Swiss Precision Turning: A Comprehensive Guide
Introduction to Swiss Precision Turning
Definition and Overview
CNC Swiss Precision Turning is a specialized method of precision machining much like traditional CNC Turning. The key differentiator lies in the operational dynamics: CNC Turning involves the cutting tool moving towards the workpiece, whereas Swiss Machining maintains stationary tooling while advancing the workpiece forward using a sliding headstock mechanism. Integral to this process is the utilization of a guide bushing that serves as a stabilizing element, akin to a “steady rest,” positioned in close proximity to the cutting tool. Through this meticulous approach, any potential part deflection is minimized, thus bolstering the overall precision and accuracy of the machining process.
Historical Background
The name comes from Swiss Watchmaker Jakob Schweizer who was the original designer of the Swiss machine for very small parts for the watch industry in the 1870s. The method for machining became more prevalent in the United States during World War 2 due to the demands of World War 2. By the 1970s, CNC versions of the machines became available.
Importance in Modern Manufacturing
Today’s models still incorporate the same sliding headstock concept, but today’s machines are now equipped with Computer Numerical Controls (CNC) along with live tooling, additional axes (some Swiss machines have as many as 13 axes), the ability to work with multiple tools simultaneously among other features to increase efficiency and improve quality of machined part. The usage of Swiss Precision Turning helps to automate previously labor-intensive operations. Utilizing live tooling and additional axes allows the machine to perform some secondary operations that would’ve otherwise been needed to be performed manually. Oftentimes, these can be performed simultaneously as the primary machining. This is a very lucrative trait of Swiss Precision Turning in 2024 given the current shortage of skilled labor.
Ripley Machine entered the Swiss Machining space to address a component for the trucking industry. The part was a headed bushing that required a countersink of a through hole on the back face of the part. When machined on a conventional CNC Lathe, the countersink added nearly 25 seconds of machine time. The production team at Ripley Machine determined that this was best done manually using a Bridgeport and a speed collet fixture. The time to manually do the countersink was similar to the machine time but allowed for more throughput. As the company got further behind on orders and the countersink operation output was dependent on unreliable labor, we decided to invest in a CNC Swiss machine. With a sub spindle that operates independently of the main spindle on a CNC Swiss, the countersink operation would now be done as part of the machining operation and with no added time. The machine would be simultaneously machining the next part while the sub spindle was doing the countersink operation. In addition, the quicker tool changes (and other factors) allowed us to reduce the cycle time of the part by nearly 30 seconds.
Swiss Precision Turning – How does it work?
Machine Setup and Configuration
Swiss Machining Centers are equipped with bar feeder that material is loaded into. Inside of the bar feeder is a channel set that the material rides inside of. Material passes from the channel set into the Swiss machine. The channel set is not exactly to the size of the material but is usually in the size range of the material. For example, a channel set with an ID of 1.250” may be used for 1” diameter material. The back side of the bar will be placed into a pusher collet that matches the actual size of the material. This will support the material in the back of the bar. Once the material is in the machining center it passes through a chucking collet and the guide bushing. The guide bushing is at the “front” of the machine in close proximity to the cutting tools. Once the material is at its desired starting position, the chucking collet can be closed on the material. The chucking collet will need to be closed far enough behind the guide bushing to allow for it to feed the entire length of the part (plus cutoff and facing stock) through the guide bushing. Once the chucking collet clamps on the material, it won’t re-clamp until the start of the next part.
A typical Swiss machining program will begin with a part off tool cutting off any bar stock sticking out of the guide bushing. Once the part off tool gets to “zero”, the chucking collet will retract to the full length of the part + part off and facing stock. While the chucking collet is unclamped and retracted, the bar feeder will be pushing the material against the part off to hold the face of the material in the same location. Once this process has been completed, the entire machining program can be cycled until the part is finished, at which time the chucking collet and part off tool will perform the same process to allow for the next part to begin.
Material Selection and Preparation
When selecting material for use on a job be sure to fully consider the operation and the implications of efficiency on the Swiss Precision Turning Operation: In cases where various materials are allowed by customer specification, be sure to factor machinability into your purchasing decision. For example, in a part where any aluminum is acceptable a 2000 series aluminum may be more costly than a 6000 series. However, the 2000 series will likely machine better and not create stringy chips that could cause issues inside the machining center. Choosing the 2000 series may cost more but would likely allow for the machine to run longer without an operator needing to remove chips from tooling, collets, etc.
