Collets 101: The Definitive Guide

 

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Overview

Collets 101: The Definitive Guide covers five popular collet series: ER collets, TG collets, DA collets, AF collets, and RDO collets. In each section, you will find: recommended uses for each type of collet, along with accuracy metrics (T.I.R.), and tips for how to care for each collet system. If you are new to all of this, please refer to the FAQ & Glossary at the end of this guide for some answers to common beginner questions.

5 Collet Types & Recommended Applications

RDG/TG Collet RDO Collet RD/ER Collet RDF/AF Collet RDA/DA Collet Milling
Drilling
Rigid Tapping
Coolant Through Woodworking Routers
European Systems Drilling
Milling
Rigid Tapping
Tapping (with Length Compensation)
Reaming
Boring
Coolant Through
External Coolant Through
High Precision Grinding Drilling
Milling
Coolant Through
(in 50, 75 & 100 series) Drilling

ER Collets: The Best Toolholding Collet System

The RD/ER Collet System is the most versatile Toolholding System for any operation utilizing a round shank cutting tool in a machining or turning center. This includes drilling, milling, tapping, reaming and boring. RD/ER Collets are commonly known in the industry as ER, ESX, DR, BR, and VSAC Collets.

RECOMMENDED USES OF ER COLLETS

ER collets are recommended for Drilling, Milling, Rigid Tapping, Tapping (with Length Compensation), Reaming, Boring, Coolant Through, External Coolant Through, and High Precision Grinding.

RD/ER Collets are available in the following series ranges to maximize efficiency in most applications:

Series

RD 8
RD 11
RD 12
RD 16
RD 20
RD 25
RD 32 Inch Capacity

1/32-3/16
1/16-1/4
1/32-1/4
1/16-13/32
1/16-1/2
1/16-5/8
3/32-3/4 Metric Capacity

.25mm-5.0mm
.25mm-7.0mm
.5mm-7.0mm
.25mm-10.0mm
.5mm-13mm
.5mm-16mm
.2mm-20mm

 

HIGHEST ACCURACY: RD/ER COLLET CONCENTRICITY &#; PER DIN

METRIC Clamping Range D L Maximum T.I.R. Precision
DIN High
Precision
DIN Min Max 1.0 1.6 6 0.015 0.008 1.6 3.0 10 3.0 6.0 16 6.0 10.0 25 10.0 18.0 40 0.020 0.010 18.0 26.0 50 26.0 34.0 60 0.025 INCHES Clamping Range D L Maximum T.I.R. Precision
DIN High
Precision
DIN Min Max 0.039 0.063 0.236 0. 0. 0.063 0.118 0.394 0.118 0.236 0.630 0.236 0.394 . . 0.709 1.575 0. 0. . 1.024 1.969 1.024 1.339 2.362 0.

ACCURACY OF ER COLLETS

The RD / ER collet system is the only popular Toolholding system in which all components (ER chucks, ER collets and ER clamping nuts) are standardized by DIN . Most Toolholding Collet systems state the collet is . or .001 T.I.R. but, that does not mean that this is the accuracy one will achieve on the cutting tool when mounted into the chuck. The accuracy of the RD/ER assembly is guaranteed to conform to the DIN Table.

ER collet systems are truly interchangeable. All manufacturers of the ER collet system should conform to the DIN standard. This becomes important to users that may have toolholding systems from different Toolholding System Manufacturers. As tools are taken out of the tool crib and reassembled for different jobs, if all the RD/ER system components are in good condition, and are from Quality Toolholding System Manufacturers, the collet and tool should achieve the DIN accuracy.

Mixing components of Toolholding Systems other than RD/ER can have varying results. While other Toolholding systems may be &#;interchangeable&#;, none of the Toolholding Systems Manufacturers know the tolerances and specifications others are using for all of the components.

