How to cutting LARGE holes

[Anthony Whitesell]

I saw in a recent magazine (which I can't find now or was on the newsstand and I didn't purchase) a saw blade holder that was a series of trays. I was thinking that would work well in my shop and I should build one before I drop a blade trying to get them off the pegboard. What I would like to do is cut a 9" hole in a piece of hardboard and then glue it to a another piece exactly the same size to make the trays.

Any ideas on how to cut 9 inch diameter holes where the outside is the piece you want to keep? I word it as such, because I have a circle cutting jig for the router table, and it is just that a circle cutting jig. It works well for cutting circles but not so well at cutting holes if you know what I mean. FWIW, I also have a hand drill, 8" drill press, 8" circle cutting for the drill press, hand router, bits and guide bushings, tablesaw, bandsaw, and spade and twist drill bits, and a selection of hole saws to about 3" at my disposal.

[Rod Sheridan]

Hi Anthony, if your blank is held to a baseplate with tape, a circle jig would be perfect to use with a router.

The other option is to make a good template out of ply or MDF, with a perfect 9" hole in the middle.

Your blanks could be roughed out with a jigsaw, then taped to the template and flush trimmed with a flush trim bit in a router or router table.

Regards, Rod.

[Chris Padilla]

Google this: Jasper circle cutting jig

Wonderful jigs or you could simply make your own if this is a one time deal.

Oh, you will need a router.... :)

[Lee Schierer]

I had to do exactly that for this clock face.
http://www.home.earthlink.net/~us71na/octagonal%20clock.jpg

I cut the pieces and glued up the hexagon. I mounted it on a piece of 1/4" plywood with double sided tape. Located a scrap block in the center of the interior and attached it to the plywood with doublesided tape. Then by measuring I found the center of the block of scrap in relation tothe hexagon as closely as I could measure. I drilled a pivot pin hole for my circle cutting jig for my router. Inserted the pin in the hole, set the router with the jig over the pin and used an up spiral bit to trim out the inner circumference.

You could do the same thing with your hardboard. Infact you could do several at a time.

[Bill White]

Router with a circle cutting base. Build it or buy it. Life is sweet.
Bill

[Mike Heidrick]

Chris has it!! Jasper jigs all the way. They even make a plate you can double stick to your piece and cut out discs with no holes in them.

[Michael Wildt]

Only problem with the double stick plate is that it only works if the circle is larger than the hole/disc and it will raise the router plate a tiny bit.

[Peter Quinn]

Very simple. Router on a trammel, make one blank, jig saw cut the rest, use the first to flush trim the rest to match. Or get a really BIG hole saw?

[Bruce Wrenn]

Just tonight I was looking at ShopNotes, issue 95, Sept / Oct 2007, and saw such a blade holder. To make holes with a trammel, you have to fasten hole that is to be removed to a piece of plywood to keep it from shifting when cuts are completed. Pivot point is in "hole."

[Chip Lindley]

They don't make Forstner bits that large do they???? lol

In all seriousness, a simple trammel base is all that's needed. Don't overThink this small task!

[Dick Bringhurst]

If they did; what would you turn it with? Dick B.

[Anthony Whitesell]

I'm not over thinking, just seeing if anyone had any options for doing this with something that I already had...and a trammel is not something I have...yet. But based on Lee's method, it solves the problem that I (and Bruce) found with trying to use a trammel to cut holes instead of circles. To cut a hole with a trammel, you need a backer board for the blank and trammel pivot to be secured to such that when the circle is cut free the pivot doesn't move.

[Chris Padilla]

Anthony,

If you go slow cutting with a router and trammel, I've found that it usually isn't a problem when the disc is cut free. Working on a rigid foam base helps as well because there is a little give to it and thus a little friction. Works for me anyway.

One other thing you could do is to cut a VERY LARGE circle...then cut out a smaller circle within it such that when you rest your router against it as a template, you cut the exact size hole you want.

[Anthony Whitesell]

Funny Chris, that's what I was just thinking. Cut a 9" circle from 1/2" stock then cut a 3/8" rabbet around the perimeter. Then use a 1/4" straight bit with a 3/4" guide bushing to make an edge following setup (based on the rabbet instead of the out edge) to route the hardboard to make the 9" diameter hole. On the first one, the circle template will get cut down by 1/8" to compensate for the 1/4" diameter (1/8" radius) of the bit.