Best router bit for cutting circles and arcs

[Phil Doyle]

I'm about to start a project where I'll need to cut some circular shapes and arcs in 3/4 walnut and 5/4 mahogany. Although my 'main' router is a 2 1/4 hp Bosch, I generally use my old Craftsman 1 hp router for circular shapes because I've built a dedicated base and trammel for circular cuts. In the past I've used a 1/4", single flute carbide straight bit, and though it gets the job done, it often leaves a pretty rough surface across the end grain portion of the cut. I'd like to get cleaner, more even cuts and have less sanding, and was hoping to draw on the considerable experience of the Creek for some suggestions as to the best bit or procedure.
Many thanks, phil doyle

[Cliff Rohrabacher]

The router is way less important than the rig you hold it with.

[tod evans]

phil, a spiral bit will give you the cleanest cut at a price. a two flute with shear will come close to a spirals cut quality at a big savings cost wise..02 tod

[Mike Cutler]

Two flutes with bottom cutters, or a spiral like Tod suggested. make multiple passes, depending on depth. One more suggestion is a 1/4" end mill.

[Byron Trantham]

My vote is a spiral bit. It's pricey but it works well as you go from "with the grain" to "across the grain."

[Doug Jones from Oregon]

It will help also if you do a rough cut about 1/16" oversize and then take just a clean up pass to the line.

[Roger Everett]

Phil:
I use a carbide spiral 1/2" bit. Don't forget when routing a circle, you're going with the grain, then end grain,then against the grain. and with a arch it's about the same, and the spiral will give the cleanest cut, because of it's shear action. If I'm shooting a circle or arch on something like MDF or particle board, I use a reg. 1/2" straight bit, because they are more abrasive on the cutting edge, and the reg. bits are less costly, and give a decent cut on these non-directional materials.
The spirals come in up or down cut, depending on which you need.


Roger

[Mark Pruitt]

Generally, as with a saw blade the greater number of teeth will produce a finer cut, so with router bits. What a spiral flute will do for you is, you will have the cutter contacting the workpiece at all times. A two flute bit will produce a fine cut, but a spiral will outdo it every time (assuming equal sharpness for each bit).

[Phil Doyle]

Thanks to all for the fast replies. Looks like the spiral bit is the clear winner (and I'm guessing that it's an upcut spiral, right?).
Thanks again, phil

[JayStPeter]

I use a 2-flute carbide bit as tod suggests. The reason is that I've had problems with small carbide spiral bits breaking. Not only expensive, but fragile also.

[Keith Christopher]

Well my experiences is that a two flute will leave some marks and potential chipout. Esp if a little dull. I would recommend using a spiral upcut for this, I have the whiteside ones and they worked wonders on the DMarks designed mirror I built. And it was made of curly maple. See pic below. (I used a shop made trammel arm as well, good solid one is a MUST.

http://i19.photobucket.com/albums/b179/goyde/Portfolio/rndmirror.jpg

[glenn bradley]

Spiral here.

[John Kain]

Upcut Spiral for me too.

If the material is not too deep, 1/4" diameter should be enough. And those aren't too expense anymore. You probably won't pay more than $20 for a servicable carbide one. I tend to use it on, at least, 1/2 of my mortises as well. So, it easily is worth it. I think I got mine at Lee Valley for something like $18.....

[Bill Pentz]

I'm about to start a project where I'll need to cut some circular shapes and arcs in 3/4 walnut and 5/4 mahogany. Although my 'main' router is a 2 1/4 hp Bosch, I generally use my old Craftsman 1 hp router for circular shapes because I've built a dedicated base and trammel for circular cuts. In the past I've used a 1/4", single flute carbide straight bit, and though it gets the job done, it often leaves a pretty rough surface across the end grain portion of the cut. I'd like to get cleaner, more even cuts and have less sanding, and was hoping to draw on the considerable experience of the Creek for some suggestions as to the best bit or procedure.
Many thanks, phil doyle

Phil,

I've cut way too many circles, mostly in plywood as the tops for cyclones and blowers. I am with the others here in recommending a good spiral bit, preferably carbide but know these are hard on the pocket book. I used all three flavors of spiral bit, but like the upcut most.

