What’s the Difference Between an “O” Flute and a “V” Flute Router Bit?

The letter designation “O” or “V” refers to the geometry of the flute, area behind the cutting edge, of the router bit. A “V” flute has a 90˚ angle behind the cutting edge. While an “O” flute has a very curved flute. The next question, “which geometry is better?” depends entirely upon what you are cutting. The general rule, is that you want to use the geometry that works with your material.

Some materials create chips that curl away. While others create chips that chunk out in tiny little blocks. Use a geometry of bit that has a shape to support the natural behavior of the material you’re routing. Soft plastics, like sintra, tend to curl and create chips that look much like grains of rice. For sintra I would recommend using an “o” flute. Whereas a hard plastic, like acrylic, has chips that come out looking a lot more like sugar crystals. A “V” flute could work well here. Although, I will point out that some of the more popular acrylic cutting bits are “O” flutes.

These are not hard and fast rules. But, they are meant to help you start thinking about what kind of bits to use for certain jobs. There may be a time where you specifically want to deter a material from its natural tendency to create long curls. For example, redwood often creates very long curls as you route it, but these long curls can cause issues for the machine, in addition to blowing out the top edge. A good solution for this issue is to use a “V” flute bit, which will break the long chips into smaller pieces.

When you keep a journal of what parameters you used to route certain jobs you can start to notice patterns, and then tweak various levers to get different results. As always, if you ever get stuck and aren’t sure which lever to tweak next, please give us a call and we’ll work through the problem together.

How Do I Select the BEST Router Bit for a Job? – Part 4

Hopefully this series on router bit selection has been helpful. Like I have said in previous posts pretty much all router bits can be used as general purpose. But, when we start to understand the nuanced differences between them, it enables us to make better selections for improved edge quality, speed or even bit longevity.

Choosing the length and diameter may seem like the easiest part of choosing a bit. But, there are some guidelines that you’ll want to make sure you follow. Router bits can be very brittle, so we want to make sure that as we route we are supporting them and working with them, rather than forcing them to work against their design.

Diameter and Spindle Speed (RPM)

Smaller diameter bits perform better at higher RPMs. Each router bit has a specific rack angle, the angle of the cutting edge itself, that is designed to cut into the material at a certain speed. If you can imagine an old vinyl record for a moment. The further you get from the center the faster the record is moving. So, if we want to maintain the same cutting-edge speed, we need increase that speed for smaller diameters and decrease it for larger diameter router bits.

• 1/16” dia 24,000 - 30,000 rpms
• 1/8” dia 21,000 - 24,000 rpms
• 3/16” dia 19,000 - 21,000 rpms
• 1/4” dia 16,000 - 18,000 rpms

This brings us back to that equation for feedrate (feedrate = chipload x RPM x # of flutes). If we increase our RPM for a smaller diameter router bit, we’ll also need to increase the feedrate to maintain the chipload. If you’re unable to maintain a feedrate that supports the required RPM you won’t be making big enough chips and the bit will burn out.

Top Tip

When working with small radii you can rough the cut with a larger diameter bit and then go back and run your finishing pass with the smaller diameter router bit. Manufacturers have specialized hoggers and roughers designed specifically for this task. But, it can be a great problem solving technique as well when you are routing tricky materials and need tight corners.

Router Bit Length

It is very straightforward to say that you want cutting edge length to be longer than your material is thick. And, 99 times out of 100 you won’t have any issues with the cutting-edge length. But, I’d like to cover some of the basics that may just save you a headache or two.

Solid Carbide is a great material for a cutting edge. It’s strong and holds a good edge. But, the same chemistry that makes it strong also makes it vulnerable, you’ll generally get about half a bounce out of a router bit. Router bits are weakest when pushed perpendicularly on their cutting edge. The longer the cutting edge, the more leverage is being applied to the fulcrum. There are two things we can do to balance this out. First, use the shortest cutting-edge length as you can. Second, use the material to support the cutting-edge length and minimize the exposed portion of the cutting-edge length.

If you are blessed with a tool changer neither of the above recommendations will be difficult for you to adhere to. But, for the rest of we now get to play a fun balancing game of length and support. While it seems like the solution to all cutting-edge length problems is to cut everything in one pass, I would only recommend doing that with foam (and that is what I recommend). The general rule for depth of cut is the diameter of the bit itself. Why? Because we want to make sure the chips we’re creating have a place to go, especially if you’re not using an up-spiral router bit.

The solution is to balance all of the recommendations as best you can (and record the results in your trusty little journal). It’s important to always remember that routing isn’t black and white, and that sometimes, even when you’re following every recommendation perfectly, things still may go haywire.

