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.
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.
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.
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".
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.
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
Reply to jclarke at ae tee tee global dot net
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
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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