What I found most important to a good clean consistent edge was cutting technique. Before cutting anything with my router, I rough cut with a new bandsaw blade after using masking tape on the cut line below. This minimizes tear out and makes controlling a router having to cut so little far easier. I made a circle cutting jig from an old Incra plastic long guide. This lets me lock in a setting that does not move and can be repeated again and again. I cut with the jigsaw to about 3/16" proud. Then it is time for the circle cutting jig where I take that little bit left off with a couple of router passes leaving the tape on to minimize tear out. When doing lots of these I add a top bearing to my router bit, again rough cut then use lots of double sided tape to lock the pieces so they don't slip.

bill

[John Fry]

I use a solid carbide, upcut, spiral bit for this cut. UNLESS, I am cutting an arc or circle out of an already veneered piece, then I use the downcut spiral to get the shear cutting action to protect the fragile veneer edge.

[Bob Reda]

Upcut spiral is my vote

[Jim Tobias]

As many others have said, spiral carbide is the way to go. John makes a good point in that if you are cutting circles or any shapes that are already veneered, the downcut will prevent tearout of your veneered top.

jim

[Phil Doyle]

Following the consensus, I went with the spiral upcut (Freud 75-102). I also had some interesting correspondence with a helpful tech service person at Freud, and I thought the information (particularly the stuff about bit cleaning) might be of interest to those who replied or might read the thread in the future. The 77-102 compression bit mentioned is a new item and may not be stocked yet.
Again, thanks for all of your input.
phil doyle

Freud's reply to my questions (below)-
First lets talk about your first question. To do what you were doing and get the absolute best cut you could have used a 77-102 that is a spiral compression bit and cut the full 3/4" at one pass. Compression bits have both up and down spirals so you get a clean cut on both sides. The other thing you could have done is use a down spiral 76-102 for that first 1/4" deep cut and then finished with the 75-102 up cut. Basically the up cuts give an excellent bottom side finish and the down cuts give an excellent top side cut.

As for cleaning, all of the commercially sold cleaners that we have tested or have seen test results for all have negative effects on the carbide (this does include Simple Green). Oven cleaner, which many people have used in the past, is even worst than those. The way we recommend cleaning of blades is by soaking them overnight in a sealed container of kerosene and then brushing off the teeth with a soft brush like a tooth brush. This is also the most economical as the off the shelf cleaners cost $4 to $5 for a few ounces while kerosene is under $2 for a gallon.

Phil Doyle wrote:


Hi- I own several Freud bits (and blades) and consider them to be top quality. I recently purchased a Freud 1/4" Up Spiral Router Bit# 75-102 for the purpose of cutting circular holes in 3/4" Birch faced plywood (the holes were 7" diameter, if that makes a difference). I have 2 questions I'm hoping you can help me with-
1. My first cut was a shallow one (about 1/8"), to get a clean cut through the face venner, but in some portions of the circular hole the grain like 'peeled back' rather than cutting off cleanly at the circumfrance. This was generally as the cut came back across the grain, and the resulting 'fuzz' leaves me with some extra clean up that (naturally) I 'd rather not do. I'm reasonably sure there's nothing wrong with the bit. Several lifetime pro woodworkers specifically recommended the spiral upcut for this job, but am wondering if the 75-102 was the right bit, or if maybe I'm missing something in the techinique area that would have given me a better cut.
2. I have gotten in the habit of removing and immediately cleaning my bits (I generally soak in Simple Green for a few minutes, and then hit them with a nylon bristle brush, and that gets most of the junk off). In this instance, I found that the residue was more difficult to remove, and was burnt on enough that I had to break out the old X-acto knife and start scraping. Would a soak in lacquer thinner or acetone help? Is there something in particular you folks recommend?

[pat warner]

"less sanding, and was hoping to draw on the considerable experience of the Creek for some suggestions as to the best bit or procedure."
____________________________________

Key here is procedure. You have the best cutter, single flute SC.
But I suspect a 1HP Sear's is a fixed base router. A 1.5HP plunger at ~1/8"/pass will yield the best finish. Tool must sharp and feed rate has to be commensurate with cut rate or all bets off. Test on scrap.

Routers (http://www.patwarner.com)