Bar Puller vs Bar Feeder

There are several ways to automate a CNC lathe. That will
depend on your goal for your tooling processes. If you are
working on lengthy stretches of unattended operation, then
a bar feeder is more effective knowing that the design is purposely
meant for longer product designs. In contrary, a bar puller is
a good alternative when we work on small or medium batches
of materials to attain an optimum result for the expenditure. That's
because a puller will cut out the time it takes between bar changes
to enable a single operator to tend multiple machines, measure
critical part features perform value-adding secondary operations.

A bar feeder pushes a bar through a lathe's spindle and into the
workzone. Then a bar puller, installed in a turret station, pulls
the bar out of the spindle. The lathe's turret positions the puller
to grip the bar and then retracts along the Z-axis, bringing the desired
portion of the bar into the workzone. Once turning and part cut-off
are completed on that section, the process will continually repeats
until the bar is totally consumed.

So how do they “grip?” Standard bar pullers use two spring-steel
fingers to provide the gripping force. During setup, the serrated
jaws on the fingers are gapped a bit smaller than bar diameter
(typically 1/8 inch smaller). When the jaws contact the bar, the spring-steel
fingers deflect and expand over the bar. This provides the gripping force for the jaws.
Similarly, heavy-duty models use internal die springs that compress to provide
the gripping force. These pullers typically work with bars that are 3 inches
in diameter and smaller (models with 6 1/2-inch capacity are available).
They are able to grip round, square and hex barstock, and their shanks can
be either round or square to work with various lathe styles.

On the other hand bar feeders are best for longer bar sizes. Then
when we talk on larger production quantities,productivity and
getting the most pieces, logically we assume a 12ft capacity
magazine type bar feeder will fit for the job. From the standpoint of
productivity longer bar feeders will reduce labor cost since
the machine can be left unattended for longer period of time.

There are types of bar feeders that are designed to load and
feed in sizes such as 2-,3- or 4ft long bars. But statistically
smaller types of loaders are rare since longer bar loaders will
help us decide the best fit for the finished products.

To fully exploit the productivity of a CNC bar machine,
it is best to have this products that serves as loaders or
holders automatically for your machines. Such a machine
that loads magazine bars for machining or the one that "grips"
the bar into the set-up.A bar feeder has been developed to
render smaller sizes of bars in addition to its capability.
Seemingly the bar pullers are also entitled to do such task
for the reason that is serves as a guide in machining. To improve
its capability, some pullers has been using coolant for the lathe
to improve the grip in the bars and achieving quality product
performance.

Your run sizes, part diameters, types of materials, accuracy
requirements, ability to run machines unattended,
and a number of like considerations, must determine
the type of bar feeder/puller that is best for your shop.
Each type has unique advantages, and you must weigh both
against your shop’s particular needs. Its up to a machine
shop what type of bar loaders or pullers is best for
their CNC machines to gain maximum profit.

The Turning Page "The Turning Revolution"

In the pursuit of doing more with what you have, this month’s article explores a unique method of “piggy-backing” with the sub spindle to produce two holes at the same time.

This method uses the time and motion of the turret as it drills in the main spindle to drill simultaneously with a part semi completed that is already in the sub spindle. This gives you two drilled holes in the time it takes to drill one hole. Since drilling is often the longest single operation in a cycle, any way to reduce it or benefit by doing something else is a bonus. (More money in your pocket) Those of us who used to work on manual turret lathes know the value of “piggy-backing” or using “trees” and “nests” to put more than one tool into the cut at one time with some good old ingenuity. The difference here is we are using the machine and it’s programming to get creative instead of a complete manual solution.

The easiest application or drilling two holes at once is where your holes are the same size and the same length. Let’s say you have a 4” long part that has a 1” hole all the way through with a 1.25 counter bore on each end. Instead of drilling the 1” hole all the way through from one side, you could drill half way with each spindle and save time and money by doing it.

When there are odd diameter holes to be drilled there are a few items to contemplate before deciding whether this method will work satisfactory.

1. Size of the holes

2. Depth of the holes

3. Type of material

If the diameter of each hole is too far off from each other, the surface footage may be too unmatched to make this work well. As an example, if the first hole in the main spindle is 1.000 inch diameter and the 2^nd hole on the sub spindle side is .125 diameter, the difference between the two diameters is .875 creating a problem in most materials.

However, even with a big difference in diameter and surface speed, a situation like this could be resolved by using a carbide drill for the 1.000 diameter on the main spindle and a high speed drill for the .125 drill.

An example of this:

A carbide 1.00 insert drill in 316 SS=400 SFM at .003 IPR
Main Spindle RPM= 1528

A High Speed .125 diameter drill in 316 S= 50 SMF at .002 IPR
Subspindle RPM= 1528

The machine I used for the article example was done on the Eurotech 735SLY, a dual spindle, single turret machine.

I hope you’ll be able to take away something of value from this month’s article and as always, keep on turning!

Oh! And by the way if you are reading this before September 14^th, check out my up and coming movie star (we pray) daughter on the AMC channel at 8PM and September 15^th at 3AM (if you are an insomniac). She is hosting “Dinner and a Date” during the breaks of the movie “Pretty in Pink”. Her name is Mary Greenawalt and I hope you will watch and be able to say you saw her when she was just starting out. Wishing you all great success and Mary, “break a leg”!

