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How can I cut a large (3.5' - 4' in diameter) circle out of a 4x8 sheet of plywood. The preferred method would be one that doesn't leave any holes/marks in the circle's plywood surface. It needs to be as near perfect as possible (shape/edges of the circle). The circle cutout will be used as a table top.

The tools that I have at my disposal are: Router, Dremel, circular saw, 10" table saw, 14" band saw, 10" drill press, jigsaw, and a lathe.

  • Define large? What size? – Joe Oct 22 '15 at 15:26
  • 3.5' - 4' in diameter – Programmer Oct 22 '15 at 15:27
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    Ah. That's different. I'm not sure I've seen a circular drill bit 4' in diameter... – Joe Oct 22 '15 at 15:28
  • I think I need to make another edit to explain this better. I need the circle cutout to be usable, not the plywood sheet. – Programmer Oct 22 '15 at 15:29
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    @Joe if you ever find one of those 4' diameter drill bits, let me know. – Dan Henderson Oct 22 '15 at 21:44
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How can I cut a large circle out of a 4x8 sheet of plywood?

You sound like the perfect candidate for a router circle jig. The one linked is available at Rockler, but they are easy enough to make yourself out of plywood.

circle jig

The preferred method would be one that doesn't leave any holes/marks in the plywood surface.

The one pictured uses a pin to keep the jig centered. This will leave a small hole in the plywood that you could either keep on the bottom side (assuming it doesn't go entirely through) or find a way to cover up.

Otherwise, you should be able to find a way to affix the circle template to the plywood in a non-marring way, such as using double-sided carpet tape.


There are other means to make a large circle, as identified in this related Question. However, in my opinion, none will leave as nice of an edge finish as the router.

  • Oh man, this would work perfectly. And the idea of putting the little hole on the bottom of the table would be just fine too. Great idea, thanks. – Programmer Oct 22 '15 at 15:41
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    @Hooplehead24, If you only have a one-sided hole for the pin, it's a good idea to have someone else hold down the center of the jig or to put some weight on it. Given the forces at work, it's not hard to yank that pin out of its seat and ruin your piece. – grfrazee Oct 22 '15 at 15:46
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    If you have some spare wood, you can also clamp two together, put the pin into the sacrificial part, saw the circle (and detach, reattach clamps as you pass them) and then the pin hole is just in the sacrificial wood part. – PlasmaHH Oct 23 '15 at 8:26
  • @PlasmaHH, good suggestion. If you use 1/4" plywood or even hardboard, this should give enough support for the jig while not reducing the available cutting depth of the router bit too much. – grfrazee Oct 23 '15 at 15:01
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    For fixing the center pivot, I use the lathe-turners trick of a glue block - fit the pin into a small disc of wood, and use a hot-melt glue gun to fix it. A couple of sideways taps will knock if off again when you're finished. – Beejamin Jul 31 at 1:40
10

You can cut a perfect circle top using your table saw.

To do this, you will need a jig (a large sheet of plywood with a pin on which the board being cut spins).

Cut off corners (on the work piece) to remove large amounts of excess material. The first set of cuts take a square piece to an octagon. Then cut off more corners.

Using the jig, you can slowly cut off the excess by spinning the work piece.

Here is one example I found showing this technique: Cutting large circles on the table saw

If you need to have both sides of the work piece without holes, you can attach it to a sacrificial board using double sided tape.

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    Thought you were crazy until I saw the video. Makes me want to go home and try this! Thanks – JPhi1618 Oct 22 '15 at 18:24
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    They wouldn't call it a table saw if you couldn't make table tops with it, right? – hobbs Oct 23 '15 at 5:45
  • I have used this technique once and I encourage extreme caution. It's surprisingly easy for work to kick back when it can rotate, even if you are paying attention. – Eric Lippert Oct 24 '15 at 1:07
  • There is a response video from the same person who talks about the dangers associated with this technique. One suggestion was to clamp the work piece to the jig. That should minimize undesired rotation of the piece. – Adam Zuckerman Oct 24 '15 at 1:47
5

Another option if you want to buy a tool for your Band saw, there are circle cutting jigs. The Carter one can cut circles over 4' in diameter. I have one of these, though I've only used it a couple times. For flat stock it works pretty good, I bought it to cut bowl blanks round. You need to have your band saw tuned up well to get best results.

[!Jig[Jig being used

  • Oops, I keep doing that. – bowlturner Oct 22 '15 at 22:30
3

Pick one according to skill level.

  1. Hook it up to your lathe after cutting it down to an octagon or hexadecagon, (squares are unruly,) and use a wide lathe bit to trim down to a penciled circle. Sand to perfect straight edges. Only try this, though, if you are good at lathing.

  2. Also, you can put a nail in the middle, hook up a hand- moved power saw to it with a string as you would with drawing a circle, and ever so carefully pull it around the string into a perfect circle. You could also use a little wood and a nail or two to make a compass, which does the same thing. You can pull this with a little less skill using a router.

  3. For a little money, you can put it on a device that spins it into a saw blade until it's perfectly circular with a pin. If you're willing to spend any money, you can buy a circle cutting jig or similar device for downwards of 400$. If needed, sacrifice a small piece of wood that holds the pin and is duct-taped on. This can be a piece you cut off to start.

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    Lol at trying to spin a 4' octagon on a lathe, trying to make a circle. #2 is much better answered by grfrazee's answer, and #3 is fully explained by Adam's answer without spending $400 on anything. – JPhi1618 Oct 23 '15 at 14:29
  • Cut it to a square, then an octagon. He's making a circle, so he won't be lathing a rectangle anyway. – Caleb Woodman Oct 23 '15 at 17:36
  • Cut a hole 3.5' after mounting an 8 ' long plywood sheet on a lathe chuck? – Narasimham Oct 23 '15 at 20:59
  • trim down to a circle. You'd need to have a big one. – Caleb Woodman Oct 23 '15 at 21:37
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If you absolutely want no marks on either side of your workpiece, use a router circle jig as above and make a template. Attach it to your workpiece with double-sided tape and use a pattern bit. Cut close to the line with a jig saw and finish with the pattern bit.

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