What the heck is a compression router bit?

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Forum topic by GaryK posted 02-24-2011 12:46 AM 27317 views 8 times favorited 30 replies Add to Favorites Watch
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10262 posts in 4187 days

02-24-2011 12:46 AM

Topic tags/keywords: resource router shaping upcut downcut compression carbide solid carbide sprial

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?


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:

Click for details

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.

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

30 replies so far

View jusfine's profile


2422 posts in 3125 days

#1 posted 02-24-2011 01:09 AM

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.

-- Randy "You are judged as much by the questions you ask as the answers you give..."

View Mark Shymanski's profile

Mark Shymanski

5623 posts in 3911 days

#2 posted 02-24-2011 01:18 AM

I learned something today! Thanks Gary.

-- "Checking for square? What madness is this! The cabinet is square because I will it to be so!" Jeremy Greiner LJ Topic#20953 2011 Feb 2

View USMC6531's profile


42 posts in 2858 days

#3 posted 02-24-2011 01:20 AM

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

View Dennisgrosen's profile


10880 posts in 3314 days

#4 posted 02-24-2011 01:26 AM

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

take care

View GaryK's profile


10262 posts in 4187 days

#5 posted 02-24-2011 03:36 AM

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

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View surfin2's profile


51276 posts in 3335 days

#6 posted 02-24-2011 03:47 AM

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…

-- Rick

View juniorjock's profile


1930 posts in 3964 days

#7 posted 02-24-2011 03:54 AM

Thanks Gary.
- JJ

View Lenny's profile


1616 posts in 3726 days

#8 posted 02-24-2011 04:22 AM

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.

-- On the eighth day God was back in His woodworking shop! Lenny, East Providence, RI

View TopamaxSurvivor's profile


18389 posts in 3875 days

#9 posted 02-24-2011 04:26 AM

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

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Dandog's profile


250 posts in 2973 days

#10 posted 02-24-2011 04:39 AM

good info only heard of up and down .

-- life an woodworking is one big experiment

View whit's profile


246 posts in 4176 days

#11 posted 02-24-2011 04:43 AM

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


-- Even if to be nothing more than a bad example, everything serves a purpose. cippotus

View Resurrected's profile


671 posts in 2891 days

#12 posted 02-24-2011 04:52 AM

yeap never used one but I read about them.

-- Who can I block now???????????????????????

View cajunpen's profile


14578 posts in 4264 days

#13 posted 02-24-2011 04:58 AM

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

-- Bill - "Suit yourself and let the rest be pleased."

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#14 posted 02-24-2011 05:00 AM

Thanks for a very useful “bit” of information!

-- Steve - Impatience is Expensive

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#15 posted 02-24-2011 05:05 AM

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

-- Random Orbital Nailer

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