HOW TO USE ENDMILLS

When using endmills or any round shank cutting tool, collets and collet chucks centralize the cutting tool, unlike conventional sidelock endmill holders that push the tool to the side of the bore of the holder with a set screw. This method creates a small contact area on the cutting tool and shifts the cutting tool from the true centerline of the Machine spindle. With the cutting tool off-center, the cutting tool edges have an uneven load and will wear out prematurely. Collets and Collet Chucks centralizing the cutting tool will result in increased tool life, higher feed rates, better workpiece accuracy and enhanced workpiece finish. Carbide endmills are usually not supplied with a weldon or locking flat for side lock endmill holders. This is because they are not designed to be used in side lock endmill holders. Many Machinists hand grind a locking flat on to the shank of the carbide end mills to use them in side lock holders, perhaps it would be better to use them in the type of tool that they are designed to be used in.

METHOD OF INSERTION & RELEASE FOR RD/ER COLLETS

INSERTING

1. Insert collet into nut at angle as shown to engage extraction
   tongue in groove of collet.
2. Screw nut onto collet holder with collet securely in nut.
3. Insert tool to be gripped and lock nut.IMPORTANT: Never screw nut onto collet unless collet is properly seated in nut.

RELEASING

Hold nut in vertical position and remove nut at an angle. Collet is automatically withdrawn from chuck by excentric ring of nut when unscrewed.

CARE AND USE OF ER COLLET SYSTEMS

The ER chuck, ER collet and ER nut must be thoroughly cleaned before assembling to maintain accuracy. Use a benchtop ultrasonic cleaner to dislodge fine chips and debris. You can also use a bottle-type brush to clean the inner diameter of the collet and a toothbrush-style brush to clean the exterior.

Once assembled, a normal machining environment will not affect the ER toolholding assembly. The ER collet must be installed into the nut (see assembly instructions) before engagement with the collet chuck to ensure the ER collet is seated into the 30 degree concave angle of the nut. Putting the ER collet into the chuck and then installing the nut will result in a condition that the eccentric ring of nut will engage only one side of the collet and produce poor results such as runout and drastically reduced holding strength.

Never try to install a cutting tool with a larger shank than the maximum or nominal diameter of the collet to expand the collet. Most ER Collets are designed to collapse 1mm or .039. For example: If the cutting tool shank is 4.2mm a 4-3mm is not suitable. A 4.5-3.5mm collet would be required.

Sealed ER Collets for coolant through applications do not have a collapse range, and must be used at exact size. The radius of the collet must exactly match the radius of the cutting tool shank in order to maintain a complete seal. If companies claim that they have sealed collets with a collapse range please keep in mind that if the radius does not match exactly coolant canals will be created by the mismatched radius of an improperly sized collet.

RD/ER Collets must be tightened correctly. Many machinists have been trained that nothing is ever too tight. This is particularly not true with collets and collet chucks. Overtightening a collet chuck will distort the collet and actually diminish the holding strength and accuracy. Maximum tightening torque for RD/ER Systems is as follows:

Series Size
RD/ER 11
RD/ER 16
RD/ER 20
RD/ER 25
RD/ER 32
RD/ER 40 Max. Tightening Torque (ft. lbs.)
20
40
60
70
80
90

Cutting tools should be inserted into the collet the full length of the bore wherever possible. Failure to insert the cutting tool into at least 2/3 of the bore may distort the collet. Collets should be cleaned and oiled prior to storage.

BENEFITS OF ER COLLETS

ER Collets are also very economical when compared with other popular collet systems. Collets work best when used at nominal or full diameter but when the economy is desired this system compares very favorably with other systems. If a user would like to cover a range of 1/8-1&#; with a toolholding system please consider that with the RD/ER System this only requires 23 collets. With a TG system of the same capacity it takes 59 collets to cover the same range. When compared with DA collets with a capacity of 1/16-3/4&#; the RD/ER system only requires 18 collets while the DA needs 45 collets to cover the same range. This represents a significant cost saving while improving accuracy, and versatility.

