven 3220: Oval Jig - Manual (Page 4)

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DIFFERENTIAL
Ovals are measured by their length and width. The difference
between the length and width is called the "differential". Using
the same edge of both pivots as a reference, measure the distance
from one edge of a pivot to the same edge on the other pivot.
Multiply this distance by 2 to get the differential. For example,
if the distance between pivots measures 4", then the differential
between the width and height of the oval will be 8". See fig. 5.
OVAL SIZE
The size of the oval is controlled by the distance from
the tool to the pivots. By sliding the tool closer or further from
the pivots (without changing the differential), you can change
the oval size. To set the oval size, loosen the ratchet handles on
both pivots and slide the bar to the desired size. See fig. 5.
For example, if the jig is set to cut a 24" x 36"
oval (12" differential) and you adjusted the router 5"
further away from the pivots (maintaining the 12"
differential) the jig would then cut a 29" x 41" oval.
You can increase the oval size range (but not the
differential range) of your Oval Jig by getting a longer
Double Track, which we offer up to 96" long.
TECHNICAL STUFF
When cutting a 4" wide oval frame, for example, the
frame will only measure 4" at the 0º, 90º, 180º & 270º points.
It will measure slightly narrower everywhere else. This
phenomenon is common to all oval jigs. Actually the jig is
cutting 4" wide everywhere, but that's measured on the travel
line of the Double Track, which is not square to the edge of
the part, except at the points mentioned above. The greater
the differential, the more pronounced this is. See fig. 6.
If you need a consistent width, cut one side of the oval
using the jig. Make a tool to follow the edge of the oval that
also holds a pencil. Draw the opposite side of the oval at the
width needed, using the machined edge as a guide. We offer a
handy tool for this purpose called the Margin Scribe, PN 3205.
Routing the inside edge first, then cutting the outside edge
with a band saw, is usually the easiest method. See fig. 8.
ROUTING & DRAWING
When cutting the inside edge of an oval, swing
the router clockwise. When cutting the outside edge
of an oval, swing the router counterclockwise.
Insert the pencil holder (3200D) in the bit opening of
the router plate, insert a pencil (with a blunt point - like a golf
pencil) in the pencil holder to draw the desired oval. See fig 7.
CAPACITIES
The chart on the right lists the cutting capacity of all of
our Oval Jigs. It’s based on the standard parts included with
your jig. If you need to cut smaller ovals you have two options.
Option 1: (3230-3250 only) Use just three of the four T-Tracks
and cut a half oval at a time (see chart for half oval sizes).
Option 2: (3230-3250 only) Cut the T-Tracks shorter,
which will reduce their differential range permanently.
Note that the 3250 chart measurements do not cover the
full differential range available because the standard bar is 72".
Get the optional 96" bar (4296) if you need to cut larger ovals.
©Copyright WOODHAVEN INC. 11/15/10
(800) 344-6657 or WWW.WOODHAVEN.COM
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Example of width variation
on 4” frame
4” @ 180º
4” @ 90º
4” At line
of travel
Less than 4” when
measured @ 90º
from edge
Full & Half Oval Sizes Smallest Largest
3220 Oval Jig
4” to 12” differential
13” x 17-25” 41-49” x 53”
3230 Oval Jig
7” to 23” differential
25” x 32-48”
9-18” x 25” half
54-70” x 77”
3240 Oval Jig
7” to 47” differential
49” x 56-96”
9-42” x 49” half
54-94” x 101”
3250 Oval Jig
7” to 95” differential
97” x 104-149”
9-90” x 97” half
97-142” x 149”