Tools for cutting circles

[hendyboy31]

I need to cut perfect circles out of 3/8 plywood that are 2 7/8, 3 7/8, and 5 7/8. The circle can't have a hole in the middle or any dent as it needs to look finished. Any ideas on how to do this other than just cutting with jigsaw or bandsaw following a penciled circle?

 

[Fretters]

Trepanning or tank cutter in a pillar drill.

 

[Ign]

Yep General used to sell (and probably still does) a trepan tool that should do this easily in wood.

 

[Grigg]

Rough cut on bandsaw and double stick tape to a face plate on the lathe for turning to final diameter.

Could get creative with some templates and a top bearing router bit if you don't have a lathe.

 

[littletoes]

Could use a drywall circle-cutter to mark the holes out, then cut!!!

 

[scw1991]

find someone to turn some blanks on a wood lathe to the diameters you require. Then cut to whatever thickness you need by using a miter saw.

 

[catalytic]

find someone to turn some blanks on a wood lathe to the diameters you require. Then cut to whatever thickness you need by using a miter saw.

This is good advice. If you have a lot of them to do or they need to be very accurate, then I would also set up a V block on the left side of the miter saw blade to hold the blanks more tightly and a stop on the right side to get the lengths even. Do be aware that round stock loves to spin when you try to cut it, so good workholding/clamping is a must (I'd be very wary of just holding it with your hand against the fence -- if you must do that, grip hard, cut slow so the saw teeth don't get a chance to bite, and be ready to duck in case the stock starts to spin and then binds in the saw blade).

If you tell us your accuracy spec's on the different dimensions, there may be a different way that works even better (i.e. how close to 3/4" thick do you really need it; how close to the diameters you posted do you need it, and how flat does it have to be).

 

[SteveW1000]

Plunge router with a tramel bar. Use double sided tape to stick block over centre of blank and pivot tramel from this. Fairly standard way of making circular table tops. Bit more fiddley as the circles are small but there are ways of making the tramel to allow this.

Steve

 

[woody 73]

I had a good idea until I saw the part about not having any marks & holes in the center...

This jig is very good but not what you are looking for:

http://www.rockler.com/accuright-circle-jig-for-bandsaws

 

[woody 73]

I like this idea but alas it also makes a small screw hole in the middle, mind you on a lathe it would be gone but not for the op:

 

[scw1991]

another option is to purchase custom dowels turned to desired diameters required, then cut to length. It might cost you a little bit but it's an alternative to finding someone with a wood lathe who can do it for you.

http://wooddowels.frankedmunds.com/item/wood-dowels/custom-wood-dowels/item-1031?&forward=1
http://www.atlasdowel.com/pages/blog/entry/46/
http://www.hastiles.com/wooden-dowels.html

 

[catalytic]

find someone to turn some blanks on a wood lathe to the diameters you require. Then cut to whatever thickness you need by using a miter saw.

This is good advice. If you have a lot of them to do or they need to be very accurate, then I would also set up a V block on the left side of the miter saw blade to hold the blanks more tightly and a stop on the right side to get the lengths even. A crosscut sled on a table saw would work nicely, too. Do be aware that round stock loves to spin when you try to cut it, so good workholding/clamping is a must (I'd be very wary of just holding it with your hand against the fence -- if you must do that, grip hard, cut slow so the saw teeth don't get a chance to bite, and be ready to duck in case the stock starts to spin and then binds in the saw blade).

If you tell us your accuracy spec's on the different dimensions, there may be a different way that works even better (i.e. how close to 3/4" thick do you really need it; how close to the diameters you posted do you need it, and how flat does it have to be).

 

[bob15]

If you take your time a hole saw will work.

 

[G_P]

If you clamp the wood down securely you can use a hole saw with the pilot drill bit removed.

 

[GuyllFyre]

CNC
Plunge router and template/bit.

 

[nickleone]

Cut templates out of plywood large enough to use a router with a guide bushing.

Nick

 

[Leaflessshadetree]

Cut circles out of 3/4 ply wood (or thicker material) using a hole saw. Then nail the piece with holes in it to your final piece. Remove the pilot bit from the hole saw the holes will guide the hole saw as you make the pieces.

 

[lilscorpion]

Plunge Router with a circle cutting fixture. Stupid easy, perfect circles.