THE CENTAUR &#;GREEN ZONE&#;

BENEFITS OF CENTAUR &#;GREEN ZONE&#; ER COLLETS

Centaur manufactures the widest variety of exact size collets in the industry to ensure you get the most out of your cutting tools, to reduce downtime and tooling costs.

Centaur offer RD/ER collets in full millimeter sizes, .5mm sizes and true inch size collets in 1/32&#; increments from inventory.

Centaur also offers Sealed High Precision Collets for coolant through applications.

Centaur Sealed ER collets are available with internal flow for oil hole tools or, with external flow (coolant canals through the collet) for use with cutting tools with or without oil holes. The external flow collets are especially beneficial for applications where there is coolant through the spindle but lower cost solid cutting tools are desired or applications where oil hole tools are used in through holes.

Centaur external flow ER collets are also extremely beneficial for through holes with oil hole cutting tools, as this will ensure that the cutting is properly cooled completely throughout the entire cycle. In many applications as the cutting tool is passing through or breaking through the workpiece the coolant may be just passing through the hole, with an external flow sealed collet one can be assured the complete cutting edge and lands of the drill are cooled throughout the complete cycle.

Centaur offers the most extensive program for ER tapping collets in the industry. ER Tapping collets will allow users to convert collet chucks used for many purposes into tapping chucks.

Centaur&#;s ER rigid tapping collets with square drive are available in inch or metric sizes, standard or sealed for internal or external coolant flow.

Centaur also offers RDT/ER tapping collets. These collets will inexpensively convert a standard collet chuck into a length compensating, Quick-change tapping chuck with square drive.

Centaur manufactures each collet from high-grade spring steel and are hardened and fully ground for absolute precision. Each Centaur collet is 100% inspected for the highest possible accuracy.

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TG Collets

RDG/TG collets achieve higher accuracy and greater gripping strength than DA collets and some other popular collet systems. This system will perform well in applications up to 10,000 RPM. RDG/TG collets are also known in the industry as DF, BG, VDF, and PG collets.

RECOMMENDED USES OF TG COLLETS

RDG/TG Collets are used for Milling, Drilling and Rigid Tapping. RDG/TG collets are available sealed for coolant through applications. RDG/TG collets. RDG/TG in 1/64&#; Increments or .5mm increments for metric sized tools.

ACCURACY OF TG COLLETS

RDG/TG Collets are within . T.I.R. The collet chucks are within . T.I.R. from the cone to the collet seat bore. The nuts are designed to float to allow for centering of the collet. RDG/TG systems when properly cleaned and assembled can achieve approximately .001 T.I.R. on a cutting tool shank in the assembly at a checking point length of about 2-3 times the diameter of the cutting tool. The collapse range of the RDG/TG Collets are 1/64&#;. As with all Collets it is recommended that the collet be used at the nominal or largest diameter. Sealed Collets do not have a collapse range and must be used at the exact size.

CARE AND USE OF TG COLLET SYSTEM

The TG chuck, TG collet and TG nut must be thoroughly cleaned before assembling to maintain accuracy. A benchtop ultrasonic cleaner will dislodge fine chips and debris or, a bottle type brush can be used for cleaning the inner diameter of the collet and a toothbrush style can be used to clean the exterior. Once assembled a normal machining environment will not affect the toolholding assembly.

The RDG/TG Collets must be snapped into the Clamping Nut prior to installing onto the Collet Chuck. Collets can be removed from the clamping nut by holding the small end of the collet and tilting the collet angularly until it is removed from the nut. Do not attempt to remove the collet from the clamping nut by forcing the collet out from the front of the collet nut using a punch or screwdriver as this will damage the collet and clamping nut. For maximum accuracy and holding strength RDG/TG Collets must be tightened correctly, maximum tightening torque is as follows:

RDG/TG 75
RDG/TG 100
RDG/TG 150 80 ft.lbs.
90 ft.lbs.
110 ft.lbs.

