LumberJocks

Cutting a circle with my router?

  • Advertise with us

« back to Woodworking Skill Share forum

Forum topic by siouxdawgs0409 posted 1494 days ago 8007 views 0 times favorited 11 replies Add to Favorites Watch
View siouxdawgs0409's profile

siouxdawgs0409

104 posts in 1680 days


1494 days ago

I have to cut a circle in a 3/4 inch piece of plywood. How would I make a simple jig to do this? My router is the Ridgid R2900.


11 replies so far

View gerrym526's profile

gerrym526

265 posts in 2395 days


#1 posted 1494 days ago

What diameter circle?
If small, you’d make a template out of 1/4 masonite with the hole cut into it, and use a top bearing straight bit.
If large, you take off the baseplate of the router and replace with a plywood base with a pivot hole in it (think of a big compass with a router on the end)-with the distance from the pivot hole to the outside edge of a straight cutting bit equal to the diameter of the cirlle to be cut.
Hope this helps.
Gerry

-- Gerry

View sandt38's profile

sandt38

166 posts in 1494 days


#2 posted 1494 days ago

Router Jig

I use a scrap piece of luanne (some people recommend plexiglass, as you can see right through it) and screw it to the router
. I measure 1/2 of the necessary cutout diameter, and set it from the OUTSIDE edge of the bit to the marked point. Now, I drill a 1/4 inch hole through the luanne and the workpiece. Cut 1/2 an inch through the wood, place tape over the cut side, flip the board and cut the rest of the way through.

-- Got Wood? --- Somewhere along the way the people in Washington forgot that they are there to represent the people, not to rule them.

View dbhost's profile

dbhost

5377 posts in 1818 days


#3 posted 1494 days ago

What the above listed lacks is adjustability. An inexpensive and functional setup is the Milescraft #1203 edge guide and circle cutting jig.

I have one for my Hitachi routers, and it works GREAT. A caveat though, The OE knobs are worthless and will let your jig slip. Get some 1/4” threaded knobs from Rockler to replace the stockers with and you’ll be fine.

-- My workshop blog can be found at http://daves-workshop.blogspot.com

View siouxdawgs0409's profile

siouxdawgs0409

104 posts in 1680 days


#4 posted 1493 days ago

6 inch diameter hole.

View sandt38's profile

sandt38

166 posts in 1494 days


#5 posted 1493 days ago

DB, he did ask for a simple jig ;)

-- Got Wood? --- Somewhere along the way the people in Washington forgot that they are there to represent the people, not to rule them.

View siouxdawgs0409's profile

siouxdawgs0409

104 posts in 1680 days


#6 posted 1493 days ago

The issue here is the hole size. I am not sure that if I can do a 6 inch diameter hole with the type of jig sandt38 has made. I have a jigsaw that I could use by just using a good ole compass and draw a line and cut it out. But I figured with a jig on my router I could get a smoother, rounder hole with out all the sanding.

View JJohnston's profile

JJohnston

1577 posts in 1878 days


#7 posted 1493 days ago

The method and jig described by Gerry and shown by sandt38 are the same, and they will work perfectly for the hole you want. Here’s a hole 6.25” in diameter in 3/4” plywood I made just last night for a downdraft table, using the commercial version of sandt38’s jig as shown. It’s adjustable in 1/8” increments. You’ll need some kind of sacrificial pad under the ply (I use Homasote) to allow the bit to go all the way through, and to provide some friction so the center of the hole doesn’t shift as you cut it free right at the end of the cut.

-- "Sorry I'm late. Somebody tampered with my brakes." "You should have been early, then."

View siouxdawgs0409's profile

siouxdawgs0409

104 posts in 1680 days


#8 posted 1493 days ago

Are you using a straight bit to cut all the way through a 3/4 inch ply? In the picture shown of your commercial model, does the pivot shaft go through one of those many hole that are in the plate? From the photo they dont look like holes but I believe they need to be in order to work like I am thinking it works.

View dbhost's profile

dbhost

5377 posts in 1818 days


#9 posted 1493 days ago

Huh, I guess you are right… Never mind…

-- My workshop blog can be found at http://daves-workshop.blogspot.com

View JJohnston's profile

JJohnston

1577 posts in 1878 days


#10 posted 1493 days ago

The jig is designed to work with a 1/4” straight bit. I plunge in several small increments, and go around several times. Yes, they are holes. Here’s a better shot of the underside. You drill a 1/8” hole at the center, then stick the rod into the chosen hole in the jig and down into the work. As you can see, the holes are arranged by the whole diameter in inches along the bottom axis, with the fractional part on the vertical. The holes for each whole inch are arranged in a spiral instead of a circular arc, so each one is 1/32” farther from the bit than the last. For the smaller holes that fall inside the base plate, the pivot rod just bottoms out against the baseplate. Also shown is the slug that came out of this hole. And I guess I misspoke – it’s adjustable in 1/16” increments. The numbers shown are the diameter, so the actual distance from the pivot to the far edge of the bit is half that.

-- "Sorry I'm late. Somebody tampered with my brakes." "You should have been early, then."

View sandt38's profile

sandt38

166 posts in 1494 days


#11 posted 1493 days ago

JJohnston has the real deal. The Jasper Jig is very nice, and one many speaker builders like to use. But TBH I like to go to my buddy’s house and use his circle cutter drill bit for holes up to 7 inches. you can find one just as nice at Harbor Freight for a lot less. While the router jig, both my home made one and the Jasper jig, work well, they do leave a little room for error when you reach the end of the cut, which is why I recommended going 1/2 way through the workpiece, taping it and flipping it over and finishing the cut. The center pivot point will not move as much, or as abruptly as the portion you are resting your router in will not fall through to the floor, which can throw off the end of your cut. I guess I should add that when I cut the second 1/2 of the hole, I place it firmly, and flat on my workbench.

Of note, I am a speaker builder and I do cut a lot of holes. I just have a few jigs made for specific size subwoofers, and use the drill bit for my smaller ones, like midrange and smaller midbass drivers, and forstner bits for most tweeters, of course using the circle cutter bit for some odd sized tweets.

Just some food for thought.

-- Got Wood? --- Somewhere along the way the people in Washington forgot that they are there to represent the people, not to rule them.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com

Latest Projects | Latest Blog Entries | Latest Forum Topics

GardenTenders.com :: gardening showcase