Thread: Circle cutting jigs for router

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.

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.

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

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.

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?

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!

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?

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.

Regards

Originally Posted by zenwood

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?

Zen, Luckily enough, my daughters dad-in-law is a glazier - very handy acquaintance!! As for working the stuff, the only time you might have trouble is if you linger too long with the router - similar to some timbers really where you get burning if you move too slow. Absolutely amazing stuff to turn in the lathe!!!! Trimming the outer edges of the Longworth chucks was a real buzz. Steady, steady with a toothpick cutter and you get a continuous stream of warm, fine shaving pile up on you but as soon as it cools and you try to move it, it crumbles to nothing!!! Skratbags link has some really good tips - well worth a look.

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.

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

Studley