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DA Collets

 

RDA/DA Collets are recommended for drilling. RDA/DA Collets were originally designed to clamp well on slightly uneven surfaces such as jobbers or taper length type drills. RDA/DA Collets are available in 1/64 increments and in .5mm increments for metric sizes. RDA/DA collets are also known in the industry as DA and VDA collets.

RECOMMENDED USES FOR DA COLLETS

RDA/DA collets are recommended for drilling only.

ACCURACY OF DA COLLETS

RDA/DA Collets are manufactured to within . T.I.R. outer diameter to inner diameter. The length of parrallelism between the two female contacting angles in the chuck controls the accuracy of the system and is held to within plus or minus .. The clamping nut floats slightly to allow the chuck to center the collet. Normal accuracy is approximately .001 T.I.R at the face of the collet chuck.

CARE AND USE OF DA COLLETS

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The DA chuck, DA collet and DA nut must be thoroughly cleaned before assembling to maintain accuracy. A benchtop ultrasonic cleaner will dislodge fine chips and debris or, a bottle type brush can be used for cleaning the inner diameter of the collet and a toothbrush style can be used to clean the exterior. Once assembled a normal machining environment will not affect the toolholding assembly.

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AF Collets

This highly accurate Acura-Flex collet system (AF collet system) was originated by Universal Engineering. RDF/AF Collets are recommended for drilling, milling and boring applications. RDF/AF collets are also known in the industry as BF collets.

AF collets are available in 1/64&#; increments and limited metrics sizes. RDF collets are designed to collapse 1/64. Size ranges are as follows:

Series
RDF 25
RDF 38
RDF 50
RDF 75
RDF 100 Inch Range
1/32-1/4
1/16-3/8
7/64-1/2
7/64-25/32
13/64-1&#;

*RDF/AF Collets in the 50, 75 and 100 series are available sealed for Coolant through applications.

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RDO Collets DIN Style

The high gripping strength RDO collet system was originated in Europe and are sometimes known as Ortlieb style collets or Full Grip Collets. Many machines designed for woodworking also use this system. This system is recommended for milling, drilling and boring applications. Many high production routing systems manufacturers have standardized on this system. Size Ranges are as follows:

Series
RDO 16 (form A style)
RDO 20
RDO 25
RDO 35
RDO 44 Inch Range
1/8 &#; 3/8
1/8 &#; 1/2
1/16 &#; 5/8
1/8 &#; 1&#;
1/8 &#; 1&#; Metric Range
&#;
2mm &#; 13mm
2mm &#; 16mm
2mm &#; 25mm
4mm &#; 32mm

*RDO 25, 35 and 44 series collets are available sealed for coolant through applications.

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If you are from the manufacturing or construction industries, the term &#;collets&#; is probably familiar to you. There are many types of collets used in many different industries and applications. For this article, we shall focus on collets used in rotary tool holders typically found in CNC machining (milling) centers.

Before we get into the nuances of collets, it is vital to understand how collets work, what impacts their performance, how to maintain collets for long service life, and how to recognize when to replace them.

What are Collets?

Collets are the critical connection between the cutting tool and the tool holder (also called a collet chuck). Most collets are round, cone-shaped, and slotted. Collets encircle the cutting tool shank to evenly distribute holding power around its center bore.

As we continue to explain more about collets, it will first be helpful to understand the basic anatomy of collets and of a collet chuck system. The illustrations below will help provide a general understanding of the parts of a collet and collet chuck system.

 

 

How Collets Work?

The tapered collet base is made to fit into the collet pocket of the collet chuck body. The tapered design of the collet base and collet pocket allows the collet to be centered in the pocket as it is pushed in by the collet nut during setup. This centering effect enables the collet to achieve a high degree of accuracy (concentricity); much more than drill chucks and side-lock style holders.

