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
I'm guessing the router is the way to go, but can you lead me to some
hints and tips, pictures, or other suggestions?
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. .
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.
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.
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.
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.
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.)
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,
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.
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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