# What the heck is a compression router bit?



## GaryK (Jun 25, 2007)

This is mainly for the members that are relativity new to woodworking.

Most all of us use a router and one type of router bit is a solid carbide spiral bit.

Did you know that there are more than one type?

Here's the most common one:










It looks just like a drill bit (minus the point) right. This is called an UPCUT bit. It's called that because it forces the chips up away from the tip of the bit.

Here's a DOWNCUT bit:










Like the name implies it forces the chips down toward the tip of the bit.

Why would you choose one over the other. Well the upcut bit is good for blind holes where you want the chips to be removed out of the hole. The only problem with this is that same upcut motion can also cause the top surface to splinter up creating a messy hole.

If you were using the same bit on the edge of a piece of wood the bottom edge would be nice and clean because the "up" shearing action of the bit. But again the top edge might be splintered.

With a downcut bit you would have the opposite problem. The top would be clean and the bottom might be splintered.

Downcut bits are great for cutting dadoes. The top edges will remain clean.

As you can see they both have their good and bad points.

How would you like to have a bit that will allow the top AND bottom surfaces to be splinter free?

Try a COMPRESSION bit:










This gives you the best of both worlds. The part of the bit closest to the tip is upcut and the other end is downcut.
That is why it's called a compression bit. It compresses the chips into the center of the bit.

It's great for cutting openings in wood.

This makes it especially great for plywood, laminates and MDF when you need both the top and bottom edges clean. You just have to make sure that the piece of wood you are cutting is thick enough so that both ends of the bit have room to work.

This is the bit I used to cut the inside and outside of the rings on my cutting board:



Example of the setup for cutting the inside circle:










Both the top and bottom are cut perfectly clean.

You can also get them in a flush trim version:










So the next time you need to use a spiral but, I hope that this will help you to choose the correct one.


----------



## jusfine (May 22, 2010)

Thanks Gary, good info even for the "old guys"... 

I have never seen a compression bit offered for sale, but to be honest, I haven't asked for one either.


----------



## FatherHooligan (Mar 27, 2008)

I learned something today! Thanks Gary.


----------



## USMC6531 (Feb 13, 2011)

Great information, just added another piece to the puzzle that is woodworking!


----------



## Dennisgrosen (Nov 14, 2009)

thank´s for taking the time to be teaching us 
ceep them coming you do a great job

take care
Dennis


----------



## GaryK (Jun 25, 2007)

They are made by most major manufacturers. Freud, Whiteside, Amana…


----------



## surfin2 (Oct 24, 2009)

Even though it's *2* bits in one it shouldn't be the price of 2 bits, Its still *one* bit…

They've been out for awhile & the price is still way to high…


----------



## juniorjock (Feb 3, 2008)

Thanks Gary.
- JJ


----------



## Lenny (Sep 28, 2008)

I was in my local Woodcraft store recently when a fellow came in and asked a salesman for a compression bit. Plans he was working from called for such a bit. The salesman had no idea what he was asking for and the customer didn't know how to properly express what he wanted. The customer had already looked at bits prior to speaking to the salesman. He explained that he saw upcut bits and downcut bits but no compression bits. I opened my big mouth and explained that a compression bit is a combination upcut and downcut all in one. The salesman spoke to the manager who eventually came out and said we don't have any in the store but I can order one for you. I guess knowledge of them is not too great and perhaps that keeps demand for them down. Either that or as mentioned above, the price. At any rate, nice tutuorial on spiral bits Gary.


----------



## TopamaxSurvivor (May 2, 2008)

Thx Gary. Count me as novice, I have never heard of it.


----------



## Dandog (Oct 21, 2010)

good info only heard of up and down .


----------



## whit (Jul 6, 2007)

Son of a gun!! You CAN teach an old dog new tricks!!

Whit


----------



## Resurrected (Jan 11, 2011)

yeap never used one but I read about them.


----------



## cajunpen (Apr 9, 2007)

And an old dog learns a new trick, once again. Thanks Gary.


