The table below contains a recommended surface speeds for common materials when using DML equipment.  These values are conservative because our primary goal is fostering a safe learning environment (for our users and our tools!), not trying to squeeze every second out of each operation.

First, lookup the recommended surface speed in Table 1 (V ≈ 250 ft/min) and calculate the spindle speed from Equation 2:

Next lookup the recommended feed per revolution for the drill bit in Table 2 (fr ≈ 0.004 in/rev) and calculate the feed rate using Equation 3:

TIP: Plunging should generally be performed at 75% of the speed and 25% of the feedrate of the calculated peripheral cutting parameters.

As we mentioned above, twist drill bits (or “twist bits”) can range in price from affordable black oxide coated bits to expensive carbide bits used in milling. When it comes to choosing a drill bit for your wood project, a nice set of high-speed steel (HSS) bits should do just fine.

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Example 2B: Calculate the speed and feed for a 1/2″ diameter, 3 flute carbide endmill if peripheral and plunge cutting in aluminum using a CNC milling machine in lab.

The purpose of the hole affects bit choice. Will the hole accommodate an anchor to hold a picture, will it be used for wire or conduit, does the fastener that goes in it need to be countersunk?

First, lookup the recommended surface speed in Table 1 (V ≈ 100 ft/min) and calculate the spindle speed from Equation 2:

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Please begin by reviewing the comprehensive course document on this topic, as it clearly explains the process of calculating these parameters for drilling and milling operations.  The governing equations are summarized below.

Spade bits have a broad, flat area for boring larger diameter holes in wood. The spade bit has no flutes so you may have to back off the bit as you go when drilling deeper holes. While a traditional spade bit has a perfectly flat face, products like the Bosch Daredevil spade bit feature a self-feed tip and a slightly curved face.

A related bit to the installer bit is the flex bit which just uses a flexible shaft to let you get into tight spaces as needed. These can exist in lengths up to 72-inches.

Next, calculate the feed rate used for plunging.  Remember annular cutters should be fed at approximately 25% of the feedrate for an equivalent sized endmill.  From Table 3, lookup the recommended feed per tooth for a 1″ HSS endmill (ft ≈ 0.008 in/tooth) and calculate the plunge feed rate using Equation 3:

TIP2: When drilling deeper holes (> 3xD) without high pressure TSC (thru spindle coolant), reduce spindle speed an additional 50%.

Note that these speed and feed values are guidelines assuming adequate (flooded) lubrication, workpiece stiffness and drill depth less than 3 drill diameters (0.75″).  When applying oil manually (as in the lab), scale the feed and speed back to 60%, so N = 900 rpm and f = 3.6 in/min (final answer).

First, lookup the recommended surface speed in Table 1 (V ≈ 625 ft/min) and calculate the spindle speed from Equation 2:

Note that these speed and feed values are guidelines assuming proper (flooded) lubrication, workpiece stiffness and depth of cut.  When applying oil manually (as in the lab), scale the feed and speed back to 60%, so N = 570 rpm and f ≈ 18 in/min (final answer).  Note also this problem assumes we peripheral milling versus plunge milling (since we never teach the students the latter in lab).

Note: when applying oil manually, scale the feed and speed back to 60%, so N ≈ 420 rpm and f ≈ 4.8 in/min (final answer).  This is close enough to 500 rpm that I would first try this tool at the low end of high range with good oil application and see how it goes.

Next lookup the recommended feed per revolution for the equivalent size drill bit in Table 2 (fr ≈ 0.006 in/rev) and calculate the feed rate using Equation 3:

Note that these speed and feed values are guidelines assuming proper (flooded) lubrication, workpiece stiffness and depth of cut.  When learning how to use the CNC, always start lower (around 60% on the spindle speed and feedrate override buttons) and work your way up as you gain confidence or purchase your own tools (lol).

TIP2: Do not plunge an annular cutter at a feedrate less than 0.001 ipt (inch per tooth) in strain hardening materials like 304 stainless or titanium.

Next, lookup the recommended feed per tooth (chipload) in Table 3 (ft ≈ 0.004 in/tooth) and calculate the feed rate using Equation 3:

Note that these speed and feed values are guidelines assuming adequate (flooded) lubrication, workpiece stiffness and drill depth less than 3 drill diameters (0.75″).  When applying oil manually (as in the lab), scale the feed and speed back to 60%, so N = 450 rpm and f = 3.6 in/min (final answer).

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TIP: IF this was being performed on a CNC lathe, typical parting feed rates vary between 0.001 in/rev (for steels) and 0.005 in/rev (for plastics).  But remember, do NOT use the power feed when parting on a manual lathe unless you own the machine!

First, lookup the recommended surface speed in Table 1 for a 1” HSS endmill cutting aluminum (V ≈ 250 ft/min) and calculate the spindle speed from Equation 2 using the aforementioned 75% speed reduction:

TIP1: Since annular cutting is a plunging operation, it should generally be performed at 75% of the speed and 25% of the feedrate of the calculated peripheral cutting parameters (as with endmill plunging).

TIP: Reamers should generally be run at half the spindle speed and twice the feed per revolution of the equivalent sized drill bit.

Example 5: Calculate the speeds for parting off 1” diameter aluminum and 1” diameter mild steel workpieces on the lathe using the standard carbide part-off inserts.

Note: since applying oil manually, scale the speeds back to 60%, so NALUM ≈ 1425 rpm and NSTEEL ≈ 570 rpm (final answer).  Note these are MAXIMUM values and lathe chuck safety must take precedence; spinning the lathe chuck at 570 rpm is about the upper limit of what we safely do in the lab, so for smaller or easier to machine workpieces, DO NOT EXCEED 600 RPM regardless of the calculation results, unless you are running a collet chuck.