As the collet is pushed into the pocket by the collet nut, the slots in the collet allow the I.D. bore to collapse and apply clamping pressure to the cutting tool shank. The result is a very strong and rigid clamping force on the cutting tool. Since the collet base is tapered to match the collet pocket, tool runout (T.I.R.) is reduced.

 

What are the different types of collets?

Collets come in many different types and sizes. Here is an overview of three of the more popular types of collets, along with the pros and cons of each system.

 

Double-Angle (DA) Collets

Double-Angle (DA) collets have been around for a long time and continue to be used in the market. There are, however, many issues associated with DA collets of which users should be aware.

One of the primary issues with DA collets is that they essentially clamp on the cutting tool shank with only two opposing faces in the I.D. bore. DA collets have four slots in the front of the collet and four slots in the back of the collet creating four clamping faces. However, when DA collets are tightened towards the lower end of their collapse range, two of the faces tend to be pushed out of the way so only two of the faces are clamping on the cutting tool shank. This may cause some runout at the nose when the tool is inspected in a presetter.

Additionally, when the tool begins cutting and side forces are applied to the cutting tool, the cutting tool tends to deflect into the area where the faces are not clamping on the tool shank. This results in excessive chatter that dramatically reduces tool life and results in rough surface finishes. You will be hard-pressed to find a quality end mill holder manufacturer endorsing the performance of their tooling in DA collets.

 

TG Collets

TG collets have about the same accuracy as DA collets, but because there are more slots, and therefore more faces clamping on the cutting tool shank, they tend to deliver greater holding power. TG can be a good solution for larger shank diameter cutting tools, but they generally limit how far down into a pocket you can reach due to interference with the collet nut, as TG collet nuts tend to be quite large.

TG collets are not as popular as ER collets for several reasons. Most notably, the larger diameter collet nuts can require the use of extended end mills to avoid interference from the collet nut when milling pockets. Also, since TG collets have a very small collapse range, they are intended for use with one size cutting tool shank. ER collets, by contrast, offer a large collapse range that can be helpful when clamping odd-shank diameter tools.

On the flip side, TG collets tend to have a bit more holding power than ER collets due to the collet base having a 4° taper as opposed to the 8° taper found in ER collets. This can make TG collets a good choice when machining with longer-length cutting tools.

 

ER Collets

The ER collet system has become very popular due to the flexibility of the system to hold a variety of cutting tool shank types including drills, end mills, and taps. Also, ER collets provide several solutions for increasingly popular coolant-through cutting tools.

Most standard ER collets have between a 0.020&#; and 0.040&#; holding range, making them a good choice when needing to hold odd-sized cutting tool shanks. This holding range also means fewer ER collets are required to hold a range of cutting tool shank diameters as opposed to other collet systems like TG.

The popularity of the ER collet system has led to several variations to hold a wide assortment of cutting tool shanks. Some ER collets have been modified with squares at the bottom to hold taps. Others have been modified to provide quick-change capabilities or compensation (also called &#;float&#;) for rigid tapping cycles as shown in the images below.

Other modifications include special slotting designs that seal around the cutting tool shank and force coolant through channels in coolant-through tooling, as well as modifications to include coolant ports in the collet that direct coolant to the cutting area.

Collet Maintenance Tips

Collets are a high-precision wear component of a tool holding system and require maintenance to ensure accuracy. First, it&#;s important to remember that collets are the softest component in a collet-based tool-holding system assembly and are designed to wear out.

Here is an overview of the wear pattern of a collet-based tool-holding system. The machine spindle is harder than the tool holder (a.k.a. collet chuck) that fits into the spindle, so any wear between these two components will mostly occur to the collet chuck. That&#;s good, as it protects the spindle from expensive maintenance. Collets are softer than both the collet chuck body and the cutting tool, so any wear forces between these items will mostly occur to the collet. Since collets are generally the least expensive component in a collet chuck tool holding system, it is preferred that the collets wear out before the other components.

