Spiral bit and straight bit: redundant?

[Benjamin Allison]

I’m new to routing. Currently, my intended uses are:

- cutting 1/8” or 1/4” wide channels
- cutting mortises and dados
- cutting recesses for hardware (example, installing a vice)
- flush trimming
- chamfering

So, the bits I’m planning on purchasing are:
- flush trim or pattern bit
- chamfer bit
- down or up cut spiral bit

If I have a spiral bit, is there any reason to have a straight bit also?

[Susumu Mori]

I used to like spiral bits more but had one incident of a bit that came loose and dug into the wood.
I posted this happening here and several pros responded. They recommended straight bits if possible because the spiral action sometimes causes unexpected events due to the vertical force; upcuts spiral pulls the bit into the wood.

[Gerry Grzadzinski]

In smaller sizes, spiral bits will tend to last longer and not break as easily.
But in 1/2" sizes, straight bits are MUCH cheaper than spiral bits.

[Benjamin Allison]

the spiral action sometimes causes unexpected events due to the vertical force; upcuts spiral pulls the bit into the wood.

Good to know. Thanks!


In smaller sizes, spiral bits will tend to last longer and not break as easily.
But in 1/2" sizes, straight bits are MUCH cheaper than spiral bits.

Cool! And for plunging and routing out a mortise, a 1/2" straight will work fine?

[John Donhowe]

Up cut (right hand thread) spiral bits are better for cutting mortises, since they tend to pull the chips out of the cut (like a drill bit). Since they pull up, they also tend to cause more splintering of the edge of a rabbet or dado. For a smoother edge, you need a down cut (left hand) bit for those cuts; the spiral pulls surface fibers down into the wood instead up and away. Since you're going to be doing a lot of different cuts, unless you want to buy two different spiral bits, just stick with a decent quality straight bit as a reasonable compromise.

[Gerry Grzadzinski]

Some straight bits are not good for plunging.

[Jim Dwight]

If you want to make a mortise you need either a spiral bit (upcut) or a straight bit with a bottom cutter. They cost a little more than a straight bit without a bottom cutter. Or you can drill a hole at the end and you don't have to plunge cut. Drilling holes is a good approach anyway, possibly slightly undersize. Routers are noisy and not all that pleasant to use. Taking most of the waste with the drill press can make cutting the mortises quicker and more pleasant.

[Prashun Patel]

Spiral bits can get pricey especially if you want one with a pattern bearing.

More critical than your type of bit is your brand of bit. Buy a quality bit and it will last longer and cut cleaner.

[Stan Calow]

I have both in duplicate sizes but prefer straight bits for hinge mortises, rabbets, and grooves. Spiral for regular mortises. As Susumu said, sometimes spiral bits do weird things on a long pass.

[pat warner]

"I’m new to routing. Currently, my intended uses are:"
************************************************** *********
Why not learn all you can about straight bits before using the spirals?
Spirals are full of surprises, sensitivities and risk.
They come in several designs (compression, up, down, left handed, etc), each with its own caveats.
Straight bits are relatively straight forward.

[Benjamin Allison]

Thanks again everyone. And yeah being new, I think getting a straight bit, and getting familiar makes sense. I'm looking at bits from Whiteside. They seem to be favourably reviewed by almost everyone, and are pretty reasonably priced.

My main concern is plunging. Hopefully they have straight bits that have bottom cutters to help make that task easier.

[Walter Plummer]

For mortising hardware I prefer to use mortise bits like this one. http://www.holbren.com/mortise-router-bits/whiteside-mortise-router-bit-5/8-cutting-diameter-3/4-cut-length-1/4-shank-2-flute/. They do not plunge straight in but for a butt hinge you do not have to. I think 1/2" diameter is the smallest but I could be wrong. I agree with everyone start with carbide straights and save some money.

[pat warner]

" Hopefully they have straight bits that have bottom cutters"
************************************************** *****************
You're concern for straight in situ plunging is well taken.
And indeed most so called plunging-carbide-on-steel bits, do not plunge unless the router is sliding around.
All straight solid carbide bits (designed for bottom & side cutting), however, do allow plunging in situ like a drill.
And, of course, all twisted solid carbide tools do too, but with surprises.
One of the most significant is the vector on up spirals.
They are constantly being pulled from the collet.
And if there are burrs in the ID of the collet, cutter is not tight enough, mistakes (an accidental over depth plunge cut, e.g.), etc you may indeed pull the cutter from the collet.

[Gerry Grzadzinski]

One of the most significant is the vector on up spirals.
They are constantly being pulled from the collet.

My experience is that a LOT of people just don't tighten their collets tight enough.
I've never had a spiral bit come loose in 25 years.

I work in a cabinet shop, and always check if the collet is tight before I use a router that somebody else set up. More often than not, the collet is not as tight as I'd like it to be.

[Doug Hepler]

This is a great thread. I'd like to add a few points that I haven't seen above. I was an experienced woodworker before I ever tried to use a router for any serious purpose and I still remember my long learning curve -- actually easy to remember because it is still going on.

1. I think that excessive force, e.g., trying to cut too much in one pass, is a common and under-appreciated cause of a bit coming out from a collet. This is especially true with 1/4" shanks and with a jig where the temptation is to cut a tenon, dovetail, etc in one pass or too fast. (DT especially because they are narrow at the neck.) I agree that proper installation and tightening are very important, but forcing the bit will still vibrate the bit out of the collet sometimes. This is probably better than breaking the bit, which is also a possibility. You have to listen to the motor and the sound that the bit is making. "ZING" is not good. (I think I learned this first from Pat Warner.)

2. An upcut spiral really can reduce tear-out in some operations, e.g., cutting tenons with a router and jig.

3. I totally agree with the OP's decision to buy a few bits and gain experience. The value of his bit collection will exceed the value of his router soon enough in any case.

4. And yes, high quality bits are usually worth the extra money. Think of the metaphor of the horseshoe nail and the kingdom. The router bit is the nail and the project you are making is the kingdom.

Doug

[Gerry Grzadzinski]

I agree that proper installation and tightening are very important, but forcing the bit will still vibrate the bit out of the collet sometimes.


Imo, no it won't. Not if the collet is tightened properly.
I've seen spiral bits on cnc machines take cut's far heavier than you'd ever consider by hand, and the bit's don't come out.

[pat warner]

And with the advantage (CNC) of large/long diameter shanks (5/8, 3/4+), sophisticated collets and flats ground into the shanks, the likelihood of a depth change is remote.
But, alas, 110 vac ($150) routers are never going to offer that kind of security.
Face it, hand routers, altho quite capable tools, are still in the dark ages when compared to CNC tools whether for metal, composites or ordinary wood.
Bottom line: Moderation, no heroics.

[mreza Salav]

Pat has given you good advice.
Spiral bits are full of surprises: they are MUCH more likely to slip out of the collet, they are more likely to plunge like a screw on a driver too deep than wanted, they tend to break more easily because of these, etc. They often cut better too. But if was going to start I'd certainly get my feet wet with straight bits and then very cautiously start using spiral ones.
IMO the most important thing to remember with spiral bits is: take very shallow cuts and make sure you are in control of the router (or the piece if you are using the table).