CNC Router Bits
CNC Router bit types and their uses is our topic today.Why so many router bits ? What’s their purpose ? Which bit do I use for a specific function ? Does the material I use make any difference in which router bit I use ? What is a router bit profile ? How long go they last, what’s their longevity ? Are they expensive, what do they cost ? These questions I needed answers to when I started out. I’ll discuss in greater detail the answers to these questions.
CNC Router bit types and their uses
I swear there’s as many router bits as there are uses for them. Certain router bits have specific functions but others can multitask. The bits you choose should do what you need. I’ve acquired several over the years but use only a handful. Although I own a cnc machine I still have handhelds for specific functions.The time to set up speciality bits, enter their data into my tool edit data base is more work then it’s worth. Production work is worth the effort but not 1-2 piece run in my opinion.
Materials will have effects on your tooling. The feeds and speeds are the concern here. Your cut depths and feed rate change with material densities. Softwood like pine, spruce and cedar will cut faster than dense hardwoods like ironwood or ebony. Wood density is measured by the Janka Scale. The Janka scale is measured by how much pound footage is required to drive a 11.28mm or .444 inch ball into the material. Where Eastern white pine requires 380 lbf, Australian Buloke needs 5,060 lbf. Wow, what a difference !
CNC Router bit types and their uses all wear out in time. No tooling lasts forever but steps are taken to give them maximum life. Your tooling life is the amount of time your tool works before failure. Feeds, speeds, plunge depth, materials, router bit types contribute to the longevity. Our shop mills only wood and the occasional composite or plastic, no metal. Let’s discuss in greater detail the factors that contribute to tool failure.
Feed rate is the speed measured in IPM or inches per minute. This is the traveling speed of your device (spindle or router) driven by the gantry and its drive motors. Larger machines have faster feed rates.
Spindle speed, the rotation speed of the tool measured in rotations per minute. A router is an alternative to a spindle. The router performs the exact action but doesn’t have the same life as a spindle. Spindles are industrial in grade but pack a larger price tag.
Step down or Plunge depth
This is exactly as it sounds. How deep into the material does the router bit go ? The deeper the bit goes the slower the feed rate is. The material will play a large part in this. Softwoods mill at faster speeds than hardwoods. Too deep and too fast creates excess friction and tool breakage.
The step over is the cutting distance each bit makes in a tool path. Let’s use an endmill for this example. Placing a .500 inch end mill in your collet. How much material do you want to remove with each pass? We know the cutting diameter is a half inch so what percentage of that diameter will cut on each consequential pass? 50% will cut out .250 of an inch, 60% will cut .300 and so on. Remember there’s a comfort zone here as well. try removing too much material too fast and tooling wears quicker.
Chip Load, the amount of material cut out per tooth. The chip size helps you to adjust your feeds and speeds. Don’t create dust, you want chips. Correct chip size pulls heat away from the tool and adds to its life. You want chips on the floor and spoiler board nit dust in the air. The bits are cool or warm to the touch, never hot enough to burn your hand. Again, no two pieces of equipment are the same. Smaller hobby machines won’t compete with their industrial counterparts.
Feed and Speeds Calculations
CNC Router bit types and their uses rely on a feeds and speeds calculator. Each manufacturer has a recommendation for its product but that’s a starting point in my opinion. Online calculators are available, like this one here. Here’s a basic formula I keep on hand as a reference for my feed rate. Chipload X cutter diameter X # flutes X spindle speed= Feed rate. Lets use the example below to better illustrate this formula. This is merely a starting point.
Chipload =.02 (Example only, refer to manufactures specs.
Cutter Diameter = .250″ (Use end mill for the example)
Number of flutes = 2 ( Actual cutting edges)
Spindle Speed = 12,000 RPM
Feed Rate = 120 Inches Per Minute
Carbide or High Speed Steel
Carbide or high speed steel both have their advantages and drawbacks. The two main deciding factors are cost and tool longevity. The high speed steel mills cost half of what carbide do. Carbide is industry standard for engravers and fabricators. Carbide has longer tooling life but bits cost a lot more. Our shop uses both because of the materials we run. I mills a lot of cedar and pine for our products. One cut through a sappy knot and my mills become gummy. I use HSS end mills for this reason. Once coated in this gooey stuff I soak them in a cleaner and reuse them. Sap dulls my mills quickly no matter what they are so this is why I utilize HSS.
Climb or conventional cutting direction
Routers spin in a clockwise motion. In CAD software you have a choice to set your machine’s cutting direction clockwise ( conventional) or counter clockwise ( Climb) . The difference in these two functions is how the material is cut and removed. Conventional cutting pushes the bit into the material and climb pulls the router bit away. I think of the climb function like trying to pull an automobile backwards while it’s in drive. Climb direction creates less tear out in the material.
Router Bit Types
CNC Router bit types and their uses are numerous. Router bits come in all shapes and sizes. Many accomplish specific tasks while others multi task. Manufactures make tooling for set materials like wood, composites and plastics. We mill no metal in our shop so I’ll be discussing wood only.Personally I use less than 10 types of router bits. My milling operations and engraving utilize no more than 4 bits. This can be confusing for someone starting out in this career field. Let’s discuss in greater detail the different bits and their function,
End mills are the multi taskers in cnc wood engraving. They cut out parts, do the hog out of larger engraving jobs. i use them to flatten areas prior to engraving. They come in many diameters and sizes for collets. End mills will have one or more cutting edges or flutes. More flutes creates less chips and give cleaner surface finish. They are upcut which pulls the chips up and out of the cutting surface. down cut end mills push the chips back down into the material.
