CIRCLE CUTTING WITH THE ROUTER    


 

Circle-cutting Jig with Fine Adjustment

by Sandor Nagyszalanczy ē Jun 4, 2015

Made from 1/2" plywood, this basic jig allows you to cut out or shape accurate circles, semicircles and arcs using a standard jigsaw or router.

Cutting a perfect circular disc out of solid wood or plywood isnít a particularly daunting challenge ó if you use a good circle-cutting jig. This one is useful not only for sawing arcs and rounds up to a whopping four-foot radius, but the base also accepts a router, for curvy shaping work. The jig, shown in the Drawing above, consists of three parts: 1. A banjo-like-shaped base plate that mounts to the jigsaw or router. 2. A long pivot bar with holes at regular intervals that serve as pivot points for different radius cuts. 3. A connector bar that joins the two parts with a sliding joint that allows fine adjustment of the jigís cutting radius.

Material List

1 Baseplate (1) 1/2″ x 6″ x 11″
2 Pivot Bar (1) 1/2″ x 2″ x 41″
3 Connector Bar (1) 1/2″ x 2″ x 81⁄4″
4 T-Knobs (2) 1/4″-20
5 Carriage Bolts (2) 1/4″-20 x 11⁄2″

All jig parts are made from 1/2″-thick high quality plywood, such as Baltic birch. Start by sawing out the jigís 6″ x 11″ baseplate. First, make two parallel cuts on the table saw to form a 5″-long, 2″-wide tongue on one end of the rectangular piece. On the band saw, cut out the 6″-diameter round portion of the baseplate.

Using a table saw and rip fence, make two 5"-long stopped cuts to form a 2"-wide tongue thatís centered on the jigís base, widthwise.

Next, using a band saw (or jigsaw), cut a 6"-diameter circle on the area of the baseplate opposite the tongue cut on the table saw in the last step.

 

Moving to the drill press, bore a 3/4″ hole through the center of the baseís round part and a pair of countersunk holes in the tongue part for two short 1/4″ carriage bolts. Now bore a series of countersunk mounting holes to attach the base of your router (with its subbase removed), as well as holes for mounting a jigsaw (with its foot plate removed). For proper cutting action, the jigsaw should be positioned with its blade teeth centered on the round baseplate, with the sawís body perpendicular to the baseplateís tongue and facing to the left (for right-handed users).

Counterbored holes bored through the circle jigís round baseplate provide the means for mounting either a jigsaw or a router.

From 1/2″ ply, cut a 2″-wide, 41″-long strip for the jigís pivot bar as well as an 81⁄4″-long piece for the connector. Using a dado blade in the table saw, cut a 1/4″-wide, 41⁄2″-long slot in the connector bar. On one side of the slot, cut the bar back 1/4″ and radius the outer edge of the other, then mark its tip with a black marker pen. The tip acts as a pointer, for fine adjustments. On the pivot bar, mark out 37 pivot holes 1″ apart and drill them with a 1/8″ bit chucked in the drill press.

Glue and nail the connector to the end of the pivot bar, positioning it as shown in the Drawing. Apply a short length of sticky-backed measuring tape to the top of the baseplateís tongue. As youíll use only the fractional graduations on the tape for fine adjustments, you can use a scrap of measuring tape left over from another jig project. Now slide the slotted end of the pivot bar onto the carriage bolts on the base and secure the connection with a pair of T-style or other hand knobs.

A short length of stick-on measuring tape allows fine-tuning of the distance between the jigsaw blade (or router bit) and the jigís pivot hole.

Setting Up for Cutting
To use the jig to cut out a round tabletop, arch-top panel, etc., set a scratch awl or nail into the pivot hole thatís closest to the radius of the desired circle or arc. To set the exact radius, measure the distance from the pivot hole to the saw blade, then loosen the hand knobs and slide the connector bar in or out as necessary, then retighten the knobs. Starting with the blade/bit at the edge of the work, pivot the jig around smoothly as you cut.

Itís best to take a trial cut and check the radius; if itís off, you can use the scale and cursor to tweak the setting. When used with a router, the circle jig is capable of accurately routing radius slots, creating curved recesses for line inlays, or for decorative shaping work.

A scratch awl inserted in one of the pivot stripís holes acts as a pivot point, for either cutting or routing circles and arcs.


My circle cutter jig.

The jig described above is rather elaborate and is suitable for ctting big circles. I use a simple jig made of a piece of acrlic,  This type of jig was describe in a website years ago.

This jig is simple to make. It has a number of holes arranged at internals horizontally  . Each hole is a center for different diameter circle determined by the distance of the hole to the far edge of the router bit. To use the jig I have to drive a nail through the hole on the jig to act as a center on the material to be cut . The jig can be any size .

 

Circle cutting jig

Jig attached to my Hitachi router .  

The jig can be of any size .

This cutout could be used as a mirror frame. If you want to make a mirror cut a groove slightly deeper then the thickness of the mirror .To cut the groove  the straight bit should cut the groove along the circumference with the outer cutter edge aligned below the cutting line. Then cut out the disc along yhe inner edge of the groove. The mirror will rest on this groove. To decorate a bit you can run a decorative bit along the front edge of the frame

  

The router is a versatile power tool. There are many different types of bits which can be purchased on like or from tool shops. 


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