Consider the tolerance of your finished part when selecting material. For jobs requiring a tighter tolerance, you will want to start with a tighter tolerance bar stock. You may need to have material ground prior to machining (see below). For jobs with looser tolerances, you may be able to use standard cold finish material. If you intend to use cold finish material, be sure to check the standard mill specification for outside diameter tolerance. A typical guide bushing only had .002” of allowable movement so if the material varies more than .002” you could have issues with material getting stuck in guide bushing or sizing issues because the material is moving in the guide bushing.
When planning a job, always consider the expected size/ tolerance of material and tolerance of your guide bushing. A guide bushing with .002” of tolerance and material with .002” of tolerance may not work together if they are on the respective wrong sides of the tolerance allowance. A general rule of thumb is that the finished part will have an improved roundness of about 50%. So, if there is .002” T.I.R. on a starting material, a Swiss machine can cut the part to about .001” T.I.R.
Utilization of Centerless Precision Ground Bar Stock
Although improvements in machine ability and tolerances of stock material have improved over the years, there are still instances where you may want to consider using precision ground bar stock for your Swiss Precision Turning Application:
The most common use of centerless ground stock in Swiss Precision Turning is to reduce the tolerance of the starting bar stock. This can be to help with the tolerance or finish of the finish machined part or to ensure there are no issues with material inside of the guide bushing. If your part allows, you may want to consider purchasing a guide bushing and chucking collet that is approximately .005” below a nominal size. This will leave enough stock for a centerless grinder to remove and ensure cleanup.
Another application where using ground bar stock may make sense is for parts where the cycle time is very short, and the quantity is very high. In this case the additional cost of having material ground to finish size may be far less than the added cycle time of turning the material to size, plus this will help to increase throughput.
Another common use of ground bar stock is in applications where the material has poor machinability. Materials like high temperature alloys have a very poor machinability and eliminating the need to turn the outside diameter of a part by grinding the bar stock to the part’s finish diameter, eliminates one tool to worry about when machining these materials. This can reduce tooling costs and increase uptime.
Another common use of ground is where concerns over segmented turning exist. As we mentioned above, if you turn the OD of a part when in Swiss mode, you don’t want to retract the material back through the guide bushing longer than the length of the pad of the guide bushing. If you have a part with a long thread where the thread diameter is the largest diameter of the part, you could grind the material to the major diameter of the thread. This would then allow you to single point the thread without worry of the part falling out of the guide bushing.
If you are in need of Centerless Ground Bar Stock, we encourage you to visit our Precision Grinding page to learn more about the services we offer!
Other Important Information about Swiss Precision Turning
Guide Bushing Mode vs. Chucker Mode
Most CNC Swiss Precision Turning Centers can be operated with or without the guide bushing. Operating a Swiss machine without a guide bushing is often known as “chucker” mode. By operating in chucker mode, the CNC Swiss machine somewhat becomes a glorified (and fast) CNC Lathe.
One benefit of not using the guide bushing is that you have more forgiveness for variance in material size. Utilizing a Swiss machine in “chucker” will also reduce the length of bar ends. As mentioned above the length of a bar end reflects the length of the collet and the length of the guide bushing. By eliminating the guide bushing, the bar end length is obviously shortened. A general rule of thumb when deciding whether to use a Swiss Precision Turning CNC Lathe in “Chucker” or “Swiss” is if the part has a length that is more than 3X the diameter you are turning, you will likely need to machine in Swiss/ Guide Bushing mode.
Rotary vs. Fixed Guide Bushing
The Guide Bushing can be rotary or fixed. A rotary guide bushing will spin with the material whereas a fixed guide bushing will not spin. Your application will typically determine what is best.
Sub-Spindle Utilization and Planning
When planning a part for processing in a Swiss Precision Turning machine, you will want to consider each sequence of the machining operation. Since a Swiss machine has a sub-spindle that runs simultaneously with the main spindle, your total cycle time will amount to the longer of the two cycle times amongst the two spindles. The more balanced that you are able to get your cycle times the shorter your overall cycle time will be.
