Do I need a plunge router to cut circles?

I have decided to use my router to cut out 12" circles. I will also have the need to do 7.5" and possibly 6" circles in the future. I'll use either the Rockler guide or the Woodhaven one.
Do I really need to have a Plunge router to use a circle cutting jig? I would like to avoid the expense of a $99 pluge base for my Bosch router if possible, but I also don't want to be unsafe either.
Brian Elfert
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No - a normal router will work. But a plunge will be easier.

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You don't need a plunge router. You can use the double-sided sticky carpet tape to hold the circle template.
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Brian,
As I asked in your earlier thread you haven't specified what thickness of ply you are using. I would not normally recommend dropping an exposed spinning bit into a workpiece, but it also depends on how deep a cut you are going to take and how big a pin you are using as a pivot. The problem I see is that without a plunge base you have to ensure that the pivot pin is in the hole while holding the router above the work, switching the router on and doing a controlled lower into the workpiece all the while keeping the pivot in the workpiece. The circle jig I have has only about 1/4" depth of pivot pin but that's adequate for a plunge operation.
In your earlier post you said you also have a shaper, does it have a miter slot? if so a pin on the sliding bar can act as the pivot pin and a stop clamped in the slot determines the final radius. With this arrangement you can feed the work into the bit safely and then continue cutting the circle.
Bernard R
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1/4" to 1/2" plywood.

I have the full size 3HP shaper from Delta. I might be able to get a spindle for it that would hold a router bit.
Brian Elfert
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writes:

miter
you
circle.
You don't need another spindle, regular straight shaper knives will do the job. Having looked on Delta's site I would get a piece of ply, screw a rail to be bottom to fit the miter slot and use the ply as the pivot base. Expanding what I said in the earlier post: as you have possibly three sizes of disk to cut, drill holes for the 3 pivot pins, a wooden rail to drop into the miter slot also marked to correspone to each of the 3 radii and clamped in position. You can now load the blank onto the pivot pin and slide the base forward till it reaches the stop, at which point you are at the correct radius, you can now rotate the blank while keeping pressure against the stop. Depending on the amount of material to be removed from the blank, it would be very easy to do it in 2 passes, for the first roughing pass just put say an 1/8" shim in front of the stop, complete the roughing cycle. Back off, remove the shim and do a finishing pass.
Bernard R
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Best question yet is does he have a bandsaw? That jig Norm uses is great and makes perfect circles every time at the expense of a piece of scrap ply and a few dowel pins. I've used mine to cut router bases to <5" and glue-ups to >36".
writes:

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Would not hurt to use a plunger to cut the circle. Very safe and efficient. Jamming a fixed base into the work may be met with some kickback and it will tear either the disc or the wall of the hole. The one (plunger) in the link has its subbase on that is already machined to create 6.00 & 12.00" circles. http://www.patwarner.com/621_Offset.html ************************************************

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Brian Elfert wrote:

Getting a clean start on the cut is harder without the plunge. As long as the bit isn't immense and the piece is reasonably well secured and you don't stick your fingers in the bit there's not really much of a safety issue.

--
--John
Reply to jclarke at ae tee tee global dot net
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Brian Elfert ...

Brian,
The main objection is that its difficult to control a spinning bit when the router base isn't flat to the material. Do you need the disk (the cut out circle) or the pattern (the circle that's left after you cut out the disk).
If you only need the disk, drill a hole through the material that is bigger than your router bit, just outside of the circle, and use that as the starting point. Put the bit in the hole, the jig in the material and make your pass. NO kicking or jerking and no plunge base.
Chuck
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You need a plunge router anyway. Useful things - worth the money.
For circle cutting, then it depends on the design of your jig. If you can start the router out of contact, then either lower or slide it into the cut, then you're OK. If the jig is rigid though (and the best sort are) then you'll need to have this "first cut" movement in the router, not the jig alignment.
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