Worn-out collets will not achieve the same level of accuracy and rigidity that newer collets can provide. The result is more chatter when cutting workpieces, less accuracy, and shorter cutting tool life. A good rule of thumb is to replace collets every 4-6 months to maximize the performance of your tooling. Again, collets are designed to wear out and are generally the least expensive component in the system. It is much less expensive to replace the collets as opposed to prematurely wearing out cutting tools.

The following tips will help you in maintaining collets:

• Clean the collet with a cloth and the interior with a little brass brush (sometimes the broken ends of tools & other debris can become lodged within).
• WD40 should be sprayed on fresh collets before being cleaned with a cloth. By doing this, the protective coating applied to collets before they are packaged will be removed (something that can make it harder to grip tools).
• Ensure that there is no debris in the slots as this could reduce the clamping force. If an obstruction is seen in a slot, use a thin object, like a knife&#;s tip, to remove the obstruction.

 

 

Wrapping Up

Given the wide range of benefits offered by collets, they are one of the most indispensable tools in the manufacturing industry. To get the most from your collet-based tooling system, it is important to use best-in-class products to produce top-notch quality.

This is exactly where Techniks Tool Group can help! Offering a wide range of collets and collet chucks, our experts will help guide you to the best solution for your needs. Our collets are trusted by some of the largest manufacturers in the world. Check out our collets and get started on your journey!

 

 

Frequently Asked Questions (FAQs)

1. How do I know when to replace collets?

Collets are designed to wear out as they lose accuracy and rigidity with use. High side-load forces during milling operations cause cutting tool deflection as illustrated below.

Over time, these side-load forces will bell-mouth the collet at its face.

As the collet experiences bell-mouthing, the cutting tool is allowed to deflect more and more during milling operations. Unfortunately, the collet may still indicate good accuracy on a presetter where there are no side-load forces. However, once the tool is put into service and begins experiencing side-load forces, the cutting tool is allowed more room to deflect, resulting in increased chatter and reduced tool life.

It is recommended to change collets out every 4-6 months, depending on usage, to ensure the most rigid and accurate collet chuck assembly.

2. Are there other signs that a collet should be replaced?

Yes. Any signs of fretting on the collet indicate the collet is vibrating in the tool holder. Fretting appears as rust-colored spots typically at the highest point where the collet sits in the collet pocket of the collet chuck.

This is not rust but rather an indication that there is a vibration between the collet and the collet pocket connection. The vibration causing the fretting is also reducing cutting tool life. If you see signs of fretting on the collet, it is advised to replace the collet. You should also ensure that collet nuts are tightened to the correct torque specifications during setup.

 

3. What is the correct method to assemble a collet and collet nut?

It is critical to properly assemble the collet and collet nut to avoid damage to the collet and make the most accurate and rigid assembly possible. The extraction groove of the collet must be properly seated to the extraction ring of the collet nut.

First, angle the collet so the extraction groove seats with the eccentric extraction ring in the collet nut as shown below.

Next, while holding the collet and nut together, place the assembly in the tool holder and begin tightening the nut. If the collet extraction groove is not properly seated to the collet nut extraction ring, the collet will appear seated below the face of the nut. This typically occurs when the collet is placed in the collet pocket of the tool holder and then the nut is threaded on the tool holder. In a correct assembly, the collet will seat at the face of the collet nut. The image below shows a correct assembly on the left and an incorrect assembly on the right.

DO NOT tighten the collet nut if the collet appears seated below the face of the nut as this will create galling on the 30° face of the collet. Galling appear as grooves or lines in the lead face of the collet.

Galling on the lead face of the collet can result in reduced clamping pressure on the cutting tool shank that may lead to the cutting tool slipping while cutting, or even tool breakage.

When trying to ensure the most rigid and accurate collet chuck assembly, don&#;t take chances.

When in doubt, throw it out!

Remember, the collet is designed to wear out and is the least expensive component in a collet chuck system.

 

 

Contact us to discuss your requirements of Types of Collets. Our experienced sales team can help you identify the options that best suit your needs.