how do I cut a 6-1/4" hole (not circle)

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I'm building blast gates.
I need to cut some clean 6-1/4" (or thereabouts) holes. Ideally, I'd cut through the 3/4" + 1/4" + 3/4" at the same time to get a perfect fit.
I'm guessing the router is the way to go, but can you lead me to some hints and tips, pictures, or other suggestions?
Thanks,
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Use your collars. Lay out your desired opening on a sheet of template material. Now determine your bit/collar difference for cutting. Say you're using 1/2" bit and a 3/4" collar. Nail your fencing strips 3/4" away from the layout lines. Now cut the pattern (it'll be 3/8" too large in both dimensions), remove the fences, use your new template to cut your openings, which will, of course be 3/8 smaller because of the bit/collar difference. .

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Teach me to change dimensions in mid-thought. Change the 1/2 bit to 3/8.
Or, use 1/4 differences with the 1/2 bit.

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George,
how do I get the round template to start with?
rough out w/ jigsaw then sand? just curious

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Sorry, I saw the "(not circle)" and assumed it was not going to be a circle.
No problem starting with a trammel point to cut a female template, though.
No problem with a circle-cutting jig and a bandsaw to cut a male jig.
Allow your offset for the collar, and note that you cut in opposite directions with the router when using female versus male jigs.

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Round is a bit hard with this method.

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On Thu, 09 Dec 2004 04:17:11 -0700, nospam snipped-for-privacy@mesanetworks.net wrote:

Get a circle cutter for the drill press. It cuts holes or circles. Run it at a slow (~400 rpm) speed, use clamps, and be careful. Depending on the size, a lathe works well too.
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A plunge router with straight bit and circle cutting jig is about as sharp and clean as any method you might try and better than most. I use a Dewalt 621 router, a 1/2" straight bit, and a Jasper circle cutting jig. I've cut numerous holes for dust collection using this method. You can make your own circle cutting jig from a flat sheet material like MDF, tempered hardboard or plywood. The method is precise enough, that I don't think you need to cut all your holes simultaneously. Most jigs work off a small pilot pin located at the center. If you drill this pilot hole in all your stock simultaneously, then cut your circles individually with the router, the holes will line up with each other.
The small Jasper circle jig is available from Woodcraft. It has settings for holes 1" to 7 1/2" in 1/16" increments.
Bob
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Is the 6.25" diameter, 3-1/8" radius going to be a challenge?
My PC690's baseblate is 5-3/4" dia. I'm going to be pivoting very close to it's edge.
On 9 Dec 2004 06:52:41 -0800, "Bob"

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It shouldn't be a problem. If the work piece in which you are cutting the hole is small (providing little support for the router), you can place some supporting stock around it. I usually use a piece of 3/4" plywood as a base, then place the workpiece and some auxillary support stock on tope of the plywood base. I'll use carpet tape and/or brads to hold everything in place. I'll also use F-clamps to hold the base on the bench. The base is sacrificial. I make sure that the center pin goes through the workpiece and into the plywood base. This prevents accidents when you cut through on the last pass with the router.
Your question is a good one, because the success of cutting clean circles with a router is totally dependent on everything being locked down tight. Don't depend on holding it with your hands.
Bob
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Circle cutter on a drill press works great and gives really clean holes
John
On Thu, 09 Dec 2004 04:17:11 -0700, nospam snipped-for-privacy@mesanetworks.net wrote:

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I've read mixed reviews on cutting holes with a drill press in the rec archives. I'm sure not all circle cutters are created equal. What brand do you use and recommend?
Bob
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On 9 Dec 2004 07:00:41 -0800, "Bob"

Many stores sell circle cutters (Home Depot, Lowes, Sears, Ace, hardware stores, etc). Look at the package and find out where it is made. Made in USA, made in Canada, made in Germany are usually good. Lowest quality (for machined tools and castings) is "Made in China." A circle cutter is about the most risky thing on a drill press, so think carefully during setup and operation.
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Bob
Don't even remember the brand, but the key is to run the drill press slow, and FEED the circle cutter slowly to get a good clean cut.
John
On 9 Dec 2004 07:00:41 -0800, "Bob"

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Did any one notice in the subject line that he says "not a circle"

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Can't you use a circle cutter to cut a hole?
Bob
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proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email

Yeah, but I for one am not sure what _is_ wanted.
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wrote:

A drill press circle cutter cuts both a circle and a hole. The cutter part can be switched around to give a cleaner hole or circle. (BTW, I checked out the Craftsman circle cutter ($20) and it's "Made in China," so I'd pass on that one.)
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Yes, that is what I meant. I want to "Keep" the piece with the hole in it and discard the piece that becomes the circle. Confusing I admit. But the shape is circular, not square, etc.
In my original post I noted I was making blast gates. So I need to cut a clean hole in 3 pieces per gate; all alligned.
I'm making a modified version of this, http://www.digitalnetworks.ca/~stevecater/wood/Blast_gates.htm but I plan to just glue in the S&D pipe instead of using the flanges.
there are other plans also, so I've "borrowed" the ideas I like best from each of them. The tape as shims, finger hole as stop, and dowel as stop are ideas I liked from this one (simple). I'm using 3/4" melamine as the body and 1/4" melamine as the slider gate. I prototyped some with particle board to get a feel for it. The 1/4" melamine looks to be on a mdf core, my 3/4" melamine is on a particle board core. Either way they "look" reasonably nice and slide very smoothly. I'm also just screwing the whole assembly together vs glueing. I glued/nailed my prototype, but like the flexibility of screws and it will allow me to make the holes independent and then reassemble. I'm not sure yet if I'll glue the pipe into the gate assembly or not. I'm hoping for a tight fit, and then like the example here will put in 3 or 4 small screws.
Another option is to glue in a half coupler vs the pipe vs a flange. Some pros/cons to each of those. The couplers allow for universal use, but you have to cut one in half, and the O.D of the coupler is probably not a true as the O.D of the pipe making the fit into the gate more challenging.
Most of my gates are going to be integrated into the 6" custom dust port of each tool, so the tool-side half will fit against/be apart of the dust hood.

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I cut circles with a router. Make a baseplate extension out of 1/8" plywood (door skin). Drill a hole at any radius you want to cut and pin it to the work piece. In thick stock you will need to make repeated passes at increasing depths. It goes pretty fast.
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