Title: Module 2 - The Bar Loader/Feeder
Course: Introduction to Swiss Programming

Module 2: The Bar Loader or Bar Feeder
Page 1 of 3
- Contents
  - Page 1
    - Module 2 - The Bar Loader/Feeder
  - Page 2
    - Major components of a bar loader:
  - Page 3
    - Major components of a bar feeder:

Module 2 - The Bar Loader/Feeder

Swiss style screw machines are almost always going to machine parts using long lengths of barstock. It is necessary to use a bar loader, bar feeder or some sort of system to 'contain' the bar as it rotates. When a new 12 foot length of bar is being machined, there will be 9 or 10 feet of that bar protruding out of the front spindle end of the screw machine. Sometimes companies do use shorter bar lengths, but most Swiss screw machines are going to use full 12' bars. Note: Many materials come standard in 9-13 foot random lengths. The standard is often 12 feet for materials made here in America. Material coming from other countries are typically 3m (approximately 9 feet) or 4m (approximately 13 feet) long. Some materials may come in longer lengths and would require a special extra long bar loader/bar feeder or to be cut into smaller lengths.

Bar loaders can automatically load a new bar of material into the machine as necessary. Many bars can be staged in the bar loader. A screw machine equipped with a bar loader can keep making parts, loading bar after bar, for long periods of time without an operator's direct involvement. Some companies load bars into their bar loaders at the end of the day and let their screw machines run by themselves at night or on weekends. Bar loaders usually use a collet to actively grab onto the end of a bar. Sometimes they use more of a "pusher" tip that is a hard steel conical recess that mates with a cone machined or ground into the end of the bar of material to be used by the screw machine. If a collet is used, the bar loader will remove the remnant after a bar of stock is consumed. If a pusher tip is used, usually the remnant is pushed out the front of the screw machine's guide bushing by the next bar.

A bar loader may have a channel size barely larger than the barstock diameter. In this case it is common to need to reduce the diameter of the end of length of barstock to a smaller diameter so a collet will fit. Bar loaders monitor the pusher bar position and can tell when the screw machine it is attached to has completed a part. They can be configured to keep letting the screw machine run until a specified position has been reached or to keep track of how many parts the screw machine has made before it sends a "change bar" signal to the screw machine.

A bar feeder will support and contain the bar as the screw machine is machining but will require an operator to remove the bar remnant, load a new bar in the bar feeder and prepare the screw machine and bar feeder to continue part production. Bar feeders only work with a single bar at a time. Some bar feeders will have multiple sizes of feed tubes available. One would choose the smallest tube the barstock can fit in.

Bar feeders just control the bar as it spins. They don't keep track of where the pusher bar is during operation, they just sense when the pusher is at its end of travel. The operator must load a new bar and remove the bar remnant every time a new bar is needed.

Bar loaders or bar feeders also need to gently 'push' the bar towards the screw machine. As the headstock of the screw machine is reset, its collet opens and the headstock retracts. Without the 'push' of the bar loader/feeder the retracting headstock could drag the bar with it.

As it turns out, the larger diameter a bar is the more likely it is for the screw machine headstock to drag the bar when the headstock retracts. This means bar loaders for large stock tend to 'push' harder than small loaders. Often it is difficult to run small stock (1/8" metal, 3/16"-ish plastic) on a loader that can handle ¾" stock.

Settings can be made to the bar loader to adjust the 'push' force but it is asking quite a bit for a bar loader to be powerful enough to push a 12' bar of heavy steel down its channel and still have enough finesse to not overpower and crush a small diameter bar.

Both bar loaders and bar feeders must be adjusted for the length part being machined by the screw machine. As the screw machine consumes a bar, the bar loader or feeder will send a signal to the machine tool when the end of that bar has been reached. A properly adjusted bar loader or feeder will let the screw machine consume as much of a single bar of material as possible. A bar feeder or loader adjusted for a part length that is longer than the actual part will result in an excessive bar remnant length when a new bar is loaded. If it is adjusted for a too short length then the bar loader may over-travel and send an alarm to the screw machine. This situation may not seem like much of a problem but depending on what the screw machine was doing at the exact moment the bar loader alarmed, damage to a cutting tool may occur. Most bar feeders will not send an 'alarm' to the machine; they will just send the signal to the machine that is time for a bar change.

Most modern bar loaders and bar feeders use the principal of "hydrodynamic support." Hydrodynamic support means the length of barstock in the bar loader or bar feeder will be in a tube or a clam-shell channel with oil pumped through the tube or channel. As the bar rotates, the bar will naturally climb to the center of the bar feeder tube or bar loader channel. The oil in the feeder tube or loader channel will lubricate the tube/channel as the bar touches the walls of the tube/channel while the spindle starts, slows down or is stopped. The oil also dampens vibrations while the barstock rotates. Often slightly warped small bars can run fine in bar loaders due to the dampening of the oil. The oil helps to dampen severely warped bars or larger bars with small bends but those bars will still not run well. If the warp is more than 'slight,' the bar should not be used or the bar needs to be cut where the bend is and both pieces of that bar can then be run through the machine.

Bar loaders and feeders work best with heavy weight or very viscous oil. The heavier or more viscous the oil is, the better it is at dampening vibrations. All bar loaders/feeders have a method to remove oil from the barstock before a section of bar reaches the screw machine. Sometimes there are brushes or air knives to remove the bulk of the bar loader/feeder oil from the bar as the bar exits the loader/feeder. Sometimes there is a tube the bar passes through between the loader and screw machine that will catch the oil slung off the rotating bar and drain it back into the bar loader. Often both methods are used.

None of these systems are 100 percent effective at removing barloader oil from the barstock, so some oil will mix with the cutting oil or cutting fluid in the machine tool. This contamination can affect the performance of the cutting fluid/oil.

Some shops run cutting oil in their bar loaders to avoid the contamination issue. Screw machine cutting oil is not as viscous as bar loader oil so the bar loader dampening performance is not as good. The tradeoff becomes cleaner cutting oil versus better performance for warped bars; each shop or company will need to make their own decision. Some shops even run cutting oil in their lubricators to avoid cutting oil contamination.

Some older, less sophisticated bar feeders are still in use and are known as 'gravity' bar feeders. These feeders do not use any oil and rely on a series of pulleys and ropes to push the bar into the screw machine. Since there isn't any oil to lube the tube the bar is in, these feeders rub the outside of the material, sometimes causing damage to the bar's exterior. Also since these don't use oil, the barstock is free to rattle around quite a bit and these feeders are usually annoyingly noisy.

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Date last modified: March 23, 2015.