For any comments, questions, or additional information, email me at larryg@eurotechelite.com

Sub Spidle " The Turning Page"

Sub spindles on today’s CNC turning centers can be part of any manufacturer’s key to producing finished turned parts in one machine set-up. A sub spindle or “pick off spindle” as referred to by most in the screw machine industry, has been around for a while. Early screw machine manufacturer’s saw its value and have been offering this option on many of their models for years.

Eurotech, (Biglia in Europe), was the first company in Europe to put a sub spindle in place where the tailstock was located on a standard 2 axis CNC turning center. The year was 1979 at the EMO show in Paris. They were able to demonstrate the machining of a part in the main spindle chuck, transfer it to the sub spindle and complete the turning on the second side. This launched the company into a fury of activity leading to more and more advancements in sub spindle and multi-axis turning designs.

Today, big or small, almost every lathe manufacturer around the world has copied this simple but innovative idea. So if everybody is doing it, what separates one builder from another when it comes to sub spindles? To answer this, let’s look at what you really need from a sub spindle.

• Spindle RPM Synchronization - If you plan to operate both spindles at the same time for cutoff and transferring the work piece, you must have spindle rpm synchronization.

This means that the machine’s control system must be capable of matching and maintaining the rpm of both spindles. An out of sync situation would cause one spindle to drag the other and could twist off or damage the part.

• Spindle Phase Synchronization – This is a synchronization that not only matches the RPM of the two spindles, but also matches the angular position of the two spindles. This is a “must have” for parts where a milled feature on the first side must be aligned to a milled feature on the second side. An example would be side holes that are produced on the main spindle and then face holes that are drilled on the sub spindle that need to meet and match the positions of those side holes. Another dramatic demonstration of phase synchronization is the transferring of Hex or irregular shaped polygons from spindle to spindle while rotating. Without this phase sync, it would be virtually impossible.
• Sub Spindle Ejection or Part Evacuation – Once the part is in the sub spindle, there must be a way to get it out. If we had to stop the machine cycle to manually remove the part, this would be defeating the whole purpose of having a sub spindle. A simple part ejector can be employed. This ejector is normally pneumatic or hydraulic and is sent forward to push the part out of the sub spindle after the machining work is completed. Some sub spindle manufacturers use a spring loaded system to push the part out once the collet is opened. The problem with these systems is that they are not a closed loop. There isn’t any feed back to the control whether the part has really left the sub spindle or not. If the spring was jammed or the collet did not open and the part remained in the sub spindle, CRASH! BANG! BOOM! (you get the picture)
• Ejector Switch Confirmation is a necessary part of any sub spindle system if the machine is intended for unattended use. The switch can tell the machine if the parts ejector is all the way forward past the collet opening and if it is not, to alarm out, thereby preventing any damage from occurring.

Air Blast and/or Coolant Through – All machining operations produce some type of chip, so it is required to try and keep these chips out of critical areas of the machine. A very critical area is the collet or work holding device. Even the smallest chip in the collet can cause a part to become scrap if they are crushed into the surface of the part and damage the part or the set-up and tolerances. Air and/or coolant flushed through the sub spindle greatly reduce the chance for this occurrence.

• Clearance, Rigidity and Capacity – These three items sort of tell you who really has provided a sub spindle engineered for it’s specific use or who just is a “me to” supplier. Clearance is an area where if the sub spindle is too large, there isn’t enough room for cutoff operations or room to machine between spindles. If the sub spindle is too small, then the capacity for size and power can be lacking. A careful balance of all three of these items is dependent on the overall planned use of the machine. For chucking work, many times a builder will design matched spindles and capacities. Clearances are less important between them because no parting off is being done. For bar work, the main spindle is normally designed with a larger capacity and power for large diameter 12 foot long bar and the sub spindle is designed around the machining of the machine’s largest bar diameter. Clearances are such to allow cutoff and machining between spindles.
• Collet Systems vs Chucks – Again, the biggest factor is what the machine is being used for. Collet systems are easier and faster to install and changeover vs chucks which are normally heavier and require bored jaws and additional set up. If it’s bar work, collets are the first choice and if it is chucking work for castings, forgings or billets, a chuck is the first choice. Collet systems are normally smaller in diameter and provide better clearances for bar machining. If an odd size is needed and cannot be found from a collet manufacturer, then an Emergency Collet can be bored out on the machine.
• Stress Control and Part Off Confirmation – Stress control is the ability to check for stress or interference when moving to or from a part. An example is when moving over a part that is finished machined in the main spindle. If say the finishing tool that was cutting the part OD broke and left the OD oversized to a degree that the collet in the sub spindle could not fit over the diameter, the sub spindle would try to push over this part resulting in damaging the part, the collet and even the machine to some degree. To prevent this, a stress control system can be used to monitor the stress as the sub spindle is moving over the part, and if the stress rises above the allowed limit, the machine alarms out with no damage to the part, set up or machine. This same system can be used in reverse to check as cut off confirmation instead of using additional wire or probe type checking systems. When checking with stress control for cutoff confirmation, a small feed move back of the sub spindle is employed with stress control on. If the cutoff tool broke, the bar would not have been separated and the load would rise when trying to move the sub spindle away with the stress control check on and give an alarm. This is an absolute must for unattended operation.

The article this month is how to write a sub spindle cutoff and transfer sequence using Macro B programming with Fanuc. The example uses a Eurotech 710S or 420S type model. The same concept can be used for many other models. The purpose of this example is to show how to reduce or “can” your sub spindle sequences so that you don’t have to write a new and unique set of instructions for each new program.

For any comments, questions, or additional information, email me at larryg@eurotechelite.com

I hope you’ll be able to take away something of value from this month’s article and as always, keep on turning!