Bar Feeder in CNC Lathe Explained: Why Use it?

CNC lathes are powerful tools that provide quick machining ability with high productivity, and a bar feeder can be used to further enhance that productivity by reducing the lead time.

A bar feeder is a device that automates the process of feeding stock or raw material to a lathe. It provides a continuous and smooth supply of workpieces through the headstock of the lathe, reducing the operator’s involvement and increasing productivity. This makes it ideal for CNC lathe operations.

It is an optional accessory that can be mounted on any lathe to reduce the time spent feeding the workpiece to the lathe.

This article discusses bar feeders in detail by going through its parts, operation, and types.

In the end, the article also discusses the advantages of using a bar feeder and the factors to consider when buying them.

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What is a Bar Feeder?

A bar feeder is a machinist-friendly, simple-to-handle device that enables unattended machining.

Generally, bar feeders are used with CNC lathes, but if there is a restriction in space and purchasing cost, a bar puller is the best alternative.

The decision is made based on the size and frequency of the jobs.

Compared to a bar feeder, a bar puller feeds a single bar of raw material to the lathe machine at a time.

They can be either spring-loaded jaw type or air/coolant-actuated pullers. As a result, they have a simple construction and do not involve any electronic machine control units.

Though a bar puller occupies a lesser floor space when compared to a bar feeder, it offers a lower production capacity.

Parts of a Bar Feeder

A bar feeder consists of some important parts that you need to familiarize yourself with for operating it.

Bed

As the name refers, the bed supports the bar stock that needs to be fed to the headstock. 

The bar feeder bed is inclined towards the transfer tray and has a set of runner guides on its surface. The runner guides support and transfer the material smoothly onto the transfer tray.

Transfer Tray

The transfer tray feeds a single raw material/stock to the machine through the chuck. For smooth functioning, the tray is aligned in line with the spindle and chuck of the lathe.

It is generally curved or angled in shape and thus forms ideal support for the stock with such features.

With the help of a bar pusher (push rod), the required length of the stock is fed to the chuck.

Shuttle

Before the feed, a shuttle slides through the transfer tray to ensure the tray is empty, i.e., to check for the presence of any material from the previous machining operation.

Optical Sensor

An optical sensor is placed at the entry of the headstock, i.e., in between the transfer tray and chuck.

It ensures that the required amount of stock is fed.

Bar Pusher

A bar pusher is a push rod that facilitates feeding the workpieces from the transfer tray into the chuck. It is driven by a hydraulic/pneumatic system or a servo motor.

Clamps

Clamps are present on the transfer tray. It prevents the stock from being misaligned and thus protects the system from vibration. In addition, it ensures stability.

Lathe Adapter

The lathe adapter, commonly known as a liner, is an attachment placed in the channel of the chuck. 

Various sizes of liners are commercially available to accommodate metal rods of different diameters. In addition, it offers a secure hold over the metal rods during machining.

How to Use a Bar Feeder?

Learning to operate a bar feeder is an easy task. Step by step procedure is discussed below.

1. Activate the shuttle to ensure that there isn't any remnant from the previous machining process.
2. Load the bed, also known as the charging tray, with the bar stocks.
3. Place a liner of appropriate size inside the spindle, based on the diameter of the loaded bar.
4. Align the transfer tray to the spindle by cranking the handwheel upwards and downwards.
5. Manually slide the bar in and out of the spindle to ensure alignment.
6. Using the control panel, enter the working parameters such as the length of the longest bar, push length, and minimum clamping length for each rod.
7. Activate the push rod by using its respective controls in the control panel. The push rod advances the bar into the spindle.
8. Perform jogging (repeated starting and stopping of the motor) until the face of the bar is even with the face of the chuck. 
9. Activate the chuck jaws to clamp the bar.
10. Set the reference position where the face of the bar stock is and push the initial length.
11. After pushing in the initial length, the CNC lathe tools perform the required machining operations of it and the bar feeder pushes in the next length of the workpiece for further machining.

Types of Bar Feeders

Bar feeders are classified based on two main criteria: size and support system.

Classification Based on The Size

Bar feeders can be classified based on the length of the bar they can handle.

Short loader bar feeder/ Spindle length loader

A short bar feeder can handle bar stocks of 2 to 4 feet and can serve the entire length of the bar to the spindle in one go. Thus, a short loader bar feeder is also known as a spindle length loader.

The feeder serves as a reservoir to accommodate the entire length of the bar stock inside the lathe headstock, so a faster machining process can be achieved by running the machine at a higher speed.

Handling shorter lengths of bar stock aids in quicker setup time and minimizes the shop-floor space. This makes the short loader bar feeder suitable for smaller production lots of around 20 to 30 parts.

This type of bar feeder also facilitates the machining of the same or different cross-sectional work pieces.

Though a short bar feeder proves to be cost-effective, it has certain drawbacks.

Handling shorter bar stocks leads to more remnant (leftover) pieces. Thus, leading to a significant loss while machining expensive raw materials.

Preparing the raw materials to suit the spindle length adds to the machining cost and preparation time. 