Specialty Router Bits

Another very important thing to remember is that when you’re routing, you’re not alone. It’s very common that some other poor soul has been tasked with the same conundrum you’re in. This is a great time to call Hartlauer Bits. If we can’t help you find a solution to what you’re facing we have relationships with the manufacturers and can work through solutions with them as well.

It’s through these conversations that specialty bits were born. Relevant to our router bit length discussion are extended reach router bits. These bits have a generally short cutting-edge length, then where the flute fades out the shank has a spinback applied. This means that you can bury the entire cutting-edge length into the material and not suffer the consequences of the shank rubbing on the material. This helps you balance a few more of the recommendations a little bit easier.

Top Tip

When you’re looking at the ratio between router bit diameter and cutting-edge length look to keep the length less than 3 times the diameter. Most router bits follow this as the maximum cutting-edge length available. The exception to this rule is high density foam. Hartlauer Bits does carry a variety of extra-long small diameter foam cutters. Be sure to only use these in foam, and make sure to always cut in one pass. You’ll support the router bit better, and will have a better finish.

How Do I Select the BEST Router Bit for a Job? – Part 3

Let’s recap what we’ve talked about so far:

• CNC Machines generally use Solid Carbide bits
• Hand routing generally requires High Speed Steel
• Carbide tipped bits are a good way to save money, especially in larger diameters
• Heat destroys bits
• The more cutting edges you have the faster you can go
• You need a chip large enough to remove the heat, but small enough to leave a clean edge

If you’re worried that a long list is only going to get longer, the good news is that above won’t change too much from one job to the next. If you have a CNC machine pretty much all of your jobs will be with Solid Carbide bits. And while some will cut a large variety of materials, all with different chip loads. Once you figure out what works in aluminum you can pretty much do the same for all other aluminum jobs. From here out we’re looking more at job specific parameters.

Router Bit Geometry

There are a lot of nuances to router bit geometry. A bit that cuts aluminum will largely look just like one for plastic. But, those specific angles and ridges make all the difference. Luckily, the engineers who design and test these things need to worry about those aspects of geometry. Suffice to say, use aluminum bits for aluminum and wood routes for wood. Any bit technically can be a general-purpose bit. But some tools are designed to perform better in one, or many materials. These are some of the aspects that you’ll just have to explore on your own and see what you like.

However, there is a very important piece of geometry that is a consideration when selecting the right router bit. Up-spiral, down-spiral, straight-edge, compression, mortise, burr, etc… How are you supposed to know what type of bit to use? Let’s begin:

Up-Spiral

I am always going to recommend to begin your router bit search with an up-spiral router bit. The simple reason is that it pulls the chips up and out of the cut. Which, removes the heat and leaves a cleaner edge with longer tool life. But, that same motion that pulls the chips up and out also pulls on the material. So, if you have poor material mounting, or a laminated material, this type of router bit may pull the material up, or even pull the material apart. Up-spiral bits also have a tendency to blow out and fray the top edge of some natural woods. For these reasons we have a vast array of router bit geometries to choose from.

Down-Spiral

While a down-spiral does solve for many of the complications that an up-spiral presents, it brings it’s own baggage. With down-spirals the chips are no longer being pulled up and out of the cut. In fact, they can push the chips back down into the cut, resulting in smaller and smaller chips. There are some ways to mitigate these perils, like reducing the depth of cut to ½ the bit’s diameter. But, these headaches often outweigh the benefits. I only recommend going down this route as a last resort if nothing else is working. Using a down-spiral requires a significant amount of babysitting to make sure that the chips are clearing the cut.

Straight-Edge

If a tradition spiral bit isn’t an option I’ll first turn to a straight edge bit. While these don’t pull the chips up and out, at least they don’t push anything back down into the cut. It solves the majority of the up-spiral issues without bringing in the down-spiral deficiencies. And, as you keep your journal diligently, you may find that for certain materials a straight edge provides a superior finish compared to spiral bits. Low-Helix bits are a blend of traditional spiral and straight edge, these perform exceptionally well in hard plastics like acrylic.

Compression

New materials are being invented all the time, and many of them are some form of laminate. These can be tricky little monsters. If spirals and straights just aren’t cutting it for you, a compression is the next step. Though, these can be quite pricey. These tools are beautiful catalogue centerfolds as the complex geometry mixes an up-spiral bit with a down-spiral. A traditional compression bit will have the cutting edge split 50/50 between up-spiral at the tip and down-spiral at the shank. A mortise compression bit adjusts that ratio to have a shorter up-spiral. This is because many materials won’t allow for an initial depth of cut to submerge the down-spiral portion into the material, and if all you’re using is the up-spiral edge you may as well use a traditional up-spiral.

