Woodhaven 3230-3250: Oval Jigs - Manual (Page 4)

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 6", then the differential
between the width and height of the oval will be 12". See fig. 9.
The differential range is controlled by the length of the
T-Tracks that came with your Oval Jig. You can increase the
differential range (but not the oval size) of your Oval Jig by
getting longer T-Tracks. We have 12", 24" and 48" T-Tracks
in stock and we can make custom T-Tracks up to 96" long.
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. 9.
For example, if the jig is set to cut a 27" x 60"
oval (23" differential) and you adjusted the router 5"
further away from the pivots (maintaining the 23"
differential) the jig would then cut a 32" x 65" 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. 10.
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. 12.
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 11.
CAPACITIES
The chart on the right lists the cutting capacity of all of
our Oval Jigs. It’s based on the standard T-Track length (or base)
included with each jig. If you need to cut smaller ovals you can
cut the T-Tracks (or base of the 3220/3210), but you will reduce the
differential range. Note that the 3250 measurements do not cover
the full potential differential range available in this jig because it
uses a 72" bar. By getting a 96" bar you can cut even larger ovals.
©Copyright WOODHAVEN INC. 6/24/08
(800) 344-6657 or WWW.WOODHAVEN.COM
3
9
10
11
Example of width variation
on 4” frame
4” @ 180º
4” @ 90º
4” At line
of travel
Less than 4” when
measured @ 90º
from edge
12
3210 Oval Jig
1” to 10” differential
Smallest Largest
1” x 3-11” 10-18” x 20”
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” 54-70” x 77”
3240 Oval Jig
7” to 47” differential
49” x 56-96” 54-94” x 101”
3250 Oval Jig
7” to 95” differential
97” x 104-149” 97-142” x 149”