Long-automatic bar feeder /12-foot bar loader

A long automatic bar feeder, also known as a 12-foot bar loader, accommodates bar stocks of 12 to 16 feet long, i.e., thrice the capacity of a short bar loader.

The ability to accommodate a long bar stock facilitates the production of huge volumes and provides extended periods of unattended operation.

Only one remnant (leftover) piece is generated compared to other bar feeders, which generate multiple remnants.

Nevertheless, long-form bar feeders are not chosen over short-form feeders as they need to be worked at lower speeds to avoid the vibration of parts, thereby leading to a slow machining rate.

Being around 12 feet long, it occupies a sizeable shop-floor space. Further, it requires regular maintenance of parts, which is time-consuming.

Six-foot automatic bar feeder

A six-foot automatic bar feeder exhibits the best features of both a short bar feeder and a 12-foot bar loader.

It can accommodate a bar with a maximum length of 6 feet, making it suitable for the machining of moderate-size workpieces.

However, a 6-foot feeder will result in comparatively more wastage in terms of the remnant pieces left at the end of the bar.

Overall, this feeder occupies lesser floor space, has a faster setup time, and drastically reduces the number of remnant materials compared to a short bar feeder.

Classification Based on the Support system

Apart from the size, bar feeders can also be classified based on how a bar stock is supported.

Hydrodynamic bar feed systems 

The bar stock is seated in an annular cylinder filled with pressurized oil in a hydrodynamic bar feed system.

Besides supporting and pushing the bar, the pressurized oil acts as a damper that absorbs vibrations during machining. This results in a quiet and smooth operation.

Though it enhances machining, this system requires manual intervention to fill the feeding track tray.

Hydrostatic bar feed systems

A hydrostatic bar feed system consists of a series of guide channels that hold the bar stock in place. A huge volume of hydraulic fluid is pumped into each channel that supports the bar.

The bar stock is fed with the help of a servomotor rather than being pushed by the oil.

A hydrostatic bar feeder can accommodate bar lengths over a wide range, thus facilitating the production of huge volumes.

The automatic feed features make this system expensive compared to hydrodynamic bar feed systems.  

Why Do You Need a Bar Feeder?

A common query that arises is, regarding the necessity of a bar feeder.

During manual machining processes, a bar feeder helps a CNC operator in preparing the workpiece, such that it can be placed in the chuck easily and accurately.

This provision eliminates even minor errors that even an experienced machinist can encounter.

In an agile manufacturing system, the manufacturer can ensure the speed and accuracy of the product delivery.

Apart from this, in the conventional method, a portion of the workpiece which is clamped by the chuck needs to be reworked. 

A bar feeder optimizes the length of the hold and reduces the forces encountered by the part due to misalignment, minimizing the setup time and the time spent in reworking.

Advantages of Using a Bar Feeder

Using a bar feeder offers certain benefits that enhance the productivity and performance of the machining process.

Automation

A bar feeder drastically reduces the operator's involvement in handling the bar stock.

It offers precision bar loading and support, facilitating complete automation from the beginning to the end of the machining operation.

Cost- Effective

The reliable and consistent operation makes the bar feeder a must-have accessory. In addition, it is cost-effective as it reduces the wastage of material (remnant) to a greater extent. 

Machining Time

A bar feeder reduces the changeover and setup time which is usually higher in the case of manual setup.

Workpiece Protection

Manual workpiece loading may cause abrasion of the workpiece. However, spindle liners employed in bar feeders prevent this from happening.

Operator Safety

The operator is the most crucial part of a production line. A huge amount of time and money is invested in the safety training of each operator.

By eliminating the need for manual feeding of the workpiece, a bar feeder eliminates the risks involved in handling heavy bars and enhances the safety of the operation.

Factors to Consider When Buying a Bar Feeder

Commercial bar feeders are available in a wide range of features and prices. Therefore, cost alone is not a factor to consider while purchasing a bar feeder.

Machine Capacity

The capacity depends on the volume of pieces that need to be produced and the availability of shop floor space.

Weight consideration

This criterion refers to the amount and weight of loaded bar stocks. A critical analysis of this factor improves extended periods of unattended machining and keeps vibrations within limits.

Availability of parts

Routine maintenance, technical support, and availability of replacement parts are of great importance.

Ease of use

The changeover and setup time need to be quicker; choosing a system with simple automated controls is advisable.

A rugged machine showing consistent performance is desirable above all other factors.

Frequently Asked Questions (FAQ)

How do you align a bar feeder?

Aligning the bar feeder to the lathe spindle is a critical operation to be conducted before the start of the process. With the help of a straight beam laser light, the bar feeder is aligned to the correct height of the lathe spindle

What are the factors affecting the performance of a bar feeder?

Wear and tear of bar feeder liners due to misalignment of the feeder with the machine is the primary reason to cause deterioration in the performance of a bar feeder. The misalignment also aggravates the vibration which might lead to machine downtime.

When were bar feeders introduced in the manufacturing industry?

Some of the earlier records of certain automation companies show that bar feeders were in business since 1961 (IEMCA). However, the automation that exists today, with computer controls, started around 30 years ago. A few examples of such bar feeders are from AEC Co. and Lexair Inc.