----------



## sras (Oct 31, 2009)

Thanks for a very useful "bit" of information!


----------



## Dark_Lightning (Nov 20, 2009)

surfin2, I'd expect it to cost more. There's a lot more machining going into those. A lot more than twice, actually.


----------



## Karson (May 9, 2006)

Gray great blog. Some great points.


----------



## tomd (Jan 29, 2008)

It was news to me, never heard of them.


----------



## CharlieM1958 (Nov 7, 2006)

How did I not know this??!


----------



## auggy53 (Jan 23, 2011)

next time i 
go to rocklers im going to show off and ask for one , hope i dont get a drill bit by mistake! thats for the knodgledge, inofoma , thats for the help!


----------



## JoeLyddon (Apr 22, 2007)

Well, I stumbled onto this... My jaw dropped!

... for almost $80, I think I will pass on this one… until they get more reasonable! LOL

Hey I also found them HERE for a little more reasonable prices!

Still… very pricey for me…

Nice to know they are around… though…


----------



## GaryK (Jun 25, 2007)

Joe - you can get a 1/4" Whiteside bit from Woodcraft for $36.

That should handle most all of your needs.

Freud bits are expensive.

You will pay almost the same price for a regular up or down cut solid carbide bit.

Spiral bits give you a lot better surface and cut a lot easier than a straight bit. The easy cutting will make them last about 10 times longer. It cuts with more of a shearing action vs the slapping action of a straight bit. Plus if you don't mind them being undersized, you can get them resharpened.


----------



## JoeLyddon (Apr 22, 2007)

Yeah, getting a cheaper 1/4" bit would do just fine… you can always move it around to cut more!

Harteville has a 1/4 for about $29 … Now, we're in the ball park!

Thank you!


----------



## GaryK (Jun 25, 2007)

Joe - Here's one for "$27.20 : Librawood


----------



## surfin2 (Oct 24, 2009)

FREUD DIAMOND COMPRESSION BITS CAN LAST UP TO 100 TIMES LONGER THAN CARBIDE IN MDF, CHIPBOARD AND MELAMINE…


----------



## JoeLyddon (Apr 22, 2007)

Gary, Thank you… never heard of them…


----------



## DLCW (Feb 18, 2011)

Compression router bits come in two styles. There is a regular compression and a mortise compression. They are both used VERY frequently with CNC machines for cutting plywood and other laminate materials. The mortise compression bit doesn't need to plunge as deep as the regular compression bit before you start cutting. If you ramp in your cut, you will get a little bit of splintering of the veneer until the upcut part of the bit passes below the surface of the veneer and the down spiral part of the bit starts down slicing the veneer. These bits are designed to plunge into the material until the downcut portion is below the surface of the material.

Like Gary said they slice cut from the top and bottom of the material. I've included some links where you can get compression and mortise compression routers bits very reasonably priced:

http://www.centuriontools.com/router_bits_toolcase/centurion_tools_showcase.html?cart=127953823210966564&splashPG=y&__max=6&pageID=1&id2=6&noitems=T&startat=1&--woSECTIONSdatarq=6&--SECTIONSword=ww

http://www.toolstoday.com/c-405-compression-spiral-solid-carbide-router-bits.aspx


----------



## Resurrected (Jan 11, 2011)

DLCW I did not know their good for CNC. Thanks. Did not read that.


----------



## JoeLyddon (Apr 22, 2007)

DLCW… Thank you for the very good links!


----------



## TheQueTip (Jul 22, 2009)

Agree with DLCW, great for use on a CNC. I like to use the .375 on the CNC since it is a little more rigged than a .25 and produces a little smoother finished toolpath.

They are usually a little more expensive than an up or down cut spiral endmill, but can save you time when it comes to finishing the top surfaces (if your preference is an up cut spiral)

Chris


----------



## FHG1 (Jan 9, 2013)

Good to know. Thanks. Here's a question for you. Is it ok to use a cnc bit on your router?


----------

