Cutting circles

[Dell Moore]

Could someone please recommend to me the best (and easiest) way to cut large circle of plywood or MDF? Router? Bandsaw?

Many thanks,

Dell

[Prashun Patel]

If you don't mind having a little hole in one side, then the easiest for me is to use a router trammel and a spiral bit. Make an aux base for yr router out of 1/4" hardboard. Screw one end loosely at the center and plunge away.

There are great circle cutting jigs for the bandsaw that you can make too.

[Lee Schierer]

Both work well for cutting circles, what you need is a circle cutting jig for either or both. The band saw will cut a true circle, but the cut will not be as smooth as that of a router. However a router will not like hogging away lots of material. For a smooth finished edge, I would use a band saw for a rough cut and smooth it out with a router.

Hint: When using a circle cutting jig with a bandsaw the front tips of the teeth must be aligned with the pivot point of the jig. If the pivot is in front of or behind the tips of the teeth, the blade will tend to wander away from the true cut line.

[Dell Moore]

I'll have to build some kind of auxillary table for my bandsaw to use it for the circle. That's another project. I may have to cut it with a jigsaw, then route it.

I THINK I remember you can buy router jigs at one of the big box stores...?

[Rod Sheridan]

Dell, all you need for a router jig is a piece of 6mm ply thats as wide as as the router base, and longer than the radius required.

Copy the holes from your router base onto the plywood, drill them out and attach it to your router.

A small nail will act as the pivot pin............Regards, Rod.

[Walter Plummer]

Another way, (especially good for mdf of other messey materials) is to use the router trammel to rout 1/4" deep then cut it out with a jigsaw staying as close to the line as you can. Then flip it over and use a flush trim bit running on the 1/4" true edge to finish it off.
I know it sounds like a lot of work but it works very well.

[Peter Quinn]

Ditto what Walter said. That is my typical strategy. Sometimes I just route the first 1/4" as a guide with the trammel (made from shop scraps), jig saw the waste close to the line made by the router, then finish the cut with a few passes using the same router and trammel set up and skip the flush trim step. One less thing to worry about.

[Wayne Cannon]

The router jig is dirt simple, but you need to set up with a scrap underneath and some way to keep the circle from moving/turning -- double-stick tape to a scrap piece of plywood serves the purpose. Because you are hogging away a lot of wood, it is a fairly slow and messy process.

The band-saw jig is simple, but not as trivial as the router jig. Using it requires significantly less preparation time, cuts very quickly, and with only normal sawdust. If you keep a steady pace, you get a pretty smooth result -- though not quite the polish of a router-cut edge.

http://videos.americanwoodworker.com...le-cutting-jig

[I used a router to cut circles for years, only making a band-saw jig several weeks ago. I wish I'd done it much earlier.]

[Dell Moore]

Thanks everyone. Walter and Peters idea is an excellent one. I think I am going to cut this thing out of some ply I have sitting around the shop. A little thinner than what would be ideal, but at least I HAVE it. Plus getting to the BB is a pain in the butt.

Many, MANY thanks for all the great ideas guys!

Dell

[Phillip Marsh]

We had to make a lot of 16" diameter discs out of plywood for a military contract and used a Hole Pro X-425 adjustable hole cutter. We used it on a hand drill with its ball bearing mounted shield as we were cutting the discs out of 4x8 sheets and trying to get as many pieces per sheet as possible, but it can also me mounted in a drill press.

The X-425 goes from 2" up to 17" but they have models that go from 2" to 12" and smaller as well. Much better than a single blade fly cutter and the blades make a clean edge.

We could have used a router but it would have added a lot of additional labor to the project which we needed to avoid.

Since getting the Hole Pro we never makes holes or discs with a router - much easier, especially in a production environment to use the adjustable hole cutter with its twin blades that change out in seconds. We were getting 100 holes per set of HSS blades cutting 3/4 marine plywood.

[Mark Patoka]

I use a trammel on my router made from 1/4" plywood and cut circles from 6-16". I use a 1/4" dowel as the pivot point so you do have hole but it doesn't matter for what I make. It is messy and you have to take 3-4 passes to completely cut through. I've also broken a few 1/4" spiral bits in the process. I still have to sand the edge but you do get a true circle.

The Hole Pro looks like something to investigate further.

[Al Sherred]

I use the tablesaw, and a sled , it works great . (Outside Circles)

[Jerome Hanby]

That thing is a little prices, but if it works, I can see it being worth the price. Thanks for the info.

We had to make a lot of 16" diameter discs out of plywood for a military contract and used a Hole Pro X-425 adjustable hole cutter. We used it on a hand drill with its ball bearing mounted shield as we were cutting the discs out of 4x8 sheets and trying to get as many pieces per sheet as possible, but it can also me mounted in a drill press.

The X-425 goes from 2" up to 17" but they have models that go from 2" to 12" and smaller as well. Much better than a single blade fly cutter and the blades make a clean edge.

We could have used a router but it would have added a lot of additional labor to the project which we needed to avoid.

Since getting the Hole Pro we never makes holes or discs with a router - much easier, especially in a production environment to use the adjustable hole cutter with its twin blades that change out in seconds. We were getting 100 holes per set of HSS blades cutting 3/4 marine plywood.