I have had this question for a while as well… I have recently started doing some inlay, and have looked for more efficient methods of hogging out the wood instead of my trusty chisels. Hopefully I can find some super small bits for my inlays as they are typically fairly small.

Can I assume that a “compression” bit is the same as a double compression spiral bit which is a combination of an up-cut and and down-cut bit?

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I know this is an old article but I have been trying to figure out the best way to cut circles in 5/4 deck boards (1″ actual thick) using the Jasper jig for quite some time. I ordered a Freud downcut spiral bit (76-109) for my dewalt plunge router but it was 4″ overall length instead of 3 1/2 as spec’d. To long for the plunge w/out a thicker base that would interfere w the jig. I still tried it but it was cutting a ton of material and seems very inefficent. I cant seem to find a bit with a 1.5″ carbide that is under 1/2″ diameter. 3/8″ comes in a 1-1/4″ carbide that might work but I am hoping someone will have some real knowledge to assist. Thanks in advance.

Any difference in performance between these and endmills? I have not tried endmills myself, but seems to me they cost a bit less….

Hey Robert. The smallest bit I use for inlay is 1/16″, and the only bit I can find for that is a straight bit. But it does seem like you can get some decent spiral bits in the 1/8″ size range for hogging out.

Rats, I submitted a reply about spiral bits not realizing this thread was about spriral bits. I’m betting they are the same, though, with one’s pronunciation affected by eggnog.

I haven’t tried using my endmills in any routers, just because I do not possess a router with a collet size larger than 1/4″.

This is good info I really appreciate it. I am getting my first router for Christmas so I am trying to learn everything I can right now. This is very useful

Up-cut Bits provide faster cutting while they pull chips up and out of the work or towards the router. They are excellent bits to use when cutting material in a router table since they tend to hold the work piece to the table itself. Ideal for mortise and tenons, grooving, slotting or routing deep blind holes. Down-cut Bits cut slower and push chips away from the router to eliminate top surface splintering. Use for pattern cutting or when going completely through the board as it allows clear vision of the cutting line. Ideal for fine finish work such as veneers, laminates, inlays and repairs because they prevent upper edge tear outs. Use Down-cuts for trimming and sizing.

Apr 27, 2011 — I'm trying to speed up a process in our VMC department. We now use an inserted side milling cutter(Sandvik 331) to ruf out the keyways in ...

Of course upcutting bits are better for mortises. If money is an issue and you need to decide between sizes, think about it this way: It’s easier to cut a 1/2″ mortise with a 1/4″ bit than it is to cut a 1/4″ mortise with a 1/2″ bit.

Great question Todd…. and also a great answer from Eric. This is exactly why I frequent this site, (and am a guild member). Thanx for the great info Marc

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Hey Mark. I looked through the archive and I can’t recall which, if any, video I showed that technique. But I could have sworn I covered it in the past. I’ll keep looking and if not, I’ll have to include that in a future project.

Compression Bits Cuts through stock and gives clean cuts in both top and bottom. No tear out as bit is designed to pull work into the center of the stock. Ideal for double sided veneer plywood, melamine, and laminates. As for size recommendations, it really depends on the specific application you intend to use the bit for. We find that the 1/8″, 1/4″ and 1/2″ Up-cut and the 1/4″ and 1/2″ Compression bits are the most popular for our customers applications. —-Eric Reed

This pack has twelve pieces of single-end mills of 1/4 inch shank diameter and an overall length of 2-1/2 inches. It is ideal for peripheral, slotting, plunging ...

Mar 14, 2018 — But it's not proportional. Chip load increases gradually as diameter increases. No. The chipload for a 1/8" tool is similar ...

Hey Dan. As far as finish side and up vs down, it kind of depends on what you are doing. For instance, a dado using a hand-held router would have the cleanest cut using a down-spiral. A good up-cut bit will leave a pretty clean cut too, but technically-speaking, the down-spiral would be a cleaner cut. So yes, the show side would be up in this case. But lets say you were using a hand held router and plunging all the way through the piece, for something like a through mortise. In that case, you would want to use an up-cut bit with the show side down. All the same rules apply at the router table. But keep in mind the bit is now upside down, and usually the workpiece is upside down as well. But again, whether your show side is up or down still depends on the operation.

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Thanks for posting that response. It was to the point and very informative. Now I have to find some money for a new set of bits!

Special thanks to Eric Reed for answering Todd’s question. And be sure to check out Eagle America’s blog, The Cutting Edge for some great woodworking content. The only thing I will add to Eric’s response is my own size/type preferences. Personally, I find 1/4″, 3/8″ and 1/2″ up-cut to be the most useful. So what about you guys? What do you like to use in your shops and for what purpose?

I have been using straight flutes for my lettering in aspen but tend to get blow out around some fine edges, I’m using a 3/8 -1-1/4 which works very good, would a up or down spiral stop the breakouts and fuzzing?

Gord; End Mills(Slot drills) have a slightly different geometry (Cutting angles) in the flutes(grooves). Endmills are used on all kinds of metal, including steel. Router bits would only work in Wood, Plastic, Non- ferros metal such as Aluminum & Brass! 2 Flute Endmills usually are also end cutting. Will End Mills work in wood? Yes to an extent but you would not likely be able to feed them as fast as a Router Bit, and they likely would not last long without burning the wood. Sorry about all the tech talk, 30 years of involvement with cutting tools does that to a guy!

Can a down spiral bit be used for signmaking in a case where you want the letters to stand out & the background to be cut away, because I’ve read that the down spiral will leave smoother edges on your letters with less burring?