 

[1foxracing]

See if someone around you has a laser cutting service. I have one and it would be perfect for that application.

 

[GuyllFyre]

Plunge Router with a circle cutting fixture. Stupid easy, perfect circles.

Unfortunately, circle cutting jigs like that require the use of a center pin.
OP wants no holes or dents...

 

[foghorn1966]

Router with a circle cutting jig to cut a template slightly smaller than the required circle diameter. Two side tape said template to material to be cut, then use same setup to cut circles.

 

[slyonedoofy]

Cut circles out of 3/4 ply wood (or thicker material) using a hole saw. Then nail the piece with holes in it to your final piece. Remove the pilot bit from the hole saw the holes will guide the hole saw as you make the pieces.

This^^^

I have done it many times and works great.

Works great when you mess up and make a hole saw cut too small and you don't have the center of the hole for a pilot bit.

 

[fivespdcat]

Do you have a bosch router? If so buy one of these:
http://www.amazon.com/Bosch-RA1054-Deluxe-Extraction-Adapter/dp/B00005RHPP/ref=sr_1_1?ie=UTF8&qid=1411247807&sr=8-1&keywords=Bosch+router+jig

 

[lilredex]

Do it with a router...no need to spend $40 for a tether. Mount your center pivot on a separate piece held on with double sided tape and install elevation blocks under your router to match.

Example one. Use a hole in the base.



Example two. Make an step in the tether to eliminate the router blocks.



You don't need a plunge router either, you can wind down a fixed base unit after it is in position and running.

 

[beamrider]

I'd give it a try with a plunge router. Figure out some way to make a large guide ring, that the base of the router will fit inside of. I'm sure there is some mathematical formula that can figure out what the inside diameter of that ring should be, given the constants of the diameter of your router base, and the diameter of the circles you wish to cut. Once you have that figured out, it should work just like a Spirograph (remember those from childhood?)

 

[Fretters]

I'm sure there is some mathematical formula that can figure out what the inside diameter of that ring should be, given the constants of the diameter of your router base, and the diameter of the circles you wish to cut.

Just add half the diameter of the circle size required plus the distance from the inner edge of the cutter to the outer edge of the router base, then set the trammel for that measurement and mark the circle.

 

[beamrider]

No trammel in this example. Think 2 circles, one inside the other. The inner circumference of the outer circle would be the guide to the round base of the router. You'd still use your method to determine the distances, tho. I need to think about this some more, maybe some sort of mechanical iris as the outer ring, that way it could be re-sized easily.

 

[Fretters]

No trammel in this example. Think 2 circles, one inside the other. The inner circumference of the outer circle would be the guide to the round base of the router.

Not when in use, but how do you mark out the large guide ring so that you can make it?

 

[Steevo]

If you clamp the wood down securely you can use a hole saw with the pilot drill bit removed.

THIS!! I was reading through this thread thinking "why make it so difficult, when you can clamp it on a drill press and hole saw it"?

 

[beamrider]

Not when in use, but how do you mark out the large guide ring so that you can make it?

That's why I said there has to be a formula, to tell you the inner diameter of the guide ring. An adjustable iris, something along the lines of this : http://vavoo.blogspot.com/2010/06/mechanical-iris-first-try.html would be the guide ring.

 

[Zeke]

If you clamp the wood down securely you can use a hole saw with the pilot drill bit removed.

I knew this answer would come up. The thing is that hole saws are measured by OD. So it would take a 4 1/8th" HS to cut the 3 7/8" circles. That's not a common size. I don't know what he'd do about the 5 inch one. He'd have a LOT of money spent on HS's when one router bit will do all 3 sizes.

The only problem is making perfect patterns. And they have to be perfect.

This will work at least for the patters.

 

[dr_clyde]

I'd have my buddy with a waterjet bang those out for a case of beer. If you don't have access to that, just make a large template and use a router. Easy peasy.

 

[spacedoutbob]

You can do like my neighbor did, He brought it over to the local High School Wood shop and they did it for him for a $5.00 donation.

Bob

 

[lilscorpion]

Unfortunately, circle cutting jigs like that require the use of a center pin.

OP wants no holes or dents...

Ahhhhhh, I get it. He wants the plug not the hole. Totally missed that the first time. Oops.

 

[sberry]

Cut one in a scrap with the holesaw, then clamp it over the next piece and remove the pilot bit.