Cutting out 40 circles

[bmuir]

I am working on a project to build 20 turntables from recycled plastic-laminated countertops whose substrate is 3/4-inch particle board.
There will be 20, 14-inch circles, and 20, 9-inch circles.
What do you all think is the best way to create these circles in just one operation for each circle that will not leave a hole in the plastic laminate and will not chip the edge of the laminate or the particle board?
As always thanks in advance for the help.
Bill

[crokett]

If you have a bandsaw, take a board and put a peg in it. Mount it to the bandsaw so the center of the peg 7" away from the blade. Drill a 1/2" deep hole in the center of one of your blanks on the particle board side. drop it over the peg, turn the bandsaw on and turn the blank till the circle is cut. Now you have a 14" circle. After you cut all your 14" circles, reset your peg to 4.5" and cut your 9" circles.

If you don't have a bandsaw you can use a trammel jig and a straight or spiral bit on a router but those may require 2+ passes to cut each circle.

[LarryG]

The method David describes is the only way I know to do it in a single operation. You'll have to experiment to see if it gives you a cut edge that's sufficiently smooth, without chipping the laminate.

If not ...

As David also says, you could cut the circles directly to final size using a plunge router, but for 3/4" thick material you'd need to make at least two passes and preferably three. That'd eat up a lot of time.

I'm pretty sure what I would do is cut the circles to rough size with a band saw (or jig saw, if you have no band saw) and then flush-trim them with a template at the router table. Obviously this is two operations, but it'll still be faster than making multiple passes with a plunge router. It will also get rid of the workpiece-holding hassles that are inherent to cutting out circles with a plunge router, and won't kill your router bit as quickly since it'll only be cutting on one side.

If you use a flush-trim bit with a 2" cutter length, you could stack two of the rough-cut blanks together, laminate-to-laminate, secured with double-stick tape, and trim two circles at once.

[jziegler]

Larry's solution is what I first thought of, but it is two operations. It should give a cleaner cut than the bandsaw jig, but takes the extra pass. It's the way I would do it.

Jim

[crokett]

If you are after speed, the bandsaw is probably fastest. If you are after the cleanest edge, Larry's method is the best way.

If you mount your board with the peg on the router table to spin the rough cut blank on, then you do not need to make a template. I've used this method a few times when I was doing repetive cuts. Just make sure you spin the blank AGAINST the rotation of the bit.

[LarryG]

If you mount your board with the peg on the router table to spin the rough cut blank on, then you do not need to make a template.

Excellent point. Most of my template routing is for irregular shapes, not circles, so this didn't occur to me (although it should have, given the band saw discussion).

Another (probable) reason to do it this way, rather than with a template: making a turntable implies the need for a center pivot point, and drilling a pilot hole of the appropriate size will give you that in the same step; and by drilling it first, it'll be perfectly centered on the disc.

[crokett]

Another (probable) reason to do it this way, rather than with a template: making a turntable implies the need for a center pivot point, and drilling a pilot hole of the appropriate size will give you that in the same step; and by drilling it first, it'll be perfectly centered on the disc.

That's why I suggested the pivot point. I made a couple one-legged stools a while back and discovered (by happy accident) that drilling the hole for the pivot point automatically centered the hole for when I attached the center leg.

[JR]

I'd be afraid of wander when using the bandsaw. I'd want to do the two-step process Larry described.

JR

[Uncle Cracker]

If you use a bandsaw, you can stack a half dozen blanks, held together with double stick tape, and do them all at once. That should more than offset any needed setup time.

[newood2]

This may be the easiest and fastest way to do it. I found this video from "The Wood Guy" George Berry.
http://www.metacafe.com/watch/432752...on_a_tablesaw/

Howie