A collet is a tool used to hold workpieces or cutting tools by compressing them between their conical jaw-shaped internal surface.
They are designed to grip the workpiece at its end and can be used in various machine tools.
Collets are typically placed in a spindle and tightened against the workpiece with a set-screw or drawbar.
It provides a constant clamping force along the workpiece's length, ensuring stability during machining operations.
This article talks about collets, their types, configurations, and applications.
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What is a Collet?
A collet is a type of chuck that holds workpieces or tools of different shapes in place for machining applications. They can hold them stationary or spin during the process.
Collet chucks are similar to milling chucks and consist of jaws for work holding.
These jaws can be tightened around the workpiece with an adjustable wrench or screwdriver, depending on the type of collet being used.
Collet has several types of jaw configurations that are used to grip the workpieces. In collet systems, these jaws are denoted by the number of ways in the chuck.
3-way and 4-way collets are the most commonly used types of collets.
Moreover, collets can be split on one side or both sides.
One-side split collets are split along the face, whereas double-side split collets are split on both sides, which means the collet has splits connecting the face and rear portions.
These collets have various clamping surface designs, shapes, slots, wear reduction systems, positioning, and insert configurations.
Types of Collets and their Applications
5C collets are normally split on one side and have three ways. It is tightened by a hinge that goes all the way to the receiving adaptor in your machine.
These draw-in collets have a hollow tube shape, allowing them to hold longer stocks.
When it is retracted into the collet sleeve, the three ways clamp onto the object.
5C collets have both external and internal threads.
These collets are widely used in lathes and mills for metalworking applications.
R8 collets have a solid drawbar that restricts the penetration depth of whatever material you put into it.
Like 5C collets, they are split on one side and have three ways. It is primarily used in milling machines.
Although the R8's body looks similar to 5C, the R8's body is much larger, and the taper on its rear is more abrupt and sharp, connecting to the locking/ejecting mechanism.
An ER collet is one of the best collet systems you can get. They are primarily used in milling machines.
They have a greater grip range than a 5C or R8 collet because they are split from both sides.
So when an ER collet closes, the entire body of the collet shrinks down uniformly on the tool or workpiece, while retaining the cylindrical shape of its bore.
The main feature of ER collets is its "collet nut." It has a feature on the inside that locks and holds the collet in place.
So they are not pulled from behind and down into the holder like an R8 or 5C collet, but they are pushed into the taper by the nut.
TG (Tremendous Grip) collets generally have a lower holding range than ER collets, but they both look the same.
They have high accuracy and great holding force like ER collets. Because of their small size, they are used for tool holding applications.
TG collets are best suitable for carbide tools and provide a tighter holding force for these tools when compared to ER collets.
Hence they are mostly used to hold carbide tools for milling, tapping, drilling, boring, and reaming operations.
Autolock collets have a threaded locking system where the shank's end screws into the collet. If the collet rotates, it further tightens the shank and locks it in place.
The collet will only be held against the taper of the cap when a cutter has been inserted. The cutter's rear engages with the centering pin, and further turning drives the collet against the cap taper.
They come in a single size and can only house shanks that match its tapper.
Because of their autolocking mechanism, they only require hand tightening and are mostly used in milling machines.
355E collets are split on one side and have a three-way clamp. These are also called grinder collets or U2 collets.
They are primarily used on knife grinding machines, lathes, milling machines, etc.
DIN 6343 - Dead Length Collets
DIN is a German standardization, and dead-length collets are standardized under its DIN 6343 standard.
DIN 6343 collets are also known as "Dead Length Collets'.
It has a pull-back design and is split on one side. Deadlock collets with three-way and four-way clamps are the most commonly used.
These collets are primarily used in turning machines and conventional lathes.
RDA/DA collets, short for Double Angle collets, are split into both sides (face and rear), allowing for better clamping like in ER collets.
Manufacturers suggest using DA collets for most generic applications, except milling, as they are prone to cracking when used for milling applications.
AF collets, also known as Acura-Flex collets, are split into both sides like DA collets. They have four ways, each in the front and rear.
RDO collets, also known as Ortlieb style and Full Grip collets, are primarily designed for woodworking applications.
It's best suited for performing drilling, boring, and milling applications. They follow DIN 6388 standardization.
