Thread: Best way to cut accurate circles

Circles and gravity Homey. It's the nature of the very universe....

Originally Posted by homey

Woodpixel,

i've used the same tool and agree it does a great job. Very clean cuts. I puzzled over getting the two cutters equidistant from the centre - seemed like unnecessarily fiddly. Then I thought maybe you use the cutters separately, i.e. Just one cutter on the bar at a time. This works fine for me, so I have one cutter on the bar if I'm cutting holes (outside cut) and the other one on if I'm cutting discs (inside cut). The slow speed and relatively light pressue have never given me issues. One cutter also halves the load on the drill so it seems to cut much easier.

Whatever I do, though, I always seem to be going round in circles...

Brian

NOT a good idea to remove one of the cutters.

I had one of those Craftsman cutters shown in woodPixel's link to youtube. With only one cutter, it tends to bend the shaft and produce terrible results. Using both cutters preserves balance in the tool.

Cheers,
Joe

Joe,

Thanks for the heads-up. I've been using mine for two years without any problem and with beautifully crisp cuts. I put very little pressure on so there's little chance of bending - but then perhaps mine is a bit more robust? I note that some brands of this type of fly cutter only come with one 'arm' which is where I got the idea from. See, for example, the illustration below from Lee Valley for their tool. Doubt they'd have these pics if thet thought there was any safety issue. There are many examples of this cutter being promoted in this way.

IMG_3236.PNG

Brian

Adjustable Wheel and Circle Cutter

This adjustable cutter makes clean cuts even in softwoods. To be used in a drill press at low speed (maximum is 500 rpm), the cutter head is adjustable for wheel diameters from 1" to 6". The 1/4" pilot drill bit prevents accidents on cut-through. The high-speed steel cutter is double ended: one end to give a clean wheel, and the other to give a clean hole. Designed specifically for use with wood, but can also be used on aluminum, copper, and plastic. It cuts much more cleanly than the multi-purpose circle cutters available to date. Ideal for toy makers.

if it's a jig you want. have a look at the Jasper circle jig http://jaspertools.com/
a bit of ingenuity and you'd have your own version

I was going to buy one of those Jaspers, but getting them here is an impossibility.

Amazon carry them, but they dont fit Festool or Triton routers without adding your own holes/mounts ... nor are they in Metric.

Shame, for its an excellent idea.

Homeys picture makes sense, but I re-watched that video I posted (and a few others) and it's clear that the cutter rubs the edges of the circle due to its length. A lot of videos show catches where its far too tight. The kerf can never be wide enough.

The idea of using the blades direction for inside/outside thing for how its cut is a good idea, although I would say when I used both it did a very good job, creating plenty of room for itself/cutters, but also creating a clean cut.

Maybe I'm using it wrong, but it sure works well!

This picture sort of shows how I align the point to the mark for accurate sizing. The inside one doesn't matter, just a few mm in to widen the kerf.

inside outside.JPG

Originally Posted by woodPixel

I was going to buy one of those Jaspers, but getting them here is an impossibility.

Amazon carry them, but they dont fit Festool or Triton routers without adding your own holes/mounts ... nor are they in Metric.

Shame, for its an excellent idea.

Jasper has a set of instructions for cutting metric holes with their imperial jigs. On a brief look, it appears that the "trick" is to use the right size metric router bit, e.g 8mm rather than 5/16" might sneak up to Dengue's 121.5 mm

WP,

Soundlabs in Australia sells them. The 200, 270, 300 and 350 at least. Soundlabs Group

Their website says they come with a pattern so you can drill your own holes to suit.

Brian

Originally Posted by woodPixel

No way! What timing, I was about to do a review of this tool:

...the Carbitool Hole Cutter Adjustable Circle Hole Cutter | Benelongs - Woodworking Accessories

I bought mine from Benelong's. I email Dan (he is an accommodating guy) and buy most of my router bits from there. He posts on the same day and allows pickups from his showroom too.

For $20 and $3 postage, this is an absolutely first class bit of gear. I was honestly expecting a two-use-wonder and an absolutely piece of junk. Boy was I surprised. This kit comes with both carbide and HSS drill bits, plus the same for replicable blades. it comes with a good quality Allan key and it fits ALL the sockets (not one of those #%^* tools that use three different keys...)

i make speakers for commission occasionally. I've done it 6 times this year alone (and another for a forum member only this week). The speaker openings need to be exact.

so I use the Incra ruler to very accurately measure the upper/lower/left/right and centre, use a nail to punch a divot on the exact cross, then drill a 5mm hole. The Carbitool hole cutter in the drill press, running at the slowest RPM makes a very clean, very accurate and predictable circle.

the setup of the edges is dead easy. This is why I use the Incra to scribe where the outside should be. The very tip of the blade hits this line. The "reverse" blade is set a smidgin inside that. Simply cut about half way, flip over and finish it off.

100% recommend this tool.

hope this help. Say hi to Dan if you buy off him.

Evan

Thanks bought one

Sent from my F1f using Tapatalk

Originally Posted by Dengue

Hello, can anyone please recommend a way to cut circles dead set accurately in 18mm thick MDF. I have the need to cut a circle with diameter 120.5mm.

just a thought ...
120.5 mm is just under 6 thou less than 4-3/4 inches.
which begs the question -- has the specifier rounded 4.75 inches to 120.5 mm?

I think it always pays to ask / check a fractional or unusual millimetre dimension for conversion from imperial.