Do any 3D milling ? Then you certainly are using a ball nose mill for this operation. Ball nose bits offer great detail with smooth contours while removing maximum material. Intricate carving, try a tapered ball nose for the best surface finish and minimal tooling marks.
Are you a sign fabricator ? V-bits or V-carving bits, V-groove bits are your tool of choice. These bits give the best results with detailed font. They’re available in 30, 60, 90, 120 degrees as well as sizes. These are the go to bits for signage and 2.0-2.5 dimensional engraving work.
Spoiler Board Bits
CNC Router bit types and their uses include the might spoiler board bit. This router bit maintains the cnc machines work surface and keeps it flat. Our shop uses this bit to also plane large stock that won’t go through the planer. Log bed slab footboards and headboards aren’t possible without this bit for me. Signage has to be flat prior to dropping a V-bit into the material for consistent milling depth.
I purposely buy my cnc router bits from a dedicated supplier that specializes in cnc tooling. I’ve used normal router bits in a pinch but professional tooling is the way to go. Router bits purchased from home improvement centers aren’t the same. The cnc machines are capable of using common tooling to perform specialized tasks. We’ll discuss other tooling below and what you can substitute to perform the same actions.
The profile of the V-groove is done with a 90 degree V-bit. V-bits as discussed above are available in different degrees and sizes. I use a V-Groove on my interior borders to to isolate an engraving in its center.
The Chamfer is created with the 90 degree V-bit as the V-Groove. I put a chamfer around all my plaques unless my client request otherwise. The V-groove is figured in with an offset during cut out. This leaves a 45 degree bevel around the border.
The profile of the dado cut is done in one of three ways. Table saws do this with special blades clearly know as dado blades. Hand routers create this profile with a straight 1-2 fluted straight cutter. The cutter has different sized diameters for specific sized slots. CNC machines do these will end mills. Dados are seen when permanent shelving is used.
To better understand a rabbet, think of it as a dado on the edge of the material. A hand router, table saw or cnc machine all do rabbets. No special tooling needed, a straight bit, end mill or dado blades on your tablesaw accomplish this. A rabbet on the interior of a door frame allows for a piece of glass to be seated.
A cove is a concave edge on the side of of material. Think of it as a reverse roundover. A round nose router bit creates this profile. A router table with a round nose does this to. In cnc a cove is created with the round nose bit in the machine and half the profile cut out. This leaves the appearance of a half moon.
Just like the cove a round nose profile uses the same router bit, Again, your cnc machine, router table or hand held router will do this for you. Round nose bits are most often used to create flutes in material. These flutes are found in moldings, door casings and hearth surrounds. They are useful for creating concave pockets in game boards like Aggravation.
The round over profile is not a tool path I create in my cnc machine. The round over bits available out there work great with a small handheld router. Specific operations and profiles are just faster by hand. Have a lot of stock, think about a small router table with a fence. My machine has a maximum milling length of 50.249 inches. I can’t even do 8 foot stock on my machine so this is why I use a hand router or a independent router table with a fence.
Dovetails, of all the router bits, different profiles and joinery, this is my personal favorite. Dovetails give joinery integrity and strength. Most often seen in kitchen and dresser drawers, these are strong as nails. I prefer a dovetail over a drawer with a rabbet bottom and a thin piece of 1/4″ luan. I personally find no strength in these or longevity.
Specialty Router Bits
CNC Router bit types and their uses include speciality router bits. These bits are for specific tasks and are widely seen used in molding applications. Slot cutters for door frames, bits for raised kitchen door panels and the list goes on and on. These speciality bits are not meant to be run in a handheld router. They are too large for the necessary control to operate them safely.
CNC Router bit types and their uses include as many bits as there are suppliers. I don’t personally purchase discounted or reduced router bits from unknown sources. Imported lower quality bits are going to show their true ability or lack thereof. A bad finished edge that requires a lot of sanding isn’t what I’m looking for. I also look to support another small business owner when possible. I’m not a tooling salesman but my investment in my tooling is crucial for my shops survival. Example, would you utilize a sledgehammer to do finish carpentry?
I’ve been very pleased over the last few years doing business with US Router Tools. The prices are fair, the tooling quality is great and I’m helping to support another small businessman. Never have I had a problem with this supplier, my tooling shows up in a timely manner and I couldn’t be happier. Research your supplier and build that relationship, it’s a win win.
To purchase a starter kit or not ?
This is why a good relationship with your supplier is so important. If you can’t have a relationship with a supplier who can’t answer questions, dump them. I want to tell my supplier what I’m personally looking to fabricate and have them tell me what I need. Anyone can sell anything to anybody, but is it what you need? My supplier has always been able to answer my question and give me the answers I’m looking for.
CNC Router bits need to be protected, this isn’t a small investment for any shop. Larger router bits come stored in their own cases. End mills are dipped to protect them in shipping but peel this coating off and there susceptible to damage. A tool storage plan is a must. I keep my old storage cases for this purpose.Router bits rolling around against each other doesn’t prolong their life.
Your router bits are important for the quality of your work. Purchase the best you can afford , they will pay for themselves. Have a knowledgeable supplier that you trust and keeps your interest in mind. A penny saved today is a dollar spent tomorrow. Understand how router bits work and function in what materials.Keep notes on your bits, the material you’re running and the feeds & speeds in which you run them. Our shop wishes you all the best in your own endeavours, happy milling.
Thank you for taking the time to read.
~An Engraver In The Woods