Watchmaker collets are used with watchmakers' lathes. The 8 mm-sized watchmaker collet is widely compatible across most lathes.
They are available in step configurations to hold small watch gears, and some collets also support inserts with waxed or cemented adapters for holding small parts.
Morse Taper Collets
Morse taper collets are the go-to tool for many makers working with lathes, drills, and milling machines.
Because of their wide compatibility, these tools are easily available and have adapters for connecting additional tools like an ER collet.
Step collets are unique with their wide flat face that can be machined for holding custom large-diameter workpieces.
A type of collet can have many different configurations.
Note that these configurations will vary depending on the type of collet you use and its manufacturer.
Following are some commonly seen collet configurations.
Clamping Surface Configurations
Collets are available with different clamping surfaces. Some come with special groves, patterns, coatings, etc., while most have a smooth design.
Those with grooves exert a higher clamping force with a larger grip on the tool or workpiece than others.
Carbide coatings give a roughened holding surface to the clamps.
Extended clamps provide more clamping force as it has a higher wrap around the object circumference it holds.
Small/large, square, hexagon, eccentric, step, inner conical, etc., are some commonly seen collet bore configurations.
Depending on the bore shape, they can hold tools and workpieces of varying shapes. For example, with conical bores, a collet system can clamp conical objects.
Step bored collets can simultaneously hold objects with varying diameters because of their step-like internal clamp.
Collets with eccentric bores are unique as they allow the user to shape the bore depending on its application.
These bores are generally made of soft metals like aluminum which you can easily erode.
Different slot configurations allow the collet to hold objects with a constant force with no clamping marks.
These configurations minimize the slot width, thereby preventing machined chips from getting trapped between the slots.
Wear Reduction Configurations
Many manufacturers like Carbinite, Oerlikon, Nann, etc., make collets coated with added materials for extra protection.
These coatings can prevent the tool or workpiece from welting to the collet. Also, these coatings are much more economical than collets with special inserts.
Some commonly used insert materials on collets are plastic, brass, aluminum, and bronze.
They prevent pressure marks on scratch-sensitive materials, and these inserts can be replaced when worn out, without substituting the collet.
Self-turning inserts provide much more flexibility to the user as you can rework them depending on your application.
Slots positioned in front, cone slope, and shaft are helpful for housing square and hexagonal shapes.
Some collets can hold complex profiles or special contours with the aid of alignment surfaces.
Following are some of the miscellaneous collet configurations that are rarely used:
|Emergency||Allows the user to customize the clamping or bore diameter.|
|Sealed||Ways are sealed to prevent chips from trapping.|
|Coolant Sealed||Prevents leakage and pressure loss of coolant flowing through the cutting tool.|
|Coolant Flushed||Coolant flows through peripheral slits in the collet.|
|Internal stop||Limits the material length it can hold.|
|Insert aid||Helps clamp and support small diameter stock at a greater length to minimize vibration.|
|Bush||Similar to insert aid, but supports stocks with a larger diameter.|
|Ejector||Helps mechanically eject the workpiece from the collet pocket with an internal spring.|
|Inner cooling||Have integrated cooling that flushes the clamped surface.|
Some special features available on collets
Collets are lightweight compared to other tool holders like 3-jaw or 4-jaw chucks, allowing them to be used in high RPM machining operations without losing grip.
Moreover, they facilitate easy clamping of the workpiece, allowing for faster machine cycles.
However, when compared to jaw chucks, collets offer less flexibility in terms of the geometry of the workpiece that they can hold.
When working with collets, always use one that's the right fit for your tool or workpiece and regularly clean them by removing trapped chips for a smoother operation.
Frequently Asked Questions (FAQ)
What is a collet nut?
Collet chuck nuts are threaded fasteners that attach collets to collet chucks. They fit into the groove at the top and are threaded onto the mouths of the collet chuck.
How collets are different than a chuck?
Comparatively, collets are used to hold small workpieces or tools, usually between 1/16" - 2", but chucks can hold larger diameter workpieces. Also, in terms of precision, collets have an advantage over chucks.
What's a router collet?
A router collet is a sleeve holder that clamps and holds a router bit in place. The collect will be connected to a spindle that rotates the collet and the router bit.
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