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Thread: Circle cutting jigs for router
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11th January 2006, 11:39 PM #1
Circle cutting jigs for router
I made two circle cutting jigs for the router today. The first was for circles smaller than the baseplate radius.
pic1: trace out the old baseplate on a piece of 4mm ply. Fit a 5mm straight router bit and plunge it through. I needed a hole of 100mm diameter, so measure from the outside of the hole to 50mm (radius), and mark the centre of the hole for the locating 'pin'.
pic2: The pin is a piece of 6mm jarrah dowel, which is a slip-fit into the 6mm hole drilled at the previously located centre mark.
pic3: To use, drill a 6mm hole at the centre of the desired circle. Put the pin in this hole, then locate the router on the pin.
pic4: After one pass at about 5mm depth.
pic5: After the final pass. Either set the depth a hair less than the depth of the workpiece, or use a backing piece. Also, remember to stop after you've cut out the circle, or the router will be wandering. You can tell by the change in resistance when you've finished cutting the circle.Those are my principles, and if you don't like them . . . well, I have others.
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11th January 2006, 11:48 PM #2
Circle cutting jigs for router - contd.
pic1: the final result: a nice clean hole, acceptably close to 100mm.
Jig 2 was for holes bigger than the baseplate and was far less successful:
pic2: The idea is to connect a piece of threaded rod to the baseplate fence attachment, with a pin piece fixed between two nuts (wingnuts in this case). Fine in theory, but in practice the holes for my fence were much larger than the threaded rod, resulting in the makeshift wedge trying to eliminate slop (you can see the wedge sticking out near the depth stop posts on the lower right of the router).
pic3: The result is still pretty ordinary. The flex in the threaded rod still allowed the router to rotate a bit, leading to a variation in the cutting radius of a few mm.
Tommorow I will make another router base for larger holes following the first design. It won't be micro-adjustable, but if I need another radius, I'll just drill another hole.Those are my principles, and if you don't like them . . . well, I have others.
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12th January 2006, 01:44 AM #3
Got an idea that might help.
Get two pieces of solid rod the same size as the guide bar holes in the router. A piece of wood that will span the two rods, and drill holes to suit. A cut from the outer edge and a screw to clamp them down on the rods, or the short version is a simple edge guide.
Stick the centre pin doohickey in that.
For extra credit, run a threaded rod through the middle to the router base, so you can dial in your adjustment.
Might help that cure wiggly edge trick, maybe not.
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12th January 2006, 08:20 PM #4
Thanks for that, Zen, at the moment I just use a fly cutter as most of the holes I've needed have been in MDF, but interested to follow your progress.
Cheers.............Sean, goin' round in circles
The beatings will continue until morale improves.
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17th January 2006, 11:42 PM #5
Zen - Check my jig out for circles down to about 15mm radius (depending on the bit size) right up to 400mm radius (or as big as you want to make it). Simple enough to make as the Perspex (6mm) can be machined with woodworking tools quite well. The slot for the centre pin guide is cut with a dovetail bit and the sides of the slide filed to suit. The handle mount is screwed each side of the slot to add strength to the end of the jig as the slot (3mm deep) doesn't leave much meat there. Drilled and tapped a few extra holes to hold the screws that attach it to the router - saves a search everytime you want to use it. Very accurate - used it to make the Longworth chucks pictured - both work beautifully.
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18th January 2006, 01:06 PM #6
That looks like a great design TTIT. A good combination of rigidity and variability. The perspex means you can see what you are doing.
Do you think the dovetail groove is worth the effort? Would a straight sided groove work as well, since the weight of the router and the pressure on the big knob would hold everything down?Those are my principles, and if you don't like them . . . well, I have others.
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18th January 2006, 11:54 PM #7
Zen. Agreed, a straight groove will work but if you make the hole for the centre pin (head of the allen screw) a close fit for a very precise curve, it tends to bind as you attempt to lift it out. With the dovetail groove, the slide cannot tip down at the screw end and stops it binding as much. Not essential - just helps! Mind you , if you change the screw to a point when you dont want a hole in the work, it doesn't matter at all!
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19th January 2006, 09:14 AM #8
Good point TTIT. Thanks.
What about working with perspex using ww tools? I'd imagine it'd be easy to melt the plastic. Any tips?
Also: where do you source the perspex?Those are my principles, and if you don't like them . . . well, I have others.
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19th January 2006, 08:07 PM #9
Hi Zenwood,
You could try City Plastics at Brompton, SA. Their address is
61 East Street
Brompton 5007
South Australia
08 8346 6500
They have a really useful page of hints at http://www.cityplastics.com.au/cutting.html which gives you all sorts of solutions to common problems in machining the stuff.
RegardsWhen in trouble, or in doubt
run in circles, scream and shout
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19th January 2006, 11:54 PM #10Originally Posted by zenwood
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20th January 2006, 09:32 AM #11
Thanks Skratbag and TTIT, great info.
I visualise some upcoming travel:
Eden Hills > Norwood - Mik (dovetail router bit) > Brompton (perspex) > maccers drive-thru (coffee) > Eden Hills.Those are my principles, and if you don't like them . . . well, I have others.
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20th January 2006, 04:18 PM #12
I have done a circle once just by screwing a bit of mdf onto the router base and putting a nail through it. Nail goes into the centre of the hole to be and off you go.
I like the designs shown here.
Zen you could use a bit of wood with a sliding dowel that is mounted on a screw thread to give you adjustment. I think this is what TTIT has done.
Don't think melting plastic is much of a risk unless you machine it with really really blunt tools
StudleyAussie Hardwood Number One
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