Up-cut spiral in a router table with the “finish” surface up for no chipout, right? If using a down-cut in a handheld router still keep the “finish” side up? just want to make sure. Do you notice any difference in the edge quality between spiral and straight bits inside a grove or on the edge of a board? Any difference in cut rate or noise? Does the router have less stress with the spiral bit?

Sep 12, 2024 — Carbide inserts are used to accurately machine metals, including steels, carbon, cast iron, high-temperature alloys and other non-ferrous metals ...

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So what exactly is a compression bit then? I learned something in this post. I didn’t know that the down cuts prevented surface tear out. It makes sense to think about it, I just have never thought about it. Thanks for the content!

Thanks for the info, Marc. These are the posts I love to see as I am a newb and am soaking up all the info I can get! I dig your site, and Wood Talk too! Keep up the great work.

Marc, Are there any videos here or on the guild site that show you making mortises with a router table or free hand with your router? I know there are not any of you making a mortise with chisels because no one has time to watch that long of a video!

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A drill angle driver typically refers to a tool used for drilling holes at an angle or in tight spaces that are difficult to access with a regular drill.

Our production quality solid carbide spiral bits combine effective chip removal with a continuous shearing action cut not obtained from a standard straight bit. You’ll get smoother cutting action with better results.

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Hey Brian. I usually let the size of the router bit dictate the speed, for the sake of safety. There are charts out there that tell you what speed you should use. Here’s an example: http://www.newwoodworker.com/ref/rtrbtspds.html

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I just realized I posted the same image twice. The second picture was supposed to be a diagram of a compression bit. Its fixed now so take a look and it should explain how the compression bit works.

I have found that spiral bits cut faster and more efficiently. And it definitely feels like the router is under less strain. Not necessarily any quieter, but I usually have ear protection on anyway.

Jozef; I am in Canada, and have recently started selling a product line from Germany, called “GUHDO”. This is an excellent product and I would think that they would possibly have a representative in your country. You can look at, and download their complete catalog online at http://www.guhdo.com. Good Luck

oh oh the secret is out lol……its a slot drill if you want to get all tec like since it will cut on the end since the flutes cross center and endmill doesnt

I have serious trouble to buy any serious router bits. I’m from central Europe and ‘local’ providers here (Bosch, Narex) has almost no flush trim bits or pattern bits, even with straight cutting edge, not saying about spiral ones. Similarly, there is no chance to get a straight router bit with working lenght more than 20 milimeters (3/8 of inches approximately). Guys, do you have any recommendataion, where these can be ordered with reasonable price and reasonable quality?

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1/4" Shank with 6 Bearings Set - 1/16", 1/8", 3/16", 1/4", 5/16", 3/8". Interchangeable Bearings with 1/2" to 1/4" Router

I have a question about spiral router bits as I have no experience using them. I have a chance to get a couple but with limited funds right now, I only want to get ones that I would use frequently. What type (up/down/compression), what diameter, and what function would you use them. From everything I’ve read it looks like an up-cut bit is used for hand-held routing when doing mortises and a down cut for router table work for dadoes, rabbets grooves. What are your thoughts? Thanks and keep up the great work!

Great graphics with your answer Marc. A picture is worth a 1000 words. Did those graphics come from Eagle? Next time I need a spiral cut bit, I’ll be sure to order it from them.

Thanks for the information. I initially found the “up/down” terminology a bit confusing because I didn’t know what that was relative to. But I think I have it clear now. “Up” and “down” is relative to the router in a hand-held position. So “up” means it pulls the chips toward the router. “Down” means it pushes the chips away from the router. Correct? Thinking of it that way makes it easier to figure out when the router is in a table and everything is upside down and “Down-cut” bits push chips up and “Up-cut” bits pull chips down. Have I got it right?

Jul 28, 2024 — Feeds and speeds are important because they're the key to Longer Tool Life, Faster Machining Speeds (through higher Material Removal Rates), and Better Surface ...

My biggest question is what speed to I need to run my router for different cuts and/or different wood…? Should you run your router faster in soft woods and slower in hard woods? Does the type of cut matter?

Generally, central Europe is full of crappy woodworking tools from one big Asian country: levels not measuring level, squares which are not square, chisels made from aluminium-like steel, etc. For instance, nobody here – including woodworkers – knows that something like parallel clamps even exists. :-(

Speaking from a luthier’s perspective, downcutting bits are more useful. They are great for inlay work because they don’t fuzz the edge of your cavities. You can sneak right up to the line with little or no cleanup afterward.

For mortising you don’t get much benefit from the compression. If you’re trimming to a pattern, though, the compression makes a noticeably cleaner cut on both surfaces. That’s what I use mine for exclusively. For shallow cuts (less than, say, 1/4″) a compression bit and an up-cut bit look the same as just the tip of the compression bit is in the up-cut geometry.

The benefit of a compression bit is seen when cutting both sides of the material. To the underside of the material (furthest from the router), the ‘up cut’ portion of the compression bit is actually performing the cut like a down-cut bit. The top half of the compression bit is doing a down-cut into the top surface.

I just looked at a Bosch 2 flute straight cutter (1/2″ shank, 1/2″ diameter, w 2 1/2″ length) today at Menards. I didn’t want to pay the $22 bucks for it when I had a brand new spiral up cut that I have never used. I tried it out today to make a hollow spiraled spindle. It seemed to work for my application okay enough. I don’t know why Bosch wouldn’t have anything more significant there, but they certainly do make them.

I was introduced to spiral bits on my current project. I needed to cut 1/4″ box joints in hard maple. My dado stack was tearing out badly, but the spiral bit worked *perfectly*. It’s a great investment.

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I think you made mortises with a hand-held router on the fancy table with the glass top. Can’t remember the episode #/name.

For this article, I consulted with Eric Reed, Product Manager at Eagle America. But first, let’s hear Todd’s router bit question.