Burr

While most router bits finesse their way through the material like a savage ninja, burr bits almost grind their way through the material. These router bits look like a miniature weapon a bad guy would use in Game of Thrones. They are covered in many very sharp little burrs. These have primarily been developed for use in aeronautics materials. Some of the honeycombs and composites are exceptionally difficult to get clean edges. Feed rates and chips loads don’t completely go out the window. But, if you find yourself having trouble routing these materials, Hartlauer Bits has a variety of resources we can connect you with.

End-Mill

What is the difference between an end-mill and a router bit? Well, in smaller diameters, not much. But, once you start getting into ¼” and above the geometry starts to make a difference. As I noted above, router bits are designed to slice like a ninja, removing chips with finesse. An end-mill will have a different helix geometry, how tight the spiral is, in addition to flute geometry. It isn’t so much finessing as it is muscling the material away. Like I said, in small diameters the two will perform in much the same way. But, in larger diameters they will act differently. I would generally reserve a large end-mill for milling large blocks of material. If there is a significant amount of lateral movement you’ll be better served by a router bit

How Do I Select the BEST Router Bit for a Job? – Part 2

Hopefully part 1 was a helpful start for selecting the best router bit. Our approach for selecting the right router bits is to use the information we do have to narrow the field. That way when we get to options where we don’t have the information our field of options is smaller. Then picking based on price or availability won’t box us into a bad place.

How Many Flutes (Cutting Edges) Do I Need?

Imagine for a moment that you are alone in the woods chopping a huge tree into firewood. You’ve got one big axe; how long do you think it’ll take you? I’m no Paul Bunyan, so I’m going to estimate 5 days… Now, let’s take that situation and imagine you and a buddy both have 2 medium size axes. With two of you the work should get done faster… but the smaller axe means that each axe will be a little less effective. So, instead of it taking 5 days… It’s safe to say with two medium sized axes, we’re looking at something closer to 3 days. We could keep increasing this example, but essentially, the more cutting edges you have the faster you can cut (higher feed rate).

There are a few caveats to keep in mind though. Notice that in my example, when we increased the number of axes… they got smaller. That’s because as you add more cutting edges to a router bit the smaller the flute becomes. The flute is the area behind the cutting edge where the “chip” or debris is developed. This is really important to be aware of because the chip is what removes the heat from the cut. And, as we discussed last post, heat breaks down the cutting edge.

So, how do we balance the amount of heat coming out of the cut with the size of the chip and the feed rate? Well, luckily there are formulas and ratios that provide a predetermined range for optimal edge quality and bit longevity. We’ll explore that in future posts, but some immediate resources can be found in our bit list, routing guides, and of course from calling us directly (800-644-2487). For this post we’ll focus more on selecting the right bit that can lead to optimal performance.

While making sure that you’re properly accounting for the amount of heat is the most important consideration. An often over looked consideration when determining the number of cutting edges is what your machine can handle. Machines will have a speed that can be maintained in straight lines, and a speed that can be maintained while cutting corners. Your machine may be able to run at 600 inches per minute (ipm) in straight lines, but if it doesn’t change direction well, you’ll find yourself dwelling in the cut in every corner. That makes complex shapes into much riskier jobs. But, this risk can be mitigated by choosing the appropriate number of cutting edges.

This is the straightforward part. If your machine has a speed limitation and you need to remove as much heat from the cutting edge as possible, then single edge bits are going to be your flavor. But, if you’ve been endowed with one of the super CNC’s, you can afford a few more cutting edges. Or, say you’re routing lots of small intricate shapes. In that case, you’ll generally want fewer cutting edges. This is why so many table surfaces have a bunch of cutting edges, it allows for less down time while you’re resurfacing the table.

Another consideration is edge quality. Often, you’ll find that additional edges can leave you with a cleaner edge. There are a variety of reasons for this, but it makes sense. Just like higher grit sandpaper leaves you with a smoother surface, the addition edges, taking smaller bites, will do the same. Just imagine not having to flame polish that acrylic. It sounds like blaspheme, but those are just some of the promises of choosing the best router bit for the job.

The number of cutting edges your router bit has is one of the most important considerations you’ll have to make when choosing the right router bit. But, what I want you to take away from this post is that you want to work within your machine’s limitations when making this decision. And, the big question is, “will my machine be able to move fast enough to remove enough heat from the cut?” I can promise you now, if you’re making dust instead of chips, you need to try again.

Chiploads

I can’t end this post without at least some specific information about chiploads. The chipload is the size of the debris you are removing from the cut. This is what removes the heat from the cut, increasing the tool’s life and quality of the material’s edge. The magic formula is:

Feed rate=Chipload × RPM × # of flutes

In today’s post, we discussed the # of flutes, and we’ll explore the other variables in future posts. But, you can start seeing the relationship between the # of flutes and the feed rate. I apologize for the math lesson. But, holding chipload and RPM constant, increasing the # of flutes increases the feed rate. But you can also see that while holding the # of flutes and RPM constant the chipload will drop if the feed rate drops. This is why it is important to know your machine’s limitations when choosing the right bit for the job!