Machining of Polygon Bar Applications
It is possible to machine parts requiring polygon shaped bar stock such as square or hex. However, there must be alignment between the main spindle collet, the guide bushing and the sub-spindle collet. This is accomplished by grinding a precision keyway in each collet. A pin is then added to ensure that the collets and guide bushings repeat at the same location for the entire setup as well as future setups.
Applications of Swiss Precision Turning
Precision Swiss CNC Turning can be used to make components for a wide variety of applications some of the most common applications are:
Medical Device Components
Aerospace Components
Space Components
Defense Components
Pumps and Valve Components
Automotive Industry Components
Oil and Gas Industry Components
Advantages and Challenges of Precision CNC Swiss Turning
Advantages of Precision CNC Swiss Turning:
Reduced Cycle Times
The utilization of simultaneous operations, shorter chip-to-chip tool changes, increased speeds and feeds and bar feeding allow for shorter cycle times.
Ability to handle more complex parts with tighter tolerances.
Elimination of secondary operations
Properly utilized live tooling and simultaneous machining allow Swiss Turning CNCs to produce a completely finished product in one operation, with minimal added cycle time.
Ability to adopt automation to meet the demands of any project.
As the world moves to a more automated and fast pace, CNC Swiss Turning Centers are able to be adapted to embrace automation. Most CNC Swiss machines can be operated in “lights out manufacturing”. Machines can be equipped with inspection equipment or parts accumulators to allow for unmanned operations.
CNC Swiss Turning Centers also have the ability to utilize programming macros to help for more automation. A macro is an automated input sequence that imitates keystrokes. They are most commonly used in Excel spreadsheets, but they can be used in CNC Programs. The most common usage of a macro in CNC Swiss Programming are checks to prevent the machine from crashing (for example, if a program is started when the cutoff tool isn’t at X=0, the machine will run a safe cutoff program to prevent any crashes). CNC Macros can be used to have a machine switch to a backup tool after a certain amount of parts. This allows machines to run longer without human interaction.
Challenges and Limitations with CNC Swiss Precision Turning
Tighter Tolerance requirements for starting material.
Swiss machines are not as rigid as most CNC Lathes and therefore can’t take as aggressive of cuts.
Material Yields can be less than a conventional CNC Lathe.
With a traditional CNC Lathe, you can typically use all material of a part besides the length of material necessary to be in the chuck or collet for the last part on the bar. With a precision Swiss Turning, your yield will be reduced by the part length + the distance from the pusher collet to the face of the guide bushing.
Longer Setup Times
As is the case with any other machine operation, proper planning and lean manufacturing can help to reduce setup times.
Higher Machine Costs
When compared to a standard 2 or 3 Axis CNC Lathe, a Swiss machine can be more than two times the cost. When compared to a Brown and Sharpe Screw Machine, the cost of a new CNC Swiss machine can be five times the cost. Obviously, there are many variables for determining the exact price but in general CNC Swiss Precision Turning Machines are significantly more expensive.
Why Choose Ripley Machine for Precision CNC Swiss Turning?
Ripley Machine has been dedicated to continuous improvement, customer service, and quality for over 30 years. Our team is fully prepared to address your precision CNC Swiss turning needs. As an ISO Certified company, we wholeheartedly embrace our quality management system, utilizing it as a cornerstone of our operations to guarantee the delivery of superior products. Our in-house Grinding department plays a critical role in our operations, enabling us to grind bar stock before machining processes commence. Additionally, we have the capability to centerless grind parts post-machining or following external services such as heat treatment or plating. Through our extensive network of strategic partners, we ensure the efficient sourcing of materials at competitive prices. Furthermore, we collaborate with rigorously vetted vendors for external services essential to your project. At Ripley Machine, our unwavering commitment lies in delivering unparalleled customer service. Our dedicated team devotes maximum effort to guaranteeing customer satisfaction, striving relentlessly to meet and exceed your expectations.
When it comes to Precision CNC Swiss Turning, we know that you have a lot of options but we firmly believe that Ripley Machine is your best option. We hope that you will contact us today to learn more about our business or to request a quote!