Self-feed bits can be a tad more aggressive than other large-diameter wood bits. They can also use either one or two cutting heads in addition to the perimeter cutting teeth. Check out our review of the Milwaukee self-feed bits and the Diablo SPEEDemon self-feed bits.

TIP: Countersinking should generally be performed at 25% of the speed and the same feed per revolution as the equivalent sized drill.

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Every metal cutting operation requires selection of proper cutting parameters for success.  As a DML TA, you need to understand basic calculations that will allow the tools you use to work as intended.

Next, lookup the recommended feed per tooth (chipload) in Table 3 (ft ≈ 0.008 in/tooth) and calculate the feed rate using Equation 3:

This is the type of bit that probably comes to mind first when you hear “drill bit.” It’s the most common type of bit and used for general purposes around the jobsite and home. Softwood can get stuck in the flutes, so gently remove it with a brush or by blowing it off.

Drill bits appropriate for wood drilling are steel, HSS, titanium coated, and black oxide coated. Those other bits work best for metals. We’ve written about black oxide coating and have reviewed the best drill bits as well as the best drill bits for metal.

Example 3: Calculate the speed and feed for a HSS countersink used to countersink a #10 clearance hole in aluminum using a manual milling machine.

First, lookup the recommended surface speeds in Table 1 (VALUM ≈ 625 ft/min, VSTEEL ≈ 250 ft/min (notice the 2.5 multiplier))

First, lookup the recommended surface speed in Table 1 (V ≈ 250 ft/min) and calculate the spindle speed from Equation 2:

Note that these speed and feed values are guidelines assuming adequate (flooded) lubrication and workpiece stiffness.  When applying oil manually (as in the lab), scale the feed and speed back to 60%, so N = 330 rpm and f = 2.0 in/min (final answer).

Wood species are divided into the two general categories of softwoods and hardwoods, but there is also much hardness variation within those categories. The wood type makes a significant difference in bit choice. Drilling a soft pine will be much easier on a drill bit than drilling a hard hickory. You can drill softer wood with steel (although we’d recommend HSS for any job) but as the hardness increases, it must be matched by bit hardness. This means a titanium or black oxide coating is appropriate for hardwood.

These odd-looking bits bore through wood or create flat-bottomed holes if the hole doesn’t go all the way through the piece. Use them when setting up cabinet hinges or similar applications.

A hole saw uses a pilot twist bit to guide a large diameter rotary saw that removes a plug from the wood. This allows conduit or wires to pass through. You also use these bits when drilling out locksets for doors. You can find hole saws for both wood and metal.

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Example 2A: Calculate the speed and feed for a 1″ diameter, 4 flute HSS endmill in aluminum using a manual milling machine in lab.

Before we get to drill bit types, you should be familiar with the various treatments drill bit manufacturers use to increase bit life and reduce friction. Drill bits are made from steel, high-speed steel (HSS)—which is steel alloyed with tungsten and/or molybdenum, HSS with a cobalt alloy, HSS with titanium coating, HSS with black oxide coating, or carbide tipped.

You’ll immediately notice a threaded tip on auger bits. This type of wood drilling bit uses the tip to quickly pull the bit through the wood. Auger bits maintain a constant flute throughout the length of the bit. These bits challenge cordless drills because they “force” the drill to maintain speed throughout the hole due to the self-feed tip.

Example 4: Calculate the speed and feed for a 1″ diameter, 6 flute HSS annular cutter in ¼” thick aluminum on a manual milling machine in the lab.

Most of us are guilty of using the wrong tool for the job—either out of necessity or laziness. Still, there’s something satisfying about using the right tool for the job. Often, using the right tool helps bring about the best possible result. When drilling, accessories matter—possibly even more than the tool you choose. Knowing the various types of wood drilling bits and how to use the right one can really increase both speed and quality.

TIP1: Recommended peck depth when drilling less than 3xD (e.g. 3 drill diameters) with flooded coolant is one drill diameter, or when applying oil manually, or under low pressure, is 50% of drill diameter.

This wood drilling bit’s distinguishing feature is in the name. The sharp point on a brad point bit helps position the bit for a precise hole. These bits don’t walk on you when you start a hole. This makes this the right wood drilling bit for when you need a truly accurate start.

Just as the name implies, these long, skinny “bell hanger” wood drilling bits are used for electricians pulling wires or performing similar installation work. In addition to their long length, installer bits often feature a hole near the front of the bit for use with pulling wire.

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By now we think it’s clear when and how to use the right wood drilling bit.  Have anything to add from your experience? Sound off on Facebook, Twitter, and Instagram to let us know what you think!

These bits perform double duty as they drill a pilot hole and countersink the hole at the same time. This ensures that the fastener head sits just below the surface of the wood.

Often confused with a Forstner bit, self-feeding bits include a threaded tip like the auger bit. This pulls the bit through the wood. These bits are meant for holes that go all the way through the wood. This is exactly the right type of wood drilling bit when you want to make a lot of larger holes for rough-in. Typically, self-feed bits are used for boring larger holes.

* multiply feed values in table by 0.5 for difficult to machine materials, flexible toolholding or workpieces, or lighter-duty machines*

A general rule of thumb for materials which are strong enough to support the drilling process is that fr is between 1 - 3% of the drill diameter, depending on the material strength.

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As you can see Acetal (Delrin) is one of the most machinable plastics and nylon is four times less machinable (which is why it should usually be avoided!).

TIP: When working with plastics with good machinability, use the cutting parameters for aluminum up until the point that the plastic melts.