This is another good time for me to make a plug for the router journal. Once you find a feed rate that gives you a good finish take note of your settings. That way, when you, or your cousin Larry, need to cut that material again you won’t have to recreate the wheel. This may sound trivial, but it makes a big difference when your training the new guy.

Top tip – Looping the corner

Dwelling in the cut is never a good idea. The small chips you already have keep getting smaller because the tool isn’t moving laterally and it just keeps cutting what’s already been cut. This builds up a considerable amount how heat. A few seconds of this can be enough to break even the most durable bits. So, instead of pausing for the machine to completely change directions, have the tool continue to move in a small loop, so that the tool is continuing to move while the router changes direction. Just make sure that you loop into the refuse, not the finished product!

Top tip – Bit running hot?

Chipload and formulas are nice… but is anyone really going to pull out a micrometer and measure enough chips to get an average size? What if the edge looks fine? Or, the bit seems to last long enough? What even is long enough? A quick way to know if you aren’t pulling enough heat out of the cut is the temperature of the bit after you’re done cutting. If the tool is so hot that touching it would burn you, then you are not using a high enough feed rate. Make bigger chips and get rid of that heat!

Thanks for reading this post. In Part 3, we’ll continue with router bit fundamentals while we take a look at the geometry of the tool.

How Do I Select the BEST Router Bit for a Job? - Part 1

Router cutting has come a long way since the early days of carbide tipped and high-speed steel bits to the purpose designed composite cutters we have today. There can be no arguing that there are a lot of different router bits to choose from, many of them seemingly overlapping, being designed to do the same thing! In a world with so much confusion how are you ever supposed to know which router bit to select.

For anyone who really can’t be bothered, give Hartlauer Bits a call and we’ll gladly walk you through any questions you have and help you pick the right tool for the job.

Next, and I can’t stress this enough, keep a journal of what you used and how it worked. A little spiral notebook right by the router can save you massive headaches down the road. All you need to do is record the material, tool, feeds and speeds, and how the finished product looked. If you’re really ambitious, you can note the air temperature, humidity and moon cycle…

Solid Carbide, Carbide Tipped and High-Speed Steel

When choosing which bit you’re going to use, a great place to start is with the composition of the bit itself. The most common compositions are going to be solid carbide, carbide tipped and high-speed steel. In general, CNC routers will use solid carbide bits, hand routers will use high speed steel and carbide tipped bits are a balance between longevity and cost.

For CNC router operators, the vast majority of the bits you’ll use will be solid carbide. Compositions will vary, but most are going to be a Tungsten-Carbide with a Colbalt binder. If you’ve ever dropped one, you’ll know how brittle they can be. But, these hold a sharp edge longer than high-speed steel. They can be ground with a wide variety of edges from a single edge spiral to a prickly burr. The biggest disadvantage to solid carbide bits will be their cost, especially if you require larger diameter cutters. And, keep in mind that heat is their enemy, it breaks down the Cobalt binder and dulls an edge very fast.

High-speed steel is a common tool for hand routers because the tool has a little bit of flex. Especially if you’re new to routing its very difficult to maintain a smooth speed. So, having that added flex can save you a lot in broken tips. High-speed steel bits won’t last as long as their carbide edge counterparts. But, they can have a sharper edge and cost a fraction of the price, especially in larger diameters. Like solid carbide, these too come in spiral and straight varieties, though most of the innovative composite cutters will only come in solid carbide.

Carbide-tipped are generally a cost saving alternative, which sounds great, but it has some limitations. These are going to be a high-speed steel bit with a tungsten-cobalt edge. It brings the cost advantages of high-speed steel with the longevity of solid carbide. However, you can’t just glue a solid carbide edge onto anything and cut with it. These bits generally only come in straight edges and seldom can you find them in small diameters. But, if you’re roughing out a lot of material and need a big bit these are perfect. V-cutters and table surfacers are almost always carbide tipped because there is a lot of material and solid carbide drives up the overall cost of the tool.

The material the router bit is made from is just one piece of the tool picking process. But, it’s an important consideration because it can have a serious impact on long-term cost. In general, CNC routers will use solid carbide and hand routers will use high-speed steel. Carbide tipped is a great way to cut down on costs when you need a large bit with a straight edge. But, also keep in mind, that if you’re doing a small, one-off, job or, if you need a really sharp edge, high-speed steel may provide the solution you’re looking for, even on a CNC.

Next we’ll talk about the number of flutes a bit has.