Spiral bit and straight bit: redundant?

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Forum topic by chodaranger posted 06-06-2016 06:14 AM 749 views 0 times favorited 4 replies Add to Favorites Watch
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4 posts in 1783 days

06-06-2016 06:14 AM

Topic tags/keywords: router bit spiral straight

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?

4 replies so far

View Fred Hargis's profile

Fred Hargis

6936 posts in 3555 days

#1 posted 06-06-2016 10:57 AM

A spiral bit and fluted straight bit do the same job, in many cases the spiral bit does it a lot better. It will plunge better, clear chips better (in a groove), and to me they cut more smoothly. Often they can cut squirrelly grain when the fluted bits cause tear out. But they also cost more, and while you can have them sharpened it’s done on the OD (compared to the ID of a fluted bit). That means that once sharpened, they are a smaller size; often significantly smaller. A fluted bit might be smaller as well, but it’s usually in thousandths after sharpening. The cost difference is fairly low in the smaller sizes, but move up to the larger ones and it’s really sticker shock. I suggest having both, use the spiral when needed, the fluted all other times.

-- Our village hasn't lost it's idiot, he was elected to congress.

View JBrow's profile


1368 posts in 1982 days

#2 posted 06-06-2016 03:24 PM


There are four styles of straight bits. These are 1) straight bit, generally two cutting edges parallel to the axis of the router; 2) shear angle, cutting edges skewed slightly from the axis of the router; 3) spiral, helical cutting edges directing chips toward the router (up-cut typically used in a router table) or away from the router (down-cut, typically used in a hand held router); and 4) compression, a spiral bit with flutes running in both the up-cut and down-cut directions. Some of these versions of straight bits are also available as pattern or flush trim bits.

I suppose all have their advantages and disadvantages, usually dependent of the material (e.g. solid wood, plywood, melamine) being routed and the router set-up and operation.

MLCS is the vendor from whom most of my router bits were bought. They have a wealth of other resources which may help inform your decision and allow you to get the most out of the router

Their instructions for the spiral up-cut and down-cut bits are at

Lastly, browsing their selection of router bits can also be helpful in selecting the right router bit. Even though I have been completely satisfied with their bits, I would think the product info they provide describing their bits would be applicable to router bits offered by other vendors

View pintodeluxe's profile


6348 posts in 3875 days

#3 posted 06-06-2016 04:17 PM

I find either will do the job. I do have some 1/4” spiral bits that do a remarkable job. Just make sure you get the carbide variety, as the HSS ones don’t cut well or last long.

Flush trim and pattern bits are invaluable in the workshop. I reach for those all the time. I especially like short length top-bearing bits for use with exact-width dado jigs. Amana #45487 has a 1/2” cutting length or #45491 has a 3/4” cutting length. You can use the short version for jigs built with 1/2” plywood, and the longer one for jigs built with 3/4” plywood.

I haven’t had good luck with MLCS (lots of chipout), but Whiteside, Amana, Rockler, and Freud bits have served me well.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View splintergroup's profile


5035 posts in 2284 days

#4 posted 06-06-2016 04:28 PM

As Fred and others have pointed out, typically the more you pay, the better the cut. Is that ‘better’ cut worth the extra $$$ ? Depends on what you are cutting and how high your standards are.

As a side note, many straight cut bits are not designed for plunge cutting. Look to see if the cutting edges at the tip extend all the way to the bits centerline.

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